VOLUME 119 NO. 2 FEBRUARY 2019 Realising possibilities from mine to market.

Resource Mine Mining & Mine Materials Mineral Tailings & Waste Smelting Transport Environment Non-Process Evaluation Planning Development Handling Processing Management & Refining to Market & Approvals Infrastructure

WorleyParsons provides innovative solutions for each step of the mining value chain. We combine world- leading, concept-to-completion expertise with design and major project delivery capabilities for the minerals and metals sector, from bulk commodities to rare earths, with complete mine-to-market solutions from inception to rehabilitation. Our Global Centre of Excellence for Mining and Minerals in South Africa has niche expertise in hard rock and precious minerals and metals, and we have achieved particular recognition for the delivery of complex processing plants and deep shaft mines.

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!+! ! + + ++ !  +! !  + !  *Deceased * H. Simon (1957–1958)  !! !""  * M. Barcza (1958–1959) Mxolisi Mgojo * W. Bettel (1894–1895) * R.J. Adamson (1959–1960) President, Minerals Council South Africa * A.F. Crosse (1895–1896) * W.R. Feldtmann (1896–1897) * W.S. Findlay (1960–1961) * D.G. Maxwell (1961–1962)  !! " !""  * C. Butters (1897–1898) * J. de V. Lambrechts (1962–1963) Gwede Mantashe * J. Loevy (1898–1899) * J.F. Reid (1963–1964) Minister of Mineral Resources, South Africa * J.R. Williams (1899–1903) * S.H. Pearce (1903–1904) * D.M. Jamieson (1964–1965) Rob Davies * W.A. Caldecott (1904–1905) * H.E. Cross (1965–1966) Minister of Trade and Industry, South Africa * W. Cullen (1905–1906) * D. Gordon Jones (1966–1967) * P. Lambooy (1967–1968) Mmamoloko Kubayi-Ngubane * E.H. Johnson (1906–1907) * R.C.J. Goode (1968–1969) Minister of Science and Technology, South Africa * J. Yates (1907–1908) * R.G. Bevington (1908–1909) * J.K.E. Douglas (1969–1970) !""  * A. McA. Johnston (1909–1910) * V.C. Robinson (1970–1971) * D.D. Howat (1971–1972) A.S. Macfarlane * J. Moir (1910–1911) * C.B. Saner (1911–1912) * J.P. Hugo (1972–1973) !""  " * W.R. Dowling (1912–1913) * P.W.J. van Rensburg (1973–1974) M.I. Mthenjane * A. Richardson (1913–1914) * G.H. Stanley (1914–1915) * R.P. Plewman (1974–1975) " ! " !""  * J.E. Thomas (1915–1916) * R.E. Robinson (1975–1976) Z. Botha * J.A. Wilkinson (1916–1917) * M.D.G. Salamon (1976–1977) * G. Hildick-Smith (1917–1918) * P.A. Von Wielligh (1977–1978)  ! " !""  * H.S. Meyer (1918–1919) * M.G. Atmore (1978–1979) V.G. Duke * J. Gray (1919–1920) * D.A. Viljoen (1979–1980) * J. Chilton (1920–1921) * P.R. Jochens (1980–1981)     ! " !""  * F. Wartenweiler (1921–1922) G.Y. Nisbet (1981–1982) I.J. Geldenhuys * G.A. Watermeyer (1922–1923) A.N. Brown (1982–1983) * F.W. Watson (1923–1924) * R.P. King (1983–1984) ""  !""  J.D. Austin (1984–1985) S. Ndlovu * C.J. Gray (1924–1925) * H.A. White (1925–1926) H.E. James (1985–1986) H. Wagner (1986–1987)  "  " "!"! * H.R. Adam (1926–1927) * B.C. Alberts (1987–1988) R.T. Jones * Sir Robert Kotze (1927–1928) * J.A. Woodburn (1928–1929) * C.E. Fivaz (1988–1989)  !! !"!"! * H. Pirow (1929–1930) * O.K.H. Steffen (1989–1990) V.G. Duke * J. Henderson (1930–1931) * H.G. Mosenthal (1990–1991) * A. King (1931–1932) R.D. Beck (1991–1992) ! ! ""!    * V. Nimmo-Dewar (1932–1933) * J.P. Hoffman (1992–1993) I.J. Geldenhuys S.M Rupprecht * P.N. Lategan (1933–1934) * H. Scott-Russell (1993–1994) C.C. Holtzhausen N. Singh * E.C. Ranson (1934–1935) J.A. Cruise (1994–1995) D.A.J. Ross-Watt (1995–1996) W.C. Joughin A.G. Smith * R.A. Flugge-De-Smidt N.A. Barcza (1996–1997) G.R. Lane M.H. Solomon (1935–1936) * R.P. Mohring (1997–1998) E. Matinde D. Tudor * T.K. Prentice (1936–1937) * R.S.G. Stokes (1937–1938) J.R. Dixon (1998–1999) H. Musiyarira A.T. van Zyl * P.E. Hall (1938–1939) M.H. Rogers (1999–2000) G. Njowa E.J. Walls * E.H.A. Joseph (1939–1940) L.A. Cramer (2000–2001) * J.H. Dobson (1940–1941) * A.A.B. Douglas (2001–2002)  !""  "!
     * Theo Meyer (1941–1942) S.J. Ramokgopa (2002-2003) N.A. Barcza J.L. Porter * John V. Muller (1942–1943) T.R. Stacey (2003–2004) R.D. Beck S.J. Ramokgopa * C. Biccard Jeppe (1943–1944) F.M.G. Egerton (2004–2005) W.H. van Niekerk (2005–2006) J.R. Dixon M.H. Rogers * P.J. Louis Bok (1944–1945) R.P.H. Willis (2006–2007) M. Dworzanowski D.A.J. Ross-Watt * J.T. McIntyre (1945–1946) * M. Falcon (1946–1947) R.G.B. Pickering (2007–2008) H.E. James G.L. Smith * A. Clemens (1947–1948) A.M. Garbers-Craig (2008–2009) R.T. Jones W.H. van Niekerk * F.G. Hill (1948–1949) J.C. Ngoma (2009–2010) G.V.R. Landman R.P.H. Willis * O.A.E. Jackson (1949–1950) G.V.R. Landman (2010–2011) C. Musingwini * W.E. Gooday (1950–1951) J.N. van der Merwe (2011–2012) * C.J. Irving (1951–1952) G.L. Smith (2012–2013) G.R. Lane–TPC Mining Chairperson * D.D. Stitt (1952–1953) M. Dworzanowski (2013–2014) Z. Botha–TPC Metallurgy Chairperson * M.C.G. Meyer (1953–1954) J.L. Porter (2014–2015) K.M. Letsoalo–YPC Chairperson * L.A. Bushell (1954–1955) R.T. Jones (2015–2016) C. Musingwini (2016–2017) G. Dabula–YPC Vice Chairperson * H. Britten (1955–1956) * Wm. Bleloch (1956–1957) S. Ndlovu (2017–2018) !   ! "!  Botswana Vacant DRC S. Maleba Johannesburg Vacant %#%*$*+ )$+ "(&)*& Namibia N.M. Namate Scop Incorporated Northern Cape F.C. Nieuwenhuys "('%*& Pretoria R.J. Mostert Genesis Chartered Accountants Western Cape L.S. Bbosa )*)'$*()& Zambia D. Muma The Southern African Institute of Mining and Metallurgy Zimbabwe C. Sadomba Fifth Floor, Minerals Council South Africa Building 5 Hollard Street, Johannesburg 2001 • P.O. Box 61127, Marshalltown 2107 Zululand C.W. Mienie Telephone (011) 834-1273/7 • Fax (011) 838-5923 or (011) 833-8156 E-mail: [email protected] 9 1 0 2 Y R A U R B E F

 
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E M U L ...... iv O V ...... 113 VOLUME 119 NO. 2 FEBRUARY 2019          ...... 105 66 ...... 97 ! ...... 133 6-- onds: Source-to-Use, 2018 onds: Source-to-Use, ...... 123 $ %# Diamonds are forever Diamonds are forever McGill University, Canada NIOSH Research Organization, USA University of British Columbia, Canada DIAMONDS — SOURCE TO USE 2018 CONFERENCE DIAMONDS — SOURCE Murdoch University, Australia Curtin University, Australia McGill University, Canada , University of Exeter, United Kingdom S. Kirkpatrick and J. Mukendwa . . . . L. Musenwa, T. Khumalo, M. Kgaphola, S. Masemola, and G. van WykL. Musenwa, T. Khumalo, M. Kgaphola, S. . . . . T. Khati and M. Matabane. . . . E. Topal, D. Vogt R. Dimitrakopoulos, D. Dreisinger, E. Esterhuizen, H. Mitri, M.J. Nicol, #')*#$'(%#$+ "(&%*+%$*" Operational changes enable Namdeb’s Southern Coastal Mining team to reduce risk and Operational changes enable Namdeb’s Southern into the Atlantic Ocean increase productivity as we advance deeper by Accurate delineation of the kimberlite-dolomite contact enabled the slot (end) position of each Accurate delineation of the kimberlite-dolomite in easier blasting of longhole rings, and sub-level cave tunnel to be optimized, resulting waste ingress. This enabled the mine to avoidance of contact overbreak and premature increased confidence in the pipe contact for 3D successfully reduce development costs, with and mitigation of early waste ingress while geological modelling, improved blast design, maintaining the contact’s integrity. The densimetric profiles of dense medium cyclone product streams have traditionally been The densimetric profiles of dense medium cyclone product streams have traditionally such as produced by using heavy liquid sink-float analysis, which has certain disadvantages, the associated safety and health risks. The RhoVol technology can generate the density This distribution of a batch of particles in a rapid, accurate, repeatable, and safe manner. technology can be applied across all commodities that use dense medium cyclones. A review of the design of the modern, fit-for-purpose diamond processing plant at Cullinan A review of the design of the modern, fit-for-purpose in 2017, was carried out to provide guidance on Diamond Mine, which was commissioned The assessment provided an understanding of what can be expected from the milling circuit. liberation, energy consumption, and the future of the new milling circuit regarding diamond diamond processing as a whole. Diamond exploration and mining in southern Africa: some thoughts on past, current, and possible future trends by W.F. McKechnie . . . . The Theory of Constraints (ToC) has been applied to focus efforts on improving overall business The Theory of Constraints (ToC) has been processes, opportunities were identified, solutions profitability. Through analysis of the mining impressive results. This paper outlines the solutions developed, and initiatives implemented with analysis. that were adopted and the results of the ToC The new Cullinan AG milling circuit – narrative of progress a by Monitoring the performance of DMS circuits using RhoVol technology by M. Fofana and T. Steyn . . . . Journal Comment: Diam by T.R. Marshall ...... Entrepreneurial exploration for diamonds in southern Africa will be tempered by the potential Entrepreneurial exploration for diamonds in southern Africa will be tempered by the value equation and security of investment. Recent developments in diamond recovery technologies provide opportunities to reinvigorate current mines and old prospects previously key factor considered too difficult or costly to exploit. Position on the cost curve will remain a for survival in an increasingly competitive environment. Contents by Kimberlite-country rock contact delineation at Finsch Diamond Mine Kimberlite-country rock contact delineation President’s Corner: by A.S. Macfarlane ...... ,   
  

  

 



   

    



 




   B. Genc  M. Tlala D. Tudor  S. Ndlovu R.D. Beck R.T. Jones  T.R. Stacey

P. den Hoed   W.C. Joughin

J.H. Potgieter H. Lodewijks N. Rampersad C. Musingwini  

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M. Dworzanowski !"('%*($+%#&'$#' ii  

  for resale. purposes, for creating new collective works, or Schenectady, New Yorkconsent 12301, does U.S.A. not This copying, extend to such otherdistribution, kinds as for of advertising copying or promotional for general paid through the Copyright Clearance Center, Inc., Operations Center, P.O. Box 765, 108 of the U.S. Copyright Law. The fee is to be paper beyond that permitted by Section 107 or copier pays the stated fee for each copy of a by any meansthe publishers. without the prior permission of copyright holder consentscopies to of the the makinguse. article This of for consent is personal given or on internal condition that the a retrieval system, or transmitted in any form or     U.S. Copyright Law applicable to users In the U.S.A. The appearance of the statement of copyright at the bottomappearing of in the this first journal page indicates of that an the article of this publication may be reproduced, stored in purposes of research or private study. No part THE INSTITUTE, AS A BODY, IS NOT RESPONSIBLE FOR THE STATEMENTS AND OPINIONS ADVANCED IN ANY OF ITS PUBLICATIONS. an article may be supplied by a library for the Copyright© 2018 by The Southern African Institute of Miningreserved. and Multiple Metallurgy. copying Allthis of rights publication the or contentspermission of parts is thereof inpermission breach without is of hereby copyright,titles given but and for abstracts theauthors. of copying Permission papers of to andshort copy names extracts illustrations of from and contributions the is text usually ofapplication given individual to upon the written source Institute, (and provided where thatis appropriate, the acknowledged. the Apart copyright) for from the any purposes fair of dealing review or criticism under of the Republic of South Africa, a single copy of E-mail: [email protected] (*)'%*+%
+)#+ )&& %*#$& ")*'(&(#+)*)&)#'$'() *(#')"++ The Southern African Institute of The Southern African Institute Mining and Metallurgy P.O. Box 61127 Marshalltown 2107 Telephone (011) 834-1273/7 Fax (011) 838-5923 E-mail: [email protected] )&)'+$#"+(&)"+ ISSN 2225-6253 (print) ISSN 2411-9717 (online) Camera Press, Johannesburg Barbara Spence Avenue Advertising Telephone (011) 463-7940 VOLUME 119 NO. 2 FEBRUARY 2019

Financing diamond projects by J.A.H. Campbell ...... 139 The lack of new significant discoveries in recent years has eroded investor’s confidence, yet no new discoveries are possible without investment in exploration. Alternatives to traditional funding mechanisms for diamond projects are discussed in this paper. The application of XRT in the De Beers Group of companies by A. Voigt, G. Morrison, G. Hill, G. Dellas, and R. Mangera ...... 149 Applications of XRT are found across kimberlite, alluvial, and marine operations as a result of intensive R&D conducted over the years, which has led to the development of a suite of machines that are capable of sorting and auditing diamonds across all size ranges. However, the technical challenge remains in the finer size fractions, for high- capacity-machines as a direct alternative to conventional diamond recovery technologies. Jwaneng – the untold story of the discovery of the world’s richest diamond mine by N. Lock ...... 155 Despite the pre-eminence of Jwaneng as the world’s richest diamond mine, the discovery story has long been clouded in mystery. This is the 45-year old untold story of the Jwaneng discovery and contemporaneous Bechuanaland/ Botswana political and socioeconomic history. A strategy for improving water recovery in kimberlitic diamond mines by A.J. Vietti ...... 165 Scarcity of a consistent and reliable water supply is a constant reminder to Southern African diamond miners of the need to minimize raw (new) water input while maintaining or expanding mine throughput. This paper presents a first-step strategy that kimberlite diamond mine operators should consider and apply to meet and exceed their water-saving targets.

PAPERS OF GENERAL INTEREST

Investigation of flow regime transition in a column flotation cell using CFD by I. Mwandawande, G. Akdogan, S.M. Bradshaw, M. Karimi† and N. Snyders ...... 173 Two alternative methods are presented in this study in which the flow regime in the column is distinguished by means of radial gas holdup profiles and gas holdup versus time graphs obtained from CFD simulations. Gas holdup versus time graphs were used to define flow regimes with a constant gas holdup indicating bubbly flow while wide gas holdup variations indicate churn-turbulent flow. Development of a blast-induced vibration prediction model using an artificial neural network by A. Das, S. Sinha, and S. Ganguly ...... 187 An artificial neural network model was developed for prediction of blast-induced vibration using 248 data records collected from three coal mines with diverse geo-mining conditions. A good correlation between the measured peak particle velocity and the model output was established. The model performance was further improved by using site- specific structural discontinuities as input. Changes in subsidence-field surface movement in shallow-seam coal mining by X-J. Liu and Z-B. Cheng ...... 201 Surface subsidence is a complex dynamic spatiotemporal process that constantly changes as mining advances. With Liangshuijing coal mine as a case study, 3DEC numerical software was used to simulate the development of the moving subsidence field from open-off cut to full subsidence on the working face. The results demonstrate that the formation of a subsidence field is directly related to coal seam depth and the extent of the mine workings. Recycling pre-oxidized chromite fines in the oxidative sintered pellet production process by S.P. du Preez, J.P. Beukes, D. Paktunc, P.G. van Zyl, and A. Jordaan ...... 207 The results of this investigation suggest that recycling of chromite-containing dust collected from pellet sintering off- gas and fines screened out from the sintered pellets (collectively referred to as pre-oxidized chromite fines) up to a limit of 32 wt% of the total pellet composition may improve cured pellet compressive and abrasions strengths. Additional benefits may lead to improved metallurgical efficiency and reduced specific electricity consumption during smelting.

         
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his edition of the Journal is dedicated to papers covering many aspects of the exploration, mining, processing, and beneficiation of diamonds: a commodity of great significance to the economy of TSouth Africa for more than a hundred years. Diamonds provide a unique source of interesting history in South Africa, and learnings from the early days of diamond mining are still relevant to the formulation of policy issues today, especially amongst artisanal, emerging, and junior miners. The first known diamond discoveries occurred along the banks of the Vaal River, near Barkly West, in alluvial deposits, after the discovery of the Hopetown diamond in 1807. These alluvial deposits were worked on claims belonging to both black and white owners. Diamonds were discovered in Kimberley after Erasmus Jacobs found a transparent rock on his father’s farm in the Northern Cape, in 1867, on the Colesberg Koppie. This 21.19 carat diamond became known as the Eureka diamond. After it became known that the alluvial tracts contained diamonds, and that the ’blue ground’ of Kimberley was diamondiferous, the first major strike occurred in 1868. Once word was out, prospectors and entrepreneurs descended upon the area, one of whom was Cecil John Rhodes in 1870, who invested three thousand pounds in the Kimberley diggings: a princely sum in those days. The real rush began in 1871, when Johannes and Diederik de Beer bought the Vooruitsig farm, in what was then the Orange Free State, and discovered diamonds on the land. The site of the farm became what is now the Big Hole, and the De Beers Mine. In 1876 Barney Barnato bought four claims in the Kimberley Mine, and this became the basis for the formation of the Barnato Diamond Mining Company. It is estimated that by 1873, some 50 000 miners were working approximately 1 600 claims over the area. These 10 m 2 claims were serviced by a criss-crossing network of ropes and pipes as the mining, through pick and shovel, saw the original koppie transform into a 240 m deep pit. Not unlike today, the potential of wealth from minerals in the ground created tensions around land ownership, and rights to the minerals and claims. According to ‘The rock on which the future will be built’, by Emelia Potenza (https://www.sahistory.org.za/archive/all- glitters-rock-which-future-will-be-built-emilia-potenza): ‘After diamonds were discovered in the Northern Cape, a battle began about the ownership of the land. The Griquas and Tlhaping who occupied the area claimed exclusive rights to the area. In addition, both Boer Republics (the Transvaal and the Orange Free State) claimed rights to the area .’ A long argument between these parties followed until Sir Henry Barkly, the Governor of the Cape, was asked to mediate. He set up a committee headed by the Lieutenant-Governor of Natal, Robert Keate, to decide on borders. For seven months this committee heard evidence from all four groups who were making a claim. On the basis of this evidence, the committee decided who had rights to the land in an agreement known as the Keate award. The Keate award favoured the Griquas’ claim. This meant that the land which eventually contained Kimberley and the richest diamond fields in the world was given to the Griquas. In the end this agreement helped the Griquas very little. Their leader, Nicholas Waterboer didn't have the power to control the diggers. In the early 1870s the population of Kimberley already numbered 30 000. There was intense rivalry between diggers as they fought over claims. This rivalry often led to racial conflict. Waterboer asked for British help. Barkly took over the area in Britain's name in 1872. A few years later Waterboer was arrested and imprisoned for attempting to free some of his subjects whom he believed had been wrongfully imprisoned and badly treated by the British. Growing unhappiness over ownership of the land and the right to make claims on the diamond fields led to a rebellion in 1878. The Griqua and Tlhaping rose up against British rule and were crushed.’ Small-scale miners, who held one claim each, were made up of people from Europe, Griqualand, India, Malaya, and China, and they in turn used migrant labour from many tribal backgrounds, including San, Khoikhoi, Griquas, Batlhaping, Damaras, Barolong, Barutse, Bapedi, Baganana, Basutu, Maswazi, Matonga, Matabele, Mabaca, Mampondo, Mamfengu, Batembu, and Maxosa. These people constantly moved in and out of the diamond fields, and became easy targets for robbery, either on their way to take up work or on their way back home. Dissent between the white claim-holders from Europe, America, and Australia, and the Griquas, Tlhaping, Malay, Indian, and Chinese holders, created racial tension that culminated in riots in 1875, based on a belief that African claim-holders were involved in illegal diamond buying. The British authorities responded by dispossessing and cancelling all claims owned by black people.

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. y r o t s i h http://dx.doi.org/10.17159/2411-9717/2019/v119n2a1 Kimberlite-country rock contact delineation at Finsch Diamond Mine by T. Khati* and M. Matabane*

with the intention of improving confidence in ;:.8<8 the resource model. The holes are drilled flat using a percussion drill and logged using a Accurate delineation of the contact between a kimberlite pipe and country GeoVista geophysics tool. Geological rock at production level depths is a challenge due to limited geological information is available as soon logging is data. Geological information is obtained from widely spaced diamond core boreholes which are drilled either from surface or from higher mining complete and the updated geological model is levels within the pipe. Kimberlite pipe/country rock contacts are communicated to the production team. The notoriously irregular and variable, further reducing the confidence in main aims of the project are to reduce the time contact positions defined by the drill-holes. At Finsch Diamond Mine delay during contact delineation, and increase (FDM), the opportunity arose to further improve the confidence in the confidence in the position of the kimberlite- contact positions relative to the planned slot (end) positions of each dolomite contact in an endeavour to fast-track sublevel cave tunnel during the development stage of these tunnels. As a the delivery of the development ends to result, the accuracy of the 3D geological model has improved. caving. Kimberlite-dolomite country rock The use of diamond drill core for this purpose is expensive due to site delineation is done from the rim tunnels or establishment requirements. The lengthy time taken during site from within the kimberlite pipe in each tunnel. establishment also delays the development of tunnels and support cycles, thereby extending the completion dates. FDM has reduced delays during The aim of planning the mining tunnel and development by adopting percussion drilling, in conjunction with gamma slot at the right location is to ensure stability ray logging. The S36 drill rig is mounted on a moveable platform and does of the tunnels and safe extraction of ore with not require a costly and lengthy site establishment. The holes are no waste being accounted for. Secondary to generally drilled (0°/flat) on grade elevation, and these holes could also be this, delineation has enabled Finsch Diamond drilled from the rim tunnels (developed in waste) into the kimberlite pipe. Mine (FDM) to locate the mudstone lenses A single-boom production drill rig is normally used to drill holes about found at the slot positions of the tunnels, 20 m in length. thereby ensuring that slot positions are not On completion of the contact delineation drilling, gamma logging of established within an incompetent lithology. the holes is conducted using the GeoVista geophysical sonde (or probe) to log the natural gamma signature of the dolomite/ kimberlite contact. The advantage of this tool is that the readings are continuous within =:5:3<065>8=99<;3> centimetre intervals, and due to contrasting characteristics between Finsch mine is located 160 km west-northwest kimberlite (rich in clay minerals) and dolomite, the contact position can be of the city of Kimberley, South Africa. The determined accurately. The better definition of contact positions also adds kimberlite main pipe is a near-vertical value to tunnel stopping distance in terms of developing the tunnel’s slot intrusion with a surface area of 17.9 ha and is at the optimum distance from the contact (easier blasting of longhole elliptical in outline. The main orebody occurs rings, avoidance of contact overbreak and premature waste ingress, and other matters relating to extraction of ore from these tunnels). This on a northeast-striking dyke called the Smuts method is highly successful and has reduced development costs (on-time Dyke and forms part of the Finsch kimberlite completion), improved definition of the pipe’s contact position for cluster, comprising the Finsch, Shone, and geological modelling, improved blast design, and mitigated early waste Bowden pipes (Ekkerd, 2005). It has been ingress by maintaining the contact’s integrity. classified as a Group II kimberlite, with an age =:748 of 118 Ma. One of the characteristics of Group natural gamma logging, contact delineation, kimberlite-dolomite contact, II kimberlites is a high potassium content. middling, waste ingress.

;97:4109<:;> * Petra Diamonds, South Africa. The objective of the project is to establish the © The Southern African Institute of Mining and Metallurgy, 2019. ISSN 2225-6253. This paper kimberlite-dolomite contact position with the was first presented at the Diamonds — Source to intention of ensuring proper planning designs Use 2018 Conference, 11–13 June 2018, and management of waste during Birchwood Hotel and OR Tambo Conference development. Contact delineation is performed Centre, JetPark, Johannesburg, South Africa.

         
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 97 Kimberlite-country rock contact delineation at Finsch Diamond Mine

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The Finsch kimberlite consists of eight main kimberlite facies, denoted F1 to F8 (Figure 2). The F5/F6 and F3 facies constitute the precursor bodies on the outer perimeter of the main pipe. These precursor bodies are mainly coherent kimberlite types. F1, F7, and F8 form part of the main pipe, with F1 and F8 being volumetrically the most significant units. F1, F7, and F8 are volcanoclastic kimberlite types. F2 and F4 occur as a hypabyssal plug and dykes within the main pipe and are postulated to represent the last stage of intrusion of the kimberlite (Ekkerd et al., 2003). Kimberlite magma, upon eruption, sampled Karoo and Transvaal Supergroup sediments, and these are now preserved in the main pipe as large xench’ths of basalt, mudstone, dolerite, and sandstone. ,<317=>&,<;80-><6/:;4>(<;=>$60<=8>)=74>5 >%% *<9=76917=>7=<= In sublevel block caving the middling between the rim tunnels and the kimberlite-dolomite contact should not be Table I more than 15 m to ensure tunnel stability in the SLC environment (Tukker et al., 2016). Moreover, the exact =;8<9<=8>$:7>=60->5<9-:$60<=8 spatial location of the pipe contact is as important as that of *<9-:5:3 =;8<9>30/ the internal kimberlite phase contacts for ensuring the stability and integrity of the rim tunnels. The designs of rings F1 2.53 were done based on trial and error or on the application of F8 2.61 Dolerite-basalt breccia (DBB) 2.6 ‘rule of thumb’ (Onederra, 2004). Moreover, rings must F3 2.54 function as designed, and it is important that engineers, F4 dyke 2.74 geologists, and mine and plant managers have access to F2 2.8 Sandstone 2.24 accurate modelling and simulation processes and cost- Mudstone 2.41 effective design parameters at the outset. According to Dolomite breccia 2.59 Onederra and Chitombo (2007), the objectives of ring design Dolomite 2.81 include (but are not limited to) reduction of dilution and efficient orepass performance, therefore FDM decided to kimberlite-dolomite contact is 7.5 m to 8 m. The reason for delineate the contact. The difference in blasting domains is a this middling is to achieve the best extraction of ore without significant factor in ensuring proper ring designs and should damaging the contact. Rings are to be designed in such be ascertained jointly by the geologist, geotechnical engineer, manner that the interaction with the contact is minimal, i.e. and drill and blast engineers. no damage to the contact and yielding more ore before waste ingression. Incompetent lithofacies such as mudstone <80188<:;> compromise the stability of tunnels (Tukker et al., 2016), At FDM, the middling between the slot position and the therefore the slot must be within competent lithofacies. 98   
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Kimberlite-country rock contact delineation at Finsch Diamond Mine

A different approach was taken when designing slot in the drawpoints which, coupled with delineation, effectively positions within the South West Precursor (SWPC). A 2 m controls excessive waste mining and loading. middling was opted for as the SWPC is extremely competent Mathebula (2004) estimates 70% waste ingression hypabyssal kimberlite that provides easy caving. As a towards the end of the block 4. The dolomite sidewalls ravel consequence, mining too close the country rock poses the risk back to a stable angle, and large volumes of waste will report of introducing large amounts of waste early (Butcher, 2000). to the bottom, which will result in low grade due the mixing Waste or dilution is better prevented than controlled as it of dolomite and kimberlite. Bull and Page (2000) characterize threatens the viability of the mine, especially in SLC where up sublevel caving as a compromise between ideal layouts and to 40% waste is encountered. To illustrate early introduction what the orebody allows. For this reason, the mine engineers of waste, Figure 3 shows a slot ring reporting 70% waste tend to focus on immediate development costs and conclude rock upon the first blast. The irregular shape of the SWPC, that less development is cheaper, thereby overlooking the poor mining practices, and failure to define the contact are negative effects on head grade (due to planned and the reasons for breaching of the kimberlite-dolomite contact unplanned dilution) and loss of production. The mine plan on the 61 level. In contrast to the 61 level, the 63 level should consider dilution and production as the most orebody boundary was redefined, with few tunnels breaching significant factors in mine design layout. During production, the contact (see Figure 8). the rings must be inclined (10–20º) to prevent waste from The SWPC (F5/F6) is coherent/hypabyssal, competent being drawn in early before most of the ore material is loaded kimberlite. Figure 4 shows the kimberlite facies at Finsch (Figure 5). mine relative to the country rock (dolomite); there is dolomite Kimberlite-country rock delineation was adopted at situated between the main pipe and SWPC. Finsch mine Finsch with the intention of reducing development costs such utilizes vertical and inclined dump ring designs. In addition as that due to breached contact support. Figure 6 shows to raiseboring, vertical dump is used to initiate free fall of ore tunnels where the contact was breached which resulted in an flow. Experience has shown that a correctly designed increase in mining cycle time, costs, and reinforcement middling will enable proper ore caving with less damage to the contact, which is already brecciated/broken, thus ensuring minimal unplanned waste ingress and ring designs to within ±1–2 m. In addition, the correct middling will SWPC enable a ring dump not less than 45°. A flatter angle will Mudstone make charging and ore extraction difficult because of the flat DBB repose angle (Bullock and Hustrulid, 2001). The steeper the angle of repose, the better the extraction due to the flow of ore under gravity. Proactive waste management practices F1 during the development of tunnels are crucial to ensure that the rings continue to hold back excessive waste ingression. F4 dyke Dilution and ore losses are drawbacks for sublevel caving. Scientific investigations have been conducted to determine the flow of ore in a cave and to identify means of F3 reducing ore losses and minimizing dilution. Dilution varies between 15% and 40% and ore losses can be from 15% to F8 25%, depending on the geological conditions. Dilution is of less importance for orebodies with diffuse boundaries where the host rock contains low-grade mineralization, or for magnetite ores, which are upgraded by simple magnetic separators (Hamrin, 1986). The geology department at FDM ,<317=>&,<;80->4<6/:;4>.<.=>/:4=5 conducts visual estimations to determine waste percentages

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 99 Kimberlite-country rock contact delineation at Finsch Diamond Mine

being at the anticipated position (see Figure 8). Delineating the contact improves geological confidence in the model and compensates for the core losses encountered during drilling as a result of core handling errors and bad ground conditions (Figure 6). Four out of five tunnels intersected the kimberlite-dolomite contact unexpectedly. If the contact is not delineated accurately, tunnels are blasted through the contact, thereby damaging about 2 m of the baked and brecciated contact margin or zone (Figure 7). ,<317=>'&:7=>$7:/>+:7=-:5=>)2''>8-:<;3>9-=>+7=00<69=4+6=4 Specifically, the visual estimation performed in 63L SW 0:;9609>:;= KT6 slot resulted in 70% waste vs kimberlite. Contact delineation has increased confidence in the resources even though there has been a volumetric decline, as shown by the requirements (class 7 support) (Onederra, 2004). As a result previous contact position (grey vs black outline in Figure 8). of breaching contacts, there will be high waste ingress in The irregular shape of the SWPC and core loss during comparison with what the waste ingress model of Page and diamond drilling is compensated with the use of contact Bull (2001) predicts (70–80%) at the end of caving. As an delineation (Figure 8). FDM experienced poor mining illustration, Figure 3 shows 70% waste vs 80% ore recovery. practices on 61 level, as shown by Figure 8, as four out of The need to delineate the kimberlite-country rock contact was five tunnels breached the kimberlite-dolomite contact. In shown by the irregularity of the SWP, and poor drilling and order to implement correct principles in controlling waste, blasting practices which resulted in contact positions not there is a need to define waste, i.e. top, side, or internal. The

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Kimberlite-country rock contact delineation at Finsch Diamond Mine reduction is by definition, design, and draw principles. Geotechnically, it is important to know the lithology being Unsupported mining in massive orebodies tends to lead to mined, especially as regards density and other properties. A high waste or dilution (40%) (Kosowan, 1999), and dilution 2 m offset or standoff is considered when designing rings increases with more muck being extracted. within tunnels next to the kimberlite-dolomite contact. This Mine design is critical as it impacts on development costs, is important in ensuring that minimal waste is allowed into drill and blast, recovery, and geotechnical stability, i.e. where the cave and there is no damage to the kimberlite-dolomite the stress field orientation and rock mass quality influence contact. the mine design. FDM experiences both internal and side The inclination of rings is 10 to 20º forward to assist in dilution, hence contact delineation is aimed at preventing or feeding the ore prefentially into the drift by providing a small reducing early ingress of waste. As identified by Butcher overhang to diluting material above (Darling, 2011). The (2000), the define, design, and draw principle is aimed at inclination is to ensure that holes are drilled on a similar preventing dilution rather than controlling it. However, if plane for improved blasting results and additional protection prevention fails, controls must be put in place. The FDM of the brow. Inclined brows improve stability and access for geology department conducts visual inspections on a daily charging of the holes. Safety is another reason for inclined basis. ring designs (Kosowan, 1999). In addition, the gradient According to Butcher (2000), the define principle is depends on the relative size and densities of ore and waste geologically significant in delineation of the orebody and rocks. When ore material is coarser than waste material, the surrounding country rock. Geology must determine the dump must be tilted backwards to avoid fine ore material boundaries of country rock and orebody. Following the being lost in the void of blasted waste rock (Kosowan, 1999). design principle, FDM set the boundary at 7.5–9 m between A forward inclined ring is best for ensuring good the orebody contact and stope boundary. This measure will breakage of rock blocks and would avoid crossing reduce the side and internal dilution through better ring discontinuities that could potentilly result in cut-offs and designs and better blasting practices. In addition to poor fragmentation. The purpose of the slot position is to prevention principles, FDM conducts daily visual estimations provide a free face when blasting (Table II and Hoek, 2016). as a control measure in the drawpoints and scanline logging The Karoo sediments found within the main pipe and in the during tunnel mapping. SWPC make drilling ahead of the development tunnels a Figure 9 shows ring designs used at FDM and their necessity. Mine planning and design flexibility is needed to benefits, i.e. a vertical front is used to initiate the rings and accommodate changes in the modelled lithological units and inclined rings have the potential to delay introduction of their effects on the geotechnical and resource model (Tukker waste from above, and shield brows from break-back. When et al., 2016). The middling between rim tunnels and actual designing rings in an SLC mining method, it is important to contacts should not be less than 15 m to ensure stability of consider lithology, density, and grade (Mathebula, 2004). rim tunnels. Geotechnically, sublevel caving requires specific Development should take place in competent rocks to rock mass conditions and stoping geometry; ring drilling may accommodate mining-induced stresses. Mudstone is vary and involve or include upholes, downholes, and even incompetent, hence FDM avoids the development of slots inclined holes (Villaescusa, 2014). within the mudstone facies. Slot position is dependent on the Figure 8 shows 61L which intersected the dolomite rock mass conditions, stope access, and extraction sequence. contact prematurely due to a sharp inward turn of the The slot should also be designed to reduce failure within the contact. The 61L SW KT6 is situated between tunnels 8 and production rings (Villaescusa, 2014). Support should be 9; contact holes were not drilled beforehand and ‘blind’ increased when mining through incompetent ground mining was undertaken in this case. This sharp turn or curve (Mzimela, 2013). Finsch kimberlite facies are hard, but upon is believed to be the reason for the 70% waste ingress when interaction with water they become as weak as soil; thus the the first ring was blasted. Contact drilling could have strength is compromised upon exposure to moisture. The mitigated this issue. In order to implement working waste emplacement mechanism influences the size and geometry, rock mass competency, and character of the pipe contact zones. These factors affect the mining method and dilution. Characterizing the clay provides important clues to the susceptibility of the various kimberlite facies to weathering. Knowledge of country rock and pipe geology is paramount. Delineation programmes should aim to ensure that the holes penetrate deep enough into the waste rock to ensure it is not a country rock xenolith. One of the geotechnical issues to consider in selecting the mining method and design is the strength and deformation characteristics of the rock mass. Some kimberlite facies are weak to moderately strong. Designing in a strong rock mass is not an issue; however, when kimberlite is exposed to moisture, swelling of smectite clays present in the matrix weakens the rock. The weathering susceptibility of kimberlite must be known in order to build this factor into the mine design and avoid surprises during development, such as a tunnel collapses due to water. ,<317=>!&#=79<065> <;05<;=4>41/.>:$>7<;3>4=8<3;

         
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 101 Kimberlite-country rock contact delineation at Finsch Diamond Mine

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Extraction heading Width (w) Maximize draw throat – maintain stability 4.2 m 2.4–6.0 m Spacing (w+W) Minimize development 14.2 m Height (H) Minize to reduce ore loss 3.5 m 2.5–4.3 m Sublevel interval (S) Related to blast-hole drilling accuracy 15 m 8–25 m Height of draw (H) Less than twice sublevel interval 29 m 12–30 m 2–3.5(w+W) Pillar width (W) Optimize ore recovery 10 m Ring gradient Angled forward- minimize dilution and maintain brow stability +80° ±70–90° Burden (V) Balance between ore recovery and waste dilution from previous ring 1.8 m 1.5–3.7 m Support Maintain brow and pillar stability

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control measures, the type of waste must be known – namely; Table III top, side, and internal waste. This will lead to waste reduction by defining, designing, and drawing (Butcher, 2000). :/.67<8:;>+=9==;>4<$$=7=;9>81..:79>05688=8 The middling between the slot position and the contact 18=4>69>,<;80->/<;=>6;4>9-=<7>7=8.=09<=>0:898 should be 7.5–8 m. Therefore, owing to the four tunnels intersecting the contact, early waste ingress was experienced 5688>81..:79 .=>:$>81..:79 16;9<9>.=7><9=/ :89>.=7>/
when the rings were blasted. This should be avoided at all Class 6 Cable anchors 70 Highest costs as failure to drill in advance results in mining through Roofbolts 84 the contact. In addition to the sharp inward turn of the Transverse straps 14 contact from previous position, waste ingress was Longitudinal straps 12 compounded by the type of ring design. An inclined front Class 3b Anchors Longitudinal straps reduces ingress of waste as it prolongs ore extraction. Transverse straps Moreover, contact delineation helps in ensuring that pockets Roofbolts Lowest near contacts are found and properly supported. Pockets of Class 3a Roofbolts water reduce the stability of the kimberlite-dolomite contact, Transverse straps Longitudinal straps rendering it weak. The cost of blasting and supporting was Class 1 Transverse straps 7 high when contact delineation tunnels were developed blindly Roofbolts 70 into the country rock, resulting in unnecessary expenditure. 102   
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Kimberlite-country rock contact delineation at Finsch Diamond Mine

This wastage is in the form support equipment, where for EKKERD, J. 2005. The geology of the block 5 resource. Internal Report. Finsch example class 6 is used instead of class 1 (class 6 support is Diamond Mine. three times the cost of class 1 support). Historically, drilling to confirm inner geological contacts has been an expensive, EKKERD, J., STIEFENHOFER, J., FIELD, M., and LAWLESS, P. 2003. The geology of challenging, and time-consuming exercise. However, at FDM Finsch Mine, Northern Cape, South Africa. Proceedings of the 8th short percussion holes about 30 m in length have been drilled International Kimberlite Conference, Victoria, BC, 22–27 June 2003. to delineate the contact, with an information turnaround time Elsevier, Amsterdam. of less than 24 hours. Contact delineation has afforded FDM with information regarding lithological units and enabled HAMRIN, H. 1986. Guide to Underground Mining Methods and Applications. quick decisions such as whether to extend a tunnel or keep to Chapter 1. Atlas Copco, Sweden. the original design. In addition, where mudstone was intersected slot positions have been moved to a more HOEK, E. 2016. Surface and underground project case histories: Comprehensive competent kimberlite facies Rock Engineering: Principles, Practices, and Projects. vol. 5. Elsevier.

:;0518<:;8 HUSTRULID, W. and KVAPIL, R. 2008. Sublevel caving – past and future. Finsch Diamond Mine experienced challenges relating to SLC Proceedings of the 5th International Conference and Exhibition on Mass development tunnels where the kimberlite-country rock Mining, Luleå, Sweden, 9–11 June 2008. Lulea University of Technology. contact was breached, resulting in increased development and pp. 124–132. support costs which in turn led to delays in turnaround times

(mining cycle). Drilling a single contact delineation hole per KOSOWAN, M.I. 1999. Design and operational issues for increasing sublevel cave tunnel is found to be workable; however, two to three holes intervals at Stobie Mine. MASc thesis, Laurentian University, Sudbury, are ideal to ensure covering all sides of the slot area. In order Ontario, Canada. to avoid delays in drilling for the contact, monthly planning should incorporate the delineation holes and the planning MATABANE, M.R. and KHATI, T. 2016. Application of gamma ray logging for and survey departments need to include these holes when kimberlite contact delineation at Finsch Diamond Mine. Proceedings of issuing survey notes. In the case of tunnels breaching the Diamonds Still Sparkling, Gaborone, Botwsana, 15–16 March. Southern contact, as shown by Figure 8, penalties should be implemented. Therefore, two to three percussion holes African Institute of Mining and Metallurgy, Johannesburg. approximately 7.5–8 m in length should be drilled per tunnel. Contact delineation has resulted in cost savings, especially MATHEBULA, V. 2004. The design and implementation of the Toop of Block regarding waste reduction. Furthermore, early waste ingress 4(TOB 4)/ BOP resource at Finsch Mine (a division of central mines). was experienced in certain areas of the mine as a result of Journal of South African Institute of Mining and Metallurgy, vol. 104. breached kimberlite-dolomite contacts. Knowledge of the pp. 163–170. position of the contacts increased the confidence in resources, as shown by Figure 8 and Figure 10, and geological MZIMELA, B. 2013. Code of Practice: The design, development/construction, safe boundaries were adjusted accordingly. At Finsch Diamond operation and maintance of draw points, tipping points, rock passes and Mine, waste ingress is the result of poor mining practices and box. Lime Acres. incompetent ground conditions. The geology department, through contact delineation, has prevented dilution early on ONEDERRA, I. 2004. Breakage and fragmentation modelling for underground rather than controlling waste, with cost savings estimated to production blasting application. Proceedings of the IRR Drilling and be in the millions. As part of enforcement, financial penalties Blasting 2004, Conference. Perth, WA. should be put in place to ensure that mining contractors do not breach the kimberlite-dolomite contact. In addition, ONEDERRA, I. and CHITOMBO, G. 2007. Design methodology for underground ring monthly planning must take the drilling of these contact holes into consideration. blasting. Mining Technology, vol. 116, no. 4. pp. 180–195.

PAGE, C.H. and BULL, G. 2001. Sub level caving: A fresh look at this bulk ?=$=7=;0=8 mining method. Underground Mining Methods: Fundamentals and

BULL, G. and PAGE, C.H. 2000. Sub-level caving – Today's dependable low cost International Case Studies. Hustrulid, W.A. and Bullock, R.L. (eds). "ore factory". Proceedings of Massmin 2000, Brisbane, Australia. Society for Mining, Metallurgy, and Exploration, Littleton, CO. p. 718. Australasian Institute of Mining and Metallurgy, Melbourne. pp. 537–556. TUKKER, H., MARSDEN, H., HOLDER, A., SWARTS, B., VAN STRIJP, T., GROBLER, E., and

BUTCHER, R.J. 2000. Dilution control in Southern African mines. Proceedings of ENGELBRECHT, F. 2016. Koffiefontein Diamond Mine sublevel cave design. Massmin 2000, Brisbane, Australia. Australasian Institute of Mining and Proceedings of Diamonds Still Sparkling, Gaborone, Botwsana, 15–16 Metallurgy, Melbourne. pp. 1133–118. March. Southern African Institute of Mining and Metallurgy, Johannesburg. DUSTAN, G. and POWER, G. 2011. Sub level caving. SME Mining Engineering

Handbook. Darling, P. (ed.). Society for Mining, Metallurgy & Exploration, VILLAESCUSA, E. 2014. Geotechnical Design for Sublevel Open Stoping. CRC Littleton, CO. pp. 1417–1452. Press.

         
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Copyright ©, Weir Minerals Australia Limited. All rights reserved. WARMAN is a trademark and/or registered trademark of Weir Minerals Australia Ltd and Weir Group African IP Ltd; AH is a trademark and/or registered trademark of Weir Minerals Australia Ltd; WEIR and the WEIR Logo are trademarks and/or registered trademarks of Weir Engineering Services Ltd. http://dx.doi.org/10.17159/2411-9717/2019/v119n2a2 Operational changes enable Namdeb’s Southern Coastal Mining team to reduce risk and increase productivity as we advance deeper into the Atlantic Ocean by S. Kirkpatrick* and J. Mukendwa†

Namdeb mining operations exploited massive land-based deposits, producing nearly 40   million carats from MA1 between 1920 and The mining operation at Namdeb’s Southern Coastal Mine (SCM) is unique. 1977 (Schneider, 2009) when mining targeted It targets gravel layers up to 30 m below sea level, which continue to dip onshore raised beaches west of the high water deeper, further west, under the Atlantic Ocean. On this storm-dominated line. Since 1977 however, SCM and Namdeb coastline, severe water seepage into mining areas, rugged orebody have developed a unique mining method to footwall characteristics, and highly variable resource grades all contribute economically extract the resource which to a challenging operational environment. Namdeb has a proud history of extends westward under the Atlantic Ocean. innovation, and as the mine progresses further westwards and associated Both the location and mining method technical and economic challenges increase, this innovative culture has unsurprisingly present a unique set of become essential to the future of the mine. The Theory of Constraints (ToC) has been widely used at SCM, and across the mining discipline, to challenges, making economic extraction focus efforts on improving overall business profitability. Through analysis increasingly difficult as the orebody dips of the mining processes, opportunities were identified, solutions deeper and deeper to the west beneath the sea. developed, and initiatives implemented with staggering results across all Innovation and operational improvement three mining disciplines, i.e. stripping, load and haul, and bedrock bulking remain crucial to extending the life-of-mine and cleaning. This paper outlines the solutions adopted and the results of (LoM) of SCM. A number of fundamental the ToC analysis. changes have been implemented at SCM over   the last 3 years which have reduced the mining, Namibia, theory of constraints, improvement, beach nourishment. operational risk and increased productivity of the core mining functions. This paper describes these changes and their direct results.

    The Orange River system (Figure 2) has Southern Coastal Mine (SCM) is one of three transported coarse gravel material, including Namdeb operations located in the diamonds, from the southern African southwestern corner of Namibia, between the subcontinent to the west coast of South Africa Orange River in the south, the Namib Desert to and Namibia since Cretaceous times (Jacob, the east and the Atlantic Ocean to the west 2005; Bluck, Ward, and de Witt, 2005). At (Figure 1). These three geographical features least two phases of uplift of the interior set the backdrop for the world’s greatest resulted in renewed river energy, increased marine diamond mining placer (Badenhorst, erosive power, and associated coarse river 2003). SCM is situated along the coastline load, manifesting as deeply bedrock-incised extending from the mouth of the Orange River fluvial channels with remnant abandoned to Chameis Bay approximately 120 km to the terraces and associated gravel deposits along north. The active mining area, called Mining Area 1 (MA1) is, however, limited to very narrow strip, 30 km in length, in the south of the licence area, close to the town of Oranjemund. Namdeb, a wholly owned subsidiary of * Mining Optimisation, Southern Coastal Mine, Namdeb Holdings, is a 50/50 joint venture Namibia. between De Beers and the Government of † Southern Coastal Mine, Namibia. Namibia. Diamonds were first discovered along © The Southern African Institute of Mining and Metallurgy, 2019. ISSN 2225-6253. This paper the Namibian coastline in April 1908, close to was first presented at the Diamonds — Source to the town of Luderitz, but mining operations Use 2018 Conference, 11–13 June 2018, started in the SCM mining area only in Birchwood Hotel and OR Tambo Conference February 1929 (Schneider, 2009). Initially all Centre, JetPark, Johannesburg, South Africa.

         

   
 105 Operational changes enable Namdeb’s Southern Coastal Mining team to reduce risk

capable of moving cobble-sized gravel at depths of 15 m (de Decker, 1988). Consequently, the sand component of the outfall of the Orange River is transported offshore and north by the longshore drift system, and at certain points it is washed back onshore to feed the Namib Sand Sea. The gravel (and diamond) component of the outfall is retained along the coast for about 300 km where it has been reworked into a series of coarse beaches underlain by the gullied and potholed Late Proterozoic metasedimentary basement. This rugged basement forms fixed trapsites which further upgrade the diamondiferous gravel on wave-cut platforms (Jacob et al., 2006). Four types of gravel beaches have been identified in the Pleistocene-Holocene gravels of the Namibian coastal strip north of the Orange River (Spaggiari et al., 2006; Schneider, 2008). Near the river mouth, gravel accumulates as spits with associated back-barrier lagoons; northwards, with increasing distance from the point source of sediment supply, spits give way to barrier beaches, linear beaches, and finally pocket beaches where the coastline forms natural bays. The active SCM mining areas are situated within the zone of barrier beaches and linear beaches. The diamondiferous orebody comprises a coarse gravel (8306<=/'$;17:8;9=.7-=,;6=7.2<5=.89893=+81<91<=76<75=892817:893 :4<=71:8 <=;0:4<69=;75:7+=)89893=76<7=89=:4<=5;0:4 facies that directly overlies and infills a rugged, gullied, and potholed predominantly schistose bedrock footwall. Clay footwall areas form a lesser proportion of the mine plan and are generally less rugged. The ore horizon is overlain by a sandy overburden comprising both marine and accreted sand with minor gravel terrace components. )89893=.<:4;2 The mining operation at SCM has transitioned from an extensive above sea-level, volume-driven mining operation, through westward expansion of the mining faces, to an operation largely below sea level. To enable movement of the mining areas westwards a process of deliberate coastal accretion is used to transport and deposit sand onto the beaches at specific areas and at defined rates. Various accretion systems are employed; these include conveyors, treatment plant tailings disposal, and the dumping of overburden material, which is part of the overburden stripping process. The sand deposition profiles are fed into an (8306<= '&6793<=8 <6=55:<.=792=+;17:8;9=;,=.7;6=1066<9:=;0:4<69 accretion model, which has been developed and calibrated ,68179=287.;92=.89<5=&67-7=1;.-+<=9;:=54;*9 over a number of years. This model is used to predict the annual +2 m contour positions used in the mine planning process. The +2 m contour is the contour that runs along the the river course. The river ultimately deposited its load of beach at 2 m above mean sea level (AMSL) and defines diamondiferous material into the Atlantic Ocean, where which areas will be available for future mining. The mine marine reworking processes subsequently further upgraded plan and accretion model are interdependent; changes in the the diamondiferous gravel during repeated sea-level mine plan alters the deposition points and volumes, resulting transgressions and regressions (Bluck, Ward, and de Witt, in changes to the accretion line predictions. Figure 3 shows 2005), resulting in a placer deposit comprising 95% gem the five-year waste deposition volumes and associated quality stones. annual accretion prediction lines. The wave-dominated west coast of Namibia is one of the The sub-sea-level mining operations at SCM, directly most vigorous coastlines in the world; 90% of the waves adjacent to the Atlantic Ocean, make operations vulnerable to have a height of 0.75–3.25 m, with an average of 1.75 m for frequent storm events. Workings are protected from storm winter and 1.5 m for summer (Rossouw, 1981; de Decker, events by seawalls constructed along the western side of the 1988). The coastline is also exposed to storm events mining area. Prior to opening a new mining cut, seawalls are associated with passing frontal systems (Smith, 2003) and constructed along the western side of the cut to a height of wave heights above 9 m. This, in combination with the long- between 7 m and 10 m above sea level, with a minimum period swell and a strong prevailing SW wind regime width of 20 m. To further mitigate risk during storm events, (Rogers, 1977) produces a strong northerly longshore drift, the seawalls are set back a minimum of 25 m east of the 106   
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Operational changes enable Namdeb’s Southern Coastal Mining team to reduce risk

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=<733<67:<2

+2 m contour and are often widened to 30 m. Figure 4 outlines a simplified version of the cycle of accretion, seawall construction, and mining. On completion of the seawall, the stripping fleet, consisting of 80 t excavators and 40 t articulated dump trucks (ADTs), then focuses on loading overburden material out of the mining cut and dumping it on the beach to the west of the seawall (Figure 5). This material dumped is thus made available for beach accretion, creating space for future mining. Material close to surface is generally dry but once the phreatic line has been intersected, seepage from the sea ingresses into the mining cut resulting in much wetter overburden material and, consequently, the need for water management. Water channels are constructed along the eastern toe of the seawall to channel water to a sump where pumps remove water from the cut. Channels and sumps are maintained and deepened as mining progresses down to bedrock. Once excavators ‘hit bedrock’, i.e. once the (8306<= ' 67-4817+=2<-81:8;9=;,=:4<=5:68--893=792=7116<:8;9=5<0<91< excavator bucket starts to scrape against the highest bedrock 7:=) points, the stripping operation has reached completion and bedrock teams can move in to start bulking operations. Bedrock teams consist of both a bulking and a cleaning crew (Figure 6) who, for security reasons, work only during day shift. The bulking process is used to clean out most of the material from bedrock gullies and potholes using hydraulic equipment to break open narrow areas, load out material, and finally scrape the bedrock clean with bullnose (8306<='4;:;5=:7<9=;9=:4<=5<7*7++=54;*893=:4<=5<7=:;=:4<=*<5:=792 buckets. The bulking fleet includes a bulldozer, a 60 t :4<=.89893=10:=:;=:4<=<75: excavator, a number of smaller 20 t hydraulic excavators, and 20 t hydraulic hammers. When cemented material is encountered, hydraulic hammers are used to break this harder material out, after which dozers and the 60 t excavator are used to transfer material to loading areas, where stockpiles can be loaded and hauled to the plant for treatment. Bedrock cleaning crews complete the final vacuuming of the bedrock, removing all fine gravel particles lodged in (8306<='4;:;5=;,=<26;1=;-<67:8;95=54;*893=0+893=;9=:4<=+<,: cracks, potholes, and gullies. Cleaning crews use industrial 792=5;.<= <6=2<<-=<26;1=30++8<5=;9=:4<=6834:

         
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 107 Operational changes enable Namdeb’s Southern Coastal Mining team to reduce risk vacuum units which suck up material into a collection bin 1992). This also requires that all other processes are focused that is then trammed to the plant. As many as 12 vacuum on ensuring the throughput at the constraint is maximized. units can be used on a single site with two operators Defining the mining processes and identifying manning each suction pipe. Profiles of the bedrock horizon bottlenecks focused the team on where opportunities exist for are undulating with variable ruggedness; some areas having value-adding improvement. Following the initial ToC a relatively flat profile while others have gullies and potholes analysis, availability of material to feed the plant was more than 5 m deep. highlighted as the key bottleneck within SCM. On further Load and haul (L&H) teams are used to transport bulked analysis, across the other mining processes, it was also noted material from the bedrock sites to the plant and ensure the that insufficient buffers existed between the various plant feed rates are maintained. The L&H fleet comprises 320 processes and that bottlenecks would therefore quickly move kW front-end loaders and 40 t rigid frame trucks which tram to the other processes if not addressed simultaneously. all diamondiferous material from the mining sites to the The mining team therefore considered the opportunities plant. to create buffers and remove bottlenecks across all three Plant feed material from both L&H and bedrock collection mining disciplines (stripping, L&H, and bedrock cleaning), bins are treated through a simple process comprising primary identified the key focus areas, and then detailed plans and secondary crusher circuits, a series of scrubbers, and around the implementation of the changes. Localized finally a dense medium separation (DMS) plant. Plant accretion is believed to be dependent on the stripping tons concentrate is taken to the Red Area Complex (RAC) for final deposited on the beach and as such. stripping and accretion diamond recovery. Plant tailings are conveyed to the sea, were considered jointly when defining the improvement plan. thus contributing to beach accretion. The improvement plan roll-out therefore began with stripping and accretion, followed by bedrock processes, and finally the !9 86;9.<9:7+ L&H operations. However, in practice, many of the improvement projects were implemented simultaneously. Namdeb has a valid environmental clearance certificate, issued under the Environmental Management Act (2007) and   
  Regulations (2012) of Namibia, for all relevant mining Before any of the improvement initiatives were introduced, it licence areas, including ML43 which covers Southern Coastal was critical that a ‘solid’ mine plan be developed; i.e. one Mine. with sufficient detail and realistic targets. Although the To ensure continued compliance, Namdeb conducts a nature of the SCM mining operation requires flexibility that number of monitoring programmes, audits, and stakeholder enables changes in the mining sequence, in reality this is engagement sessions that include: time-consuming and disruptive to the process. The Annual coastal marine monitoring of its beaches development of the plan therefore went through numerous Annual ISO14001 environmental management system reviews and revisions, considering various options and audit addressing possible risks. To mitigate risk budget planning Third-party legal audit conducted every two years included all key stakeholders, especially the high tension Annual Namdeb Environmental Stakeholders Forum electrical team (HT) and the dewatering team. The timing of Quarterly meetings of the De Beers Marine Risk seawall moves, especially during winter months, was also platform changed to reduce budget plan risk profiles. Namdeb Marine Scientific Advisory Committee. With a more ‘rigid’ plan in place, execution became critical. A weekly drive-through planning session was ?.-6; <.<9:5 therefore initiated that included all relevant stakeholders, in order to align the whole team around the plan. All tasks and    priorities were defined for each area with tracking of As the SCM operation has advanced westwards beneath sea compliance to plan. This forum also improved communication level, the operation has been exposed to ever-increasing risk; across departments, enabling proactive engagement, greater possibility of a seawall breach, increased overburden operational input, and assistance when required. The drive- stripping volumes and costs due to deeper mining cuts, through also became a key forum for ensuring the increasing water seepage into the workings, which increases progression of improvement projects. pumping volumes and costs, as well as lower confidence in the resource estimation due to practical sampling constraints.   These factors all impact on an already marginal operation. When the ToC was applied within stripping, the key Before progressing with improvement initiatives, a solid bottlenecks and improvement opportunities identified mine plan and effective execution were deemed to be included: paramount to the success of any improvement projects. Long circuit distances that resulted in longer cycle Following the stabilization of the operation, the Theory of times and reduced productivity Constraints (ToC) has been widely used at SCM, and Under-loaded trucks that resulted in reduced payloads especially across the mining discipline, to focus efforts on and lower productivities improving overall business profitability. The ToC is a Poor underfoot conditions that increased rolling management philosophy introduced by Eliyahu M. Goldratt resistance, reduced tramming speeds, and consequently in 1984, that states that a system output is limited by one or lowered productivity rates more constraints and that an optimum system runs the Lack of redundancy of equipment that resulted in constraint or bottleneck at maximum capacity (Goldratt, reduced fleet capacity when equipment was unavailable 108   
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Operational changes enable Namdeb’s Southern Coastal Mining team to reduce risk

Poor water management in the cut that led to same- This philosophy has a number of advantages in addition bench loading and reduced productivity rates to the obvious benefit of reduced cycle distances and cycle Dozing on the groynes that increased ADT queuing times. For example, with the initial paddock on bedrock and times and delayed tipping operations. with pumping infrastructure in place, water management is far more effective, i.e. water flows away from the stripping        cut. This allows for mining of bigger benches with increased To reduce circuit distances, the mining philosophy and bucket fill factors, and in addition, drier footwall conditions layouts had to be completely redesigned. Previously ADTs enabled more material to be loaded using a more productive, had exited the mining area on the eastern side of the cut, top loading configuration; i.e. excavator on the bench above trammed along the crosswalls, and dumped the overburden the ADT. Both the bucket fill factor and loading set-up have material on 20–30 m wide groynes which pushed westwards added benefits by way of reducing loading times and into the sea. The most obvious solution was to build a ramp improving productivity. straight out of the mining cut, to the top of the seawall and then directly out onto the beach. This layout, however,      caused significant challenges with water seepage into the The payload of the ADTs was noted to be well below loading mining cut through the seawall. capacity. Two options for improving payload were therefore The solution was to divide the mining cut into a number considered; namely, installing greedy boards and/or tailgates. of 200–300 m wide, north-south ‘paddocks’ and focus Greedy boards are fixed extensions to the side of the ADT stripping on one paddock at time as illustrated in Figure 7. bucket (Figure 8), while a tailgate is a mechanism installed at Stripping operations now commence at the paddock with the the back of a truck to allow more material to be loaded. deepest bedrock elevation, Paddock 1, with a temporary ramp Tailgates were considered more effective for loading wet just within Paddock 2. Mining continues in Paddock 1 until material, but the higher cost and potential mechanical the phreatic line is intersected and water starts to seep into breakdowns of the tailgate mechanism was considered a the mining cut. The water is then channelled to the deepest major disadvantage. Greedy boards were successfully trialled side of the paddock where a sump and pump remove the on two trucks and then rolled out to the entire fleet. The water, pumping it back out to sea. Mining then continues in greedy boards have increased the average payload capacity this paddock until bedrock elevations have been reached and by 6 t or 20%. permanent dewatering channels, a sump, and pumping infrastructure can be installed. Stripping teams then move to  
  the second paddock where the previous temporary ramp is Underfoot conditions as a result of the ‘soft’, wet nature of mined out and a new temporary ramp positioned just inside the overburden beach sand were not conducive to creating Paddock 3. By removing the first temporary ramp, water is hard, compact roads and as a result, the road conditions then able to flow back into Paddock 1 where pumping deteriorated quickly once stripping commenced. The poor infrastructure is now in place. This mining sequence is road conditions resulted in high rolling resistance and followed until the entire mining block has been completed. reduced tramming speeds. To improve road conditions additional support equipment was purchased; two wheel dozers and an additional grader. The additional support equipment has subsequently become an integral part of the stripping process. Improved road conditions in the mining areas in conjunction with more compacted temporary ramps have resulted in higher average tramming speeds into and out of the mining cut.     The ToC indicated that excavators remained a key bottleneck within the stripping process. As the prime mover, ADTs were reliant on the excavator availability to achieve production targets. With no redundancy within the system, whenever an

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 109 Operational changes enable Namdeb’s Southern Coastal Mining team to reduce risk excavator was taken out of production for scheduled the advance rates of the bulking crew were lower than that of maintenance, repairs, or auxiliary work such as digging the cleaning crew. Analysis of equipment hours reinforced sumps and channels, the stripping fleet was unable to this observation. Reasons for slower bulking rates included achieve the required production targets. To mitigate against deeper gullies, cemented material, and machine downtime. these scenarios, a fourth 80 t excavator, referred to as a The obvious solution was to increase the amount of ‘swing unit’, was added to the fleet, increasing the utilization machine hours of the bulking fleet. This could be achieved by of the entire stripping fleet and improving production either increasing the size of the bulking fleet or increasing capacity. the operating hours. Bedrock operations, both bulking and cleaning, were originally limited to day shift due to security     concerns, despite the fact that the security risk generally only While redesigning the stripping layouts and implementing the applies to bedrock cleaning. Therefore an additional new mining philosophy, it was suggested that a new afternoon bulking shift was implemented, increasing overall accretion methodology be considered for SCM. The new bulking advancement, creating bulking reserves, and methodology, called beach nourishment, required a change enabling higher productivity of the bedrock cleaning crews. from tipping on the groynes, or point deposition, to building elevated pads along the length of the beach. Although the        SCM application of beach nourishment is unique in its aim to With additional bulking capacity following the provide access to future offshore resources, this methodology implementation of the backshift bulking team, it was now is widely recognized and used around the world to protect possible for the bulking teams to increase the amount of onshore structures and infrastructure. bedrock broken out, especially when narrow gullies and The beach nourishment methodology was initially highly fractured areas were encountered. Traditionally the implemented as a trial in one of the mining areas. Temporary bulking teams would not break out these areas, cleaning out ramps were extended from the top of the seawall onto the only the loose material and leaving the cleaning teams to beach. Material was then tipped along the length of the clean all the cracks, fractures, and narrow gullies. This beach, maintaining a floor elevation of 2–3 m AMSL. The reduced cleaning rates but previously, as bulking remained beach nourishment pad created a bigger dumping area than the bottleneck, the cleaning teams would soon catch up. was previously available when tipping on the crosswall Additional bulking capacity enabled the bulking teams to also groynes, with the added benefit of eliminating the delays break out these areas, removing the cracks and gullies that experienced previously. The proximity of the dumping area previously slowed down the cleaning teams. Consequently, was also generally closer to the temporary ramps, reducing what had originally been a bottleneck for the cleaning teams tramming distances further. is now removed by the bulking team with a knock-on overall The beach nourishment methodology showed improved productivity improvement of the bedrock teams. localized advance rates of the beach westwards and exceeded       predicted accretion lines in all active areas. An added In the past, when cemented material was encountered the significant benefit has been the protection that the beach bulking and cleaning rates were significantly reduced. nourishment pads have afforded the active mining areas. Breaking out cemented material was most effectively done These pads have moved the erosive surf zone westwards, using the hydraulic hammer, but often only one hydraulic away from the seawall, and provided a barrier to dissipate hammer was available per bedrock site. The hydraulic wave energy. During a 1:20 year storm event which hit the hammer therefore became the bottleneck within the operation west coast of Namibia on 7 June 2017, bringing with it +8 m as soon as cementation was encountered. To address this waves, many of the seawalls remained unaffected by the with problem, bedrock teams would move all hydraulic hammers the beach nourishment pads taking the full force of the storm to the site encountering the cementation, ultimately impacting and protecting the seawalls. on bedrock cleaning rates in other areas. Two changes were  therefore adopted. Firstly, all excavators were fitted with hydraulic systems suitable for a hammer installation, and The ToC analysis at the bedrock operation identified the secondly, a larger hammer that could be fitted to the 80 t following bottlenecks: ‘swing unit’ excavator was purchased. The fitting of the Low bedrock bulking rates, resulted in no bulking hydraulic hammer kits has enabled all the spare hammers to reserve for the bedrock cleaning process be fitted to excavators when cemented material is Areas with cracks and narrow gullies experiencing encountered, reducing the bottleneck. In extreme cases where reduced cleaning rates cementation either covers vast areas or is very thick, the Cementation reducing bulking rates. bigger hammer is fitted to the 80 t swing unit excavator and the higher energy and greater breakout force increases the    bulking rates. Although cementation remains a challenge to Historically, bedrock business improvement projects have achieving bedrock production rates, improved tools have focused on bedrock cleaning and generally resulted in reduced the bottleneck. improved cleaning rates. However, the ToC analysis identified bedrock bulking as the bottleneck.   The area that has been bulked by the hydraulic ToC analysis at the plant feed identified the following equipment but not yet cleaned with the vacuum units is bottlenecks where capacity was not optimally used: referred to as ‘bulk reserve’, and it was highlighted that not L&H fleet capacity only was there limited buffer between the two processes but Mining delays impacting plant feed capacity. 110   
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Operational changes enable Namdeb’s Southern Coastal Mining team to reduce risk

   could be removed. Consequently, mining was relocated to another area, with longer tramming distances and lower The L&H fleet originally comprised three FELs and seven efficiencies during this period. Once the pipeline was trucks. In contrast to stripping, where the bottleneck was removed, the SCM stripping team reached a record high excavators, the L&H bottleneck was the trucks. With high production rate in Q4 2017 of 35 414 t/d, up 49% from the tramming distances and long cycle times the FELs had productivity achieved in Q1 2016 (Figure 9). Complementing significantly more capacity than the trucks and any delays on the new mining philosophy, the introduction of beach the trucks therefore had a marked impact on productivity. A nourishment, greedy boards, excavator redundancy, and ‘spare’ truck was therefore added to the L&H fleet as a support equipment has assisted in achieving continued redundant unit, used when one or more of the other trucks productivity improvement. were unavailable.      An afternoon bulking shift, known as the back shift bulking The fundamental bottleneck impacting plant feed capacity team, was successfully trialled from July 2016, with a 55% was a mismatch between the L&H fleet capacity and the plant increase in hydraulic excavator hours and a 77% increase in feed requirements, especially for mining areas far from the vacuum hours. This project has translated into a 32% plant. The L&H fleet, however, works continuous operations improvement, increasing monthly bedrock production from (CONTOPS) and therefore runs more hours than the plant, 30 798 m2/month to 40 612 m2/month (Figure 10). The providing additional capacity while the plant is not running. additional bulking capacity has enabled bulking to create and The rehandling cost, however, had historically resulted in a sustain a bedrock buffer between the bulking and cleaning reluctance to build stockpiles at the plant tipping bin and teams, as well as improve cleaning rates by removing cracks stockpiles were therefore minimal. and gullies that are difficult to clean. Cemented material will The ToC analysis of L&H highlighted a lower hourly remain a challenge for bedrock using the current cleaning production rate of the L&H fleet than the required plant feed techniques, but the introduction of additional hammer rates and, furthermore, minimizing stockpile levels left no capacity has increased bulking rates in these conditions. buffer available to maintain the required feed capacity. This often translated into plant feed delays due to material   unavailability while the plant was running. The L&H teams A buffer stockpile ahead of the plant feed has had a number therefore changed their focus to building stockpiles close to of positive impacts on the operation. Consistent plant feed the plant tipping bin while the plant was not operational. has increased the plant feed rates from 755 t/h at the They also positioned a FEL permanently at the tipping bin beginning of 2015 to an average of 936 t/h in the last half of while the plant was running, enabling plant feed to be 2017 (Figure 11), an increase of 24%. This has resulted from supplemented from the stockpiles and maximizing plant feed a 50% reduction of mining-related delays and a reduced capacity. Allowing the L&H fleet to grow the tipping bin impact of unscheduled delays. Although it is acknowledged stockpile also ensured that L&H productivity was maintained that the philosophy of stockpiling material comes with an at all times. additional cost of rehandling, the benefits have shown that having a buffer ahead of the tipping bin has added <50+:5 significant value to the business. Work is currently underway to improve the current stockpile layouts and reduce loader  cycle times. The stripping operation has consistently improved quarter- on-quarter since Q2 2016 when the new mining philosophy ;91+058;9 and revised layout were introduced at SCM. In Q3 2017 a Through the ToC process, the mining discipline was identified pipeline used during a previous dredge mining project was as the bottleneck at SCM. On further analysis of the mining intersected in the stripping cut. The pipe was open to the sea processes, numerous local bottlenecks were identified that and required that a concrete plug be pumped into it before it prevented optimum productivity. Buffers, which if managed

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 111 Operational changes enable Namdeb’s Southern Coastal Mining team to reduce risk

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(8306<=//' <673<=-+79:=,<<2=67:<5=-<6=.;9:4=-<68;2=,6;.= /=:;=<92=;,= / better could build capacity, were identified. Through a <,<6<91<5 focused effort to address these bottlenecks and create buffers, BADENHORST, S.H. 2003. The unique Namdeb trilogy – Our past, present and solutions were developed and implemented that have greatly future mining applications in this unique deposit. Journal of the South improved productivity, and in the case of beach nourishment African Institute of Mining and Metallurgy, vol. 103, November. reduced the risk of a storm breaching the seawall defence at pp. 539–349. Namdeb. BLUCK, B.J., WARD, J.D., and DE WITT, M.C.J. 2005. Diamond mega-placers: southern Africa and the Kaapvaal craton in a global context. Mineral SCM will continue mining operations up and down the Deposits and Earth Evolution. McDonald, I., Boyce, A.J., Butler, I.B., coastline and, more importantly, westward to exploit Herrington, R.J., and Polya, D.A. (eds). Special Publication 248. Geological resources further into, and deeper under, the Atlantic Ocean. Society, London. pp. 213–245. The associated challenges for the Namdeb team will continue DE DECKER, R.H. 1988. The wave regime of the inner shelf south of the Orange River and its implications for sediment transport. South African Journal of to grow but we have embarked on a process of innovative Geology, vol. 91. pp. 358–371. and continuous improvement using the ToC method. The GOLDRATT, E.M. and COX, J. 2004. The Goal - A Process of Ongoing bottlenecks are expected to shift from one process to another Improvement. 3rd edn. North River Press, Great Barrington, MA. as we find solutions that make previous processes more JACOB, J., WARD, J.D., BLUCK, B.J., SCHOLZ, R.A., and FRIMMEL, H.E. 2006. Some efficient and productive. The ultimate challenge is to apply observations on diamondiferous bedrock gully trapsites on Late Cainozoic, marine-cut platforms of the Sperrgebiet, Namibia. Ore Geology Reviews, the ToC continuously to define new bottlenecks and then vol. 28, no. 4. pp. 493–506. focus on innovative solutions to remove these bottlenecks. JACOB, R.J. 2005. The erosional and Cainozoic depositional history of the lower Improved productivity and associated unit cost reduction will Orange River, Southwestern Africa. PhD thesis, University of Glasgow, have significant benefit not only on the profitability of the UK. mine in the short term, but also on the LoM potential of SCM Rogers, J. 1977. Sedimentation on the continental margin off the Orange River and the Namib Desert. Bulletin no. 7. Geological Survey/University of Cape going into the future. Town Marine Geoscience Unit, South Africa. 212 pp. ROSSOUW, J. 1981. Wave conditions at Oranjemund: Summary of wave rider 19;*+<23<.<9:5 data. March 1976-April 1980. Report no. T/SEA 8106. CSIR, Stellenbosch, South Africa. pp. 1–4. The authors are grateful to Namdeb for the opportunity to SCHNEIDER, G. 2008. The Treasure of the Diamond Coast – A Century of compile this paper, with special acknowledgement to Paul Diamond Mining in Namibia. 1st edn. Macmillian Education Namibia, Lombard, the SCM Mine Manager, for guidance and more Windhoek. importantly support. To the entire SCM Mining Team for SPAGGIARI, R.I., BLUCK, B.J., and WARD, J.D. 2006. Characteristics of openly embracing the changes and provided continual diamondiferous Plio-Pleistocene littoral deposits within the palaeo-Orange River mouth. Ore Geology Reviews, vol. 28. pp. 475–492. feedback and suggestions. To the SCM Management team, for SMITH, G.G. and SOLTAU, C. 2003. Shoreline modelling insights from projects in the teamwork and support. Finally, Lynette Kirkpatrick for Southern Africa. Proceedings of Coastal Sediments ’03. World Scientific your support and hours of editing. Publishing. https://doi.org/10.1142/5315 112   
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http://dx.doi.org/10.17159/2411-9717/2019/v119n2a3 The new Cullinan AG milling circuit – a narrative of progress by L. Musenwa*, T. Khumalo*, M. Kgaphola*, S. Masemola*, and G. van Wyk†

of a modern, fit-for-purpose processing plant  at CDM, with a throughput capacity of 6 Mt/a. This has replaced the previous plant at CDM, In 2017, Petra Diamonds completed the construction and commissioning of which was originally commissioned in 1947 a modern, fit-for-purpose diamond processing plant at Cullinan Diamond and which had undergone numerous Mine (CDM). The design of CDM’s milling circuit is unconventional in that it comprises an autogenous (AG) mill with a grate discharge with large refurbishments over the years. Due to its age ports, low-revolution jaw crushers, and high-pressure grinding roll and operational complexity, it had become crushers with large operating gaps. In this paper we review the design to expensive to maintain, requiring significant provide guidance on what is expected from the milling circuit and to stay-in-business capex, and costly to operate, demonstrate how the design aims to address challenges experienced in the particularly given its large 26 ha footprint. The old plant, which was based on staged crushing technology. We assessed plant was also mostly based on old crushing the performance of the CDM AG milling circuit from commissioning and technology, which is known to be inefficient early production stages to examine its impact along multiple dimensions. for the recovery of large stones. The design of In the assessment we sought to understand the lessons from our milling the new plant was therefore aimed at circuit regarding diamond liberation, energy consumption, and the future improving recoveries at a lower cost and of diamond processing as a whole. reducing diamond breakage. The new plant  was also designed to use more kimberlite processing, autogenous milling, high-pressure grinding roll, environmentally friendly processes, which is diamond liberation, diamond damage. vital for the long-term sustainable future of the mine. The new plant utilizes gentler processing methods – comminution by attrition and abrasion instead of extensive staged crushing.   The new comminution methods used are AG Cullinan Diamond Mine (CDM), previously milling and high-pressure grinding rolls known as Premier Mine, is an underground (HPGRs), which are expected to reduce diamond mine owned by Petra Diamonds. diamond breakage and improve recoveries Petra Diamonds is a leading independent across the full spectrum of diamonds, diamond mining group and a growing supplier including the larger/exceptional stones for of rough diamonds to the international market. which the mine is renowned. The top cut size Petra Diamonds is listed on the Main Market of of 75 mm will cater for diamonds of more than the London Stock Exchange under the ticker 3000 carats, such as the Cullinan Diamond. ‘PDL’. Petra’s total resource of 305 million The plant has a much smaller footprint of just carats ranks third by size after De Beers and 4 ha, and the engineering infrastructure has ALROSA (Petra Diamonds, 2018). been significantly reduced. CDM was established in 1902. The mine rose to prominence in 1905, when the 3106 carat Cullinan Diamond — the largest rough diamond of gem quality ever found — was discovered there. The mine has produced over 750 stones that are larger than 100 carats and more than a quarter of all the world's diamonds that are larger than 400 carats. Cullinan is renowned as a source of large, * Petra Cullinan Diamond Mine, South Africa. high-quality gem diamonds, including Type II † Thyssenkrupp, Johannesburg, South Africa. stones, as well as being the world’s most © The Southern African Institute of Mining and Metallurgy, 2019. ISSN 2225-6253. This paper important source of very rare blue diamonds was first presented at the Diamonds — Source to (Petra Diamonds, 2018). Use 2018 Conference, 11–13 June 2018, In September 2017, MDM Engineering Birchwood Hotel and OR Tambo Conference completed the construction and commissioning Centre, Jet Park, Johannesburg, South Africa.

         

   
 113 The new Cullinan AG milling circuit — a narrative of progress

"D6B??B=5DB=D9B@6>=9D8<>7C;;B=5 This is an essential step in mineral processing as proper liberation allows for maximum recovery of minerals in the Traditionally, Southern African diamond processing plants downstream processes. Undergrinding leads to inefficient are designed to include various stages of crushing to liberate recoveries (Steyn, 2011) and overgrinding, especially in the diamonds from the host rock. These types of plants have diamond processing context, leads to major value loss due to been operated to process kimberlite deposits in Southern breakage of the final product. Knowledge of the ideal product Africa over a number of years, and include the old CDM plant size is essential in the design of any comminution circuit. which was commissioned in 1947. The crushers in a The new plant has been designed to improve the conventional plant use compression and impact forces efficiency of material flow, thereby significantly lowering between two steel surfaces to break the feed material. operating costs. The new plant’s footprint is significantly less Although the crushers are optimized to operate at the than that of the old CDM processing plant. Some of the maximum possible crushing gap, there is still the potential comparisons to the old plant are summarized in Table I. for breaking diamonds between the steel surfaces. Furthermore, cone crusher products, having steep product &'%"#$' &!!'%  distributions, are associated with poor liberation of diamonds The new CDM plant process flow is illustrated in Figure 1. from the host rock (Daniel, 2010). The new mill plant is designed to handle run-of-mine (ROM) In recent years AG milling has been slowly introduced in ore as well as reclaimed tailings. The ROM ore is conveyed diamond processing in Southern Africa. AG milling is an from a 5000 t capacity ROM silo to the mills. The reclaimed established comminution process (van Niekerk, 2013), and and recirculated ore is conveyed from a 3000 t capacity silo to has been used in Russia over the past 40 years. The Russian the mills. The ROM ore from the silos is blended with experience cannot, however, be translated directly to the reclaimed tailings in the desired proportion for optimum processing requirements in Southern Africa. Russian grinding. The plant is designed for 6 Mt/a, and will initially methods have historically focused on maximizing diamond process 4 Mt/a ROM plus 2 Mt/a reclaimed ore. The mill is liberation (Janse, 2007). The Russian government designed for an overall fresh feed rate of 750 t/h feeding two regulations require very strict auditing of operational mills in parallel. This is blended as follows: performance to ensure that the orebody is being completely ’exhausted’, typically down to 1 mm. 500 t/h ROM ore Catoca mine in Angola was the first significant Southern 250 t/h reclaimed ore. African diamond operation to install AG mills. ALROSA, the Each mill is designed for a fresh feed rate of 375 t/h and Russia-based diamond producer, is a major shareholder in a 152% circulating load. the Catoca mine. The first diamonds were recovered in 1997 The mill discharge slurry (–150mm) flows onto a and the plant was expanded in 2005, raising the combined dedicated scalping vibrating grizzly installed for each mill. processing capacity to over 10 Mt of ore per annum. All of the The grizzly oversize is conveyed to the jaw crushers. The jaw Catoca plants are equipped with AG mills as the main crusher product is conveyed to the recycle ore silo. The jaw comminution devices. The Catoca mine’s main orebody or crushers were designed with a bypass option to return excess pipe consists of volcanogenic-sedimentary rocks, with the load to the mills or bypass the crushers during maintenance. inner ring of the vertical pipe made up of porphyric kimberlite, while the central part is filled with kimberlitic breccias. This type of material can be classified as relatively Table I soft and is therefore ideally suited for AG mill processing (van Niekerk, 2013). '>68@=D>4DA:CD>?9D@=9D=C0D'+1D8?@=A; In 2012 Karowe mine was successfully commissioned by Lucara in Botswana. The Karowe plant is equipped with an *?9D8?@=A C0D"D6B??B=5D8?@=A AG mill as the major comminution device. The Karowe Throughput per annum 2.8 Mt ROM 6.0 Mt ROM capacity operation has been modified and optimized over a number of 2.5 Mt tailings Initial feed: 4.0 Mt ROM years to process various material fractions through the plant. 2.0 Mt tailings At Karowe the material varies from soft and friable to very Total footprint Approx. 27 ha Approx. 4 ha competent. The operation has been very successful, Major installed equipment especially as the world’s second-largest gem diamond, at Conveyors 151 belts (15 km) 22 belts (3 km) 1111 carats, was recovered in November 2015 (Lucara, Conveyor transfer points 179 32 2018). Screens 88 22 Pumps 121 7 :CD=C0D'+1D6B??B=5D8?@=AD9C;B5= Crushers 18 4 (excluding mills) Feeders 21 14 The CDM comminution circuit was designed to reduce Substations 17 2 diamond breakage and improve recoveries across the full Electrical motors 589 84 spectrum of diamonds; including the larger/exceptional Improved electricity efficiency stones for which the mine is renowned. When applied Power consumption 22.5 MW 25.0 MW correctly, AG milling offers a diamond-friendly comminution Power consumption per ton 4.7 4.2 environment (Daniel, Bellingan, and Rauscher, 2016). The Improved water consumption purpose of any comminution process is to liberate or expose m³ per ton 3.5 1.2 locked-up valuable minerals within the host rock or gangue. 114   
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The new Cullinan AG milling circuit — a narrative of progress

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The grizzly screens undersize (–75 mm) gravitates to section reports to the recycle silo. The HPGR section is also dedicated mill product sizing screens for each mill stream. equipped with a bypass option to bypass excess material past The sizing screen oversize (–75 +12 mm) is conveyed to the the HPGR or bypass material when the crusher is offline. primary X-ray luminescence (XRL) sorting plant for recovery The DMS treats the –6 +1 mm size fraction. The –12 +6 of large diamonds. The sizing screen undersize gravitates to mm size fraction is separated on the DMS preparation screen the de-sliming section for the removal of –1mm slimes and treated through the mids diamond recovery plant, which through a series of trommels and dewatering vibrating consists of four BV sorters. The –6 +1 mm) size fraction is screens. The –12 +1 mm product from the de-sliming section treated though four 510 mm DMS cyclones. The concentrate is conveyed to the dense medium separation (DMS) and mids from the DMS cyclones and the mids diamond recovery is diamond recovery sections. conveyed to the secondary recovery section. The mids The main purpose of the XRL section is to sort the –75 diamond recovery tailings are conveyed to the HPGR section. +12 mm diamonds in the mill product. The feed to XRL is The DMS tailings are discarded. concentrated on the basis of luminescence by five large (–75 In the final recovery plant at CDM, concentrates from the +25 mm) and five coarse (–25 +12 mm) diamond XRL XRL large and coarse recovery, mids diamond recovery, and the DMS are treated using BV sorters for further sorters supplied by Bourevestnik (BV). The coarse diamond concentration of diamonds. XRL sorter tailings (–25 +12 mm) are conveyed to the HPGR crushing section. This coarse fraction can be bypassed to the  '&($'$&!$'' &!%$!' recycle silo if so desired. The large diamond XRL sorter The JKTech drop weight test (JKDW) is used to identify rock- tailings (–75 +25 mm) are conveyed back to the recycle silo specific parameters that are then used for simulating and or, if required, are directed to the HPGR crushers. predicting equipment performance. The drop weight tests are Concentrates from the large diamond XRL sorters and the used in conjunction with SAG mill comminution (SMC) test coarse diamond XRL sorters are combined and conveyed to results to model comminution equipment (Weier, 2013). The the final recovery section for further processing. output from this work can be used when modelling mill The HPGR crushing section is designed to incorporate two throughput, energy consumption, and product size crushers to assist with the rock breakage before the material distribution, relative to ore hardness. Effects of changes in is returned to the mill. Initially, only one HPGR unit was the in feed size distribution to the mill as well as operating installed. The second unit will be added as a future variables such as mill filling and critical speed can also be installation. Coarse XRL tailings (–25 +12 mm) and the mids examined. diamond recovery tailings (–12 +6 mm) feed this section. The Material testing was conducted on the most option exists to route the large XRL tailings (–75 +25 mm) to representative ore fractions from the CDM orebody, using just the HPGR section if this size fraction builds up in the circuit two samples representing grey kimberlite and hypabassal and requires further crushing. The crushed product from this kimberlite. The results of these tests are displayed in Table II.

         
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 115 The new Cullinan AG milling circuit — a narrative of progress

Table II The AG mills were designed to incorporate a discharge grate with very large ports with openings ranging from + D@=9D1'DAC;AD= illustrated in Figure 3. The open area of the discharge grate is "/"/@ 8.36%. With no previous experience of such large port sizes,

Grey kimberlite 88.80 0.45 39.96 0.45 2.68 Hypabassal kimberlite 71.90 0.55 39.55 0.55 2.80 Blend 78.60 0.51 39.71 0.51 2.75 Table III '+1D6B??D;8C7B4B7@AB>=; The lower the Ta value, the more competent the ore, i.e. 1B??D8@<@6CAC<8C7B4B7@AB>= the higher the resistance to abrasive comminution. Figure 2 shows that the CDM blend resides in the most competent Type Wet AG mill, grate discharge type region of the current kimberlite database. The shaded areas Design Shell supporting with slide shoe bearings represent the domains of the CDM and Jwaneng kimberlites Make/supplier Polysius/ThyssenKrupp for comparative purposes. This is illustrative of the order-of- Diameter (inside shell) 9.20 m magnitude difference in throughput and power consumption Effective grinding length 4.88 m of CDM compared with Jwaneng ores. As a further reference Percentage of critical speed 60–90 % Required motor power 6 400 kW point, Karowe mine has Ta values ranging from 0.26 to 1.56 (van Niekerk, 2013) and Williamson diamond mine is off the Motor speed 995 r/min scale with Ta values of 1.6 plus. Max. operating ball charge 0% Feed size –450 mm '(%%'!&(("$( #! Circulating load 130–200 % The two Polysius mills installed at CDM were supplied by Mill liner material Steel liners Mill shell liner thickness 278.4 mm ThyssenKrupp. Table III shows the specification for both (incl. lifter) mills. Material properties were used by CITIC-SMCC Process Discharge grate Full ported, 170 mm ports Technology to specify and design the grinding circuit.

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The new Cullinan AG milling circuit — a narrative of progress the CDM mill circuit was expected to deliver higher operating speed and achieved maximum power draw levels. throughputs and high recirculation loads of 130–200%. The This meant that despite the large pebble openings and open reason for large port sizes is the presence of large stones, i.e. area the mill could still be operated at a significant load level. value protection. Initially, the circuit was not operated with the full recycle The mill liner design was optimized to limit impact load due to the delay in the completion of the large diamond collisions inside the grinding chamber and enhance the recovery section. At the time it was therefore impossible to attrition and abrasion forces, as shown in Figure 4. determine the final operating conditions in the circuit. Once Particular care was taken to satisfy all of the special the large diamond recovery section was completed the plant requirements specified in the equipment data-sheet. The liner was able to be operated as per the intended design. The design was enhanced in the pulp chamber to accommodate commissioning team did not immediately achieve the design the flow of large particles. capacity and some fine tuning and adjustment were required to improve performance. The performance test was, however,  '!&(("$( #! successfully completed in November 2017. The production The CDM HPGR specifications are displayed in Table IV. The team continues to optimize the process to find the ideal recipe HPGR is one of the notable features from the old plant design for all conditions. The following sections highlight some of that was in incorporated in the new design. The first HPGR in the challenges and successes achieved during commissioning a kimberlitic operation was installed at CDM (then called the of the plant. Premier Mine) in 1987. The HPGR was included in the new '""(%"(%($' '%"!!(("$( #'"#'&"$& (# mill circuit because of its ability to minimize diamond damage in comparison to impact crushing. Comminution &(&#$' takes place primarily through interparticle crushing due to The most significant issues during plant start-up were large operating gaps, which are usually bigger than the feed classification and dewatering equipment breakdowns. The particles (Ntsele and Sauermann, 2007). The CDM HPGR was grizzly screens and trommel screens in the circuit suffered designed to operate at a gap of 55 mm to ensure optimal frequent breakdowns during the commissioning process. value protection. The grizzly screens, which are located immediately after the two mills, posed the most significant challenge in the '>66B;;B>=B=5 comminution circuit. The grizzly screen panels experienced a number of failures due to the impact and load of large Commissioning of the new plant was started in the third particles of up to 170 mm discharged from the mills. A newly quarter of 2017. The old plant was shut down before the developed deck and new panel design were supplied to construction of the new plant was completed. Some of the old improve the reliability of the process. The screening apertures sections were utilized while construction of the new plant were also reduced from 75 mm to 55 mm because some continued. The new processing plant incorporated the fines particle shapes in the mill product resulted in very large DMS section (–6 +1 mm) which was commissioned in 2012 particles reporting to the XRL section. The mine team, in as part of the dump treatment plant. Because this DMS conjunction with the panel and screen suppliers, continues to section was already operational, the plant could commission develop the screening panels and structure of the grizzly some of the major comminution equipment even before the screens to improve the reliability of the process. large diamond recovery section was completed. This meant The plant is designed to utilize motorized trommel that large particles in the circuit could either be trucked back screens to dewater the mill discharge pulp before the final to the mill or stockpiled to be processed later. fines screening stage. The trommel screens are very efficient Start-up of the AG mills was relatively simple without at removing the water from the processing stream, but the any significant issues. The mills were ramped up to full units were initially not mechanically reliable. Modifications were made to the support wheels to improve the availability of these units.

((%$(&!'(#' &!!(#' &%"(&'$"(%(#!'"$& ("% The plant was designed to treat a significant portion of reclaimed tailings material to supplement ROM ore. The introducing of this fraction of material was very challenging for the commissioning team.

Table IV +1DD;8C7B4B7@AB>=;

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Make/supplier Polysius/ThyssenKrupp Roll diameter 2.8 m Roll width 0.5 m (B53<.D@AD@88<>%D D73AD2%D>4DA:CDA>A@?DC=C<5.DB;D7>=;36C9D/.D=><6@?D7>??B;B>=;D@=9 Circuit capacity 750 t/h -%D/.DA@=5C=AB@?D7>??B;B>=;D!@AA= D!1,D,?C76CA@?D2

         
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 117 The new Cullinan AG milling circuit — a narrative of progress

The first challenge was the handling and conveying of the rate of the finer feed to this mill. The installed plugs reduced material, which is sometimes fine, sticky, and wet, and the total open area of mill no. 2 from 8.36% to 7.38%. causes blockages in transfer chutes. The second challenge Plugging the discharge had no significant effect of the was that a significant portion of this material is finer than performance, and the mill is still operating with these plugged 2.5 mm. Material in this size fraction is heavily influenced by holes. the flow of water in the mill and is discharged quite quickly without effective grinding (Steyn, 2011). This has at times (%%' $'"#"%!(! caused feed rates higher than 350 t/h to DMS, resulting in The mill plant design does not cater very well for physical the DMS being unable to treat all the mill product and sampling of the mill feed and product streams. Due to the subsequent stockpiling of DMS feed material. The third plant layout and physical constraints it is extremely difficult significant challenge in treating tailings has been the to take samples of the mill feed and discharge product. This presence of dense, old recovery tailings which resulted in constraint necessitated the installation of four Split-Online high yield to the final recovery. cameras, one on the feed conveyor and one on each of the Solutions to these challenges have been implemented three mill product streams, shortly after the commissioning of with a large degree of success. The tailings feed grizzly and the plant, to track important size fractions within the process. conveyor transfer points were changed to cater for the fine, Figure 7 illustrates the data that can be generated using the wet, and sticky material. The sizing screen panels were Split-Online system. With this system, the plant team is able changed to 8 mm square apertures to redirect the –12 +8 mm to keep accurate track of the particles reporting to each mids diamond recovery feed to the XRL section, which has process. The system has been subsequently developed to excess processing capacity. Lastly, the dense, old recovery quickly track any deviations from the expected size fractions tailings are carefully blended with old DMS tailings to reduce in each product stream and initiate appropriate corrective the recovery yields to manageable levels.

# &%("(%($' '(%%'% "'&"! &&#$! The load in the AG mill is determined by load cells installed under the supporting bearings on the non-drive end of the mill. This load level signal is used to run the mill under an automated control loop to optimize the feed rate to the mill. The load cells only give the relative mass of the load in the mill and not an absolutely mass. Measured load values tend to be unreliable due to the scaling of the control signal and/or load reading variations caused by changes in the density of the feed material, i.e. variations in bulk density of the finer recycled material relative to the coarser ROM ore. Figure 5 illustrates the difference in the mill loading for the same load reading. The mill feed rate control is dependent on this load value, and for this reason it is essential to have the most accurate measurement possible. This load information is not only essential for optimizing the throughput of the mill, but (B53=D>4DA:CD3=4D?>@9D7C??D can also be used to ensure the mill is operated in the most 8:>A>5<@8:;D0C C@9D7C?? diamond-friendly way. =D>4DA:CD9B44C4DA:CD4CC9DA>D6B??D=>%D2 the mill to reach operating load by reducing the discharge @=9D6B??D=>%DD93CDA>D;C5=D0BA:B=DA:CD;A><@5CD;B?>; 118   
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action to prevent any adverse effect on diamond recovery. Understanding the impact of the variability of the feed The performance of the system is continually verified with particle size distribution (PSD) and other mill operating physical samples to ensure that the plant can continue to rely parameters on the immediate mill product was one of the on the system. main aims in the early operational stages of the new plant. Below are some of the main lessons learnt about the mill CAAB=5DA>D3=9C<;A@=9DA:CD'+1D"D6B?? circuit to date Post-commissioning phase, the challenge remains to continue to get the best out the CDM mill circuit. One of the biggest (& &#$'(%%(#' &(&!'"#' & "$( #"%'%&
((%($ challenges in optimization of an AG mill is the fact that it The results obtained from the various tests done on the mill uses the feed ore as the grinding medium. The loading of have indicated that the mill is capable of producing a wide grinding medium therefore depends on the feed rate, size, range of product PSDs. An analysis of the mill product and hardness. When these parameter are highly variable it showed that the mills can be operated under different milling becomes quite difficult to run the mill under stable conditions regimes (Petersen, 2018). The CDM mill circuit can be (Napier-Munn et al., 1999). In the case of the CDM mill operated under three different milling regimes, depending on circuit, the feed rate is well controlled and the hardness is not process requirements. These regimes range from gentle highly variable, as supported by the narrow range of Ta milling to aggressive milling, with a transition regime in- values in Table II. The feed size is, however, highly variable, between. The gentle and aggressive regimes established are as illustrated in Figure 7, which makes it difficult to run the illustrated in Figure 8. Aggressive milling generates a large mill under stable conditions. percentage of fines (–1 mm), i.e. ≥40% passing 1 mm on a

         
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 119 The new Cullinan AG milling circuit — a narrative of progress

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first-pass basis and ≥80% passing 1 mm on the overall state for the purpose of this analysis is defined as instances process mass balance. Gentle milling, on the other hand, when the mill was operated at constant feed with the same generates between 20% and 30% passing 1 mm on a first- settings for at least 2 hours. The illustration in Figure 9 pass basis. shows that the water-to-ore ratio has a strong correlation to Aggressive milling was achieved, as illustrated in Figure the production of –1 mm mill product. Lower water-to-ore 8, on 16–28 February 2018, while operating the mills at a ratios generally result in the generation of more fines, which high percentage of critical speed (+85%) and low water-to- is favourable because it allows for higher throughput and ore ratio set-points (0.2–0.4). Gentle milling, as illustrated in reduces recirculation loads and the load on downstream the second diagram, labelled ‘March’, was achieved at a lower processes. percentage of critical speed (70–85%) and high water-to-ore Figure 10 illustrates that the operating mill load and ratio set-points (≥0.7) speed do not have as strong a relationship to grindability as The variability of the mill product PSD generated by the the water-ore ratio, and this is suggested by the linear different milling regimes directly impacts the mill relationship between speed and power. recirculation load and mill throughput. The average The operational flexibility of the new mill plant presents a recirculation loads for the gentle and aggressive milling wide range of options for the operational team compared to regimes in Figure 8 were calculated to be 180% and 127% the old plant. CDM’s goal is to optimize liberation and reduce respectively, which is within the design capabilities of the diamond damage. The insight gained thus far only takes into circuit. The mill circuit was designed to handle recirculation consideration the ability of the mill circuit to grind the feed to loads of up to 200%. The mill can therefore be operated in the achieve the required throughput and recirculation loads. different regimes to cater for the desired product without Future work is required determine the impact of the mill operating below the design throughput of 750 t/h. circuit on the final product. The next step for the CDM production team is to understand the impact of the aggressiveness of the milling regime on other aspects such as diamond liberation, diamond (3A3< damage, and energy efficiency, in addition to throughput. Napier-Munn et al. (1999) stress that optimization of an AG Efforts to identify the perfect recipe for both mills must take mill should never be regarded as complete. It should rather be into account the fact that aggressive milling is obtained at viewed as an ongoing process which is aimed at ensuring high rotational speeds, which may results in more impact that the circuit is operating at maximum efficiency regardless damage, while on the other hand gentle milling involves a of other conditions. With this important consideration in high recirculation load, which is also not favourable for mind, current and future work includes the following. diamond protection. The scatter plots in Figure 9 and Figure 10 illustrate some ($&#(#'(%%' #$ %! of the insight gained during normal production when the The CDM production team is currently looking at different mills were operated under steady-state conditions. Steady options for automated mill control. Some of the options under 120   
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The new Cullinan AG milling circuit — a narrative of progress

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consideration include controls based on DMS feed yield or $(("$( #'($'$&'&#' $'(#'(# possible incorporation of the online feed and product PSD The main aim of the CDM mill circuit is to liberate diamonds monitoring system. The production team is also considering from kimberlite. The circuit is also specially designed to the addition of a field instrument that uses vibration preserve the value of large diamonds. It is therefore monitoring on the mill bearing housings and mill shell to important to optimize the circuit with these goals in mind. generate accurate and instantaneous signals of the mill filling Current work involves test work with ceramic simulants and levels and the toe angle of the load in the mill (Gugel, valuation of large diamonds recovered under different milling Rodriguez, and Gutierrez, 2015) as illustrated in Figure 11. conditions. This information is not only essential for optimizomg the throughput of the mills, but can also be used to ensure that the mills are operated in the most diamond comminution- '>=7?3;B>= friendly way. CDM has successful commissioned their AG milling

         
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 121 The new Cullinan AG milling circuit — a narrative of progress

(B53?@AD>4D9@A@D4<>6DA:CD B/<@AB>=D6>=BA>0B=5DB68@7AD>=CD!A>CD@=5?C DB=;B9CDA:CD6B??D!+B5BA@?D'>=A<>?D)@/D2 %

comminution circuit treating a relatively competent http://www.digitalcontrollab.com/docs/AutoSagControl_MineExpo2016_ kimberlitic ore. The commissioning team has thus far v4.pdf managed to achieve the design throughput. The mill circuit is JANSE, A.J.A. 2007. Global rough diamond production since 1870. Gems and capable of producing a wide range of product PSDs to cater Gemology, vol. 43, no. 2. pp. 98-119. for different production requirements in comparison with a LUCARA DIAMOND COMPANY. 2018. http://www.lucaradiamond.com [accessed 10 conventional stage-crushing circuit. The challenge now February 2018]. remains to fully understanding the impact of the mill circuit ME ELECMETAL. 2016. DEM simulation of particle trajectory and discharge on liberation and diamond damage. Future work will focus on behavior. Client presentation. completing the optimization cycle of the circuit. We plan to NAPIER-MUNN, T., MORELL, S., MORRISON, R., and KOJOVIC, T. 1999. Mineral present this work at subsequent conferences, with the hope Comminution Circuits - Their Operation and Optimization. 2nd edn. Julius of increasing the benchmark of the largest diamond ever Kruttschnitt Mineral Research Centre, University of Queensland. recovered. NTSELE, C. and SAUERMANN, G. 2007. The HPGR technology – the heart and future of the diamond liberation process? Proceedings of Diamonds – C4C

CLAASSEN, I.C. 2006. Cullinan Diamond Mine – autogeneous milling evaluation. Johannesburg. http://www.saimm.co.za/Conferences/Diamonds GME Metallurgy Projects Reports. De Beers. SourceToUse2007/010-Sauermann.pdf

DANIEL, M.J. anD MORLEY, C. 2010. Can diamonds go all the way with HPGRs? PETERSEN, K. 2018. Cullinan milling project: milling testwork results report. Proceedings of the Diamonds – Source to Use 2010 Conference, 1–3 March MetalDog Minerals.

2010. Southern African Institute of Mining and Metallurgy, Johannesburg. PETRA DIAMONDS. 2015. The new Cullinan plant. Company presentation. http://www.saimm.co.za/Conferences/DiamondsSourceToUse2010/201- https://www.petradiamonds.com/wp-content/uploads/Cullinan-Plant- Daniel.pdf Presentation-27-July-2015-FINAL.pdf [accessed 15 March 2018].

DANIEL, M.J., BELLINGAN, P., anD RAUSCHER, M. 2016. The modelling of scrubbers SMCC PROCESS TECHNOLOGY. 2014. Review of the proposed twin line AG mill and AG mills in the diamond industry and when to use them. Proceedings circuit for Petra Diamonds Cullinan underground mine @ 6Mt/a. of Diamonds Still Sparkling, 14–17 March 2016. Southern African Indooroopilly QLD, Australia.

Institute of Mining and Metallurgy, Johannesburg. STEYN, C.W. 2011. Optimisation of a fully autogenous comminution circuit.

DIGITAL CONTROL LAB. Not dated. MillSlicer. http://www.digitalcontrollab.com/ MEng thesis, University of Pretoria, South Africa.

millslicer.shtml [accessed 15 May 2018]. VAN NIEKERK, L.M., NDLOVU, G.N., and SIKWA, N.A. 2013. Commissioning and

GUGEL, K., RODRIGUEZ, J.C., and L.J. GUTIERREZ, L.J. 2015. Automated SAG mill operating an autogeneous mill at Karowe Diamond Mine. Proceedings of speed control using on-contact vibration sensors. Proceedings of the Diamonds—Source to Use 2013. Southern African Institute of Mining and International Conference on Semi-Autogenous and High Pressure Grinding Metallurgy, Johannesburg. pp. 175–192.

Technology, Vancouver, 20–24 September. WEIER, M. 2013. JKDW & SMC test report Cullinan Mine. JK Tech, Brisbane. 122   
 #*)$1,D22-          
http://dx.doi.org/10.17159/2411-9717/2019/v119n2a4 Diamond exploration and mining in southern Africa: some thoughts on past, current, and possible future trends

by W.F. McKechnie

areas inherently prospective for diamonds, being underlain by portions of the Earth’s (7<*8;8 crust that are tectonically stable and older than Southern Africa is generally thought to be well explored, with only limited 1.5 billion years (Clifford, 1992). Although potential for major new diamond discoveries. However, Chiadzwa in the Democratic Republic of Congo (DRC) Zimbabwe and reports of a significant new kimberlite find in Angola are would, in a geographic context, be considered testimony to the dangers attached to an attitude that ‘there is nothing left to find’. to be part of Central Africa, for the purposes of Since the major discoveries in the central interior of South Africa in this review it is included in southern Africa the 1870s, diamond exploration in the region has been led by market and since northeast Angola and the adjacent parts political factors that influence the key exploration drivers of opportunity of the DRC form part of the same geological and value proposition. Unexpected new discoveries by new players always terrane and diamond production from both impact on existing producers and, from time to time, denial of opportunity countries needs to be considered together. through political or protectionist policies has inhibited investment in Historical and current diamond production exploration. from the northeastern parts of the DRC around Entrepreneurial exploration appetite in southern Africa will be Kisangani is not considered to be significant tempered by the potential value equation and security of investment. and its inclusion in the overall numbers for the Overlaid on this, developments in diamond recovery technologies provide DRC does not materially affect the overall opportunity to reinvigorate current mines and old prospects previously considered too difficult or costly to exploit. Position on the cost curve will picture presented here. remain a key factor for survival in an increasingly competitive Hence, in this review, the countries environment. considered are South Africa, Zimbabwe, Namibia, Angola, the DRC, Lesotho, Botswana, >( <=68 and eSwatini (previously Swaziland), the first five of which each has a history of diamond diamond exploration, production, trends, outlook. production stretching back more than 100 years, and in the case of South Africa, 150 years (Table I).

A;89<=;5:4?*>=8*>59;&>8 79=<6259;<7 The first wave of diamond exploration in The diamond industry in southern Africa southern Africa was initially driven by boasts a history of 150 years of discovery and opportunistic, entrepreneurial spirit and mining, forming the cornerstone of endeavour but inevitably, and quite quickly, development of the core, modern economies at operational and market factors led to the southern tip of Africa. consolidation of the operating companies and Since the discovery, in the 1860s and lateral and vertical integration of the different 1870s, of the secondary diamond placers and industry components. primary diamond-bearing kimberlite deposits From 1870 until shortly before the start of in the central interior of the then Cape Colony the First World War the diamond mines of and Orange Free State, southern Africa has South Africa accounted for almost 100% of endured as the pre-eminent diamond- producing region in the world. Notwithstanding periodic competition from significant new discoveries in other parts of the globe and the paucity of recent, new discoveries in the region, its ranking is * Snowden Group, South Africa. unlikely to change in the short to medium © The Southern African Institute of Mining and Metallurgy, 2019. ISSN 2225-6253. This paper term. was first presented at the Diamonds — Source to In a geological context the region contains Use 2018 Conference, 11–13 June 2018, the Kaapvaal-Zimbabwe and Angola-Kasai Birchwood Hotel and OR Tambo Conference cratons, identified in terms of Clifford’s rule as Centre, JetPark, Johannesburg, South Africa.

         
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 123 Diamond exploration and mining in southern Africa:

in West Africa, most notably Sierra Leone, (Levinson, Table I Gurney, and Kirkley, 1992). The exceptional quality of the :9>8?<0?0;=89?6;:.<76?6;85<&>=;>8?;7?8<29'>=7 West African production had an enormous impact, with the 0=;5:?";48<7-?3+/?$>&;78<7-?2=7>(-?:76?;=4>(- result that, through to the 1960s, world diamond production 3++/? :78>-?/11?6>?;9? -?/13%! was dominated by these major secondary diamond fields to the virtual exclusion, for a time, of the South African <279=( :9>?<0?0;=89?6;85<&>=( ;:.<76?8<2=5>8 kimberlite mines, most of which either closed or drastically South Africa 1867 Vaal River placers and cut production in the inter-war period (Janse, 2007). Kimberley and OFS kimberlites Following the Second World War De Beers, launched its Zimbabwe 1903 Somabula placer and kimberlites ‘A Diamond is Forever’ marketing campaign to exploit an DRC 1907 Tshikapa placers anticipated post-war economic boom in the USA and Europe. Namibia 1908 Luderitz placers The company embarked on an ambitious investment Angola 1912 Lunda placers programme to reopen and modernize its mines in South Lesotho 1958 Kao kimberlite Africa and South West Africa, and also purchased the Botswana 1966 Orapa kimberlites Williamson Mine in East Africa. New diamond production eSwatini 1973 Ehlane placer and from major discoveries in Russia in the late 1950s threatened Dokolwayo kimberlite De Beers’ market leader status, and this encouraged it to increase investment in diamond exploration throughout Africa, commencing in East Africa, extending southwards global diamond production. During the latter part of this into Bechuanaland (now Botswana) and into Angola and period the main diamond-producing company of the time, De Zaire (now the DRC). Newly independent Botswana was host Beers, enjoyed a virtual monopoly in diamond supply from its to the fabulous discoveries at Orapa and Jwaneng. Smaller kimberlite mines. This situation started to change shortly finds in Southern Rhodesia (now Zimbabwe) and Swaziland after the turn of the 19th century when the Premier Mine at (now eSwatini) spurred renewed interest in South Africa, Cullinan, east of Pretoria, came into production. Kimberlites leading to the discovery of Venetia and other smaller mines had been discovered in 1897 at Rayton to the south, just in South Africa and Botswana. before the South African War (Draper, 1898), but lay fallow Figure 1 shows a chart of diamond discovery and mining until hostilities ended and economic conditions normalized. in southern Africa for all of the countries listed in Table I Independent production from the Premier Mine led to covering the period 1867 to present. Although the trend has increased market competition and volatility of diamond the appearance of being fairly continuous, three definite prices, but the situation worsened considerably in the discontinuities are noticeable, shown as A, B, and C. following decade for the established producers (Innes, 1975). ‘A’ in Figure 1 represents the initial period of industry In the period between 1907 and 1912, massive secondary consolidation in Kimberley, which led to the formation of De diamond deposits were discovered in German South West Beers Consolidated Mines and its initial monopolization of Africa (now Namibia), at Tshikapa in the Belgian Congo the industry. Additional factors that diminished interest in (now the DRC), and in the Lunda Provinces of Portuguese diamond prospecting during that period were the discovery of West Africa (now Angola). the Witwatersrand goldfields in 1886 and political events Immediately following the end of the First World War, leading up to the South African War of 1899 to 1903. further new major diamond placers were found at Mbujimayi Period ‘B’ followed the discovery of the huge placer in the DRC, in the Gold Coast (now Ghana), in Namaqualand, deposits in Namibia, Angola, the DRC, West Africa, and and around Lichtenburg in South Africa, and other countries Namaqualand and Lichtenburg in South Africa. These had a

;,2=>?3 ;.>4;7>?<0?6;85<&>=(?0<=?.:;7?6;:.<76?<552==>75>8?;7?8<29'>=7?0=;5:?0=<.?9'>?3%18?98?<0?,=>>7?)2))4>8?:=>?85:4>6?:55<=6;7,?9< <=;,;7:4?*;*>?82=0:5>?:=>:?;>8?<0?)42>?)2))4>8?:=>?):8>6?<7?2:4;9:9;&>?>89;.:9>?<0?9'>?>5<7<.;5?;.*<=9:75>?<0?9'>?*4:5>=?6>*<8;98?";48<7-?3+/ $>&;78<7-?2=7>(-?:76?;=4>(-?3++/? :78>-?/11?6>?;9? -?/13%! 124   
 $ #?33+          
Diamond exploration and mining in southern Africa:

;,2=>?/<=46?6;:.<76?*=<6259;<7?";7?5:=:98!?0=<.?9'>?3%18?98>79>6?0<=?0;=89?(>:=?;7?>:5'?6>5:6>?0=<.?$>&;78<7-?2=7>(- :76?;=4>(?"3++/!?6:9:?0<=?/11 -?/131-?:76?/13%?8<2=5>6?0=<.?;.)>=4>(?=<5>88?9:9;89;58?0<=?9'<8>?(>:=8

devastating effect on the South African diamond mining from re-examination of older mines and prospects. The two industry. Investment in existing mines and exploration for, exceptions are the Luaxe kimberlite in Angola (Alrosa, 2017) and development of, new kimberlite operations ceased in and the Chiadzwa placer in Zimbabwe, which has had a South Africa and exploration for primary deposits elsewhere significant influence on the industry for approximately 10 was also deterred. The Great Depression of the 1930s years (Kimberley Process Statistics, 2004–2016; Manenji, undoubtedly played a part, but the greatest influence came 2017). from the low-cost production of high-quality, gem diamonds from West Africa, Angola, and other independent producers. ;:.<76?*=<6259;<7 In South Africa, the industry situation was so dire that in Figure 2 summarizes annual world diamond production in 1927, the Union government passed the Precious Stones Bill carats (ct) from 1870 through to 2016, showing the forbidding prospecting and digging for diamonds on state- phenomenal growth since the 1950s. Three main production owned land in the Cape Province. This restriction was only periods are shown. The period 1867 until 1910 was lifted in 1960 following the discovery of the diamond-bearing dominated by South African kimberlite mine production. dykes at Bellsbank, followed shortly afterwards by the Finsch Production from 1910 to about the mid-1960s was Mine discovery (Janse, 1995). Similar restrictions were in dominated by the large African secondary deposits which, for place elsewhere in the region. In Southern Rhodesia (now a considerable period, produced more than 50% of global Zimbabwe) De Beers held exclusive rights to prospect for production in value terms. diamonds through the British South African Company The period from the 1960s through to the present has (BSAC), founded by Cecil Rhodes, which were ceded to the again been dominated by large kimberlite and lamproite government only in the 1940s. In Angola and the Congo, mines, with the result that, by the turn of the millennium, exclusive diamond rights were held by Diamang and more than 75% of world production by volume and value Forminière respectively. came from primary deposits, a reversal of the situation that The main influence in period ’C’ was the Angolan civil prevailed from 1920 through to 1960 (Janse, 2007). During war, which affected the whole subcontinent from its the last 30 years, new kimberlite and lamproite primary commencement in 1975 to 2002. Although diamond mining deposits brought into production in Australia and Canada continued in Angola throughout most of this period, have further reduced southern Africa’s market share in exploration was not possible until the early 2000s and there volume and value to an average of approximately 50% of were spillover effects into neighbouring countries. Zimbabwe total world diamond production (Kimberley Process statistics, was also not fully accessible between 1975 and the late 2004–2016). 1980s. The effect of all of this was that, for an extended Annual production data reported by the Kimberley period in southern Africa, diamond exploration was restricted Process Certification Scheme since 2004 provides valuable to South Africa and Botswana, both relatively mature insight into southern African diamond production. Records exploration terranes by that time, and post-Venetia, the only from 2004 to 2016 show that world diamond production significant new deposits found were small and short-lived peaked at almost 177 million carats in 2005, but reduced to operations. An additional factor was the significant an average of 125 million carats between 2009 and 2015, exploration successes in in other parts of the world, such as increasing again to almost 145 million carats in 2016, mainly Australia and Canada, which increased competition for on the back of significantly increased production from exploration spend. Russia. On average, for that period, southern Africa produced In recent years new diamond discoveries in southern 51% of the world’s diamonds in carats, representing 56% of Africa have been scarce, with most new production coming global dollar revenue (Figure 3 and Figure 4).

         
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 125 Diamond exploration and mining in southern Africa:

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;,2=>?<29'>=7?0=;5:7?*>=5>79:,>?8':=>?<0? <=46?6;:.<76?5:=:98?*=<6259;<7?/11/13%?";.)>=4>(?=<5>88?89:9;89;58-?/11?9

Botswana is the dominant producer of the region in terms low average values reported for Russia as a result of the low of volume and value, followed by South Africa, Angola, and bottom size cut-offs used in Russian operations, often as low Namibia. Lesotho is a relatively minor producer, as 0.5 mm compared to 1.25 mm or 1.5 mm for other notwithstanding the very high-value gems produced by its producers. Another feature of this chart is the general long- Letseng Mine. Since 2006, Zimbabwe has produced a term upward dollars per carat trend in average diamond significant volume of generally low-value diamonds, values since 2004. The strong initial post-GFC price recovery increasing the region’s share of world production at times to was short-lived and average diamond values have been almost 60% between 2010 and 2013. Zimbabwe’s variable but effectively flat since 2011, and negative the in production is currently in decline and Botswana’s mines have last two years. lowered production by approximately one-third since 2008 in Average diamond values for the different countries in response to challenging market conditions, causing southern southern Africa are compared in Figure 6 on a logarithmic Africa’s share of global production to dip below 50% for the scale, which allows visual separation of the different country first time in 10 years. eSwatini’s only diamond mine in production profiles. closed in 1996 and is not included in Figure 2 or Figure 3. Average values for South Africa, Botswana, and Angola cluster together around the $100 per carat line. Diamond   values for Lesotho and Namibia are considerably higher, Figure 5 compares average dollar per carat values since 2004 being influenced by the unusually high-value production for total world diamond production, as reported by the from the Letseng kimberlite in the case of Lesotho, and the Kimberley Process, to the average values for southern gem-quality diamonds typical of the Namibian west coast African producing countries. placer deposits. Lower value production separates out Average values for southern Africa are slightly higher towards the lower end of the value scale, representing the than the global average, which is considered to be due to the Zimbabwe secondary Chiadzwa operations and DRC 126   
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Diamond exploration and mining in southern Africa:

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production, the latter mainly influenced by the diamond The diamond discovery and production history of population typical of the Mbujimayi area. southern Africa bears testimony to the inherent prospectivity of the region, which justifies continued interest in exploration 292=>?*=<6259;<7?:76?>*4<=:9;<7?9=>768 for new diamond deposits. Previously remote parts of the In the medium term (5 to 10 years), given the time needed to region and areas inaccessible due to conflict or other reasons develop any new discoveries, the diamond production profile are now more accessible. The region’s geology is now better of southern Africa is not expected to change significantly. understood compared to when the first kimberlite discoveries However, Botswana, having reduced output in recent years, were made in Angola and Botswana in the middle of the last is expected to be able to ramp up supply again should market century. Cover sequences younger than the last phase of circumstances change. In the longer term South Africa’s and kimberlite intrusion in the region are also better mapped and Botswana’s share of global and regional production will understood, although these continue to present challenges to eventually trend downwards as open pit mines go deeper or kimberlite exploration that are not yet fully overcome. Other move underground. The new Luaxe discovery in Angola, parts of the region, such as South Africa, Zimbabwe, announced recently by the Endiama/Alrosa JV, will increase Lesotho, and eSwatini, where young cover is generally not that country’s share of production significantly in due course considered a problem, have been more intensively explored. (Alrosa, 2017; Rough Polished, 2017). Diamond production This lowers the residual prospectivity and leads some to in the other countries in the region is not expected to change believe that there remains only limited potential for discovery much from current levels and, for the foreseeable future, of new large, long-life deposits in these areas. southern Africa is expected to comfortably maintain its approximately 50% production share in carat and value    terms. It is generally accepted that the potential for the discovery of

         
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 127 Diamond exploration and mining in southern Africa: new mega-placer deposits of the type exploited in southern In Botswana, some greenfield work continues but most Africa for the last 100 years is very low. A mega-placer is a recent diamond exploration interest is being generated diamond deposit that holds at least 50 million carats with around existing mines and reinvestigation of old prospects, 95% or higher of gem quality (Bluck, Ward, and de Wit, mainly as result of the Karowe experience and the idea that 2005), acknowledged examples being the west coast diamond the application of new diamond recovery technologies and deposits of Namibia and South Africa. The combined inland different processing flow sheets may revitalize some of these diamond fields of Angola and the adjoining portion of the (Sasman, Deetlefs, and van der Westhuyzen, 2018). Despite DRC would also meet this definition. The diamond-bearing improved geophysical technologies, the Kalahari cover in conglomerates of the Umkondo Series sediments in Botswana continues to hamper exploration, making the Zimbabwe might narrowly fit the definition in carat terms, discovery process difficult; however, potential for new finds but not in terms of gem diamond content. remains. The potential for significant new placer discoveries seems South Africa was considered a mature area for diamond therefore to be limited to extensions of known occurrences in exploration potential even in the 1950s, but this did not Namibia, Angola, and elsewhere in the region. The feasibility prevent two major new discoveries 100 years after the of exploiting the in-situ conglomerates at Chiadzwa in original Kimberley and Free State finds; at Finsch, only 150 Zimbabwe is yet to be proven, but extensions of this field km from Kimberley, and 20 years later at Venetia in the far may still be found. Other potential placer targets might be north of the country. Since then, other smaller, but surficial deposits proximal to new kimberlite discoveries, nevertheless economic discoveries have also been made, with such as those being exploited at the Krone-Endora deposit small mines developed at The Oaks, Klipspringer, and adjacent to Venetia. Such small deposits are unlikely to be of Marsfontein. Many new kimberlites were found in the interest to major mining companies but would be suitable for Northern Cape Province from airborne geophysical surveys, exploitation by juniors. but to date the only deposit being exploited as a result of that work is the Kareevlei kimberlite, owned by BlueRock   Diamonds. It is evident therefore that most future diamond exploration Similarly, in Zimbabwe, also considered a relatively well in southern Africa must be directed towards the discovery of explored part of the region, the Murowa kimberlites and the as yet undiscovered kimberlite deposits. The parts of Angola Chiadzwa placer deposits lay hidden for almost a hundred and Botswana covered by younger strata appear to hold years after the first alluvial diamonds and kimberlites were promise for new opportunity, with Angola, as result of found. Factors discouraging diamond exploration historically having been inaccessible during its civil war years, holding were the same economic factors applicable in South Africa, pole position in terms of potential. combined with exclusive rights to prospect and mine for In Angola, Diamang, the original state-owned diamond diamonds being restricted for various reasons and, to some mining company, discovered and developed the Angolan extent, perceptions that there was nothing new to be found diamond deposits over a period of 60 years. Until 1971, Current diamond exploration activity in Lesotho is mainly Diamang was the only company authorized to explore for and restricted to investigation of old prospects, also using new mine diamonds in Angola. It exploited alluvial deposits with diamond recovery technologies to improve efficiencies and great success and, starting in the 1950s, its exploration work reduce costs. A countrywide diamond exploration programme led to the discovery of kimberlite deposits such as Catoca, was reported to have been carried out in eSwatini in the early Camatchia, and Camútuè (Chambel, Caetano, and Reis, 2000s but nothing new appears to have come from this work. 2013). More than 40 years after Diamang‘s replacement by Diamond-bearing kimberlite deposits are not easy to find and, generally having a limited surface expression, require the new state company Endiama, the recent discovery at painstaking and diligent work to ensure discovery. Luaxe by the Endiama/Alrosa joint venture appears to be the Traditional methods of exploration based on soil and only kimberlite deposit capable of being exploited in Angola drainage sampling for indicator minerals have proven very so far not found by Diamang. effective in the past and will continue to be the most Study of any map of the distribution of kimberlites in important exploration tool. In areas where the effects of northeast Angola leads to the inescapable conclusion that unusual geomorphology or younger cover further inhibit most of the known kimberlites occur in, or proximal to, river direct discovery, it will be necessary to supplement sampling valleys, suggesting that these have been found as a result of programmes using geophysical technologies. Airborne having been exposed by erosion and that others lie magnetics has generally been the method of choice, undiscovered under younger cover (Chambel, Caetano, and sometimes combined with electromagnetic systems, but the Reis, 2013). A number of companies have undertaken results from airborne gravity systems have been unfulfilling airborne geophysical exploration on the uneroded interfluves to date. and some new kimberlites have been found, notably the Mulepe cluster by De Beers, but until the Luaxe discovery nothing of significance had emerged. In 2015 the *4<=:9;<7?>*>76;92=>?9=>768 government of Angola embarked on an ambitious Estimates of annual exploration spend are prepared each year geophysical survey of large parts of the country, the results of by S&P Global Market Intelligence (S&P GMI) based on which were expected by the end of 2017 (Ponce de Leão, surveys of a large number of mining and exploration 2015). It is not clear how the Angolan government intends companies throughout the world. Data retrieved from S&P dealing with the results from these surveys but, once GMI in April 2018 has been used in the analysis of diamond available, new exploration targets are likely to be generated. exploration data presented here. 128   
 $ #?33+          
Diamond exploration and mining in southern Africa:

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Figure 7 shows that almost $1 billion was spent exploration budgets was reported for 2017 (S&P GMI, 2018b) cumulatively in 2007 and 2008 on diamond exploration but did not appear to carry through to diamond exploration. throughout the world, with almost half of that being spent in S&P GMI (2018b) estimated the total global, non-ferrous Africa. For the three-year period from 2006 to 2008, over metal exploration budget at $8.4 billion for 2017, but only $400 million was spent annually on African diamond $208 million (2.5%) was allocated to diamond exploration exploration. (S&P GMI, 2018a). Current estimates indicate that the total The global financial crisis (GFC) of 2008–2009 caused diamond exploration budget for southern Africa in 2017 was significant disruption to the diamond industry and this approximately $56 million, with 80% split fairly evenly translated through to significantly reduced expenditure on between Angola and Botswana (Figure 8) (S&P GMI, 2018a). exploration, which has flowed through to the present (S&P The immediate reasons for the post-GFC trends were most GMI, 2018a). Post-GFC, world diamond exploration budgets likely the inherent risks associated with exploration and the more than halved in 2009 compared to the previous year, and need for companies to conserve cash, especially smaller similar or greater reductions carried through to African companies. As the recovery in diamond prices has been exploration budgets. Budgets reduced further in 2010 and slower than hoped for and the long-promised upward price recovered in 2011 and 2012; but this was short-lived, and a drive has not been forthcoming, the level of annual budgets steady and continuous decline in global annual budgets is allocated to diamond exploration has also diminished. noted, from $520 million in 2012 to $208 million in 2017 Based on analysis of S&P GMI data, supported by a (S&P GMI, 2018a). review of company annual reports, more than half of the This downward trend in budgets is not confined to global diamond exploration budget is spent by just two diamonds, but has been general across all mineral companies, Alrosa and De Beers. Alrosa in particular has commodities since 2012. A slight up-kick in overall become increasingly active outside Russia and in southern

         

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 129 Diamond exploration and mining in southern Africa:

Africa is undertaking exploration in Angola, Botswana, track history and the ease of doing business there. Zimbabwe Namibia, and Zimbabwe. Alrosa’s JV with Endiama in the has recently announced changes to its mining investment Catoca mine appears to be successful and is a strong pillar of regime, but the picture for diamonds is not yet clear, with the the Angolan diamond mining industry. The new Luaxe Zimbabwe Consolidated Diamond Company enjoying what discovery will add to that success, and according to recent appear to be exclusive diamond rights, at least in the reports will double Angola’s annual diamond production once Chiadzwa area. The situation for South Africa is also unclear, mine development is completed (Rough Polished, 2017). given current uncertainty concerning amended mining legislation (which is still to be put in place) and the time 294<<?0<=?6;:.<76?>*4<=:9;<7?;7?<29'>=7?0=;5: taken to process prospecting right applications. In Angola all Key factors to be considered in undertaking diamond rights to explore for diamond deposits are vested in the state exploration are the inherent prospectivity of the target area, company Endiama, and private companies may obtain especially if there is a proven track record of production, ease prospecting rights only by virtue of a concession contract of access, security of tenure and investment, political approved by the Angolan Council of Ministers. This is often stability, and an open and transparent operating and fiscal a lengthy and expensive undertaking, which generally means regime. The foregoing has shown that southern Africa scores that only well-equipped and well-financed exploration very highly on the first factor but, as reported in the Fraser companies can go through this process. Institute Annual Survey of Mining Companies 2017 (Fraser As shown earlier in this paper, in southern Africa the Institute, 2018) and evidenced by prevailing legislation diamond exploration playing field has never been level, with applicable to diamond exploration and mining, the region is a various countries effectively closed off to exploration at times mixed bag as regards the other factors. However, this is not due to legislation or exclusive rights awarded to preferred always a deterrent for explorers and investors operating in companies, or conflict. One reason for this is certainly the African diamond exploration and mining field, some of because governments often regarded diamond mining as whom are prepared to operate under high levels of being of strategic interest, requiring special oversight and uncertainty. protection. This situation still prevails in parts of southern Africa, and indeed other parts of the world, limiting areas   easily accessible to private or listed exploration entities. In An important consideration for investors is the potential southern Africa, with the exception of Botswana and value of the prize that might be obtained as a result of the Namibia, the right to undertake diamond exploration and exploration investment. All things being equal, areas with mining is not an open door for prospective explorers and potential for higher value diamonds will usually attract investors. higher levels of interest than others, as mines that produce better quality diamonds, especially if the diamond grade is 
  also high, tend to be more robust in market downturns than those that produce poorer quality diamonds. Price stability of the product is a key factor to be considered All diamonds are not equal, and a number of factors in developing a diamond mine, and from the very early days, producers and marketers recognized this need. The rationale influence the desirability and value of individual rough for restrictive practices in the past was provision of market stones. These are the size or weight of the diamond in carats, support to ensure price stability and surety of mining morphology (or shape), colour (shades of white through to investments already made, as well as revenues going forward yellow and other colour varieties, described as ‘fancies’), and (Innes, 1975). In the post-Second World War years, De clarity (the impact of inclusions, cracks, or other impurities). Beers’ dominance brought a semblance of stability to the Levinson, Gurney, and Kirkley (1992) commented that diamond market, interrupted at times by new independent rough diamonds that yield good-quality polished gems, discoveries such as in Russia, Australia, and later in Canada. especially 0.5 ct or larger, are not common, and that stones This situation prevailed for some decades but increasing anti- over 1.5 ct are particularly rare. The reduced output of trust and competition law pressures, initially from the USA secondary diamond sources over time, which tend by their and later from the European Community, forced a policy nature to contain larger and better quality stones than rethink. Consequently, De Beers relinquished its policy of kimberlite sources, also means that relatively fewer of these market dominance, with the result that its market share has better quality stones are being produced than in the past. fallen from more than 90% in the 1980s to less than 40% Also, although 50% of the world's rough diamonds were today, and it might be argued that the industry has paid for classified as cuttable at that time, only about 2% to 2.5% this in terms of increased price volatility. were expected to yield good-quality stones of 1 ct or larger. In Most market commentators report a stable and positive the author’s experience, these estimates are considered outlook for the diamond industry going forward and predict reasonable on average, although diamond qualities vary that for the period through to 2030, rough diamond demand according to the source area. For instance Siberian and will grow at average rates of 1% to 4% (Bain and Company, Canadian kimberlite pipes generally contain a higher 2017). Industry fundamentals also suggest a supply-demand proportion of better quality diamonds than southern African shortfall going forward, which is expected to influence prices sources, and variations exist within each region. positively. However, this is predicated on normal business The DRC is therefore unlikely to attract explorers except continuing as it has in the recent past. In the past, new for small-scale alluvial operations in the Kasai. Botswana will discoveries, especially large finds, have always impacted on continue to attract exploration investment due its discovery existing producers. The impact of the new discovery in 130   
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Diamond exploration and mining in southern Africa:

Angola is still to be seen but, if it is as important as implied DAMARUPARSHAD, A. 2007. Historical diamond production (South Africa). Report in recent press articles, then the overall balance of the R61/2007. Department of Minerals and Energy, Pretoria. industry may be affected, and more so if further exploration DE BEERS GROUP OF COMPANIES. 2018. De Beers to launch new fashion jewelry success is achieved. brand with laboratory grown diamonds. Media release, 29 May. https://www.debeersgroup.com/en/news/company-news/company- A further external factor confronting the natural diamond news/de-beers-group-to-launch-new-fashion-jewelry-brand-with- industry is competition from laboratory-grown gem laborato.html diamonds. A report by Frost and Sullivan (2014) postulated DE WIT, M.C.J. 2010. Identification of global diamond metallogenic clusters to that the predicted developing supply-demand gap for natural assist exploration. Proceedings of Diamonds Source to Use, Gaborone, gem diamonds could, at least partly, be taken up by synthetic Botswana, 1-3 March 2010. Southern African Institute of Mining and Metallurgy, Johannesburg. gem diamonds. A key constraint for such a scenario is the http://www.saimm.co.za/Conferences/DiamondsSourceToUse2010/015- cost of building production facilities and consumer resistance, deWit.pdf but the report argues that, as natural gems become scarcer DE WIT, M.C.J., BHEBHE, Z., DAVIDSON, J., HAGGERTY, S.E., HUNDT, P., JACOB, J., and more expensive, the barriers to market entry for grown LYNN, M., MARSHALL, T., SKINNER, C., SMITHSON, K., STIEFENHOFER, J., ROBERT, diamonds may reduce. In a 2017 report ABN AMRO (2017) M., REVITT, A., SPAGGIARRI, R., and WARD, J. 2016. Overview of diamond suggested that, in the coming decades, laboratory capacity for resources in Africa. Episodes, vol. 39, no. 2. pp. 199–237. production of laboratory-grown gem diamonds could exceed DRAPER, D. 1898. On the diamond pipes of the South African Republic. the mined production of gem-quality diamonds. However, it Transactions of the Geological Society of South Africa, vol. IV. p. 5. is considered that laboratory-grown diamonds are more likely FRASER INSTITUTE. 2018. Annual Survey of Mining Companies 2017. to impact on the market for diamonds below 0.5 ct in size, as https://www.fraserinstitute.org/studies/annual-survey-of-mining- companies-201 described earlier, than the larger and rarer categories of gem diamonds. The recent foray by De Beers into this field is an FROST AND SULLIVAN. 2014. Grown diamonds: Unlocking future of diamond Industry by 2050. https://ww2.frost.com/news/press-releases/grown- interesting development that will be closely watched (De diamonds-key-unlocking-future-diamond-industry-finds-frost-sullivan/ Beers, 2018). INNES, D. 1975. The exercise of control in the diamond industry of South Africa: Some preliminary remarks. African Studies Institute, University of <75428;<78 the Witwatersrand. African Studies Seminar Paper, March 1975. Southern Africa is inherently prospective for diamonds and JANSE, A.J.A. 1995. A history of diamond sources in Africa: Part I. Gems and Gemology, vol. 34, no. 4. pp. 228–255. has the potential to continue as the pre-eminent producer of natural diamonds for the foreseeable future. This has been JANSE, A.J.A. 1996. A history of diamond sources in Africa: Part II. Gems and Gemology, vol. 35, no.1. pp. 2–30. confirmed by recent discoveries in Angola and Zimbabwe, but some parts of the subcontinent have greater exploration JANSE, A.J.A. 2007. Global diamond production since 1870. Gems and Gemology, vol. 43, no. 2. pp. 98–119. potential than others. Entrepreneurial exploration appetite in southern Africa will be tempered by perceptions of the KIMBERLEY PROCESS ROUGH DIAMOND STATISTICS, 2004 to 2016. https://kimberleyprocessstatistics.org/public_statistics potential value equation and security of investment in diamond exploration. The uneven investment climate that LEVINSON A.A., GURNEY J.J., and KIRKLEY M.B. 1992. Diamond sources and productivity: Past, present and future. Gems and Gemology, vol. 28, no. 4. prevails in the region will also affect levels of exploration pp. 234–254. investment, but recent changes in the political environment MANENJI, T. 2017. The trajectory of Zimbabwean Marange diamond revenue may provide potential for new exploration opportunities. remittances from 2016 to 2013. Scholedge International Journal of Business Policy and Governance, vol. 4, no. 6. doi: 10.19085/journal.sijbpg040601 @>0>=>75>8 PONCE DE LEÃO, T. 2015. Geological mapping of Angola; An example of ABN AMRO. 2016. Diamond sector outlook, nothing is forever … 19 January knowledge share between GeoSurveys of Europe and Africa. Proceedings 2016. https://insights.abnamro.nl/en/2016/01/diamond-sector-outlook- of the EGS-ASGMI Director’s Joint Workshop, October 2015. nothing-is-forever/ EuroGeoSurveys, Brussels, Belgium. ABN AMRO. 2017. Diamond sector outlook, nothing is forever – part 2… 8 ROUGH POLISHED. 2017. Luaxe kimberlite to help Angola double output by 2022. December 2017. https://insights.abnamro.nl/en/.../diamond-sector- 10 February 2017. http://www.rough-polished.com/en/news/105846.html outlook-nothing-is-forever-part-2/ S&P GLOBAL MARKET INTELLIGENCE. 2018a. User platform. ALROSA. 2017. ALROSA to participate in the development of the largest deposit in Angola. http://eng.alrosa.ru/alrosa-to-participate-in-the-development- S&P GLOBAL MARKET INTELLIGENCE. 2018b. World Exploration Trends. A Special of-the-largest-deposit-in-angola/ Report from S&P Global Market Intelligence for the PDAC International Convention. March 2018 BAIN AND COMPANY INC. 2017. The global diamond industry 2017. The enduring story in a changing world. 33 pp. STOCKLMAYER, V. AND STOCKLMAYER, S. 2015. A review of diamonds in Zimbabwe http://www.bain.com/publications/articles/global-diamond-industry- – a century on – part 1, Geological Society of Zimbabwe Newsletter, report-2017.aspx October 2015. pp. 4–11.

BLUCK, B.J., WARD, J.D., and DE WIT, M.C.J. 2005. Diamond mega-placers: SASMAN F., DEETLEFS B., and VAN DER WESTHUYZEN, P. 2018. Application of southern Africa and the Kaapvaal craton in a global context. Special diamond size frequency distribution and XRT technology at a large Publication 248. Geological Society, London. pp. 213–245. diamond producer. Journal of the Southern African Institute of Mining and https://doi.org/10.1144/GSL.SP.2005.248.01.12 Metallurgy, vol. 118. pp. 1–6.

CHAMBEL, L., CAETANO, L., and REIS, M. 2013. One century of Angolan WILSON, A.N. 1982. Diamonds: From Birth to Eternity. Gemmological Society of diamonds. Report prepared by Sinese – Consultoria Lda and Eaglestone America, Santa Monica, CA. Advisory Limited. ZIMNISKY, P. 2014. The state of the global rough supply 2014. Paul Zimnisky CLIFFORD, T.N. (1966. Tectono-metallogenic units and metallogenic provinces of Diamond Analytics. 8 pp. http://www.paulzimnisky.com/the-state-of- Africa. Earth and Planetary Science Letters, vol. 1. pp. 421–434. global-rough-diamond-supply-2014

         
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 131

http://dx.doi.org/10.17159/2411-9717/2019/v119n2a5 Monitoring the performance of DMS circuits using RhoVol technology by M. Fofana* and T. Steyn*

radio frequency tracers have been also used 37 494 for the determination of cyclone efficiency (Partition Enterprises, 2017). One of the most important performance indicators of a dense medium cyclone (DMC) circuit is the Tromp curve, and by extension the separation Density fractionation (the sink-and-float process) is a traditional practice used density and Ecart Probable (Ep) values. The densimetric profiles of DMC product streams have been traditionally acquired using heavy liquid sink- throughout mineral processing laboratories to float analysis, which has certain disadvantages, such as the associated ascertain the efficiency of density-based safety and health risks. More recently, non-toxic media such as lithium separators. It has also been used as a yield hetero-polytungstates (LST) have been used, with the desired densities predictor in the coal and iron ore industries, being achieved by maintaining the solutions at specific temperatures. where the density profile of the crushed run- However, the high costs of these liquids can be prohibitive. The long of-mine (ROM) ore is correlated with the plant turnaround time of the sink-float analysis is a further disadvantage for yield. timeous interventions to the operating set-points of the DMC process. Densimetric evaluation methods have The RhoVol technology can generate the density distribution of a batch of particles in a rapid, accurate, repeatable, and safe manner. historically used heavy liquids, Additional data of interest, such as particle size and shape, are also tetrabromoethane (TBE) of various densities. measured and reported on a per-particle basis. Furthermore, samples can but these liquids carry health and be sorted into discrete sorting bins based on any of the measured environmental risks (Wills, 1987). More parameters of the particle, making further analyses of the material recently, non-toxic lithium hetero- possible. polytungstates (LST) have been used, where This technology has applications across all commodities that use the the desired densities are achieved by DMC, particularly in the size fractions –25 +8 mm and –8 +3 mm. To date, maintaining the solutions at specific laboratory results have proved very encouraging – separation densities are temperatures (Koroznikova et al., 2007). within 5% of traditional sink-float results, and the technology is being Although sink-float densimetric analyses give introduced to diamond DMC plants. a useful indication of cyclone performance, ?: 75-4 their practicalities in providing information to dense medium cyclone, RhoVol, particle size, particle shape, density. effect timeous plant-control and optimization are often limited. Long delays (up to 12 weeks) between sample collection and availability of results are not uncommon (Ndlovu, 2015). Furthermore, the repeatability >3857-0,8973 of data can often be poor due to the Dense medium separation is a commonly inconsistent nature of its operation, since sink- applied beneficiation technique for the density float analysis is a manual process and very separation of valuable products from crushed dependent on the dexterity and experience of ores. The industrial applications of dense the operator. medium separation have been summarized The RhoVol process begins by accurately and reviewed by various authors (Scott and measuring the mass of each particle, followed Napier-Munn, 2000; Bosman, 2014; Napier- by a 3D reconstruction of its volume using Munn, 2018). Dense medium cyclones (DMCs) images from multiple cameras (Forbes, Voigt, are widely used in the coal and diamond and Bodika, 2003; Forbes et al., 2006). The industries to produce clean coal or to pre- concentrate kimberlitic ores, respectively. Cyclone performance (separation density monitoring) techniques are varied. In the * mineral industry. Density tracer tests (Napier- De Beers Technologies, South Africa. Munn, 1985, 2014; Davis, Wood, and Lyman, © The Southern African Institute of Mining and Metallurgy, 2019. ISSN 2225-6253. This paper 1985) without mineral material, are widely was first presented at the Diamonds — Source to used, although their accuracy in predicting Use 2018 Conference, 11–13 June 2018, operating cut-points becomes limited once Birchwood Hotel and OR Tambo Conference mineral material is introduced. More recently, Centre, JetPark, Johannesburg, South Africa.

         
) ';..   
 133 Monitoring the performance of DMS circuits using RhoVol technology particle density is then simply the ratio of the mass to overestimate the particle volume (Wang et al., 2009; Okonta volume. Additional particle features such as size and shape and Magagula, 2011; Mangera and Morrison, 2016). The (compactness, flatness, or elongation) are readily available. volume correction factor is primarily shape-dependent, but it The process is rapid, repeatable, accurate, and safe. In is also material-dependent, since ultimately the nature of the addition, sample size is much smaller compared to material defines its final shape after comminution. Figure 2 requirements in conventional sink-float techniques, which presents an example of a 3D model of the volume of a particle amount to tens of kilograms. This is because it has been generated by the RhoVol. proven statistically that only a thousand representative Because particle shape is one of the most critical particles are required to generate repeatable and consistent parameters affecting volume accuracy, a relationship between data (Mangera, Morrison, and Voigt, 2016). shape and volume correction factor was established. Hence, The objective of this paper is to present RhoVol as a all samples were sorted on the RhoVol based on three shape competitive alternative to sink-float techniques. Ultimately, a factors, namely compactness, elongation, and flatness. The comparative case study will be conducted by analysing data compactness factor was ultimately used in all subsequent from both conventional sink-float and RhoVol methods, studies, because preliminary tests found better correlation using similar samples. This study will include the generation with the volume correction factor. The definitions of the of partition curves, and the determinations of operating cut- shape factors are deduced from measurements made, using points and Ecart Probable (Ep) values. the 3D model of the particle as inputs (Voigt and Twala, 2012): (7)72;6 656804;-:4,59 8973 a, b, c—Caliper diameters along each of the particle’s RhoVol is a densimetric measurement device developed and principal directions, resulting in three orthogonal manufactured by De Beers Technologies SA. The machine measurements where ‘a’ is the longest caliper, ‘b’ the operates in an automated batch process configuration. intermediate, and ‘c’ the shortest; all measured in Particles in a particular batch are individually weighed and millimetres their volumes are estimated by 3D reconstructions (Forbes, Flatness—A value larger than unity related to the Voigt, and Bodika, 2003; Forbes et al., 2006). The device flatness of the particle and defined by the ratio of b to discretely generates mass, volume, density, size, and particle c. A sphere has flatness equal to unity shape descriptors such as compactness, flatness, and elongation. It also has the capability of re-processing samples multiple times (in multi-pass mode) to increase measurement accuracy. The multi-pass algorithm can re-identify any individual particle in a sample and merge the data when it is reintroduced subsequently, and ultimately reconstruct a higher fidelity 3D model. Furthermore, the sample can be sorted into discrete bins based on any of the measured parameters of the particles, making further analyses of the material possible. The sample processing time is specified at 1000 particles per hour, resulting in statistically valid sample data being obtained in just over an hour in single-pass mode. Currently, the machine is available in two configurations, a fines machine for particles in the 3–8 mm fraction (including sorting as an option) and a coarse machine for particles in the 8–25 mm fraction (where the sorting option will be available soon). The requirements for the samples are that they should be dry, free of dust, and properly screened to the specified size fraction. Figure 1 illustrates the multi-stage internal functions of the RhoVol device. It entails a feed presentation stage which uses two feeders. The weighing station makes use of a high-speed weighing cell to ensure accurate measurement of particle mass. The 3D volumetric model of the particle is constructed by analysis of multiple images provided simultaneously by several cameras, offset at #9*05:;.(:;/0289486*:;938:5362;103,89734;71;8(:;(7)72;/6,(93: various angles. Sorting is done by an algorithm that can classify particles based on any of the obtained particle features, such as density, mass, size, or shape parameters.

(7)72;-686;,629568973; Prior to generating any accurate density profiles by the RhoVol, an appropriate function for the volume correction factor for the 3D reconstructed volumes of particles needs to be established. Previous studies have proven that multi-view #9*05:;6/ 2:;71;%;/7-:2;*:3:568973;71;8(:;720/:;71;6; 6589,2: silhouette-based volume reconstruction methods will always ;8(:;(7)72;-:9,: 134   
 ) ';..          
Monitoring the performance of DMS circuits using RhoVol technology

Elongation—A value larger than unity related to the Figure 4 shows the compactness distributions for the elongation of the particle and defined by the ratio a:b. DMC float and sink products. Similarities can be observed A sphere has elongation equal to unity between the two compactness distributions. Namely, the Compactness—A value smaller than unity related to the shapes of the bulk of the material are shifted toward higher compactness of the particle and is defined by values of compactness, hence the particles are expected to be ( bc )1/3. A sphere’s compactness measures unity predominantly rounder. This could have positive implications a2 for separation in the DMC, since it is well known that the   behaviour of flat particles has always been challenging to   predict accurately. Furthermore, easy access to shape distribution of any given material, provided by the RhoVol Two kimberlite samples were utilized in this test work; device, would be welcome since it can give some indications namely, DMC float-and-sink audit products (2016) from of the nature of the separation to be expected in the DMC. Venetia Mine in the size fraction –8+2.8 mm. The kimberlite Figure 5 illustrates the correction factors obtained using material types were identified as KO1 and KO2 MVK. DMC sink and float products. The results indicate similarities Compactness values ranging from 0.45 to 0.85 in steps of between the two trends; which was expected because of good 0.04 were set on the RhoVol and the float-and-sink audit parallels between the two shape distributions seen in Figure products were run separately. This generated for each product 4. Hence, a single correction factor function was adopted in twelve sub-samples (or shape classes of material) for the all subsequent studies. This was done by using mean values shape factor compactness. The first ten were realized from of correction factors for each compactness category from the the initial compactness values plus two additional shape DMC sink and float samples. Figure 6 shows such an classes of material, one less than 0.45 and another greater example. The data demonstrates a good linear correlation than 0.85. A calibrated gas pycnometer was used for the between correction factor and shape (compactness) class; R2 volume measurements. Gas pycnometer evaluation consisted was found to be 0.99. of determining the mean volume of each of the twelve sub- samples. Finally, a volume correction factor for each shape 64:;480-<;-:349/:859,;63624:4;71;):3:896;-/, class was established as the ratio of corresponding volumes 60-984;46/ 2:4 from the gas pycnometer and the RhoVol. Lastly, the volume correction factor function (VCFF), relating volume correction  factors to shape classes (for the compactness shape factor), The kimberlite material used was identical to that described was established. in the previous section. Representative samples were The photographs in Figure 3 illustrate compactness for generated by riffling; one set for RhoVol analysis and another kimberlite after classification in the RhoVol. The material was for sink-float analysis. The sink-float samples were sized sourced from the DMC float. These pictures are a typical into –8 +6.7 mm, –6.7 +4.75 mm, –4.75 +3.35 mm, –3.35 example of the sorting capability of the RhoVol, from flatter +2.36 mm, –2.36 +1.18 mm, and –1.18 mm fractions. shapes (in the 0.45 to 0.49 range) to rounder shapes (in the However, due to RhoVol’s bottom size limitation for fines, of 0.81 to 0.85 range). A similar compactness sorting was also found when the DMC sink material was studied, although not presented here. This shape classification can be ascribed to the nature of the material being analysed, in this instance, kimberlite.

#9*05:; 7/ 6,83:44;-94859089734;175;):3:896;'93:;+9/:5298:$;%' 127684;63-;493+4; ;//

(a) Kimberlitic material sorted based on compactness in the range of 0.45 to 0.49; –8+2.8 mm material

(b) Kimberlitic material sorted based on compactness in the range of 0.81 to 0.85; –8 +2.8 mm material

#9*05:;(787*56 (4;71;,7/ 6,83:44;-9485908973;175;%' ;127684 #9*05:; 755:,8973;85:3-4;0493*;):3:896;+9/:5298:;/68:5962;49:$;  +9/:5298: ;//;%' ;12768;63-;493+;/68:5962

         
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 135 Monitoring the performance of DMS circuits using RhoVol technology

+2.8 mm, the samples were only sized as –8 +6.7 mm, –6.7 :40284;63-;-94,044973 +4.75 mm, –4.75 +3.35 mm, and –3.35 +2.8 mm. For particle sizes finer than 3 mm, the resolution of the current weighing  
   scale is insufficient to register adequate particle mass, Previous studies (Mangera, Morrison, and Voigt, 2016) have especially for material such as coal. In addition, material demonstrated the repeatability of results by RhoVol if data handling for such fine sizes with the current feeder system for at least 1000 particles is captured from a given sample. It will also be challenging. was also found that the standard deviation of the median density (
50) of the sample, after multiple analyses, was   negligible. Figure 9 shows an illustration of the overlapping    of the density distributions after multiple analyses, as a function of sample size, for a kimberlite sample. The results In the sink-float evaluation process, tetrabromoethane (TBE) indicate a general improvement in the repeatability of the liquids covering a range of densities from 2.5 to 3.6, in density distribution as the sample size increased, culminating incremental steps of 0.1, were used. Then, representative in optimum data when 1000 particles (or more) were samples (as described in the section Sample preparation) of analysed. This is an important finding as it can, in future, the various size fractions were separately added to the liquid help reduce the size of samples to be treated for densimetric of lowest density first. After stirring and allowing the mixture analyses. Moreover, the finding also suggests that RhoVol to settle, each float product was removed, washed, and put can deliver consistent and repeatable results. This is unlike aside; while each sink product was transferred to the next sink-float operations, for which repeatability of data is a higher density, and so forth. The final sink and float challenge due to the fact that sink-float is a manual process products were drained, washed, and dried, along with all the and prone to human error. previous float products. Finally, all the products were weighed to give the overall density distribution of each   sample, by mass (Figure 7). The separation density and probable error (Ep) of the fines    DMC (Module 1, DF1, Venetia Mine) were determined using After establishing the VCFF (volume correction factor sink and float products. Subsequently, density fractionation function) all the RhoVol samples, as described in the section was performed (as described in the section Sink-float test Sample preparation, were processed. Hence, information on work) followed by tests in the RhoVol device (explained in mass, volume, size, and shape factors of individual particles the section RhoVol test work) to establish the relevant size- was collected; from which sample density, size, or shape by-size partition curves. distributions could be created (Figure 8). The measured     
   volume of each particle in each size fraction sample was adjusted by first determining its appropriate correction factor. Figure 10a presents the individual partition curves of all the This was achieved by using particle compactness and the sink-float size fractions (described in the section Sample fitted curve of the plot in Figure 6. Lastly, the corrected preparation) alongside the curve for the overall fraction of – volume was just the product of volume measured by the 8+1 mm. Table Ia summarizes the corresponding separation RhoVol and the correction factor. densities and Ep values. Figure 10b illustrates the partition curves of the RhoVol size fractions; as well as the curve for the combined fraction of –8 +2.8 mm. Table Ib, similarly, shows all the separation densities and Ep values. The separation densities and Ep values were all derived from experimental data fitted using the partition equation developed by Scott and Napier-Munn (1990). The partition curves and Ep results in Figure 10 and Table I show a general increase in separation density and Ep with decreasing particle size; a phenomenon that is a commonly observed in DMC separations. It is a physically related phenomenon of size-by-size cyclone partition curves (Scott, Davis, and Manlapig, 1986; Napier-Munn, 1990, #9*05:;  755:,8973;16,875;103,8973;175;):3:896;+9/:5298:;/68:5962 2018; Dunglison, 1999). RhoVol gives smoother partition 49:$; ;;// curves, including the clear presence of a ‘pivot point’; which

#9*05:;
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#9*05:; 0/02689:;-:3498;-94859089734;64;6;103,8973;71;46/ 2:;49:;!&$;.&&$;&&$;63-;.&&&; 6589,2:4";175;+9/:52989,;/68:5962$;618:5;/0289 2:;(7)72 63624:4

Table I 0//65;-686;175;,08 79384;63-; 620:4;175 ):3:896;193:4;%' $;/7-02:;.;!%#."$;493+12768;63- (7)72;5:40284;&. ;60-984

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+1–2 mm 3176 94 +2–3 mm 3109 39 +3–4 mm 3086 38 +4–6 mm 3063 29 +6–8 mm 3068 28 Overall (+1–8 mm) 3091 42

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+2.8–3 mm 3243 82 #9*05:;.&; ;11:,84;71; 6589,2:;49:;73; 65898973;,05:4;175;):3:896;193:4 +3–4 mm 3214 55 +4–6 mm 3178 15 %' ;/7-02:;.;!%#."$;493+12768;63-;(7)72;5:40284;&. ;60-984 +6–8 mm 3174 10 Overall (+2.8–8 mm) 3205 31 tends to occur in some DMC separations and has been used in the past for modelling purposes (Scott and Napier-Munn, reason for these differences between the two densimetric 1992). The deteriorations in separation efficiency for the methods is still being studied. Nonetheless, it is common finest size fractions, particularly below 4 mm, appear more knowledge that the sink-float method has its drawbacks for pronounced in the sink-float results. Noise in these finer near-density particles. That is because those particles may fractions, which previously may have been attributed to not have enough time to reach the sink or float product and short-circuiting, may be measurement artefacts. The Ep could be misplaced into the wrong product during collection. values generated as a result of tests on the RhoVol are for the Conversely, the RhoVol device accurately measures particle most part lower, except for one outlier for the +3 –4 mm mass with excellent volume estimates, hence with fairly fraction. accurate particle density calculations. Figure 11 and Table II present the comparative separation data (where available) generated by the sink-float and 73,2049734 RhoVol methods. The RhoVol densities are consistently Density fractionation (the sink-and-float process) is a higher than the sink-float densities, albeit within 5%. The common practice used throughout mineral processing

         
) ';..   
 137 Monitoring the performance of DMS circuits using RhoVol technology

Table II 0//65;-686;175;,08 79384;63-; 175;):3:896;193:4;%' $;/7-02:;.;!%#."$;493+12768;63-;(7)72;5:40284; &. ;60-984

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+3–4 mm 3086 38 3214 55 4.1 +4–6 mm 3063 29 3178 15 3.8 +6–8 mm 3068 28 3174 10 3.5

=,+37 2:-*:/:384 Venetia Mine is thanked for the use of its operational data. The work presented in this paper would not have been possible without the considerable effort of the RhoVol team, past and present.

:1:5:3,:4 BOSMAN, J. 2014. The art and science of dense medium selection. Journal of the Southern African Institute of Mining and Metallurgy, vol. 114. pp. 529–536. DAVIS, J.J., WOOD, C.J., and LYMAN, G.J. 1985. The use of density tracers for the determination of dense medium cyclone partition characteristics. Coal Preparation, vol. 2, no. 2. pp. 107–125. #9*05:;.. 7/ 65689:; 65898973;,05:4;175;):3:896;193:4;%' ;/7-02: DUNGLISON, M.E. 1999. A general model of the dense medium cyclone. PhD thesis, JKMRC, University of Queensland, Australia. .;!%#."$;493+12768;63-;(7)72;5:40284;&. ;60-984 FORBES, K., VOIGT, A., and BODIKA, N. 2003. Using silhouette consistency constraints to build 3D models. Proceedings of the Fourteenth Annual Symposium of the Pattern Recognition Association of South Africa (PRASA 2003). pp. 33–38. laboratories to ascertain the efficiency of density-based FORBES, K., NICOLLS, F., DE JAGER, G., and VOIGT, A. 2006. Shape-from-silhouette separators. Although the method does provide useful with two mirrors and an uncalibrated camera. Proceedings of the 9th European Conference on Computer Vision (ECCV 2006), Graz, Austria, indications of cyclone performance, its practicality in May 7-13, 2006. Springer. pp. 165–178 supplying information to effect timeous plant control and KOROZNIKOVA, L., KLUTKE, C., MCKNIGHT, S., and HALL, S. 2007. The use of low- toxic heavy suspensions in mineral sands evaluation and zircon optimization is often limited. fractionation. Proceedings of the 6th International Heavy Minerals The RhoVol machine is capable of rapidly and safely Conference ‘Back to Basics’. Southern African Institute of Mining and Metallurgy, Johannesburg. pp. 21–29. providing repeatable and accurate data, with significantly MANGERA, R., MORRISON, G., and VOIGT, A. 2016. Particle volume correction smaller sample size requirements, i.e., only thousands of using shape features. Proceedings of the Pattern Recognition Association of South Africa and Robotics and Mechatronics International Conference particles as compared to tens of kilograms in sink-float (PRASA-RobMech), Stellembosch, South Africa, 30 November - 2 analyses. Additional particle features such as size, volume, December, 2016. IEEE, New York. NAPIER-MUNN, T.J. 1990. The effect of dense medium viscosity on separation mass, and shape are readily available, and sorting on any of efficiency. Coal Preparation, vol. 8. pp. 145–165. these properties is an option. This latter feature of RhoVol NAPIER-MUNN, T.J. 2014. Statistics for Mineral Engineers; How to Design sets it apart from many other types of laboratory equipment. Experiments and Analyse Data. JKMRC, University of Queensland. 628 pp. Section 6.9.1. Ultimately, particle density versus size could be used to study NAPIER-MUNN, T.J. 2018. The dense medium cyclone – past, present and future. mineral liberation, for instance. Minerals Engineering, vol. 116. pp. 107–113. NDLOVU, S. 2015. Venetia Mine DMS evaluation report. Ven-R00545-718-001, Comparative densimetric analyses were conducted on 10-11-2015. DebTech. sub-samples riffled from a main common kimberlite sample OKONTA, F. and MAGAGULA, S. 2011. Railway foundation properties of some South African quarry stones. Electronic Journal of Geotechnical that originated from Venetia Mine fines DMC float and sink Engineering, vol. 16 B. pp. 179–197. products. The size fractions were varied between 8 and 1 mm PARTITION ENTERPRISES. 2017. http://www.partitionenterprises.com.au/ [accessed in the sink-float method, while fractions between 8 and 20 March 2017]. SCOTT, I.A., DAVIS, J.J., and MANLAPIG, E.V. 1986. A methodology for modelling 2.8 mm were used for the RhoVol tests due to the bottom size dense medium cyclones. Proceedings of the 13th Congress of the Council limitations of +2.8 mm material. The partition curves and Ep of Mining and Metallurgy Institutions, Singapore, May. Australasian Institute of Mining and Metallurgy, Melbourne. pp. 67–76. results, using both methods, show a general increase in SCOTT, I.A. and NAPIER-MUNN, T.J. 1990. A dense medium cyclone model for separation density and Ep with decreasing particle size; a simulation. Proceedings of the Fourth Samancor Symposium on Dense Media Separation, Dense Media 90, Cairns, Australia. Samancor Ltd. phenomenon that is commonly observed in DMC separations. SCOTT, I.A. AND NAPIER-MUNN, T.J. 1992. A dense medium cyclone model based However, the RhoVol gives smoother partition curves from on the pivot phenomenon. Transactions of the Institution of Mining and Metallurgy, vol. 101. pp. C61–C76. which conclusions are more easily drawn. In addition, the VOIGT, A. and TWALA, C. 2012. Novel size and shape measurements applied to density difference between the two methods has consistently jig plant performance analysis. Journal of the Southern African Institute of Mining and Metallurgy, vol. 112, no. 3. been within 5%, with reference to the sink-float technique. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S2225- This finding is significant because it indicates convergence of 62532012000300007 WANG, L., LU, Y., LANE, D., and DRUTA, C. 2009. Portable image analysis system results within a small margin of error. Ultimately, RhoVol for characterizing aggregate morphology. Transportation Research Record: data shows that it can be a very competitive alternative to the Journal of the Transportation Research Board, vol. 2104. pp. 3–11. sink-float method, which is still very manual and labour- WILLS, B. 1987. Mineral Processing Technology. 4th edn. Pergamon Press. intensive and suffers from accuracy problems. pp. 420–456. 138   
 ) ';..          
http://dx.doi.org/10.17159/2411-9717/2019/v119n2a6 Financing diamond projects

by J.A.H. Campbell*

is possible only through the development of =@6;A; new discoveries. This is what junior explorers are best at – but they need investors to fund Investment in diamond exploration has been declining over the past their evaluation activities from early in the decade, in spite of positive long-term industry fundamentals and a project development continuum. growing interest in diamonds as an investment category. The lack of new significant discoveries in recent years has eroded investor confidence, yet Junior explorers usually rely on equity no new discoveries are possible without investment in exploration. Junior financing to fund their early stage exploration ‘mine finders’ have been the hardest hit. Their agility, tenacity, and and resource development until such time as appetite for risk are not sufficient to attract the funding required, even at an Indicated Resource is declared, along with the greenfield stage. Developing new discoveries into mineral resources completion of a bankable Feasibility Study can be crippling without solid financial support. Junior incubators could (BFS) and debt funding becomes potentially play a crucial role, especially at the project evaluation stage – but where accessible. With availability of traditional are they? Alternatives to traditional funding mechanisms have become forms of financing becoming increasingly available, many still untested in the junior diamond exploration space. constrained, miners are considering alternative Valuable lessons can be drawn from the past and used to inform emerging financing options. new strategies.

B @?7; A>9@=7CA=78;9B=<>4; diamond exploration, project development, financing, revenue streaming, crowdfunding, incubators. Diamonds are traditionally less prone to volatility and uncertainty than mainstream mineral commodities. With almost no exposure to speculative capital (roughly 1%), diamonds have proven significantly more stable than =

         
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 139 Financing diamond projects

who stopped promoting diamonds for the whole industry in the early 2000s. A new trade body called the DPA (Diamond Producers Association) has a $60 million annual budget to attempt to reinvigorate the category and drive future consumer demand, particularly targeting millennials. Three new diamond mines have come on stream during 2017: Stornoway’s Renard and Mountain Province’s Gahcho Kué in Canada, and Firestone’s Liqhobong in Lesotho. New supply from two of these mines may offset the loss of production from Alrosa’s Mir mine – which remains closed indefinitely – with limited impact on the long-term supply forecast (The Diamond Loupe, 2017; Ziminsky, 2017b). Despite the challenges that the diamond industry is /A38?BC5' A;<@?A:>4C6?A:BC(@4>9@=7;C:@96>?B7C<@ facing on many fronts, the diamond market’s long-term [email protected]?@9C822AB47C>=7C &B44&>;%C015- outlook remains positive with rough diamond demand expected to grow 1–4% per annum and rough diamond supply remaining stable until 2030. The ’base case’ forecast for a sustained supply-demand shortfall in the years ahead New investment mechanisms have been introduced in will trend diamond prices generally upwards (Bain & recent years to stimulate investment in diamonds. In August Company, 2017). 2017, the Indian Commodity Exchange (ICEX) became the world's first exchange to start trading in diamond futures contracts; shortly thereafter, India’s Multi Commodity Exchange (MCX) also applied for the launch of futures trading in diamonds. Although it is still early days to assess the success of some of these mechanisms, there are clear indications that diamonds are beginning to attract interest as an investment category. The supply-demand outlook is modestly optimistic (Figure 3); however, the diamond industry faces three key challenges – namely the slowdown in demand for diamond jewellery, the impact of laboratory-grown diamonds, and the financial stability of the midstream segment of the value chain (Bain & Company, 2017). In an effort to address such key challenges, rough diamond producers are investing significantly to promote diamond sales; an estimated $150 million was invested in generic and branded marketing in 2017, representing an increase of about 50% from recent years. This was in addition to retailers’ own marketing spend (Bain & Company, 2017). The diamond industry has recently mobilized to fill /A38?BC0'@83&C7A>9@=7C6?A:BC6B?2@?9>=:BC@(B?C<&BC4>;7B the gap in generic consumer advertising left by De Beers, .A9A=; %C015>-

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Financing diamond projects

+64@?A=3C2@?C7A>9@=7;C?A;C>=7C8=:B?<>A=< The collapse of the commodities boom post-2011 has led to an upswing in resource nationalism and increasing Exploring for diamonds is a business with high uncertainty indigenization requirements in some sub-Saharan African and risk and little, if any, guarantee of reward. The primary countries (Table I) (Davenport, 2016). A recent change to the risk of exploration lies with the mineralization in the ground; Tanzanian mining regulations requires that government have this is inherent in any form of mineral exploration, but diamond mineralization has a higher degree of complexity than other types. Such primary risk is partly mitigated by increasingly refining the understanding of the mineralization through a process of systematic mineral resource development which leverages new and past geological data. International codes such as SAMREC, JORC, or CIM govern such processes and stipulate the reporting parameters for the different categories of mineralization and Mineral Resource (Figure 4). On top of the geological and resource risk are country and political risks: explorers must go where the right geology and diamonds can be found, and neither of these follow human- imposed country boundaries (Figure 5). Risk appetite differs from one exploration company to the next, and more markedly between majors and juniors. Some juniors are prepared to trade some political risk for the advantage of ‘being at the right address’, i.e. where the geological risk is /A38?BC'4>;;A2A:>4CB;@8?:B;C.>2<:= on investment (Leon, 2018). :@8=96 B44%C015-

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 141 Financing diamond projects

Table I *@:>4C@=B?;&A6C?B 8A?B9B=<;C2@?C9>A=C7A>9@=7C6?@78:B?;CA=C$2?A:>C.6?@78:<>C2?@9CA9 B?4B C ?@:B;;-

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DRC 23.2 72.80 0 5% govt free carry (10% proposed) Botswana 20.5 77.62 5 None Angola 9.0 57.22 5 Govt entitled to acquire 10% at production stage South Africa 8.3 53.62 10 28% BEE Zimbabwe 2.1 41.84 0 51% local ownership Namibia 1.7 66.11 3 Proposed 25% NEEEF Lesotho 0.3 72.78 5 Govt reserves right to acquire up to 20% in any large mine Tanzania 0.2 60.45 16% govt free carry (up to 50%)

a 16% free carry interest in any future mining project (this Explorers with a track record of commercializing was accompanied by a blanket ban on the export of discoveries know that technology and deep expertise are key unprocessed minerals). Namibia appears to be following the enablers when it comes to mitigating risk and extracting South African economic empowerment approach, while the early value. To quote Dr. John Teeling, ’Exploration begins new Zimbabwe government has retained the 51% anew every 20 years with improvement in technology’ indigenization requirement for platinum and diamonds, (Teeling, 2017). which it had initially considered repealing. The Angolan Technology plays a fundamental role throughout the government is entitled to hold a 10% equity in mining diamond pipeline, from early exploration through evaluation, production through a State-owned company. Botswana is the mine design, and diamond recovery, and further downstream only diamond-producing country in Africa to require no local where technology is used to identify, grade, and mark ownership in mining companies. natural diamonds. Considerable improvements have been made in diamond recovery technology, especially in the &BC 8?7B=C@2C?B;@8?:BC7B(B4@69B=< identification of diamonds within kimberlite prior to crushing Explorers operate at the tough end of the diamond funding using X-ray transmission (XRT) technology, such as the XRT pipeline, where the odds are stacked against them due to sorters installed at Karowe (Tassell, 2017). Nevertheless, prevalent risk aversion and scepticism. As confidence in the breakage of diamonds during processing remains one of the mineralization grows, so does investors’ appetite (Figure 7). key risk factors that producers have to mitigate in order to However, the resource risk mitigation process attracts maximize value, or even determine viability. Unlike other additional costs which increase exponentially as a project commodities, diamonds are valued according to nonlinear advances through the development pipeline. models; diamond size is the main driver of diamond price, While the announcement of a new diamond discovery along with colour, quality, and shape. generates positive sentiment in the market – often with a For established producers, especially mines that are favourable impact on share price – this important milestone known to yield large stones, the public acknowledgement of for any explorer is only the beginning of the demanding and diamond breakage (most recently by Gem Diamonds and capital-intensive process of proving up a diamond resource. Stornoway Diamonds) can be a downgrading factor in terms This is a journey that can span decades, and which requires of investor confidence. On the other hand, the recovery of a the ability to maximize optionality by adopting a phased large, valuable stone constitutes a ‘material event’ that can approach to resource development, with targets set by phase influence the company’s share price and the market’s and clearly identified triggers and decision points, in order to perception of the company’s value. Such events are more extract value or cut losses early (Still, 2016). material the smaller the size of the company and the higher the value of the diamonds recovered (Ziminsky, 2017c). Material events require prompt and full disclosure to markets and regulators; their newsworthiness, however, depends on the company’s appetite for exposure and publicity. Privately owned diamond mining companies have seldom publicized the recovery of individual diamonds, although this is changing for many of them. For small diamond miners, on the other hand, the recovery of a single high-value diamond is a newsworthy event and its announcement can have a significant impact on share price. The journey from discovery through evaluation to production can differ depending on the geological settings and jurisdictions, as well as the companies involved. The recent history of Karowe mine is a particularly telling /A38?BC'&BC6?@B:

&BC7B(B4@69B=?@BC9A=B In 2009, Lucara Diamonds, facilitated by African Diamonds, was able to buy 70% of a $1 billion business for Karowe mine, located in the Orapa region of Botswana, is an $49 million, proving once again that ‘cash is king’, and open pit kimberlite operation and one of the world’s top especially so at the bottom of the economic cycle. Lucara’s diamond producers by value. The mine began production in market capitalisation prior to this acquisition was just C$30 2012 and has an anticipated life of mine of 15 years. million. In 2010, Lucara purchased African Diamonds’ share Estimates for 2018 are 270 000–290 000 carats for a revenue of $170–200 million. Since 2010, Karowe is fully owned by at a 30% premium. Lucara Diamond Corporation, a TSX and Stockholm Stock From an economic perspective, the AK6 story Exchange listed company with a market capitalisation in demonstrates that the right set of technical and corporate excess of C$800 million. skills, coupled with the right opportunity and timing, can A highly profitable producer, Karowe has generated generate attractive returns for shareholders through revenue in excess of $1.02 billion to date, at an average price increased share price (Figure 8). of $566 per carat. The mine is a proven large stone producer, African Diamonds raised cash at 2 p, listed at 7 p in famous for its magnificent Type II diamonds. The second 2004, and sold AK6 for an equivalent 52 p. African largest diamond ever found, the 1 109 ct Lesedi La Rona, Diamonds’ exploration assets were spun off into Botswana was unearthed at Karowe in 2015. Diamonds plc. The original shareholders of African AK6 (now Karowe) was discovered by De Beers in 1969. Diamonds made forty times their money through shares in The potential of AK6 was not apparent at the time of its Botswana Diamonds and dividends and capital growth in discovery and early assessment in the 1970s and 1980s. One Lucara Diamonds (Figure 9). Much of the experience that ought to consider that this was a time of economic was hard won through the AK6-Karowe journey from a sub- stagflation, when high inflation combined with slow growth marginal project to one of world’s greatest diamond mines is and high unemployment crippled the global economy. today retained within the Botswana Diamonds team. Worldwide, diamond sales were declining sharply and diamond prices collapsing. A radically transformed market ?B=7;CA=CB64@?>:?BC6?A:B hardest hit. 011011C.;@8?:BC>7(2=:@9-

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Throughout 2016, the largest mining companies were with a healthy appetite for risk. Exploration spend is the responsible for the majority of exploration spending. For the lifeblood, yet these juniors typically have no production cash third consecutive year, companies allocated more to minesite flow to fund their exploration activities. work than to grassroots exploration, as the former is Funding of early stage exploration and resource perceived as a less expensive and less risky means of development activities usually comes from ‘family and replenishing resources. With early-stage exploration being friends’ (Teeling, 2017) with some appetite for risk; only driven by the majors, overall spend on greenfield exploration once an Indicated Resource is declared, along with completion fell to new lows, while proportionally more was spent on of a BFS, does debt funding potentially become accessible. moving late-stage projects towards production or making This is largely because institutional investors look for them attractive for acquisition (mining.com, 2017) positive cash flows, low or mitigated risk, high returns and, (Figure 11). preferably, some form of tax incentive. Against this background of restricted exploration As a company de-risks its projects, more value is funding, investors’ appetite for diamond exploration has been unlocked for shareholders. The Lassonde curve (Figure 12) further curbed by the lack of new significant discoveries in illustrates the value that the market attributes to each stage the last decade (with the exception of Alrosa’s Luele of the life-cycle of a mining company from exploration to kimberlite at Luaxe in Angola and Lucara’s Karowe mine in production. Botswana); as a result, funding for diamond exploration The discovery phase is high-risk, high-potential, and remains extremely tight. The paradox is that the lower the early investors can see substantial gains in a short time- exploration spend, the fewer the chances of new discoveries. frame. Once the mineralization is delineated, the project enters the development phase. This period can be accompanied by a lack of news as companies work on E8=A@?CB64@?>

The remarkably successful Lundin Group has recently been shifting its focus towards the consolidation of the mid- size mining space (Business News Network, 2017). The 162 Group focuses on high-potential natural resource start-ups, providing seed capital and initial management and taking the venture to market normally within three years. Over time the 162 Group has established 15 listed resources companies with interests across the globe, including AIM- listed Botswana Diamonds which is actively exploring in South Africa and Botswana. The perception that Canadian and Australian institutional investors may be less risk-averse than their London-based counterparts has prompted certain London-listed junior /A38?BC50'*>;;@=7BC:8?(BCA448;C8=A@?CB64@?B? miners to seek secondary listings in Toronto in the hope of .;@8?:BC+64@?>=:A=3C@2C7A>9@=7C6?@B:<;C
C&>?BC<&B speculators exit the scene, the company enters an ‘orphan period’ from which it may not recover unless funding is >4

Stock exchange Mining-specific reporting requirements (post-listing) Mineral reporting standard Diamond companies (selected)

ASX Annual and half-year financial report JORC Merlin Quarterly report by CP on production and development activities Lucapa (incl. expenditure); exploration activities; mineral results and ore results JSE Annual and quarterly financial report. SAMREC Trans-Hex Description of exploration and mining activities by CP; Mineral Resource and Reserve statement TSX/TSX-V Annual and quarterly financial report. CIM (NI 43-101) Diamcor DFI Kennady Lucara Mountain Province Peregrine Rockwell Stornoway Tsodilo Dundee Minerals LSE/AIM Annual and half-year financial report. JORC, SAMREC, CIM, Botswana Diamonds Interim management statement. other selected codes Firestone Resource updates by CP (AIM). Petra Blue Rock

         
#!*",+C55)   
 145 Financing diamond projects

now own equity in an emerging mining company for as little as $500. Unlike ‘crowdselling’, a common strategy practiced by institutional investors which left many mineral exploration companies on the brink of insolvency (Lasley, 2016), crowdfunding has the ability to reach a vast number of potential investors through social networks, thereby expanding the pool of potential investors far beyond the confines of banks, venture capitalists, and other mining companies. However, it is imperative that communications with this audience be frequent, direct, and transparent; and the information clear and current. This will require a major shift in the marketing strategy of most mining companies. Dedicated crowdfunding platforms for mining companies have been launched in Canada and Australia and others are in development, such as ResourceFunding in the UK. Mining companies using such online investment platforms commit to transparency of information to investors and undergo rigorous due diligence processes which are designed to protect the crowd (Breytenbach 2016). Regulators in Canada and the USA have already adopted rules allowing the sale /A38?BC5'/A=>=:A=3C@6=AB;C.>2

The JSE, South Africa’s long-established stock exchange, DUFFIELD, C. AND SHELLHAS, K. 2013. Could diamonds outperform gold this prides itself in having the world’s highest migration rate from decade?http://www.traderplanet.com/articles/view/163898-could- diamonds-outperform-gold-this-decade-gld/ [accessed 1 March 2018]. the small-cap secondary board (the AltX) to the main listing EASTMAN, N., GRAVES, B., and MARIAGE, F. 2017. Global financing alternatives: a platform. Why then are so many junior explorers active in primer on royalty and stream financing. https://gettingthedeal South Africa not listed on AltX? Perhaps the value through.com/area/22/article/29109/mining-2017-global-financing- proposition of some of the firms operating as JSE/AltX alternatives-primer-royalty-stream-financing/ [Accessed 11 February 2018]. sponsors or designated advisers could be enhanced by ELS, F. 2016. Private capital is ready to invest $7 billion in mining. offering business incubator services to potential new http://www.mining.com/private-capital-is-ready-to-invest-7-billion-in- entrants. mining/ [Accessed 10 March 2018]. The rise of crowdfunding in mining presents an attractive ELS, F. 2017. Mining exploration spending drops to 11-year low. http://www.mining.com/greenfields-share-exploration-spending-drops- option for juniors seeking exploration seed funding. Could it record-low/ [accessed 4 February 2018]. become a viable alternative at a time when traditional EULER HERMEs. 2017. Country risk map Q1 2017. http://www.eulerhermes.com/ methods for raising exploration capital are failing junior economic-research/publications/Pages/country-risk-map-q1- explorers? Could it become the future of fundraising? 2017.aspx?postID=1033 [accessed 11 February 2018]. EXPLORATION INSIGHTS. 2016. Fatal flaws in the junior mining sector. https://www.explorationinsights.com/articles/fatal-flaws-in-the-junior- @=:48;A@=; mining-sector/ [accessed 10 March 2018]. Diamond exploration is a complex business with a high GRIEVE, N. 2018. Juniors asked to consider royalty, streaming project finance deals. http://www.miningmx.com/news/energy/31512-junior-asked- failure rate. It requires trusted teams of ‘mine finders’ with consider-royalty-streaming-project-finance-deals/ [accessed 9 March proven skills, deep commitment, and healthy doses of 2018]. tenacity and optimism. LASLEY, S. 2016. Crowdfunding awakens. https://www.miningnewsnorth.com/ It requires the careful, ongoing assessment of the story/2016/01/10/news/crowdfunding-awakens/3551.html [accessed 10 March 2018]. interplay between geological and country risks and the agility LEON, P. 2018. Mining sector needs a strong dose of Ramaphosa’s Eskom to respond promptly to any changes in the latter – be they treatment. https://www.businesslive.co.za/bd/opinion/2018-02-05- improvements in fiscal regime or sudden indigenization mining-sector-needs-a-strong-dose-of-ramaphosas-eskom-treatment/ legislative changes. [accessed 2 March 2018]. It also requires financing: right from the early stages, ODENDAAL, N. 2017. JSS eyes R1bn capital raise to fund junior miners. http://www.engineeringnews.co.za/article/jss-eyes-r1bn-capital-raise-to- when public listing is neither viable nor acceptable by the fund-junior-miners-2017-01-27 [accessed 10 March 2018]. main stock exchanges, and increasingly so through the PALISADE RESEARCH. 2017. Junior mining’s infamous guide to investing. evaluation stage, when confidence in the mineralization is https://palisade-research.com/junior-minings-infamous-guide-to- not yet sufficient to entice the more risk-averse investors. investing/ [accessed 8 March 2018]. PWC. 2013. 3 things you need to know about alternative financing in the Entrepreneurs with a following and isolated ’junior mining industry. https://www.pwc.co.uk/assets/pdf/alternative-financing- incubators’ have had a crucial role to play in the growth of in-the-mining-industry.pdf [accessed 22 February 2018]. certain diamond exploration companies; however, these are PwC. 2017. Junior mine 2017: Confidence rekindled. few and far between. New and alternative financing https://www.pwc.com/ca/en/industries/mining/publications/junior-mine- 2017.html [accessed 9 March 2018]. mechanisms have appeared in the recent years, including SAMREC. 2016. South African Mineral Resource Committee. The South African crowdfunding. Their viability in the diamond exploration Code for the Reporting of Exploration Results, Mineral Resources and space, however, remains to be ascertained. Mineral Reserves (the SAMREC Code). 2016 Edition. http://www.samcode.co.za/codes/category/8-reporting- B2B?B=:B; codes?download=120:samrec SRK. 2017. Could coal mining be the SA mineral sectors business incubator? BAIN & COMPANY. 2017. The global diamond industry 2017. https://www.srk.co.za/en/za-could-coal-mining-be-sa-mineral-sectors- http://www.bain.com/publications/articles/global-diamond-industry- business-incubator [accessed 10 March 2018]. report-2017.aspx [accessed 11 February 2018]. STILL, R. 2016. Lessons from the exploration business. Presentation at the BANKS, J. 2016. Crowdfunding - a credible new source of investment for Junior Indaba, Johannesburg, South Africa. mining? http://www.stratum-international.com/blog/crowdfunding- TASSELL, A. 2017. XRT technology ushers a new era in diamond recovery. investment-in-mining/ [accessed 10 March 2018]. Modern Mining, May 2017. BREYTENBACH, M. 2016. Alternative fundraising model seen flourishing but TEELING, J. 2017. Have I a deal for you? Presentation at the Junior Indaba, regulatory issues could stifle uptake in South Africa. Johannesburg, South Africa. http://www.juniorindaba.com/presentations http://www.miningweekly.com/print-version/despite-game-changing- [accessed 1 March 2018]. expectations-regulatory-challenges-remain-key-concern-of- crowdfunding-for-mining-sector-2016-05-20 [accessed 10 March 2018]. THE DIAMONDLOUPE.COM. 2017. ALROSA rough Sales $258M in August, to close Mir mine indefinitely.https://www.thediamondloupe.com/articles/2017- BUSINESS NEWS NETWORK. 2017. Rick Rule interviews Lukas Lundin on what sets the Lundin Group apart from competitors. 09-07/alrosa-rough-sales-258m-august-close-mir-mine-indefinitely https://www.bnn.ca/investment-trends/video/rick-rule-interviews-lukas- [Accessed 25 February 2018]. lundin-on-what-sets-the-lundin-group-apart-from-competitors~1264442 VAN PRAET, N. 2014. Stornoway financing deal pushes Quebec's first diamond [accessed 18 February 2018]. mine closer to reality. http://business.financialpost.com/commodities/ CAMPBELL, J.A.H. 2005. The continuing transformation of De Beers – a case mining/stornoway-financing-deal-pushes-quebecs-first-diamond-mine- study. Presentation to the Executive MBA Study Tour of South Africa. closer-to-reality [accessed 8 March 2018]. Tanaka Business School, Imperial College, London, UK ZIMINSKY, P. 2017a. Quarterly review of rough diamond prices in the 10 years CAMPBELL, J.A.H. 2017. Country models that are working and why. Panel since the Global Financial Crisis. http://www.paulzimnisky.com/10-year- discussion at the Africa Mining Summit, Gaborone, Botswana. quarter-by-quarter-recap-of-rough-diamond-prices-since-global-financial- DAVEPORT, J. 2016. Time for African countries to rethink mining policies. crisis [accessed 4 February 2018]. https://www.howwemadeitinafrica.com/time-african-countries-rethink-mining- ZIMINSKY, P. 2017b. 2018 Global diamond industry primer. policies/55089/ [Accessed 9 February 2018]. http://www.paulzimnisky.com/2018-global-diamond-industry-primer [accessed 4 February 2018]. DENINA, C. and LEWIS, B. 2017. Small mining companies shun London market after IPO flops. https://www.reuters.com/article/us-mining-ipo/small- ZIMINSKY, P. 2017c. The discovery of newsworthy diamonds is increasing. mining-companies-shun-london-market-after-ipo-flops-idUSKBN1CU26A http://www.paulzimnisky.com/the-discovery-of-newsworthy-diamonds-is- [accessed 10 March 2018]. rising [accessed 4 February 2018].

         
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To discuss any pressing process challenges, CONTACT: Professor Selo Ndlovu ;LHT3LHKLY"+:;59-:(9*O09LZLHYJO*OHPYPU /`KYVTL[HSS\YN`HUK:\Z[HPUHISL+L]LSVWTLU[ [email protected] www.wits.ac.za/chemmet/research www.saimm.co.za Tel: +27 11 834 1273 http://dx.doi.org/10.17159/2411-9717/2019/v119n2a7 The application of XRT in the De Beers Group of companies

by A. Voigt*, G. Morrison*, G. Hill*, G. Dellas*, and R. Mangera*

" !#! X-ray transmission (XRT) sorting has become the preferred recovery technology option in several parts of the diamond-winning flow sheet. In the De Beers Group, applications of XRT are found across kimberlite, alluvial, and marine operations. This is the result of intensive R&D conducted over the years to arrive at a suite of machine embodiments capable of sorting and auditing diamonds across all size ranges. The first applications in the marine environment used the technology in an auditing mode, and served as a useful early predictor of diamond content weeks ahead of sorthouse returns. The same machines are now available with ejection capability to produce high final product grades. The next application was tests on coarse alluvial gravels as an alternative to dense medium separation. The results were very encouraging, and tests # %& %$#& &$&$%"% &#"%!$" are planned for both green- and brownfield kimberlite environments, as !!% well as to explore an alternative to conventional techniques in final diamond recovery. At the Jwaneng mine Large Diamond Pilot Plant (LDPP), the objective is to recover diamonds in the size fraction –45 +25 mm. The technical challenge remains in the finer sizes, for high-capacity- machines as direct alternatives to conventional diamond recovery technologies. This is an area of ongoing R&D and it is only a matter of time before the breakthrough emerges.

'% ! XRT, diamonds, De Beers, DMS, sorting.

# %&$%!& & %"% & &$"&#  $& $"!#!!# "&"$%"$! %"% &
 &#$%!& &#$ "#% !&$% #$ XRT makes use of X-ray imaging techniques $!!#"&%& $&#"%!$"&$% $ to analyse objects and materials, and has a wide range of applications from baggage two sensors, one responding to low-energy X- scanning for security purposes (Martz et al., rays and one to high-energy X-rays. Feed 2016), to recycling of waste material (Owada, material can be imaged either while on the 2014). During the last decade XRT has been belt, or while in flight. applied to an increasing extent in the minerals Examples of raw X-ray images of processing industry (von Ketelhodt and diamondiferous feed material are given in Bergmann, 2010; Sasman, Deetlefs, and van Figure 2. Particles appear as shadows in the der Westhuyzen, 2018). Dual-energy XRT (DE-XRT), in which images of the target material are obtained at both high and low X- ray energies, allows for elemental analysis and * De Beers Technologies (SA), Johannesburg, South therefore can be used to discriminate between Africa. various minerals. © The Southern African Institute of Mining and Metallurgy, 2019. ISSN 2225-6253. This paper A DE-XRT system makes use of a dual- was first presented at the Diamonds — Source to energy X-ray line scan sensor to generate Use 2018 Conference, 11–13 June 2018, images of transmitted X-rays (Figure 1). Dual- Birchwood Hotel and OR Tambo Conference energy refers to the camera, which contains Centre, JetPark, Johannesburg, South Africa.

         
  &   
 149 The application of XRT in the De Beers Group of companies

#<0/7=>$"=6/4:>8.>9>:5=87=:<394>6:/2,>8.>58(> 97<8/6>1<;=7946>9*687*>5<05+>9;2>48(+=;=70,>%+79,6 ><918;26>39;>*=>2<6:<;0/<65=2>.781>8:5=7>1<;=7946 *96=2>8;>:5=<7>9*687-:<8;>8.>5<05+>9;2>48(+=;=70,>%+79,6

image, as X-rays are absorbed by the particles and fewer X- Image processing techniques are used to identify particles rays arrive at the detector. The shadows appear darker in the in the classified image. Various tests are carried out on each low-energy image than the high energy-image, since low- particle before it is identified as a target or non-target. In a energy X-rays are more readily absorbed than high-energy sorting machine embodiment, the target particles are typically X-rays. ejected from the material stream using an air ejection system. The extent to which materials absorb X-rays depends on In addition to identifying particles, the XRT absorption the elements present, density and thickness of the material, images contain information from which the size and mass of as well as the characteristics of the X-rays. Each mineral particles can be inferred. This allows for diamond auditing absorbs high- and low-energy X-rays in different ratios. applications, which are discussed further below. Figure 3 shows the theoretically predicted absorption of high- and low-energy X-rays for various minerals of varying >6/1197,>8.>%")><;>:5=>=>==76>A78/- thickness, derived from the material properties (XCOM, The first XRT system in De Beers was developed by the De 2018). It is evident that diamond can be distinguished from Beers Diamond Trading Company in 1990. This is a other minerals. Note that Figure 3 represents the ideal case. laboratory system used for detecting and analysing liberated In practice, detector noise and other variations result in diamonds in the Kimberley Microdiamond Laboratories, and imperfect discrimination. This is especially true for small a version is still in use today. particles. Following this, in the early 1990s, the De Beers Mineral The high- and low-energy images can be combined, and Processing Division in Johannesburg evaluated XRT as one of each pixel coloured according to its classification as shown in the technologies for detecting unliberated diamonds within Figure 4. kimberlite. At that time, fast neutron radiography was identified as the preferred method for detecting these unliberated stones. During this work, XRT again showed great potential for the detection of liberated diamonds, although the commercially available excitation and detection technology was not yet mature enough for application to kimberlite processing or diamond recovery. The major advantages that XRT offered were: All diamond types would be recovered with no concerns regarding low-luminescing stones Ultra-low yields would be possible, making new flow sheet designs feasible #<0/7=>$>
;>:5<6>34966<.<=2><190=&>07==;>7=0<8;6>7=-7=6=;:>2<918;2 9;2>*4/=>;8;+2<918;2 >)5=>07==;>7<16>978/;2>;8;+2<918;2>-97:<34=6 Lower sensitivity to dust and masking effects than 97=>7=0<8;6>(5=7=>:5=>19:=7<94><6>:88>:5<;>:8>*=>34966<.<=2>3877=3:4, conventional optical techniques. 150   
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The application of XRT in the De Beers Group of companies

However, challenges remained for XRT on multiple fronts (as described later by Buxton and Crosby, 2008): Predicted throughputs were low at the targeted size ranges The robustness of the enabling technology was poor The cost of developing a viable sorter to compete with existing equipment was prohibitive Reliable performance benchmarks were nonexistent, and thus trust was low. Nevertheless, during the next decade the underlying excitation, detection, and data processing technologies made steady progress and the development of viable sorting machines became a possibility in the mid-2000s. The following application areas for XRT were identified #<0/7=>$%")>7=38;3=;:79:<8;>1935<;=>)''><;6:944=2>8;>9 and pursued: =*197<;=>91<*<9>1<;<;0> =66=4 >)5=>1935<;=>-783=66=6>:5=>.<;94 7=38 =7,>-49;:>38;3=;:79:=>*=.87=>39;;<;0 To provide online diamond auditing information. The first XRT auditing trials were run in 2013 on offshore marine vessels. resolution images of the feed material are captured and the To complement X-ray luminescence (XRL) sorting absolute X-ray absorption of a particle depends on its size machines in the recovery plants to produce and mineralogy. The carat mass of individual diamonds can concentrates containing a high weight percentage of therefore be estimated as they are processed. diamonds. XRT reconcentration machines have been Real-time DSFD information provides particular benefit in operating on offshore marine vessels since 2016. the marine mining environment. In a typical marine As a low-OPEX alternative to coarse DMS that would operation, the sea floor is systematically mined in well- be insensitive to feed density. The first XRT pilot plant defined sections. The final concentrates, usually the product was operational in 2014 at Namdeb. of X-ray reconcentration unit processes, are canned on board. To recover large diamonds early in the flow sheet. The Consignments are exported to land on a regular basis, where Jwaneng mine LDPP will operate from 2018 to 2019. they are sorted and sized in a hand-sorting facility. It is only at the end of this process (which can take several days) that Going forward, challenges remain as regards fine the recovery statistics for a particular mining area become diamond recovery, particularly with wet fine material. In known. Plant metallurgists rely on proxy measures, such as addition, applications in the re-deployable and ultra-coarse the number of ejections recorded by the diamond recovery domains are being watched with interest and may be able to machines. These measures vary significantly depending on unlock further value for De Beers. the machine set-up parameters and the mineralogy of gangue material being fed to the circuit. !97<;=>9/2<:<;0>9;2>687:<;0>9--4<39:<8;6 De Beers Marine (DBM), De Beers Marine Namibia XRT can provide real-time estimates of diamond size (DBMN), and De Beers Technologies (SA) began a frequency distributions (DSFD). This is because high- collaborative XRT test programme in 2013. A mine test unit

#<0/7=>$877=49:<8;>*=:(==;>:5=>:8:94>3979:6>7=38 =7=2>*,>:5=>687:58/6=>9;2>:5=>%")>=6:<19:=

         
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 151 The application of XRT in the De Beers Group of companies

(MTU) was installed on the Debmarine Namibia DebMar Atlantic Mining Vessel. The final concentrate underwent XRT analysis before being canned for export. Over a one-year test period, the XRT estimate of DSFD and total carat content was compared with the sorthouse results. The tests were successful, showing that XRT provides an accurate and timeous estimate of the DSFD and carat content of the final concentrate. The XRT unit process (BDT1122) has since been commercialized and installed on five DBMN mining vessels as shown in Figure 5. The machines are available in either an auditing configuration (providing carat and DSFD information), or a reconcentration configuration (where sorting functionality is included). Figure 6 shows a typical correlation between carats recovered in the sorthouse versus the total carat content estimated by XRT, for +3ds material. XRT generally provides #<0/7=>$)5=>%")>-<48:>-49;:><;6:9449:<8;><;>79; =1/;2&>91<*<9 >)5= an accurate estimate of total carats recovered, and has 6,6:=1>38;6<6:=2>8.>9>38;:9<;=7<=2>5<05+:578/05-/:>1935<;=>38/-4=2 replaced other proxy methods as a real-time measure of (<:5>9>38;:9<;=7>58/6<;0>:5=>6=7 <3=6>7= /<7=2>:8>7/;>:5=>-49;: recoveries on many marine operations. While the application of XRT in the marine mining environment has proved useful so far, a few challenges cost alternative to DMS. These machines are predicted to run remain. These are primarily associated with the detection of at lower operating costs and to produce lower and more fine (–3ds or –1.3 mm square mesh sieve) material. Such consistent yields that will result in downstream treatment material is at the limit of the resolution capability and noise cost benefits and simplifications. A comparison is shown in characteristics of dual-energy X-ray detectors. In order to Table I. ensure that fine diamonds are detected, and recovered, the algorithm parameters are such that a significant number of During 2014 to 2016, Namdeb and De Beers false detections occur, increasing the yield on the finer Technologies SA collaborated to run a joint pilot test material. Indeed, the outlier cases seen in Figure 6 can be programme with the goal of evaluating high-throughput XRT associated with a period that had a high incidence of dusty or in the alluvial application as an alternative to DMS plants. gritty material in the feed. In such cases, XRT overestimates Figure 7 shows the installation in Oranjemund. A number of the carat content. novel operational features were evaluated, including feed rate The reconcentration version of the machine (BDT1122) control loops, and generation of DSFD information. includes a multi-channel ejection system. Its purpose is to The machine used in the tests was the De Beers provide a high diamond by weight (DBW) product, and it is Technologies SA XRT Coarse Concentrator (XRT-CC) being piloted at various marine and land-based plants. The BWT1186. This containerized sorting machine has a 900 mm same challenge exists with fine material, as discussed in the wide belt and is designed to process material from 6 mm to previous paragraph. 75 mm. Various initiatives are underway to address the The programme tested the technology with material in challenges presented above. These include improved dust size ranges between 6 mm and 32 mm. Dry and wet and grit removal systems, as well as higher resolution X-ray materials were specifically tested separately to determine the camera technology. effect of moisture on sorting performance. In addition, as this was an alluvial operation, the impact of marine shell in the %")>96>9;>94:=7;9:< =>:8>2=;6=>1=26=-979:<8; feed was also investigated. The test programme set out to High-throughput XRT machines were identified as a lower determine the following critical parameters: The optimal feed rate per size fraction Diamond recovery efficiency at these throughputs Table I The availability and reliability of the XRT technology ;><44/6:79:< =>381-97<68;>8.>8-=79:<;0>386:6>(5=; The operating costs of the XRT technology. 7=-493<;0>9>38976=>!>(<:5>9;>%")>684/:<8; The results indicated that the XRT-CC machine is well :7=9:<;0>:5=>691=>:578/05-/: >94/=6>97= suited as an alternative to coarse DMS. The tests also showed ;87194<=2>:8>:5=>:8:94>!>386: that feed preparation is important as increased undersize material in the feed reduces the throughput to less than the 87194<=2>386:>-=7>:8; optimum for 100% diamond recovery. Wet fine material 86:><:=1 %") ! required special consideration due to the material sticking to Electricity 14% 36% the belt, leading to either higher-than-expected yield (for top- Labour 11% 8% down ejection systems) or more frequent maintenance (for Maintenance and consumables 7% 32% bottom-up ejection systems). It is worth noting that these Downstream costs 2% 23% findings are not XRT-specific concerns but would apply to Total 34% 100% any belt-fed sensor sorting system. 152   
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The application of XRT in the De Beers Group of companies

970=>2<918;2>7=38 =7, The high throughput and low yielding performance of XRT sorting machines enable them to be applied upstream of existing concentration circuits to target the large liberated diamonds above the conventional top particle cut-off size. This configuration allows this revenue to be recovered as early as possible and reduces the probability of damage to the large stones (Sasman, Deetlefs, and van der Westhuyzen, 2018). The LDPP at Jwaneng mine in Botswana (Figure 8) will undergo a 12-month test programme during 2018 and 2019 to quantify the occurrence rate of large diamonds at that operation. The plant will treat the 25 mm to 45 mm scrubber oversize size fraction with two De Beers Technologies (SA) BWT11162 machines. This containerized sorting machine has an 1800 mm wide belt and can process material from 6 #<0/7=>$)5=>3/77=;:>4=.:>9;2>182<.<=2>7<05:>.48(>65==:6>9:>=;=:<9 mm to 75 mm. 1<;=&>8/:5>.7<39 >/77=;:4,&>:5=>7=38 =7,>-49;:>:7=9:6>944>6<=>.793:<8;6 >.<;=6&>1<224=6&>9;2>38976=> >8;>2=2<39:=2>3<73/<:6 >)5=>182<.<=2>.48( 65==:><;34/2=6>%")>:=35;8480,>:59:>:7=9:6>:5=>38976=>.793:<8; 4:=7;9:< =6>.87>38976=>2<918;2>7=38 =7,>-86:+! <;2=-=;2=;:4,>.781>:5=>7=38 =7,>-49;:&>(5<35><6>;8(>7=38;.<0/7=2>.87 :5=>.<;=6>9;2>1<224=6>.793:<8;6>8;4, As much as the application of high-capacity XRT machines is seen as an alternative to DMS and upfront large diamond recovery, it also enables alternative flow sheet configurations (Valbom and Dellas 2010). Venetia mine is installing a De Beers Technologies (SA) XRT-CC machine after DMS, However, the throughput requirements in the DMS targeting the coarse (–25 +8 mm) size fraction, as shown in application make any sensor-based sorting system (including Figure 9. XRT) commercially unviable due to the current CAPEX and As feed to the plant becomes harder and denser, and with OPEX estimations for such projects. varying PSDs, the limitations of the current flow sheet Apart from the commercial considerations, the treatment configuration have become evident. High-throughput XRT of fine material at high throughput presents various technical technology will alleviate both the capacity and PSD variation challenges to sensor-based sorting machines. While the challenges by a simple modification of the flow sheet as demand placed on the detection and classification system is shown in Figure 9. highest, the feed presentation system and the ejection system The main advantage of the new configuration is the are also strained. separation of the coarse circuit from the final recovery plant into a standalone high-capacity circuit. The recovery plant     will then be reconfigured for the fines and middles size Systems dealing with large particles are fairly robust to dust fractions at improved capacity. and grit that is entrained with the material. However, as the size fraction being treated becomes smaller the detection #<;=>2<918;2>7=38 =7,>9:>5<05>:578/05-/: system is less able to operate effectively. Added to this is the XRT machines that treat fine material could find application challenge of feeding fine, wet material which sticks to the belt in the recovery plant and as a replacement for fines DMS. and tends to clump. This adversely affects the recovery efficiency and yield.

      The biggest challenge presented by finer material relates to requirements placed on the detection system. Difficulties arise because finer particle sizes require smaller pixels on the X- ray sensor. To ensure that a reasonable signal is achieved on these smaller pixels, a number of engineering solutions are possible. Increasing the signal integration time, resulting in reduced throughput due to the associated reduction in the speed of the material passing the sensor Bringing the X-ray source closer to the sensor, resulting in reduced throughput due to reduced belt width #<0/7=>$)5=>970=><918;2><48:>49;:><;6:9449:<8;>9:> (9;=;0>1<;=& Increasing the X-ray power, placing greater pressure on 8:6(9;9&>658(<;0>:5=>:(8>%")>1935<;=6>6<2=+*,+6<2= >8;:9<;=7<=2 the engineering of X-ray safety and resulting in 1935<;=6>6<1-4<.,>65<--<;0>9;2><;6:9449:<8;>9;2>=;9*4=>-7=+ increased failure rates of the X-ray generation and 3811<66<8;<;0>:8>*=>28;=>9:>:5=>.93:87,&>(5<35>6587:=;6>:5=>8;+6<:= 3811<66<8;<;0>:<1= detection components.

         
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 153 The application of XRT in the De Beers Group of companies

#<0/7=>'$)5=>%")>:=6:>-49;:>9:>:5=>=>==76>)=35;8480<=6>>391-/6&> 859;;=6*/70

To achieve high throughput when treating fine material, a material. Potential applications in the re-deployable and much higher data processing rate is required. This is due to ultra-coarse domains are being considered, and may be able the finer detector resolution, which requires a high number of to unlock further value for De Beers. small pixels. Another challenge associated with small pixels is that the signal-to-noise level is decreased. The resulting data is noisier, which makes the task of the classification 3?;8(4=20=1=;:6 system more difficult. Sincere gratitude goes to the following: De Beers Consolidated Mines Venetia mine, Debmarine Namibia, Debmarine South   Africa, Debswana Corporate Centre, Debswana Jwaneng mine, For handling fine material, the ejection system needs to be and Namdeb Diamond Corporation. more precise. Ejectors can be thought of as having a footprint – the bigger this footprint, the greater the number of "=.=7=;3=6 ‘passenger’ particles that will be recovered with each ejection of a target particle. As the material becomes finer, the ejection BUXTON, M. and CROSBY, R. 2008. Ore sorting – An Anglo American perspective. Proceedings of Sensor Based Sorting 2008, Aachen, Germany. GDMB, footprint needs to be reduced, otherwise the grade of the Clausthal-Zellerfeld, Germany. recovered material will be too low. MARTZ, H.E., LOGAN, C.M., SCHNEBERK, D.J., and SHULL, P.J. 2016. X-Ray Imaging: Fundamentals, Industrial Techniques and Applications. CRC )=6:>.93<4<:,><;> 859;;=6*/70 Press.

A permanent and secure XRT test facility is located at the De OWADA, S. 2014. SBS technology for creating environment friendly process of Beers Technologies (SA) campus in Johannesburg (Figure various metals recycling – Advances and problems to be solved. Proceedings of Sensor Based Sorting 2014, Aachen, Germany. GDMB 10) and forms part of the Mineral Sample Treatment Plant Clausthal-Zellerfeld, Germany. pp. 11–23. (MSTP). Several performance parameters, including recovery efficiency, yield, throughput, and size range, as well as the SASMAN, F., DEETLEFS, B., and VAN DER WESTHUYZEN, P. (2018). Application of diamond size frequency distribution and XRT technology at a large interaction between these parameters, can be studied under diamond producer. Journal of the Southern African Institute of Mining and controlled conditions. Metallurgy, vol. 118, no. 1. pp. 1–6.

VALBOM, D.M.C. and DELLAS, G. 2010. State of the art recovery plant design. 8;34/6<8;6 Proceedings of Diamonds – Source to Use 2010. Southern African Institute of Mining and Metallurgy, Johannesburg. pp. 243–252. XRT technology has had a positive, expanding impact across the De Beers Group. As we have discussed in this paper, this VON KETELHODT, L. and BERGMANN, C. 2010. Dual energy X-ray transmission covers a wide range of applications from auditing in the sorting of coal. Journal of the Southern African Institute of Mining and Metallurgy, vol. 110, no. 7. pp. 371–378. marine environment to large diamond recovery at Jwaneng mine. XCOM. 2018. National Institute of Standards and Technology Physical Measurement Laboratory X-ray cross-sections. The remaining challenges are associated with the fine https://physics.nist.gov/PhysRefData/Xcom/html/xcom1.htm [accessed 3 diamond processing applications, particularly with wet fine March 2018]. 154   
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http://dx.doi.org/10.17159/2411-9717/2019/v119n2a8 Jwaneng — the untold story of the discovery of the world’s richest diamond mine by N. Lock*

praise and interviews. In contrast, it was not until many years after its discovery that Jwaneng was the subject of praise from Harry $5:-494 Oppenheimer. The discovery, which spanned Despite the pre-eminence of the Jwaneng Diamond Mine as the world’s some five years from 1969 to 1973, has never richest diamond mine, the discovery story has long been clouded in received the same publicity as Orapa. mystery. This is the 45-year old untold story of the Jwaneng discovery and This paper will trace the background contemporaneous Bechuanaland/Botswana political and socioeconomic events and the Botswana political and socio- history. Diamond exploration by De Beers in Bechuanaland began in 1955, economic history leading to the untold story of with the first true kimberlite discovery near Letlhakane in 1967, before the drilling of the Whateley’s Wish discovery Clifford’s Rule was applied and before the use of indicator mineral chemistry. Surface deflation soil sampling and bioturbation by termites percussion drill-hole in December 1972, with was the foundation for exploration into the Kalahari. The 1962 drill core confirmation of Jwaneng 2424D/K2 reconnaissance programme south of Jwaneng had failed to make any in early 1973. discoveries. Improved sampling methods were applied to the Kalahari- The discovery presented another covered areas in 1969 and positive results were received by year-end. The conundrum because of the 45 m cover of Whateley’s Wish percussion drill-hole in December 1972 was confirmed as Kalahari sediments that made then- Jwaneng 2424D/K2 with drill core in early 1973. Jumper drills were conventional evaluation techniques ineffective. required to penetrate the Kalahari sand cover. Diamond resources were Evaluation proceeded by large-diameter demonstrated despite multiple technical problems. drilling (LDD). The first ever three- ;$ :814 dimensional diamond resource demonstrated Botswana, Jwaneng, kimberlite, diamond, discovery. economic viability for mine development, despite the multiple technical problems and complex parameters that required integration to achieve a reasonable level of confidence.

>568:1+069:5 @.;<-:3969073<751<;0:5:,90<0:56;6 The Jwaneng Diamond Mine is, by value, the The Bechuanaland Protectorate has a central world’s richest diamond mine. Harry place in African colonial history, not least Oppenheimer is quoted as saying that Jwaneng because the territory straddled the route of is ‘the most important primary deposit found Cecil Rhodes’ projected Cape to Cairo railroad. anywhere in the world since the discovery at He said ‘I look upon this Bechuanaland Kimberley more than a century ago.’ (Taylor territory as the Suez Canal of the trade of this III, 1982) The mine opened in 1982 after some country, the key of its road to the interior …’ nine years of evaluation and construction (Keppler-Jones, 1983). The so-called since discovery in February 1973. Debswana ‘Missionaries Road’ crossed the Protectorate (2017) states that 2015 production was 7.87 Mt of ore from which 10.408 million carats were recovered at a grade of 132 carats per 100 t (cpht). Although the value is not reported, it was noted that Jwaneng contributes 60–70% of Debswana’s total revenue from all mines, including Orapa, Damtshaa, and Letlhakane (Debswana, 2017). * Retired, Private Consulting Geologist, South Despite the value and economic pre- Africa. eminence of Jwaneng, the discovery story has © The Southern African Institute of Mining and Metallurgy, 2019. ISSN 2225-6253. This paper long been clouded in mystery. In 1967, Orapa was first presented at the Diamonds — Source to was front-page news in the South African Use 2018 Conference, 11–13 June 2018, press shortly after the discovery, with the Birchwood Hotel and OR Tambo Conference discovery geological team receiving personal Centre, JetPark, Johannesburg, South Africa.

         
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 155 Jwaneng — the untold story of the discovery of the world’s richest diamond mine from south to north, and the Batswana Dikgosi (chiefs) Protectorate Administration before the first Mines and strengthened their relationship with the missionaries as a Minerals Proclamation of 1932, which ensured that defense against the expansionist machinations of Rhodes’ Botswana’s mineral wealth was preserved for the people of British South Africa Charter Company. The representations of Botswana (Crowder, 1985). the revered three Dikgosi, when they visited London in 1895 Tshekedi Khama and Sir Ronald Prain, Chairman of to defend Tswana independence, and the disastrous Jameson Rhodesian Selection Trust, met for lunch in London in the Raid into the South African Republic in the same year, paved mid-1950s (Prain, 1981). After lunch they discussed the the way for what eventually became independent Botswana. outline for what became the last mineral concession in The failure of the Charter Company to consolidate control Bechuanaland under pre-independence mineral law, and the of the Protectorate at the end of the nineteenth century road to the evaluation and development of the Selebi-Phikwe resulted in a long period of disinterest in development in the Ni-Cu mine. This relationship also included consideration for territory while attention was concentrated to the north and diamond exploration and the Consolidated African Selection south. At this time Tshekedi Khama (the uncle of and regent Trust Ltd (CAST) Crown Grant to explore for diamonds across for the future first Botswana President, Sir Seretse Khama) the eastern part of the Bamangwato Tribal Territory. It was and the tribal elders believed ‘mineral development should this CAST concession that recovered the first diamonds from only come when the people could welcome these the Motloutse River near Foley in northeast Bechuanaland in developments on their own terms’ (Prain, 1981). 1959 (Willis, 1960). Traditional cattle ranching dominated tribal life and the The agreement was only finally signed when Tshekedi country remained one of the poorest in the world. The Khama lay on his deathbed in London. His goal to preserve Bechuanaland Protectorate government was very much of a and protect mineral development for the Batswana was laissez faire nature until British Prime Minister MacMillan’s secured. The machinations of Europeans, Cecil Rhodes and ‘Winds of Change’ speech that heralded the post-Second his British South Africa Charter Company, and elements of World War world of the 1960s. Even in the early 1960s, the British Protectorate Administration were largely defeated, some members of the Bechuanaland European Advisory but that is another story (see Crowder, 1985; Lock, 1988). Council advocated the incorporation of the Protectorate into either Rhodesia (now Zimbabwe) or the Union of South Africa. Fortunately, the winds of change were blowing @.;<)9846<9,?;8396;<1940:%;8$<76<';63.775; strongly and Bechuanaland moved towards independence Serious diamond exploration by De Beers began in 1955, but with the establishment of political parties and progressed to it was another decade before kimberlite discoveries were self-government and parliamentary rule in 1965. Full made in the Letlhakane village area. Along the way it is clear independence followed as the Republic of Botswana with Sir that corporate patience was tested, the targeting strategy Seretse Khama as the first President on 30 September 1966. evolved, and sampling and processing methods were Although Botswana was expected to require British transformed. government grant-in-aid for the foreseeable future, fiscal De Beers followed up the CAST work in 1962 and was prudence achieved a surplus before mineral revenue began to able to duplicate the results. It is possible that De Beers’ accrue in the early 1970s. exploration effort could have died through corporate lethargy The opening of the Orapa diamond mine in 1971 was the but for an idea first expressed by CAST (Willis, 1960). While first step on the road to the transformation of the Botswana the official CAST conclusion, a basal Karoo conglomerate economy and the rapid expansion of social services and origin for the diamonds, may have been directed by corporate national infrastructure. Investment has been made in schools pressure, Willis also recognized the possible effects of crustal and hospitals, roads and power, piped clean water to urban warping on the Motloutse drainage as envisaged by Lester areas, and telecommunications benefiting from new King in his classic book, South African Scenery: A Textbook technologies that leapfrog older landline links. of Geomorphology. published in 1943. Dr Gavin Lamont, who Janse (2007, compiled from sources listed in Table I ) was the Country Manager for Kimberlitic Searches, illustrated global diamond production by volume (millions of subsequently De Beers Botswana Prospecting, from 1955 carats) since 1869, with the Orapa and Jwaneng production until his retirement in 1979, independently came to the same startup dates. It is notable that Botswana’s contribution made conclusion (Lamont, 2011) through consideration of Alex du a more marked global impact from 1982 when production Toit’s Kalahari-Rhodesia Axis (du Toit, 1933), but he also from Jwaneng began. This fact is further demonstrated if read the CAST report (Lamont, 2001; Lock, 2012). production value is considered (Janse, 2007). Grateful as the De Beers’ Consulting Geologist Arnold Waters was country must have been for the new Orapa mine, the big step persuaded by Dr Lamont in 1964 to test this theory. A road forward came from the Jwaneng mine. The much higher reconnaissance sampling programme over the watershed to grade and value ensured the success of consecutive National the west into the Letlhakane area was eventually undertaken Development Plans for socioeconomic investment. in 1966. This was a seminal moment in the Botswana diamond story as Waters’ patience had been tried and almost @.;<;%:3+69:5<:)<,95;873<37 <751<0:50;449:54< exhausted. The immediate recovery of kimberlitic garnets and Tshekedi Khama was Regent for the Bamangwato from 1926 ilmenite quickly led to the discovery of kimberlites 2125B/K1 to 1949, and a strong political voice until his death in 1959. north of Letlhakane village and 2125A/K1 west of It was his struggle, during the period 1929 to 1932 with the Letlhakane village near a cattle post named Orapa in March British South Africa Charter Company and the British and April 1967 respectively. 156   
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Jwaneng — the untold story of the discovery of the world’s richest diamond mine

&-3:8769:5<-.93:4:-.$<751<47,-395/<6;0.59=+;4 Karoo sequences of central Botswana. With hindsight, it is thus possible to conclude that much of the early De Beers Tom Clifford was the senior lecturer in metamorphic diamond exploration fortuitously targeted potentially petrology at Leeds University in the 1960s and early 1970s at diamondiferous cratonic terrain. the time of the Research Institute of African Geology, part- funded by Anglo American Corporation, and during the Also, detailed mineral chemistry analysis in diamond author’s time as an undergraduate there. Figure 4 in Clifford exploration had not yet begun in the mid-1960s; the now (1966) empirically supports the association of famous G10 garnet was only defined in 1975 (Dawson and diamondiferous kimberlites with cratons stable since Stephens, 1975). Observation of garnet colour usually 1 500 Ma. Although Clifford had nothing to do with the allowed discrimination of metamorphic from naming of this observation, it has been adopted as Clifford’s magmatic/mantle garnets. The metallic lustre on conchoidal Rule in the diamond industry. Clifford’s Rule still stands the fracture surfaces is a distinguishing feature of picro-ilmenite. test of time, but was never explicitly applied in the Part of De Beers’ success was the consequence of Bechuanaland and early Botswana exploration. evolving sampling techniques. Early stream sediment The largest portion of Botswana is Kalahari Desert sampling in eastern Bechuanaland was inappropriate in the (Carney, Aldiss, and Lock, 1994). Only in the east is Kalahari regions of the central and western parts of the traditional geological mapping possible. The Kalahari Group country. Even in eastern Botswana stream development was in Botswana is preserved as a sequence of early fluvial poor and did not provide a uniform areal coverage. sediments and later aeolian deposits. It contains remnants of Lamont (2001) wrote ‘It is of interest to mention that in landforms from both wetter and drier periods. The current the Tuli Block in 1955 I devised the continuous scooping sand surface is variously vegetated with grass and scrubland, method of soil sampling to cover the interfluve areas between and sporadic trees. the drainage lines. When I demonstrated this new sampling Although only limited geological mapping had been method to Arnold Waters he was not particularly impressed undertaken in Botswana pre-independence, the occurrence of and he called it "the lame duck method" because every ten to ancient Archaean basement rocks in the countries fifteen paces the man taking the samples stoops down to surrounding Botswana was well documented and the scoop up some soil. Anyway it was thanks to this soil- extension of most of these rocks into Botswana was also sampling method that we eventually found Orapa and known. A new geological map of Botswana was published in Letlhakane and then Jwaneng.’ We can now appreciate that 1973 (Jones, 1973; Figure 1). Geophysical studies (e.g. this was far from being a lame duck method! Reeves and Hutchins, 1976; Terra Surveys Limited, 1978) Lamont (2001) critiqued the sample processing method have provided much knowledge and detail as to how these thus: ‘In 1962 Jim Gibson and Jim Platt were still using the geological terrains come together under the Kalahari and gold pan to concentrate their soil-samples and that is

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 157 Jwaneng — the untold story of the discovery of the world’s richest diamond mine certainly why they missed the 1 millimetre and smaller DGL were usually adequate for drill-hole targeting in the garnets from the Jwaneng pipes halo.’ Gibson and Platt Orapa area. undertook this reconnaissance sampling along the Kanye to Imperial grid dimensions (miles and yards) were changed Ghanzi trans-Kalahari road; gold panning was discarded in to metric (kilometres and metres) in the Jwaneng area at the favour of gravitating subsequent to this failed road time of the duplicate sampling in late 1972, described below. reconnaissance and prior to the Letlhakane road reconnaissance in 1966. @.;<8:71<6:< 75;5/ De Wit (in press) has provided some detail on the change The Trans-Kalahari road in the 1960s and early 1970s was a from gold pan concentrating to hand gravitating by shaking broad double sand track maintained to enable the transport and rotating a screen under water, and the continuous scoop of cattle from the Ghanzi farms in the west to the Botswana sampling technique developed by Lamont in Bechuanaland Meat Commission export abattoir in Lobatse. During the during the early 1960s. summer rains it often became almost impassable for days at Lamont (2001) correctly hypothesised that bioturbation a time because the tracks were graded deeper and deeper by white ants (termites) would transport kimberlite indicator during maintenance, with the rain converting these into minerals (KIMs) to the surface in areas covered by Kalahari pools or small lakes. sediments. Bioturbation is the disturbance of loose soil or Lamont wrote ‘I decided to try some soil-sampling on sedimentary deposits by living organisms and is not limited either side of the road that goes out from Lobatse to Ghanzi to activity by termites. However, it is termites’ thirst for where the sand-cover is relatively thin. Jim Gibson and Jim moisture that motivates their excavations down to the water Platt carried out this work but nothing of interest was found table, with ‘waste’ including KIMs deposited at surface. in their samples although they worked to within some twenty Lamont (2001) wrote ‘Some years after I retired I paid a kilometres south of today’s Jwaneng mine, and they certainly visit to Jwaneng and by that time the open pit was well covered ground where there are small kimberlitic garnets in developed. Around the sides of the pit the interface between the "halo" of indicator minerals that surrounds the Jwaneng the kimberlite and the overlying fifty metres of Kalahari sand group of kimberlites. This was the first time that we had and other sediments were (sic) exposed, and there we were moved into the Kalahari environment and our sampling able to see a few small fossil tunnels that had been made methods in those days could not cope. That is how we hundreds of thousands of years ago when the first miners at missed Jwaneng in 1962 …’ (Lamont, 2001). Jwaneng, the termites, burrowed down to get moist clay with De Beers had surmised that areas of the Kalahari with which to build their large mounds at the surface; in bringing thin sand cover surround isolated bedrock outcrops. This up moist clay from the kimberlite, they also brought up the observation and the changed sampling methods provided a small kimberlitic garnets and ilmenites, and it was these locus for renewed exploration. Only after the Orapa discovery mineral grains that our soil-sampling programmes found and were the improved sampling and treatment techniques that led us to the Jwaneng pipe.’ applied, moving west into the Kalahari in 1969. As with the In the early 1980s, similar termite tunnels in the 1966 Letlhakane area road reconnaissance, the first underground sampling development drives at depths up to indications of the discovery to come were quickly 150 m were observed by both the author and the project demonstrated by laboratory results. geologist, Stuart Vercoe. The KIMs brought to surface are subject to concentration 940:%;8$<95<;0;,?;8<2*<751<0:5)98,769:5<95 by rain and wind and natural deflation into a weak heavy ;783$<2* mineral anomaly, especially around roots of grasses and A comprehensive Kalahari sampling programme commenced shrubs that may provide windbreaks similar to trap-sites in in early 1969. The author was involved in this programme as stream sediment sampling. The deflation anomaly may well a field assistant/officer in the vicinity of Molepolole, before become weaker with increasing thickness of sand cover. It is probably important to comment that bioturbation is never a one-step process; it is incremental and cumulative over geological time. After the Jwaneng discovery it was possible to develop a profile through the Kalahari sediments. This demonstrated to Vercoe that there were at least three deflation surfaces; the oldest immediately on the eroded kimberlite surface, interpreted as the African Surface at about 60 Ma; and two further younger surfaces. Reconnaissance soil sampling (RSS) was conducted on traverses at one mile (1.6 km) intervals (Figure 2), with sub- samples along these lines allowing a preliminary graphic plot. Detailed soil sampling (DSS) was conducted over a reduced grid scale (quarter mile or 500 m) collecting spot samples, with similar sample treatment and plotting as for RSS. Finally, detailed grid loaming (DGL) was undertaken over selected priority anomalous areas of limited extent at a grid spacing of 100 m or 50 m. Grain count contour plots from 9/+8;< 0.;,7690<197/87,<:)<8;0:557944750;<4:93<47,-395/ 158   
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Jwaneng — the untold story of the discovery of the world’s richest diamond mine leaving in July 1969 to study geology at Leeds University in thick sand cover and drilling intersected kimberlite within the the UK. A number of geologists were involved in this drill’s capability. A headgear used at Orapa was brought to programme but it was the RSS work of Mike Whateley that site and two pits were sunk to 35 m depth to further prove produced the first signs of potential discovery. Table I shows the presence of kimberlite and recover small samples to test the discovery timeline together with the individual geologists for diamond content. involved at each stage. Botswana Mining Law limited the depth of surface Lamont (2001) reported ‘By the end of the third quarter pitting/trenches to 120 feet (37 m). 2424D/K1 was shallow of 1969 the Anglo American Research Laboratories reported enough for this sampling method, which had been used at the first definite and probable ilmenites from reconnaissance Orapa, but representative samples sent to the Diamond soil-samples taken over 150 square miles (390 km2) across Research Laboratory in Johannesburg returned negative the Kweneng/Ngwaketse boundary, and these ilmenites are results. therefore considered the first indication of the Jwaneng Whateley’s Wish (2424D/K2) was also drilled by kimberlite province’. Bickerstaff in 1972, but the drill limitation prevented further RSS work continued over the whole licence area before kimberlite discovery at this time; the hole or holes did not anomalous areas were covered with DSS, and priority targets reach the base of the Kalahari. It was suggested that the were sampled with DGL. The details of the phased holes may have been mislocated to the south of the anomaly. programme results up to the end of 1971 (as with all the These disappointments resulted in Bickerstaff being results discussed in this paper) are no longer available to the relocated to other projects while Lamont and the Stuart author but are illustrated in Figure 3, from Lock (1985), Vercoe reviewed all the results to date and developed a new annotated with the eventual kimberlite numbers. The geologists also named the KIM targets, with 2424D/K1 and 2424D/K3 named Malan 1 and 2, 2424D/K2 named Whateley’s Wish, and 2424D/K4 named Lynn’s Luck. Whateley left the company in the first half of 1971 and thus missed the first kimberlite discovery in 1972. 1972 marked a seminal moment in the Jwaneng story. Peter Bickerstaff led a stepped-up programme that moved quickly from ground magnetics and gravity to drilling. The magnetic survey was undertaken using the cumbersome Scania vertical-field magnetometer that required levelling for each station reading. It was thus very slow but provided a good outline on which to plan a drilling campaign. A gravity survey displayed a similar-shaped anomaly. A Holman tractor-mounted, down-the-hole hammer VOLE drill, first used at Orapa, was relocated to the southern Kalahari in early 1972. It was limited to 120 feet (37 m) depth, and it was thus not suitable for thick overburden areas. However the sand thickness was not specifically known until the first hole was drilled, although there was rock outcrop at Jwana Hill nearby and another rocky hill was visible on the skyline. Fortunately, 2424D/K1 did not have a 9/+8;< 3:6<:)<8;/9:573<<93,;596;

Table I 940:%;8$<69,;395;

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1962 Road reconnaissance Jim Gibson/Jim Platt Barren samples 1963–1968 No activity 1969 Reconnaissance soil sampling Mike Whateley/Keith Huxham and others First KIM recoveries confirmed by DRL* 1970 Detailed soil sampling Whateley/Bruce Lynn Progressive KIM spatial disbution results 1971 Detailed grid loaming Whateley/Lynn Progressive KIM spatial distribution results 1972 Ground magnetics and gravity/drilling Peter Bickerstaff 2424D/K1 - March 1972 1972–1973 DSS/DGL/ground magnetics/drilling Stuart Vercoe/Norman Lock 2424D/K2 - December 1972 and into early 1973 1974 DGL/ground magnetics/drilling/airborne magnetics Vercoe and others 2424D/K4 & 2424D/K3 1975 DGL/ground magnetics/drilling Vercoe and others 2424D/K5 & 2424DK6 - Q3 1976 DGL/ground magnetics/drilling Vercoe and others 2424D/K7 - Q3 1977 DGL/ground magnetics/drilling Vercoe and others 2424D/K8 - Q2

*DRL: Diamond Research Laboratory, De Beers Campus, Crown Mines, Johannesburg)

         
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 159 Jwaneng — the untold story of the discovery of the world’s richest diamond mine work plan for implementation from September 1972. This simple moving average and root mean square algorithms to work plan required repeat DSS and DGL sampling on a new smooth of the erratic sample counts that sometimes jumped metric grid over Whateley’s Wish (2424D/K2) and a repeat from low single digits to hundreds, and back again in ground magnetic survey using the newly introduced adjacent samples (Lamont, 2001). This approach, entirely Geometrics proton precession magnetometer. manual being before the advent of field computers, proved Vercoe supervised the soil sampling, assisted by Moses most efficacious with a fairly robust low domal feature being Rapoo, and submitted sample concentrates to an onsite heavy defined (Figure 4). liquid separation laboratory with KIM grain picking under a The proton magnetometer survey was carried out by this binocular microscope. The mineral recoveries were dominated author, assisted by Tabona Machinye. This early Geometrics by ilmenite, with a subordinate pyrope garnet component. model was entirely manual with readings recorded on paper Despite these favourable results, grid plotting did not result and all levelling carried out back in camp in the evening. A in a coherent contoured plot. This may have been due to 50 m × 50 m grid provided corrected readings for contouring surface disturbance by cattle from the local cattle post, and/or at 5- and 10-gamma intervals. The result was a weak domal by the thousands of annually migrating hartebeest and anomaly (Figure 5) that coincided well with the smoothed wildebeest, as was feared by Lamont. This author devised ilmenite plot.

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Jwaneng — the untold story of the discovery of the world’s richest diamond mine

Target selection for a new drilling campaign was now kimberlite to be reported (Murray, 1973d) as ‘… an oval possible with reasonable confidence of success. shape approximately 850 m long by 350 m to 400 m wide.’ It is worthy of note that when an aeromagnetic survey Clement (1974) reported that ‘… preliminary examination was undertaken in 1974, 2424D/K1 showed a weak but well indicates quite clearly that the pipe is, at least in part, defined magnetic high whereas 2424D/K2 displayed only a overlain by kimberlitic sediments and/or kimberlitic tuffs.’ broad weak domal high that may not have been selected as a This description is broadly consistent with modern priority without the supporting sample results. terminology in Webb, Stiefenhofer, and Field (2003) who The first new drill target, N44/12, returned suspected note ‘… two contrasting textural types of kimberlite, which kimberlite at 138 feet depth at 11 am on 16 December 1972 have been interpreted as (a) resedimented volcaniclastic (Lock, 1972, Figure 6). kimberlite and (b) dark pyroclastic kimberlite.’ Although the drill chips were very fine pink clayey The challenge of using this underpowered drill was material with no recognizable texture, the presence of underlined when, a few holes after the discovery, the whole abundant KIMs was sufficient evidence for Murray (1973a) drill string was lost, at great expense. to report ‘One hole went into what is thought to be kimberlite ...’ The drill chip samples were concentrated using a simple &%73+769:5<0.733;5/;4<751<;0:5:,90<%97?9396$ hand-operated Gerryts jig that had been designed by Bert The Naledi valley is a broad very shallow grass-covered Gerryts in the 1950s as a substitute for other methods of paleo-valley. A small rural community was domiciled around concentrating loam samples. A further four holes logged by the low Jwana Hill, where a single water borehole sustained this author intersected kimberlite over the next seven weeks. the cattle post and helped De Beers in the early days of Core drilling in early 1973 (Murray, 1973b, 1973c) exploration. provided rock samples from below the Kalahari-kimberlite Lamont (2001) wrote ‘Stuart then took over the drilling interface, although official confirmation awaited a 1974 programme around Norman's kimberlite intersection, and as petrology report by Clement (1974). The discovery was the pipe got bigger and bigger we knew we were really onto officially recognized as 2424D/K2 in the second quarter of something significant.’ (N.B. this refers to Norman Lock’s 1973 (Murray, 1973c), in line with the De Beers scheme of intersection of the 2424D/K2 kimberlite in drill-hole N44/12, that time, but the name ‘Whateley’s Wish’ persists informally Figure 6). Lamont continued ‘It was clear that we needed with those involved. By the third quarter of 1973 enough much heavier drilling equipment to cope with the Kalahari drilling had been undertaken for the Jwaneng 2424D/K2 sand-cover, and I thought about the percussion "jumper"

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 161 Jwaneng — the untold story of the discovery of the world’s richest diamond mine drills that Jim Gibson and I had used in the early days at    Orapa to drill the first water-supply boreholes.’ The standard Five-metre drill samples averaged 1.5 t, computed from jumper drill bit for water boreholes was 4½ inches (114 mm), caliper logging and density. Caliper logs showed break-back but specialized bits for this and future sampling programmes and contamination of lower levels by the less competent were progressively increased in size to 24 inch (610 mm). upper tuffaceous pyroclastic/debris flow horizons. Initial outline drilling of the 2424D/K2 kimberlite was The 2424D/K2 15-inch (381 mm) jumper drill sample supervised by Vercoe using the VOLE drill. A series of holes sludge was classified into three fractions (0.5–1.5 mm; 1.5– was drilled along the assumed northeast-trending long axis 4 mm; >4 mm) using Sweco screens. Samples were dried and of the kimberlite at 100 m intervals, controlled by KIM and weighed. Density by water displacement was only a first magnetic data. The dimensions of the South and Central approximation of the true bulk density. The two smaller size Lobes of the tri-lobate Jwaneng pipe were of the order of fractions were concentrated by Pleitz jigging and then 900 m by 500 m. A great deal of difficulty was experienced combined for milling with neoprene-lined mills using ceramic using this depth- and power-limited drill in penetrating the balls. The >4 mm fraction was transferred directly for milling Kalahari overburden. separately. Milling was required for pre-conditioning prior to Six water bores to replace the village supply were sunk diamond recovery over grease. Hand sorting was conducted around the margins of the pipe using a jumper drill (cable on site. tool drilling rig) with the first hole providing 1 200 gallons Over 200 holes were drilled, producing 5 000 t of per hour or 546 L/h containing 1 200 ppm total dissolved kimberlite. The work resulted in the delineation of about solids (TDS). 90 Mm3 of kimberlite for the 54 ha surface area. The The rig was then used, with other jumper drills, drilling sampling data at Jwaneng was down to 0.5 mm diamond size 6-inch (152 mm) diameter holes to further delineate the and thus overlapped with the typical microdiamond sample kimberlite. The jumper drills used had the advantage of: size range. However, factorization to larger bottom cut-offs was undertaken for practical production purposes. The low cost per metre A simple construction, low cost, and ease of  
    maintenance and repair From the beginning of 1978, samples were obtained from A larger sample from the 6-inch (152 mm) or 8-inch shafts, three in the Central Lobe, two in the South Lobe, and (203 mm) hole size compared to the VOLE drill. one in the North East Lobe. This bulk sampling provided The disadvantage was the slow penetration rate of material for: approximately10 m per 8-hour shift compared to the VOLE Metallurgical test work drill. Geology and emplacement model concepts The holes were cleaned of drill cuttings and water by a Comparisons of diamond release from shaft and drive dart or flap valve bailer into half-drums in one-metre samples with that of highly comminuted drill slurry. sections. Dried kimberlite samples were shipped to the Anglo For this latter purpose three 15-inch holes to 200 m American Research Laboratory/Diamond Research Laboratory were drilled around each shaft in Johannesburg. Collection of a larger diamond parcel for valuation. Initially, the material was treated in rotary pans (for    shafts 1–4) with final recovery by jigging, milling, and grease It was not possible to sink shallow prospecting shafts, as had recovery. Once the bulk sample plant was completed and been done at Orapa. Preliminary evaluation therefore used commissioned, material from shafts 5 and 6 was treated by the jumper drill with strengthened 15-inch (381 mm) chisel conventional DMS and X-ray recovery. From selected bits. The initial thirty holes of 15 inch (381 mm) diameter horizons, 20-t samples were sent to DRL for metallurgical test were drilled at 100 m line spacing and 200 m hole spacing to work. 150 m depth. Mineral resource estimation using ordinary kriging was Potentially significant economic grades were undertaken in Kimberley. This was the first time that De demonstrated despite the spatial inhomogeneity of grade. Beers had cumulated a sample database to support a full Underground bulk sampling was rejected by the Botswana three-dimensional resource estimate. Government, which favoured continued large-diameter The estimation challenges at Jwaneng, which required jumper drilling despite a number of data integrity issues. several adjustments, included: Diamond recoveries showed that the Central Lobe was the Sample size richest area and the South Lobe less so. There was very poor Downhole break-back contamination grade correlation between sampling drill-holes. No sampling Shafts not representative of the whole orebody data for the North East Lobe was available from this initial Differences in treatment methods and efficiencies programme. between jigging/grease recovery and rotary Closer spaced sampling data was required with holes pans/DMS/X-ray drilled on a 100 m sampling grid to 200 m depth and finally Possible diamond breakage by drilling at 50 m centres, also encompassing the North East Lobe. Drill Density variations with depth sampling by jumper drills was completed in 1982. Poor Main Treatment Plant crushing to 25 mm rather than horizontal and vertical grade correlations and other issues 12 mm used to feed rotary pans, and intense listed below persisted. comminution of drill samples 162   
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Main Treatment Plant lower cut-off of 1.65 mm vs recorded for the year 1972. Subsequently, Botswana 0.5 mm for drill samples and rotary pans Geological Survey Bulletin 37 (Carney, Aldiss, and Lock, Poor understanding of the orebody geology and 1994, p. 94) contained a similar statement of the Jwaneng emplacement mechanism discovery history. This publication should have authority as Diamond security could also have been better. the definitive historic statement, but any new edition should The results supported a very positive outcome and the amend the dates consistent with this paper. decision in 1978 to build a mine. It is fair to say that market pressures were developing during the 1970s with new and increased production from 940+449:5<751<0:503+49:54 Orapa, and the Argyle project development, after its 1979 There are a number of little-known or unknown facts and discovery, moving ahead in parallel with the Jwaneng opinions surrounding the Jwaneng story from the 1960s and evaluation (see Figure 2 in Janse, 2007). Notwithstanding 1970s, and beyond, that deserve mention. these pressures, the Jwaneng Mine opened at the start of a Lamont commented on how different history might have dramatic upturn in the market through the 1980s and was been if Jwaneng had been found in 1962, before Orapa. There sustained, even with new Canadian and additional Russian is no indication what thoughts may have been in Lamont’s production, until the global financial crisis in 2008. Whatever mind, but the following two points would surely have had impact these pressures may have exerted on the market and significant possible consequences if the Jwaneng kimberlite De Beers, the Botswana government held rather different had been found in 1962: development objectives. The very high Jwaneng profit margin Pre-independence Bechuanaland was a very different would always have sheltered Botswana from the impact of a place to the Independent country we know today. market squeeze. Indeed, during the 1980s Debswana One of the first post-independence Acts of Parliament accumulated its own stockpile to protect local employment. was the Mineral Rights in Tribal Territories Act, under This stockpile was used in 1987 to purchase a 5% interest in which the various tribes voluntarily ceded their De Beers Consolidated Mines (Marole, 1988, Masire, 2006). ownership of mineral rights to the new state of Perhaps history will link the parallelism of events following the Orapa Mine opening in 1971. With the timeline Botswana. This simple act of cession has allowed to the opening of the Letlhakane Mine, ongoing negotiations Botswana to avoid the challenges of many African and reviewing the Debswana Joint Venture concluded in 1975 other countries worldwide in the post-independence with a revised 50/50 equity relationship (Marole, 1988; era. Masire 2006). President Masire commented in his The implications of different decisions with regard to autobiography (Masire, 2006) that ‘In 1976, only a year after these points are left to the opinion of the reader, with perhaps we had finalised the new agreement for the 50/50 the thought that any consequences could well have been partnership, De Beers came to tell us that they had found highly detrimental for the future of the country. another payable deposit. It was Jwaneng, 80 kilometres west De Beers and Debswana record the Jwaneng discovery as of Kanye in Ngwaketse.’ There were clear differences and being in 1972, whereas the Jwaneng 2424D/K2 kimberlite difficulties in the negotiations between the joint venture was arguably properly confirmed with drill core only in early partners expressed by President Masire that can perhaps be 1973. summed up in his conclusion (Masire, 2006) that ‘… De 2424D/K1 had been found the previous year, 1972, but Beers knew more about the potential than we did, so we were there was a hiatus in exploration while the challenge of the at a disadvantage in discussing the terms of an agreement thickness of the Kalahari sand cover was considered. In that would be fair to both sides.’ contrast with Orapa, there is a diversity of reporting of the As noted in the introduction, Jwaneng is Debswana’s and Jwaneng discovery; the following examples are provided: the world’s richest diamond mine. Published future mine In his discussion of the Debswana Joint Venture, Mr planning for Jwaneng Cuts 8 and 9 will extend the open pit to Blackie Marole (1988) stated ‘Shortly after the some 850 m below surface over the next 20 years. It is not establishment of the Letlhakane Mine, a further inconceivable that Debswana will still be mining Jwaneng diamond bearing pipe was discovered at Jwaneng.’ In well after 2050 and it is reasonable to predict a future reality, the Letlhakane Mine was established in 1975, underground mine to perhaps 1 000 m depth or more, with some two years after the Jwaneng discovery. the life of mine exceeding a century since discovery or even An important worldwide catalogue of kimberlite mine opening. occurrences (Janse and Sheahan, 1995) strangely Stuart Vercoe and I have always emphasised the team reports 1975 as the discovery year (as did Marole, see effort that, in the words of Isaac Newton, allowed us to ‘see above). farther by standing on the shoulders of giants.’ Dr Lamont’s At least two well-known books about diamonds memoirs make clear the contributions of several geologists provide the historically accurate discovery date of 1973 over a number of years, from the early work of Mike (Bruton, 1979; Wannenburg and Johnson, 1990). Whateley in 1969 to the discovery drill-holes in 1972/3 and Three books (Brook, 2012, 2016a, 2016b) report beyond (see discovery timeline in Table I). Fairly discovery dates of 1971 and 1973, 1971, and only the apportioning credit among the many geologists, and others date of mine opening in 1982, respectively. who worked on the project, would have been problematic, Lock (1985) published the distinction between the though the discovery drill-hole marks a point in time. This 2424D/K1 discovery in 1972 and the 2424D/K2 discovery in paper can hopefully stand as a definitive factual historic 1973, although in hindsight both may reasonably be record.

         
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 163 Jwaneng — the untold story of the discovery of the world’s richest diamond mine

05: 3;1/;,;564 KEPPLER-JONES, A. 1983. Rhodes and Rhodesia. The White Conquest of Zimbabwe. 1884-1902. McGill-Queens University Press, Kingston and Stuart Vercoe was the project geologist at the time of the Montreal. 427 p. discovery that was shared with the author here. His contribution in the form of personal communication, LAMONT, G.T. 2001. My Memoirs. Unpublished. documents, and photographs has been very important to the LAMONT, G.T. 2011. The quest for diamonds in the Bechuanaland Protectorate completeness of this story; full credit is given here to his and Botswana. Prospecting in Africa. De Wit, M.C.J., Köstlin, E.O., and input even though he left preparation of the manuscript to Liddle, R.S. (eds). De Beers Consolidated Mines Limited. pp. 171–202. this author. LOCK, N.P. 1972. De Beers Prospecting – Botswana. air drill log N44/12. I wish to thank the De Beers Group for permission to access original maps and reports relating to the Jwaneng LOCK, N.P. 1985. Kimberlite exploration in the Kalahari region of southern discovery in their archives, and to present the information in Botswana with emphasis on the Jwaneng kimberlite province. Proceedings this publication. In particular I am very grateful to the peer of Prospecting in Areas of Desert Terrain, Rabat, Morocco 1985. reviewer who in 2018 first drew attention to my deficient Institution of Mining and Metallurgy, London. pp. 183–190. memory of the timing of events some 45 years ago, and LOCK, N.P. 1988. A history of mineral rights, ownership and law in Botswana. facilitated this permission and access. Proceedings of a Seminar on Mineral Policy in Botswana. Special Publication no. 1. Botswana Geoscientists. Association. pp. 5–15.

;);8;50;4 LOCK, N.P. 2012. Orapa Mine: the role played by CAST geologists in its discovery. Letter to Geological Society of South Africa. Geobulletin, BROOK, M.C. 2012. Botswana’s Diamonds – Prospecting to Jewellery. Self- vol. 55, no. 3. published. 286 p. MASIRE, Q.K.T. 2006. Very Brave or Very Foolish. Memoirs of an African BROOK, M.C. 2016a. Botswana Diamond Jewellery. Self-published. 136 p. Democrat. Lewis Jr, S.J. (ed.). Macmillan Botswana. 358 p. BROOK, M.C. 2016b. Botswana. 50 Years of Growth. Self-published. 81 p. MAROLE, B. 1988. Debswana Joint Venture; a case study. Proceedings of a CARNEY, J.N., ALDISS, D.T., anD LOCK, N.P. 1994. The geology of Botswana. Seminar on Mineral Policy in Botswana. Special Publication no. 1. Bulletin 37. Geological Survey of Botswana. 113 p. Botswana Geoscientists. Association. pp. 26–29.

CLEMENT, C.R. 1974. Preliminary notes on core specimens from Jwaneng, MURRAY, L.G. 1973a. Quarterly report, State Grant 7/72, Ngwaketsi District. Botswana. De Beers Consolidated Mines Limited, Geology Department. Report on prospecting activities for the period 1st October to 31st 7 p. December 1972. De Beers Prospecting Botswana (Pty) Limited. p. 1.

CLIFFORD, T.N. 1966. Tectono-metallogenic units and metallogenic provinces of MURRAY, L.G. 1973b. Quarterly report, State Grant 7/72, Ngwaketsi District. Africa. Earth and Planetary Science. Letters, vol. 1. pp. 421–434. Report on prospecting activities for the period 1st January to 31st March 1973. De Beers Prospecting Botswana (Pty) Limited. p. 2. CROWDER, M. 1985. Tshekedi Khama and mining in Botswana. 1929-1959. African Studies Seminar Paper. African Studies Institute, University of the MURRAY, L.G. 1973c. Quarterly report, State Grant 7/72, Ngwaketsi District. Witwatersrand. 23 p. Report on prospecting activities for the period 1st April to 30th June 1973. De Beers Prospecting Botswana (Pty) Limited. p. 1. DAWSON, J.B. and STEPHENS, W.E. 1975. Statistical classification of garnets from kimberlite and associated xenoliths. Journal of Geology, vol. 83, no. 5. MURRAY, L.G. 1973d. Quarterly report, State Grant 7/72, Ngwaketsi District. pp. 589–607. Report on prospecting activities for the period 1st July to 30th June 1973. De Beers Prospecting Botswana (Pty) Limited. p. 1. DE BEERS GROUP. 2017. Jwaneng Mine. http://www.debeersgroup.com/en/our- story/our-history.html#1960 PRAIN, R. 1981. Reflections on an Era. Metal Bulletin Books, London. 262 p.

PRETORIUS, D.A. 1966. Conceptual geological models in the exploration for gold DEBSWANA. 2017. Jwaneng Mine. http://www.debswana.com/Operations/Pages/ mineralisation in the Witwatersrand Basin. Information Circular no. 33. Jwaneng-Mine.aspx Economic Geology Research Unit, University of the Witwatersrand. DE WIT, M.C.J. 2018. Prospecting history leading to the discovery of Botswana’s REEVES, C.V. anD HUTCHINS, D.G. 1976. The national gravity survey of Botswana, diamond mines: from artefacts to Lesedi La Rona. Proceedings of the 11th 1972-3. Bulletin no. 5, Geological Survey of Botswana, Lobatse. 36 p. International Kimberlite Conference, Gaborone, Botswana (in press). TAYLOR III, A.L. 1982. A gem that lost its luster. Time Magazine. 30 August DU TOIT, A.L. 1933. Crustal movement as a factor in the geographical evolution 1982. http://content.time.com/time/magazine/article/ of South Africa. South African Geographical Journal, vol. XVI. pp. 3–19. 0,9171,921271,00.html GURNEY, J.J and SWITZER, G.S. 1973. The discovery of garnets closely related to TERRA SURVEYS LIMITED. 1978. Reconnaissance aeromagnetic survey of diamonds in the Finsch Pipe, South Africa. Contributions to Mineralogy Botswana, 1975-1977. Botswana Geological Survey Department and and Petrology, vol. 39, no. 2. pp. 103–116. Canadian International Development Agency. 199 p. JANSE, A.J.A. 2007. Global rough diamond production since 1870. Gems & WEBB, K., STIEFENHOFER, J., and FIELD, M. 2003. Overview of the geology and Gemology, vol. 43, no. 2. pp. 98–119. emplacement of the Jwaneng DK2 Kimberlite, Southern Botswana. [Long JANSE, A.J.A. and SHEAHAN, P.A. 1995. Catalogue of world wide diamond and abstract]. Proceedings of the 8th International Kimberlite Conference. kimberlite occurrences: a selective and annotative approach. Journal of Victoria, British Columbia, Canada, 22–27 June 2003. Mitchell, R.H. (ed.). Geochemical Exploration, vol. 53. pp. 53–111. Elsevier, Amsterdam.

JONES, C.R. 1973. Geological map of Botswana. 1:1 000 000 scale. Geological WILLIS, J.H.A. 1960. Final report on the Bechuanaland investigation. Central Survey and Mines Department. African Selection Trust Ltd. 164   
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http://dx.doi.org/10.17159/2411-9717/2019/v119n2a9 A strategy for improving water recovery in kimberlitic diamond mines by A.J. Vietti*

dewatering process (typically gravity )73+282 thickening) simply by increasing the density of the tailings being discharged. In practice, Drought conditions and the possible lack of sufficient raw water supply however, the unique mineralogy of each are a constant reminder to the Southern African diamond miner of the need to minimize raw (new) water input while maintaining or expanding kimberlite deposit and the chemical profile of mine throughput. the raw water source used imply that at some Since water input volume is directly related to water output (loss) mine sites, solid/liquid separation (or settling) volume, mainly to the tailings, it is obviously beneficial to dewater the of tailings slurries at the dewatering process is tailings as much as possible. However, this may not always be as easily more easily achieved than at others. In these achieved as first thought. Owing to the unique mineralogy of each cases, simple practical steps such as firstly kimberlite deposit and the unique chemical profile of each raw water improving the flocculant reagent make-up and source, dewatering of the slurry is not a standard process that can be dosing control, and secondly focusing on applied equally across the entire diamond industry. thickener discharge control, are the only This paper presents a first-step strategy that kimberlite diamond mine requirements for enhancing water recovery at operators should consider and apply to meet and exceed their water- the dewatering circuit. At other mine sites saving targets. however, solid/liquid separation of the tailings >9) 35,2 may not be achieved at all, in which case clays, colloids, thickening, water recovery, water conditioning. efforts to increase water recovery by improving reagent dosage and thickener control would be fruitless unless the colloidal properties of the thickener feed slurry are modified. This paper describes a strategy that can be 7653,/16837 implemented at most kimberlitic diamond A common metric for measuring water use mines to ensure that solid/liquid separation of efficiency in a metallurgical plant is the the tailings slurry occurs efficiently and that amount of raw water used per ton of head feed the subsequent improvements in water treated (m3/t). The metric includes all water recovery and quality (in terms of clarity) at the recycled from the dewatering process and from dewatering unit process can take place. the tailings storage facility (TSF), and the only inputs are tons of ROM ore and cubic metres of >8(&9508681:648087.2:2308,;08 /8, raw water make-up to replace water lost to 29+4546837:*/7,4(976402 evaporation, seepage, and lock-up at the TSF (Figure 1). Diamond processing, as with other mineral The volume of new raw water available to commodities, uses water in to assist in the process is not unlimited and a maximum removing gangue minerals and concentrating monthly allowance is typically set during the the valuable products. Unlike most other ores, mine permitting process. Consequently, if the kimberlite contains a high proportion of clay volume of water lost exceeds the volume of minerals, which when wetted can interact with new water available or alternatively, in times the plant process water to generate either of drought where the allowable volume is settling or non-settling slurries. Notably, in unavailable, the plant has no other option but to reduce throughput. However, if the plant operator is able reduce the volume of water lost to the TSF, the * plant will have additional capacity to either Vietti Slurrytec (Pty) Ltd, South Africa. increase tonnage throughput or sustain © The Southern African Institute of Mining and Metallurgy, 2019. ISSN 2225-6253. This paper nameplate capacity during periods of severe was first presented at the Diamonds — Source to drought. The obvious conclusion, therefore, is Use 2018 Conference, 11–13 June 2018, to reduce the volume of water lost to the Birchwood Hotel and OR Tambo Conference tailings by improving the efficiency of the Centre, JetPark, Johannesburg, South Africa.

         
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 165 A strategy for improving water recovery in kimberlitic diamond mines

The degree of osmotic swelling depends largely on the nature and concentration of the cations in the contacting water and the degree of octahedral substitution of the clay type. Monovalent cations in low concentration tend to cause unlimited swelling, a condition commonly referred to as uncontrolled dispersion, since they are small and can ’dissolve’ more easily in the semi-crystalline water layers that surround the clay particles, thereby drawing more water between the adjacent particles by osmotic action. Divalent cations, on the other hand, tend to cause limited swelling since they have a disruptive effect on the structure of the water layer and can provide links between charged sites on adjacent silicate sheets. This condition is commonly referred %8./59:-$4 : 4695:87+/6:47,:3/6+/6:(3,90 to as controlled dispersion (Sequet, de la Calle, and Pezerat, 1975; Mering, 1946). From a practical point of view, kimberlite mines that draw most cases the dominant clays belong to the 2:1 smectite or their raw water from surface sources such as rivers, dams, or swelling group of clays and the settling or solid/liquid lakes will tend to introduce good quality water into the separation properties of these slurries are determined largely process water circuit, which will result in the process water by the chemical quality of the process water. Consequently, having a relatively low cation content and low conductivity. controlling the chemical conditions in the process water This quality of process water will promote uncontrolled circuit is the first step in improving plant water recovery. dispersive conditions and the resulting slurries will tend to Before describing a strategy for controlling the chemical respond poorly, or not at all, to anionic polymer flocculant quality of the process water it is necessary to describe the dosing, and even after excessively high flocculant doses the fundamental mechanisms by which kimberlitic clay slurries recovered thickener overflow clarity is generally poor (Figure are generated and which control their colloidal behaviour. 3). Under this condition it is normally necessary to dose a cationic polymer coagulant before flocculant addition to           achieve solid/liquid separation and good overflow clarity. As In a typical kimberlite metallurgical circuit, the first contact a result, operating costs are high. between freshly mined ore and the plant process water is at On the other hand, kimberlite mines that draw their raw the scrubbing or milling unit process. This step is critical in water from deep wellfields or brackish water sources will determining the colloidal characteristics of the resulting have process water circuits with elevated cation contents and slurry, since the clays within the ore absorb water and other high conductivities. This quality of process water inhibits clay polar molecules between their unit layers, which initiates the swelling and dispersion, resulting in slurries that are easily swelling and ultimately the dispersion process. Two forms of flocculated at low doses without the need for additional swelling are known, which depend on the moisture content to coagulant dosing. Recovered thickener overflow will have which the clays are exposed. excellent clarity, and there are further beneficial spin-offs Firstly, under conditions of low moisture content a limited such as better thickener underflow density and lower stepwise expansion of the clay unit layers, known as underflow yield strengths, due to the absence of excessive interlayer (or type I) swelling, begins. This form of swelling amounts of polymer reagent (Figure 3). occurs once the virgin ore is exposed to atmospheric moisture after blasting or crushing. Water molecules are drawn       between the dehydrated clay platelets and up to three layers Soil scientists and agriculturalists have long recognized the of water molecules are covalently bonded to the tetrahedral effects of water quality on the behaviour of the clay surfaces in a semi-crystalline structure that resembles that of component in a soil (Mitchell and Soga, 2005; Richards, ice. This mode of swelling leads to at most a doubling in the volume of the dry clay and may be responsible for a weakening of the rock matrix (Grimm, 1968). The second form of swelling occurs at saturation (i.e. during the scrubbing or milling process) and can lead to an unlimited or complete separation of individual clay layers. This is known as osmotic (or type II) swelling. Under this condition, the exchangeable cations dissociate from the clay surface and move to the hydrated region between the clay particles; as such, they are regarded as being ’in solution’ and hence lower the activity of the water between the particles. This allows more water from the surroundings to move into the interlayer region by osmotic forces, thereby increasing the interlayer swelling. This form of swelling may continue indefinitely and result in a slurry suspension in which normal electrical double layers separate the individual %8./59:$'47.9:87:04)95:2+4187.:3*:4:-:104): 86':871594287.: 40 clay particles from one another (Figure 2). 1371976546837::6)+9::47,:6)+9::2 90087.:58((:-! 166   
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A strategy for improving water recovery in kimberlitic diamond mines

However, in practice, determining the ESP of the ore is not a simple procedure and is prone to experimental error due to mineral contaminants in the ore. A simpler method is to measure the cation content of the contacting water. The sodium adsorption ratio (SAR) value of the contacting water can then be used instead of the ESP to determine whether a process water is likely to generate slurries which are dispersive or not. The SAR is defined as:

[2]

Since the SAR is easily derived from a normal chemical analysis of the process water (in meq/l) and since it is related %8./59:$0/55):130038,40:&9'4"83/5:4*695:137653009,:47,:/7137653009, to the ESP, it is more widely used. Process waters with SAR ,82+952837 values greater than approximately 10 are likely to generate uncontrolled dispersive slurries, while those less than 10 are likely to generate coagulated or settling slurries (Mitchell and 1969). To understand the mechanisms controlling these Soga, 2005; Richards, 1969). clay/water interactions, a diagnostic system using three criteria was developed, which enables the soil scientist to  
determine the potential deleterious effect of the water on the Once in an uncontrolled dispersive state, the pH of the slurry soil (Richards, 1969). These criteria can equally be applied to is the second factor which can control coagulation and kimberlitic ores to indicate the slurry dispersive potential solids/liquid separation. Since clay particles have a plate-like which the raw/process waters may impart to a particular ore morphology, the charges at the particle face and edge may be type. of similar or opposite sign, depending on the slurry pH. These changes in charge and charge distribution at the clay    surface can also affect the slurry solid/liquid separation The cation exchange capacity (CEC) is the total capacity of a behaviour. soil (or kimberlite ore) to hold exchangeable cations The dominant surface of a clay particle is the flat face, (irrespective of type or valence), in meq/100 g and is directly which has a permanent negative charge due to imperfections in the clay crystal lattice (isomorphous substitution), which related to the specific surface charge and charge density of results in excess negative charge at the face. This excess the clays in the ore (Mitchell and Soga 2005). Once the CEC negative charge is compensated by the adsorption of cations has been determined, the proportion of sodium ions which onto the crystal lattice surface (Figure 5). Once in a slurry are adsorbed onto the surfaces of clays is a useful parameter state, these compensating cations may be exchanged with to know. This has an important influence on the colloidal cations from the solution, depending on how strongly they behaviour of the slurry and can be expressed as the are bound to the crystal surface. For this reason, they are exchangeable sodium percentage (ESP) of the suspension, known as exchangeable cations and their concentrations can defined as: be used as a measure of the amount of lattice charge, or cation exchange capacity (CEC), of the clay (van Olphen, [1] 1977). Clay particle edges, on the other hand, can be positively This measure provides an indication of slurry sodicity. or negatively charged depending on the pH of the slurry. Slurries exhibiting high ESP values tend to be alkaline and Under acidic conditions, hydroxyl- (OH-)-bearing groups at colloidally dispersive, while slurries with low ESP values tend the clay crystal edge become protonated to carry an overall to be naturally coagulated and settling (Figure 4). positive charge, leading to edge-to-face attraction which may

%8./59:$#**916:3*:871594287.:23,8186):37:6'9:2/2+972837:&9'4"83/5:3*:4:8(&9508681:104):2/2+972837

         
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 167 A strategy for improving water recovery in kimberlitic diamond mines

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result in particle aggregation. Under alkaline conditions, the concentration is known as the critical coagulation OH- groups will become deprotonated until an overall concentration (CCC) (Gregory, 1989). negative edge charge dominates, leading to edge-to-face The CCC can equally be termed the critical coagulation repulsion and causing the clay particles to become colloidally conductivity (in mS/cm), which would be the process water dispersed (Svarovsky, 1981) (Figure 5). conductivity at which coagulation occurs for a particular ore The pH of a kimberlite clay suspension therefore greatly type and at which solid/liquid separation is achieved. This is affects the charge associated with the clay particle edges. At a measurable variable which can be used in a feedback loop low pH, tailings slurries are coagulated naturally and settle to control the conductivity at which a process water circuit under gravity, while at high suspension pH they tend to should be maintained, and forms the basis of the strategy for remain dispersed and non-settling (Figure 6). improving water recovery.

    =531922: 4695:1851/86:137,8683787.:265469.) The third and overriding mechanism for controlling the An example of the effectiveness of a process water colloidal properties of a slurry is the absolute ionic conditioning strategy for improving water recovery and concentration. This is commonly defined by the conductivity quality is provided below by way of case studies for two of the slurry and is typically measured in units of mS/cm. kimberlite mines in Southern Africa. The interaction between adjacent particles in dispersed Mine A derives its raw water supply from shallow colloidal systems is described by the Derjaguin, Landau, boreholes located along a major river course. Consequently, Verwey, and Overbeek (DLVO) theory of colloid stability and the plant process water circuit has a relatively low average is based on the interaction between the van der Waals conductivity. The mine suffers from periods during the year attractive force and the diffuse double layer repulsion force in which the process water clarity deteriorates and additional occurring between approaching particles (Figure 7). At low polymer coagulant dosing is required ahead of flocculation to conductivity, a net potential energy barrier presents an clarify the thickener overflow. obstacle to aggregation and the particles remain in a The process water clarity issues are not related only to dispersed state. At moderate conductivity levels, the height of the ore types being treated; they are also a seasonal the energy barrier is reduced, and the particles may remain phenomenon. During the summer rainfall months, an weakly coagulated in a secondary minimum well. As the increase in the use of polymer coagulant reagent use has ionic content of the dispersion is increased a point is reached been recorded, while during the winter season, the operation where the energy barrier disappears, and the particles are of the thickener tends to improve, resulting in better overflow spontaneously coagulated (Figure 8). This ionic clarity and lower reagent costs (Figure 9). 168   
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A strategy for improving water recovery in kimberlitic diamond mines

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These observations appear to be directly related to the continuous dosing. ClariVie44® is dosed into the process seasonal wetting and drying cycle to which the kimberlitic ore water circuit to increase the conductivity; thereafter, smaller in the pit or in stockpiles is exposed. During the summer top-up doses are required to compensate for the diluting season, the clays undergo uncontrolled dispersion when effect of the raw water make-up (Figure 11). wetted with zero-conductivity rainwater in situ. When To test the principle, a notoriously difficult ore from introduced to the plant, the process water conductivity is kimberlite mine A was contacted with plant process water insufficient to overcome the CCC of the clays and often that had been treated with ClariVie44® to increasing the additional coagulant dosing is required before flocculation conductivity. The dispersion and natural settling behaviours becomes effective. were measured as illustrated in Figure 12. During the winter season, the ore reporting to the plant At process water conductivities below 3 mS/cm (plant is either dry or has not been previously wetted. When this process water conductivity was measured at 2.9 mS/cm), ore is contacted with the plant process water, the clays uncontrolled dispersion was encouraged, resulting in the therein undergo controlled dispersion since the conductivity establishment of colloidally stable suspensions. At higher of the water exceeds the CCC of the clays. Additional conductivity, controlled dispersion was favoured, resulting in coagulant dosing ahead of flocculation is therefore not the formation of colloidally unstable suspensions which required (Figure 10). achieved better clarity. To accommodate the seasonal change in clay dispersion In the case of mine A, the recommended strategy would properties and the varying CCC requirement of clays in be to maintain the process water circuit conductivity at a different ore types, a minimum conductivity threshold for the minimum of 3.3 mS/cm to ensure that effective solid/liquid mine process water circuit needs to be set, at which controlled separation after flocculation occurs at the thickener. dispersive slurries will be generated when any ore type is A similar strategy has been employed at another treated. kimberlite diamond mine (mine B) since January 2017. In Vietti Slurrytec (VST) has developed the ClariVie44® this case, raw water to the plant is sourced only from rainfall process water conditioner, which is a blend of specific cations or snowmelt. The pristine quality of the raw water is, designed to increase the conductivity of process water unfortunately, detrimental to the recovery of clear overflow without introducing environmental or corrosive pollutants. from the dewatering thickener. ClariVie44® has been Since the process water conditioner is not polymer-based, it implemented to condition the process water circuit to a is recycled in the process water circuit without the need for minimum conductivity target of 1.2 mS/cm, with excellent

         
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 169 A strategy for improving water recovery in kimberlitic diamond mines

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%8./59:-$#**916:3*:871594287.:137,/168"86):37:6'9:2/2+972837:&9'4"83/5:3*:8(&950869:(879: :20/55):0458 89659469,:20/55892:'8.'08.'69,:: results showing a clear correlation between increasing Non-problematic mines—The tailings slurries at these process water conductivity and decreasing flocculant mines are non-dispersive and easily flocculated at consumption (Figure 13). relatively low reagent dose. The thickener underflow densities are generally relatively high (depending on <821/22837 the type of dewatering equipment selected), overflow In general, kimberlite mines can be categorized into two types clarities are generally excellent, and water recoveries in terms of tailings slurry colloidal and dispersive properties. are good. The metallurgical plant therefore operates 170   
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A strategy for improving water recovery in kimberlitic diamond mines

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with clean process water. These mines do not need to 3710/2837 further condition the process water as the natural For the kimberlite diamond mine operator, increasing water conductivity of the raw water supply is sufficient to use efficiency in terms of cubic metres per ton of feed prevent uncontrolled clay dispersion. Further processed means treating more tons with the existing water improvements in water recovery would only require supply volume or treating existing tons with less water. In interventions to optimize reagent make-up and dosing both cases, achieving this outcome depends on improving the control and/or the thickener discharge control. The water recovery efficiency at the dewatering unit process by latter is not straightforward since the new thickener increasing the density of the tailings being discharged. control philosophy of generating higher underflow The basis of this strategy depends on the colloidal state of densities would need to be compatible with the the tailings slurry being such that solid/liquid separation capabilities of the existing hydraulic tailings discharge takes place naturally. Some kimberlite mines are in the infrastructure and the existing TSF operating and fortunate position of having saline or brackish raw water management methodology. sources which impart a high conductivity to the plant process Problematic mines—The tailings slurries at these mines water. Under these conditions, the smectite clays in the are highly dispersive and difficult to flocculate and kimberlitic ore are unable to swell and disperse once in settle. High flocculant and/or polymer coagulant doses suspension and are flocculated easily at the plant thickener. are required before solid/liquid separation will occur, The mine operator is then able to concentrate on the real underflow densities are generally low, and water drivers for improving thickener underflow density, such as recoveries are generally poor, even after treatment. At reagent make-up and dosing control and, more importantly, these mines the natural conductivity of the raw water thickener underflow discharge control. supply is too low, and conditioning of the process water However, at other kimberlite mines where the raw water would be required to improve water recovery and for supply is drawn from low-saline sources, the primary step of returning clarified process water back to the plant. solid/liquid separation does not readily occur naturally due to Once the colloidal properties of the slurry have been the dispersive slurry properties generated. In these cases, a brought under control, the subsequent strategies for strategy for increasing the process water conductivity by increasing water recovery as described above can be introducing a water conditioning reagent such as ClariVie44® implemented. There are, however, some mines in this is required before the subsequent drivers for improving water category that operate normally by returning unclarified recovery can be implemented. process water to the process plant. This is possible since the viscosity of highly dispersive process water 9*9597192 can remain low even up to relatively high solids loadings (10 to 15% by mass of the –20 μm fraction). GREGORY, J. 1989. Fundamentals of flocculation. CRC Critical Reviews in Above this solids loading, however, the ultrafine solids Environmental Control, vol. 19, no. 3. CRC Press. pp. 185–230. begin to influence the water’s viscous properties and GRIMM, R.E. 1968. Clay Mineralogy. 2nd edn. McGraw Hill, New York. may affect diamond recovery efficiency in the dense Mering, J. 1946. The hydration of montmorillonite. Transactions of the media separation (DMS) circuit. There is a danger, Faraday Society. vol. 42. pp. 205–219. however, that by implementing a process water MITCHELL, J.K. and SOGA, K. 2005. Soil-water-chemical interactions. conditioning strategy at this point, the solids in the Fundamental of Soil Behaviour. Wiley, Hoboken, NJ. Chapter 6. process water may in fact ’gel’ instead of achieving RICHARDS, L.A. 1969. Diagnosis and improvement of saline and alkali soils. solid/liquid separation. In this event, the water in the Handbook no. 60. US Department of Agriculture. entire process circuit would take on the consistency of SEQUET, H., DE LA CALLE, C., and PEZERAT, H. 1975. Swelling and structural yoghurt and would need to be flushed out and replaced organization of saponite. Clays and Clay Minerals, vol. 23. pp. 1–9. with fresh water, thereby dramatically increasing water SVAROVSKY, L. 1981. Solid-Liquid Separation. 2nd edn. Butterworths, London. loss. VAN OLPHEN, H. 1977. Clay Colloid Chemistry. Wiley, New York.

         
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 171  
   Skills for the future – yours and your mine’s



Glenhove Conference Centre, Melrose Estate, Johannesburg

BACKGROUND Previous SAIMM Mine Planning forums have clearly highlighted deficiencies in mine planning skills. The 2012, 2014, and 2017 colloquia all illustrated developing skill-sets with a variety of mine planning tools in a context of multiple mining methods. Newer tools and newer skills for the future of mining will feature in 2019.

OBJECTIVES WHO SHOULD ATTEND Using a backdrop of a generic description of the multidisciplinary mine Mine planners and practitioners planning process, the forum provides a platform for the mine planning Mine designers fraternity to share mining business-relevant experiences amongst Technical support staff peers. While different mining environments have their specific Cost and financial modellers information requirements, all require the integration of inputs from Chief planners different technical experts, each with their own toolsets. The forum’s presentations will highlight contributions from a series Mineral resource managers of technical experts on current best practice, and will be augmented by Mine managers responsible for planning displays of state-of-the-art mine planning tools in order to create a Consultants learning experience for increased planning competencies. Independent mine planning consultants

FOR FURTHER INFORMATION CONTACT: Camielah Jardine • Head of Conferencing • SAIMM Tel: +27 11 834-1273/7 • Fax: +27 11 833-8156 E-mail:[email protected] •Website: http://www.saimm.co.za http://dx.doi.org/10.17159/2411-9717/2019/v119n2a10 Investigation of flow regime transition in a column flotation cell using CFD

by I. Mwandawande*, G. Akdogan*, S.M. Bradshaw*, M. Karimi†, and N. Snyders*

Uribe-Salas, 1991). The identification of this %4;19?9 critical or maximum superficial gas velocity is therefore important for optimal operation of Flotation columns are normally operated at optimal superficial gas flotation columns. velocities to maintain bubbly flow conditions. However, with increasing Xu, Finch, and Uribe-Salas (1991) and Xu superficial gas velocity, loss of bubbly flow may occur with adverse effects on column performance. It is therefore important to identify the maximum et al. (1989) investigated three phenomena superficial gas velocity above which loss of bubbly flow occurs. The that can be used to identify the maximum maximum superficial gas velocity is usually obtained from a gas holdup superficial gas velocity in column flotation: versus superficial gas velocity plot in which the linear portion of the graph loss of interface, loss of positive bias flow, and represents bubbly flow while deviation from the linear relationship loss of bubbly flow. Loss of interface occurs indicates a change from the bubbly flow to the churn-turbulent regime. when the hydrodynamic conditions in the froth However, this method is difficult to use when the transition from bubbly zone of the column become identical to the flow to churn-turbulent flow is gradual, as happens in the presence of conditions prevailing in the collection zone. frothers. We present two alternative methods in which the flow regime in This will result in the loss of the cleaning the column is distinguished by means of radial gas holdup profiles and gas action associated with the froth zone. holdup versus time graphs obtained from CFD simulations. Bubbly flow was characterized by saddle-shaped profiles with three distinct peaks, or In column flotation, wash water, which is saddle-shaped profiles with two near-wall peaks and a central minimum, continuously added at the top of the column, or flat profiles with intermediate features between saddle and parabolic maintains a net downward flow of water that gas holdup profiles. The transition regime was gradual and characterized prevents entrained particles from reaching the by flat to parabolic gas holdup profiles that become steeper with concentrate. This net downward flow of water increasing superficial gas velocity. The churn-turbulent flow was is referred to as positive bias flow. By distinguished by steep parabolic radial gas holdup profiles. Gas holdup minimizing entrainment of unwanted particles, versus time graphs were also used to define flow regimes with a constant a positive bias maximizes the concentrate gas holdup indicating bubbly flow, while wide gas holdup variations grade. Loss of positive bias occurs when the indicate churn-turbulent flow. superficial gas velocity is high enough to cause D@%*;<39 a reversal of the net flow of water at the flotation column, maximum superficial velocity, flow regime, bubbly flow, froth/collection zone interface. transition, churn-turbulent flow. On the other hand, the loss of bubbly flow occurs when the superficial gas velocity is sufficiently high to bring about a transition from bubbly flow conditions to churn- C4=<;387=?;4 turbulent flow. The increased mixing Two types of flow can be distinguished in gas- associated with churn-turbulent flow is liquid flows in bubble columns: bubbly flow unfavourable for mineral recovery in the and churn-turbulent flow. The bubbly flow column. regime is characterized by uniform flow of Considering the froth and liquid (pulp) bubbles of uniform size. Churn-turbulent flow, phases as distinct flow regimes with different on the other hand, is characterized by a wide liquid holdups, Langberg and Jameson (1992) variation in bubble sizes with large bubbles investigated the hydrodynamic conditions rising rapidly and causing liquid circulation. under which the froth and pulp phases can Flotation columns are normally operated in the bubbly flow regime, which is the optimal condition for column flotation (Finch and Dobby, 1990; Yianatos and Finch, 1990; Ityokumbul, 1992). However, it has been * University of Stellenbosch, South Africa. † generally observed that flotation column Department of Chemistry and Chemical Engineering, Chalmers University of Technology, performance deteriorates when the superficial Sweden. gas velocity is increased beyond a certain limit © The Southern African Institute of Mining and where the flow regime changes from bubbly Metallurgy, 2019. ISSN 2225-6253. Paper received flow to churn-turbulent flow (Xu, Finch, and Sep. 2017; revised paper received Jun. 2018.

         
 "!A22&   
 173 Investigation of flow regime transition in a column flotation cell using CFD coexist in a flotation cell. The effects of superficial gas flow regime in the flotation column (Shen, 1994). Wide velocity and bubble size on the limiting conditions for flow variations in the gas holdup versus time graph characterize regime coexistence and for countercurrent flow across the churn-turbulent flow conditions, while gas holdup is almost froth-liquid interface were studied using a one-dimensional constant under bubbly flow conditions. two-phase flow model. Their study identified two hydrodynamic limiting conditions relevant to the operation of !@=6;39A0;=?;4 flotation cells and columns: the limiting condition for the The relationship between gas holdup and superficial gas coexistence of the froth and liquid (pulp) phases, and the velocity can be used to define the prevailing flow regime in limiting condition for countercurrent flow. the flotation column (Finch and Dobby, 1990). In the bubbly Of the three phenomena used to identify the maximum flow regime, the gas holdup increases linearly with increasing superficial gas velocity in column flotation, the loss of bubbly superficial gas velocity. However, the gas holdup deviates flow is the most difficult to determine (Xu, Finch, and Uribe- from this linear relationship when the superficial gas velocity Salas, 1991; Xu et al., 1989). The relationship between gas is increased above a certain value, as shown in Figure 1. The holdup and superficial gas velocity is used to determine the superficial gas velocity at which deviation from the linear loss of bubbly flow in the column. In this method, a linear relationship occurs is thus the maximum or critical velocity, gas holdup versus superficial gas velocity relationship above which the flow regime changes from bubbly flow to represents bubbly flow while deviation from linearity defines churn-turbulent flow. In other words, it is the maximum loss of bubbly flow. However, the loss of bubbly flow is superficial gas velocity for loss of bubbly flow. difficult to identify using this method because of the gradual Xu et al. (1989) applied the gas holdup versus superficial nature of the transition from bubbly flow to churn-turbulent gas velocity relationship to determine the maximum conditions in the presence of frother (Xu et al., 1989). During superficial gas velocity for loss of bubbly flow in a pilot-scale the transition from bubbly flow to churn-turbulent flow, the flotation column. However, they reported difficulties in the bubble size increases rapidly due to bubble coalescence. identification of the regime transition point as a result of the However, the presence of frothers suppresses bubble gradual nature of this transition, particularly in the presence coalescence, causing the transition to churn-turbulent flow to of frother. The present study therefore applies the following become gradual. alternative methods to distinguish the different flow regimes In this research, the maximum superficial gas velocity for and thus identify the maximum velocity above which the transition from bubbly flow to churn-turbulent flow was transition from bubbly flow to churn-turbulent flow will studied using computational fluid dynamics (CFD). Besides occur. the gas holdup versus superficial gas velocity relationship, two alternative methods of flow regime characterization were &$& )(& )% )"%$ ' employed to identify the loss of bubbly flow in a pilot-scale Two general gas holdup profiles are known to exist, the column flotation cell. The first method involves examining parabolic profile and the saddle-shaped profile. Kobayasi, the evolution of radial gas holdup profiles as a function of Iida, and Kanegae (1970) studied the characteristics of the superficial gas velocity. The shape of the radial gas holdup local void fraction (gas holdup) distribution in air-water two- profile has been recognized as a function of the flow pattern phase flow. They reported a ‘peculiar’ distribution, different in two-phase flows (Kobayasi, Iida, and Kanegae, 1970; from the previously accepted power law distribution in Serizawa, Kataoka, and Michiyoshi, 1975). A graph of gas bubbly flow conditions. The distribution associated with holdup versus time can also be used to identify the prevailing bubbly flow had its peaks near the pipe wall. On the other

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  "!A22&          
Investigation of flow regime transition in a column flotation cell using CFD hand, the distribution in slug flow had its maximum at the operated continuously, with air introduced into the bottom of centre of the pipe. the column through a cylindrical stainless steel sparger, 3.8 Serizawa, Kataoka, and Michiyoshi, (1975) also studied cm in diameter and 7 cm in length. This sparger geometry various local parameters and turbulence characteristics of gives a ratio of column cross-section to sparger surface area concurrent air-water two-phase bubbly flow. They found that of about 1:1. A schematic diagram of the column is presented the distribution of void fraction (radial gas holdup) was a in Figure 2. A detailed description of the experimental set-up strong function of the flow pattern. The void fraction is presented in Xu, Finch, and Uribe-Salas (1991). distribution changed from saddle-shaped to parabolic as the gas velocity increased. A saddle-shaped distribution is ,A5@=6;3;:;/% therefore associated with bubbly flow conditions, while a parabolic one represents slug flow.  !$& ')%' A Eulerian-Eulerian (E-E) multiphase modelling approach & )% )'"  )!$')("& was used in this study. The Eulerian-Eulerian model was A plot of gas holdup versus time can also be used to identify selected on the basis of its lower computational cost the existing flow regime in a column The gas holdup versus compared to other modelling approaches such as the volume time will be relatively constant when the column is in the of fluid (VOF) and the Eulerian-Lagrangian methods. A VOF bubbly flow regime. On the other hand, the gas holdup will model would entail tracking of the interface between different show wide variations when the column is operating in the phases, while the Eulerian-Lagrangian method would involve churn-turbulent regime (Shen, 1994). A similar method has tracking of the motion of individual bubbles using an been used by previous researchers who used variations in equation of motion. Both of these methods are therefore not conductivity signals to characterize the flow regime in the suitable for systems that involve large numbers of bubbles, downcomer of a Jameson flotation cell (Mecklenburg, 1992; such as those in the present research. In the E-E approach, Summers, 1995). both the continuous phase and the dispersed phase are considered as interpenetrating continua and both are @97

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 "!A22&   
 175 Investigation of flow regime transition in a column flotation cell using CFD

Interaction between the phases was accounted for by inclusion of the drag force between phases. The drag force is [7] included in the respective conservation of momentum equations as a source term. The volume-averaged mass and where Re is the relative Reynolds number for the primary momentum equations are written as follows: phase L and the secondary phase G defined as:

[1] [8]

and μe is the effective viscosity for the bubble-liquid mixture [2] given by: where k is the phase indicator, k = L for the liquid phase and [9] k = G for the gas phase, k is the volume fraction, k is the In the distorted bubble regime the drag coefficient is phase density, and uk is the velocity of the kth phase, while given as follows: Sk is a mass source term. MG,L is the interaction force = between the phases, and g is the gravity force, while  k is the kth phase stress-strain tensor, given by: [10]

[3] where RT is the Rayleigh-Taylor instability wavelength, defined as: The volume fraction (or gas holdup) of the secondary phase was calculated from the mass conservation equations [11] as: and is the surface tension, g the gravitational acceleration, [4] and GL is the absolute value of the density difference between the phases G and L. where  is the phase reference density, or volume- rG For the strongly deformed, capped bubbles regime, the averaged density of the secondary phase in the solution following drag coefficient is used: domain. The volume fraction of the primary phase was calculated from the secondary phase one, since the sum of the volume fractions is equal to unity. The multiphase model [12] was implemented and solved using the CFD code ANSYS FLUENT 14.5. Under churn-turbulent flow conditions, the drag coefficient is calculated using Equation [12]. Further details
   about the universal drag laws are available in a recent The interaction force between the two phases was modelled multiphase flow dynamics book (Kolev, 2005). through the drag force incorporated into the multiphase model. The drag force per unit volume for bubbles in a " '')%' $( swarm is generally presented as: Turbulence in the continuous phase was modelled using the k- realizable turbulence model, a RANS (Reynolds-Averaged [5] Navier-Stokes)-based model in which the time-averaged Navier-Stokes (RANS) equations are solved in place of the where CD is the drag coefficient, dB is the bubble diameter, instantaneous Navier-Stokes equations to produce a time- and u G – u L is the slip velocity. There are a number of averaged flow field. Alternative turbulence modelling empirical correlations that can be used to calculate the drag approaches such as direct numerical simulation (DNS) or coefficient, CD. The drag coefficient is normally presented in large-eddy simulation (LES) would require very dense these correlations as a function of the bubble Reynolds computational grids and small time-steps, with subsequent number (Re), defined as: increase in the computational effort required for the simulations. These methods are therefore not available when [6] using the E-E multiphase model in ANSYS FLUENT. The averaging procedure introduces additional unknown terms; In the present study, the drag coefficient was calculated the Reynolds stresses, which are subsequently resolved by using the universal drag laws. In this case, the drag employing Boussinesq’s eddy viscosity concept where the coefficient is defined in different ways depending on whether Reynolds stresses (or turbulent stresses) are related to the the prevailing regime is in the viscous regime category, the velocity gradients according to the following equation: distorted bubble regime, or the strongly deformed capped bubbles regime. The different regimes are defined on the [13] basis of the Reynolds number (Kolev, 2005). The subsequent expressions for the drag coefficient are derived from single- where t is the turbulent or eddy viscosity, kE is the bubble equations, which are then modified to account for turbulent kinetic energy, and ij is the Kronecker delta. The bubble swarm effects. In the viscous regime the drag Kronecker delta is important in order to make the eddy coefficient is presented as: viscosity concept applicable to normal stresses where i = j. 176   
  "!A22&          
Investigation of flow regime transition in a column flotation cell using CFD

The turbulent viscosity is in turn related to a velocity scale functions to calculate turbulence quantities in the region near and a length scale of the turbulence according to the Prandtl- to the walls of the column. Kolmogorov formula, which can be written as: '%'!")&)'  [14] For the purposes of the present research, the model considers only the collection zone of the flotation column. Therefore the The velocity scale is calculated from the turbulent kinetic froth zone was not included in the model. A further energy (kE) equation, while the length scale is obtained from simplification was achieved by leaving the sparger out of the the turbulent dissipation ( ) equation. The k- model is model geometry. Instead, the air was introduced from the therefore a two-equation model in which two separate bottom part of the column over the entire column cross- transport equations are solved to determine the velocity scale section. This will not affect the required gas holdup prediction and the length scale of the turbulent motion. Turbulence in since the ratio of column cross-section to sparger surface area the near-wall region was modelled using standard wall was about 1:1 in the experimental flotation column. The result of these simplifications is that the model geometry is reduced to a cylindrical vessel of height equal to the collection Table I zone height (305 cm in this case) and diameter equal to the diameter of the experimental flotation column. 6@A0?$@A5@96A9?@9A>43A=6@?<>7=@:A =?5@A)6( sizes are summarized in Table I, together with their 8>:?=% respective attributes. Mesh 1 13 940 17 510 0.9318 2.5 The axial water and bubble velocity profiles obtained for Mesh 2 34 160 39 474 0.939 4.5 the different mesh sizes are shown in Figure 3 and Figure 4, Mesh 3 79 755 88 560 0.773 14 respectively. Grid independence was achieved with mesh 3 to Mesh 4 98 112 108 433 0.831 16 mesh 4 and 5. Mesh 3 (79 755 elements) was therefore Mesh 5 114 696 126 764 0.878 17 selected for all subsequent simulations in this study.

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 "!A22&   
 177 Investigation of flow regime transition in a column flotation cell using CFD

%&")%$!$% graphs were obtained from a surface monitor located at the column mid-height position, from which area-weighted Air bubbles were introduced into the column through mass average gas holdup measurements were recorded at 5-second and momentum source terms at the column bottom. The intervals. source terms were calculated from the respective superficial It is important at this stage to clarify the definition of gas velocities and were applied over the entire column cross- regime transition and churn-turbulent flow regime as used in section at the bottom (source) and at the top (sink) of the the present study. Churn-turbulent flow is normally collection zone. associated with a wide bubble size distribution, including For the liquid phase, the top of the collection zone was large bubbles. However, the CFD simulations in the present modelled as a velocity inlet boundary where inlet velocity was research were conducted with a single mean bubble size specified as equal to superficial liquid velocity Jl. Since the assigned for each superficial gas velocity. Furthermore, in computational domain being considered is the collection zone order to investigate the flow regime transition for conditions of the column, the superficial liquid velocity must include the relevant to column flotation, the other set of CFD simulations feed rate plus the bias water resulting from wash water was performed with the bubble size held at a constant value addition. The superficial liquid velocity is therefore equal to of 1.5 mm while increasing the superficial gas velocity to the superficial tailing rate, Jt. determine the maximum superficial gas velocity for that The bottom part was also modelled as velocity inlet where particular bubble size. The reference to churn-turbulent flow exit velocity was set equal to minus superficial liquid velocity. in the present study is therefore not based on a wide bubble At the column wall, no slip boundary conditions were applied size distribution consisting of of large bubbles in the for both the air bubbles and the liquid phase. presence of smaller ones. On the other hand, a CFD model '"$& ) % !$%)'!% coupled with a bubble population balance model can be used to predict bubble size distributions in the column. However, The momentum and volume fraction equations were bubble population balance modelling was beyond the scope of discretized using the first-order upwind scheme. The first- the present research. A possible alternative that can be used order upwind scheme was also employed for turbulence to simulate bubble size distributions is to apply a Eulerian- kinetic energy and dissipation rate discretization. A time step Lagrangian model. This approach was not applied in the size of 0.05 seconds was used in all the simulations. The present study due to its higher computational cost. A simulations were run up to a flow time of at least 240 Eulerian-Lagrangian model would also require prior seconds. Time averaging was carried out over the last 120 knowledge of the largest and smallest bubble sizes. This seconds. information was not readily available in the present research. According to Lockett and Kirkpatrick (1975) there are @98:=9A>43A3?97899?;4 three main reasons for breakaway from ideal bubbly flow: If the entire range of bubble sizes encompassing the different flooding, liquid circulation, and the presence of large bubbles. flow regimes is known, CFD simulations can be conducted for It should therefore be possible to identify regime transition a range of superficial gas velocities covering the different from changes in the pattern and intensity of the liquid flow regimes. A plot of gas holdup versus superficial gas circulation in the column even if changes in bubble size are velocity can then be used to determine the point of departure negligible or absent. However, the absence of large bubbles is from bubbly flow conditions, as described earlier. For a likely to have an effect on the prediction of the location of the system comprising water and air without frother, an empirical transition zone as well as on the shape of the radial gas formula derived by Shen (1994) can be used to calculate the holdup profile. On the other hand, the liquid circulation Sauter mean bubble size as a function of the superficial gas pattern and its intensity depend on the prevailing radial gas velocity. However, a similar empirical equation derived for holdup profile in the column (Hills, 1974). column flotation conditions where frother plays an important Saddle-shaped gas holdup profiles have already been role in determining the bubble size is limited to superficial related to bubbly flow conditions in two-phase flows gas velocities ranging from 1 to 3 cm/s. The first set of CFD (Kobayasi, Iida, and Kanegae, 1970; Serizawa, Kataoka, and results presented in this study is therefore obtained using Michiyoshi, 1975). However, the bubbly flow regime is bubble sizes calculated for a system without frother. The gas generally characterized by a radially uniform gas holdup holdup versus superficial gas velocity relationship obtained is distribution (Ruzicka et al., 2001; Vial et al., 2001; Shaikh, then used to delineate the different flow regimes prevailing in and Al-Dahhan, 2007). Both saddle and flat gas holdup the column. profiles can therefore be considered to indicate the existence Once the flow regimes are identified, the evolution of of the bubbly flow regime in the column. On the other hand, radial gas holdup profiles and gas holdup versus time graphs the churn-turbulent flow regime is generally distinguished by can be examined for the flow regimes determined from the a non-uniform radial gas holdup distribution causing bulk gas holdup versus superficial gas velocity graph. Radial gas liquid circulation. Parabolic gas holdup profiles are therefore holdup profiles and gas holdup versus time graphs are then interpreted to signify churn-turbulent flow conditions in the used to determine the maximum superficial gas velocity for a column. column operating with an average bubble size of 1.5 mm, which is comparable with typical bubble sizes in industrial &!'")&)&$")% ) $!%!)"%!'" flotation columns. The radial gas holdup profiles were For the water and air only (no frother) system, CFD obtained at the mid-height position (152.5 cm height) in the simulations were carried out for superficial gas velocities column. On the other hand, the gas holdup versus time ranging from 1.01 to 14 cm/s to encompass both the bubbly 178   
  "!A22&          
Investigation of flow regime transition in a column flotation cell using CFD flow and churn-turbulent flow regimes. The Sauter mean water and air only system without frother. This value bubble size for a multi-bubble system without frother (i.e., compares well with the maximum superficial gas velocity of water and air only) can be calculated as a function of the 5.25 cm/s for loss of bubbly flow predicted from drift flux superficial gas velocities from the following empirical formula theory by Xu, Finch, and Uribe-Salas (1991). (Shen, 1994): Having delineated the different flow regimes using the gas holdup versus superficial gas velocity relationship, the [15] evolution of the radial gas holdup profiles was examined as the superficial gas velocity increased from 1.01 cm/s to This empirical formula was derived for a laboratory 14 cm/s. flotation column with a porous stainless steel sparger similar to the one that was used in the column modelled in the   present work. The equation was therefore used in the present A number of different types of radial gas holdup profiles were work to calculate the average bubble sizes that were obtained from the CFD simulations, including saddle-shaped, subsequently used in the CFD simulations. flat, and parabolic profiles. These profiles were then related to       the flow regimes defined from the gas holdup/superficial gas velocity relationship (Figure 5). The graph of gas holdup versus superficial gas velocity Three types of radial gas holdup profiles were observed in obtained from CFD simulations is presented in Figure 5. The the bubbly flow regime. At the lower superficial gas velocities different flow regimes can be cleared delineated as follows: (Jg 1.01–2.73 cm/s), saddle-shaped profiles with three Bubbly flow regime; Jg 1.01–6.12 cm/s (linear portion distinct peaks were observed with one peak at the centre and of the graph) two other peaks located near the walls of the column, as Transition; 6.12 < Jg  11.71 cm/s (deviation from shown in Figure 6 for Jg = 1.84 cm/s. The profiles then linear relationship between gas holdup and superficial changed to ones with two near-wall peaks and a central gas velocity) minimum point as the superficial gas velocity increased to Jg Churn-turbulent flow; Jg > 11.71 cm/s (third portion of = 4.44 cm/s, as illustrated in Figure 7. With further increase the gas holdup versus superficial gas velocity graph). in the superficial gas velocity the central minimum point The maximum superficial gas velocity (Jg max) before disappeared and the radial gas holdup profile became flat. loss of bubbly flow is therefore equal to 6.12 cm/s for the The maximum superficial gas velocity (Jgmax = 6.12 cm/s)

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 "!A22&   
 179 Investigation of flow regime transition in a column flotation cell using CFD

- %+/0 00.&-.,0 .)0$',&%(0(+'"-,/)0.*0 00! )0-#0*$/0%,0",'0+/ - /0$/0).&&,/)$.(/&0(+'"-,/0-)0!$.+.!*/+-/&00*'0#/.+.,,0(/.
)0.#&0. !/#*+.,0 -#- % 0.,%/

- %+/0 0.&-.,0 .)0$',&%(0(+'"-,/0.*0 00! )0  
0)$'-# 0.0",.*0(+'"-,/0-*$0"/.*%+/)0-#*/+ /&-.*/0/*//#0).&&,/0.#&0(.+.',-!0(+'"-,/)

- %+/0.&-.,0 .)0$',&%(0(+'"-,/0.*0 00! )0-#0*$/0!$%+#*%+%,/#*0",'0+/ - /0$/0*(-!.,0(+'"-,/0-)0.0)*//(0(.+.',-!0)$.(/ before loss of bubbly flow is therefore characterized by a flat characterized by steep parabolic gas holdup profiles as shown radial gas holdup profile with intermediate features between in Figure 9. saddle and parabolic profiles, as shown in Figure 8. The transition from bubbly flow to churn-turbulent flow   
   was gradual and characterized by flat (Jg = 7.41 cm/s) to Another method that was used to distinguish flow regimes in parabolic (Jg 8.70–11.71 cm/s) radial gas holdup profiles. The the water–air system using CFD simulations was by means of parabolic profiles became progressively steeper as the gas holdup versus time graphs. The two extreme cases, bubbly superficial gas velocity increased. Eventually the flow regime flow and churn-turbulent flow, are compared in Figure 10. It changes into churn-turbulent flow (Jg > 11.71 cm/s), which is can be seen that the gas holdup versus time was mostly 180   
   0          
Investigation of flow regime transition in a column flotation cell using CFD

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Table II

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#( )75'9(>8=@4A.8..:@A >9A6;:381A >9A6;:381A >9A6;:381A ;55@4=9 9?@A )75()0<>7=?;4>:( 1<;0?:@ '"  =?5@

1.01 0.33 0.045 Saddle with three peaks Constant Bubbly flow 1.84 0.38 0.083 Saddle with three peaks Constant Bubbly flow 2.73 0.42 0.125 Saddle with three peaks Almost constant Bubbly flow 4.44 0.47 0.209 Saddle profile with Almost constant Bubbly flow two near-wall peaks 6.12 0.51 0.279 Flat profile with Small to moderate Bubbly flow intermediate features variations (maximum superficial between parabolic gas velocity) and saddle profiles 7.41 0.53 0.315 Flat Moderate variations Transition 8.70 0.55 0.333 Flat-like parabolic Moderate variations Transition 9.56 0.57 0.345 Parabolic Significant variations Transition 10.42 0.58 0.353 Parabolic Significant variations Transition 11.71 0.60 0.348 Steep parabolic Large variations Transition (last point) 13.00 0.61 0.367 Steep parabolic Wide variations Churn-turbulent flow (large variations) 14.00 0.62 0.377 Steep parabolic Wide variations Churn-turbulent flow (large variations)

Table III 855><%A;0A=6@A76><>7=@

,:;*A<@/?5@ @97<>7=@

Bubbly flow • Characterized by saddle-shaped radial gas holdup profiles accompanied by a constant gas holdup versus time graph

• The profiles at lower Jg have three peaks that give way to profiles with two near-wall peaks and a central minimum and eventually flat profiles as Jg increases Transition • Characterized by flat to parabolic gas holdup profiles

• The profiles become increasingly steep with increasing Jg while gas holdup versus time varies from moderate to large fluctuations Churn-turbulent flow • Characterized by steep parabolic profiles with very wide variations in gas holdup versus time

constant in the bubbly flow regime (Jg = 1.84 cm/s), while very The results from the CFD simulations of the water and air wide variations in gas holdup were observed in the churn- only (no frother) system, where bubble sizes are calculated turbulent flow regime (i.e., Jg = 14 cm/s). The transition from from the superficial gas velocity according to Equation [15], bubbly flow to churn-turbulent flow pattern was gradual and are summarized in Table II. The progression from bubbly characterized by moderate to large fluctuations in gas holdup, flow conditions to churn-turbulent flow can also be clearly with the gas holdup variations becoming increasingly intense appreciated from this table. The distinguishing characteristics as the superficial gas velocity increased. of the flow regimes are summarized in Table III.

         
 "!A22&   
 181 Investigation of flow regime transition in a column flotation cell using CFD

&!'")$!)"%!'") & )$)% ) %!&!$% constant during the simulations while increasing the superficial gas velocity to encompass both bubbly flow and In flotation columns, the bubble size depends not only on the superficial gas velocity, but also on other physical chemical churn-turbulent flow conditions. characteristics of the gas-liquid system. In this case, the &$) '"$$& )(& )' %$!)%")&)%  bubble size can be calculated as a function of the superficial %'"&!$()$!) ))&'"&(') ') $' gas velocity according to the following relationship (Finch and Dobby, 1990; Yianatos and Finch, 1990). CFD simulations were performed with a constant bubble size of 1.5 mm for superficial gas velocities ranging from Jg = 1.01 [16] to 6.12 cm/s. The liquid superficial velocity was maintained at Jl = 0.38 cm/s. Radial gas holdup profiles were examined where C and n are constants. The constant C is a fitting for all the superficial gas velocities together with their parameter which depends mainly on frother concentration, corresponding gas holdup versus time plots. the sparger size, and column size. Simulations were carried out for the experimental conditions used by Xu, Finch, and   Uribe-Salas (1991) and Xu et al. (1989), particularly the case Saddle-shaped radial gas holdup profiles with three peaks in which the frother concentration was 10 ppm. The value of were observed for Jg = 1.01 to 1.54 cm/s. The radial gas C was therefore equal to unity while n was 0.25. holdup profile for Jg 1.01 cm/s is presented in Figure 12 for The gas holdup obtained from the CFD simulations is elaboration. The profiles then changed to ones with two plotted as a function of superficial gas velocity in Figure 11. distinct peaks near to the column wall as Jg increased (Jg = The experimental data from Xu et al. (1989) is included in 1.84 to 2.73 cm/s). On the other hand, a flat profile with the figure for comparison. It can be seen that the predicted intermediate features between saddle-shaped and parabolic gas holdup is in good agreement with the experimental data profiles was observed for Jg = 3.12 cm/s. The column was up to superficial gas velocity Jg = 3.60 cm/s. Above Jg = 3.60 therefore operating under bubbly flow conditions from Jg = cm/s, the relationship in Equation [16] is not applicable 1.01 to 3.12 cm/s. In the churn-turbulent regime, steeper because the value of the exponent n (0.25) is valid for parabolic radial gas holdup profiles were observed from Jg = Jg 1–3 cm/s (Yianatos and Finch, 1990). Unfortunately, there 5.28 cm/s, as shown in Figure 13. is no equation relating bubble size and superficial gas velocity for flow conditions above Jg = 3 cm/s. Therefore, the    gas holdup versus superficial gas velocity graph obtained Gas holdup versus time graphs were used to confirm the from CFD simulations cannot be used to determine the existing flow regime in the column. A relatively constant gas maximum superficial gas velocity since the range of bubble holdup versus time was observed for Jg = 1.01 to 1.84 cm/s sizes for the different flow regimes cannot be completely while moderate fluctuations in gas holdup were observed determined. from Jg = 2.28 to 3.12 cm/s, confirming that the column was Xu et al. (1989) used the gas holdup versus superficial indeed in the bubbly flow regime in this range of superficial gas velocity relationship to identify the maximum gas gas velocities. In contrast, very wide variations in gas holdup velocity for loss of bubbly flow. However, they reported a versus time were observed when the churn-turbulent flow gradual and unclear transition from bubbly flow to churn- regime prevailed in the column. The two extreme conditions, turbulent flow conditions. The maximum superficial gas bubbly flow and churn-turbulent flow, are compared in velocity for conditions applicable in flotation columns can be Figure 14 for Jg = 1.01 cm/s and Jg = 5.28 cm/s. obtained using radial gas holdup profiles and the gas holdup versus time graphs as already described. In this regard, CFD          simulations are performed in the present study for a The maximum (critical) superficial gas velocity for transition stipulated bubble size of 1.5 mm, which is similar to common into churn-turbulent flow was identified by the first bubble sizes used in column flotation. The bubble size is held appearance of flat radial gas holdup profiles with

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  "!A22&          
Investigation of flow regime transition in a column flotation cell using CFD

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intermediate features between parabolic and saddle-shaped Salas (1991) and Xu et al. (1989) with reference to loss of profiles at Jg = 3.12 cm/s. The maximum superficial gas interface. Indeed, these authors did report that loss of velocity (Jg,max) before loss of bubbly flow is therefore interface and loss of bubbly flow occurred at approximately 3.12 cm/s for a flotation column operating with an average the same superficial gas velocities. The predicted gas holdup bubble size of 1.5 mm at superficial liquid velocity (Jl) equal at Jg,max is equal to 20.1%, which compares favourably with to 0.38 cm/s. This compares favourably with the maximum the maximum gas holdup of 20 to 24% reported by Dobby, gas velocity of 3.60 cm/s reported by Xu, Finch, and Uribe- Amelunxen, and Finch (1985).

         
 "!A22&   
 183 Investigation of flow regime transition in a column flotation cell using CFD

The radial gas holdup profile at Jg,max is shown in Figure $
$)' %$!)'!%" 15, and its corresponding gas holdup versus time graph in Figure 16. It can be seen that the maximum superficial gas Two different flow patterns were observed, depending on velocity is characterized by a flat gas holdup profile superficial gas velocity and bubble size. With increasing accompanied by moderate gas holdup fluctuations. The superficial gas velocity the well-known ‘Gulf Stream’ results from the CFD simulations for 1.5 mm bubble size are circulation pattern, in which the liquid rises in the centre of summarized in Table IV. The progression from bubbly the column and descends near the column wall, was flow conditions to churn-turbulent flow can be clearly seen in observed. In contrast, an ‘inverse’ circulation flow pattern, in the table. which the liquid rises near the column wall but descends in

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Table IV 855><%A;0A,A9?58:>=?;4A<@98:=9A0;

#( )75'9(>9A6;:381A)( >3?>:A/>9A6;:381A1<;0?:@ >9A6;:381A$@<989A=?5@ ,:;*A<@/?5@

1.01 6.27 Saddle-shaped with three peaks Constant Bubbly flow 1.54 9.66 Saddle-shaped with three peaks - Bubbly flow 1.84 11.60 Saddle-shaped with two peaks Very small variations Bubbly flow 2.28 14.47 Saddle-shaped with two peaks Moderate fluctuations Bubbly flow 2.73 17.46 Saddle-shaped with two peaks Moderate fluctuations Bubbly flow 3.12 20.10 Flat, intermediate between saddle and parabolic profiles Moderate fluctuations Bubbly flow (Jgmax) 3.60 23.23 Flat profile Larger fluctuations Transition 4.03 26.27 Parabolic profile Larger fluctuations Transition 4.44 29.05 Parabolic Large variations Transition 5.28 35.51 Steep parabolic Very large variations Churn-turbulent flow 184   
  "!A22&          
Investigation of flow regime transition in a column flotation cell using CFD the centre and immediately adjacent to the walls, occurred at lower superficial gas velocities. This is the first study to report such an inverse flow pattern in column flotation. However, similar flow reversals have been observed in experimental work on fluidized bed reactors (Lin, Chen, and Chao, 1985). The inverse circulation pattern has been theoretically investigated in bubble columns and is associated with fully developed saddle-shaped radial gas holdup profiles (Clark, Atkinson, C., and Flemmer, 1987; Clark, van Egmond, and Nebiolo E. 1990). In the present study, the inverse circulation pattern was observed at Jg = 1.01 cm/s and Jg = 1.54 cm/s for simulations with bubble size = 1.5 mm and superficial liquid velocity = 0.38 cm/s. Saddle-shaped gas holdup profiles with two distinct peaks near the walls of the column were also present under these conditions. The liquid velocity vector plots obtained from CFD simulations are presented in Figure 17 and Figure 18 for the two circulation patterns. Clark, van Egmond, and Nebiolo (1990) have described the sequence of events that may initiate liquid circulation in bubble columns. In general, liquid circulation in bubble columns is initiated by density differences in the gas-liquid mixture, depending on the prevailing radial gas holdup profile. If the concentration of air bubbles is higher in the central part of the column compared to the outer annular region, the mean density of the mixture will be lower near the ,?/8<@A2 # ? 8?3A$@:;7?=%A$@7=;<9A>=A5?36@?/6=A?4A=6@A7;::@7=?;4A;4@ centre of the column than in the outer annulus. The 0;5A7?<78:>=?;4A1>==@<4( hydrostatic pressure head will therefore be higher in the outer annulus, hence a radial pressure difference is set up inside the column. This will cause an inward radial movement of liquid and initiate liquid circulation. The inverse circulation pattern will occur if the concentration of bubbles is higher in the outer annular region, as in the case of saddle- shaped gas holdup profiles.

;47:89?;49 In this study, the evolution of the shape of the radial gas holdup profile in a pilot-scale flotation column was studied using CFD to delineate the maximum gas velocity for loss of bubbly flow. With increasing superficial gas velocity, the gas holdup profile passes through different stages, which can be used to define the prevailing flow regime in the column. The different flow regimes were also verified by the intensity of the local variations of the gas holdup. In the bubbly flow regime, saddle-shaped and flat radial gas holdup profiles were obtained. These profiles were accompanied by minor to moderate gas holdup variations in the column. The transition regime was gradual and characterized by flat to parabolic gas holdup profiles. The parabolic profiles became progressively steeper as the superficial gas velocity increased. The corresponding gas holdup versus time graphs in the transition regime showed moderate to wide variations in gas holdup. On the other ,?/8<@A2# ? 8?3A$@:;7?=%A$@7=;<9A>=A5?36@?/6=A?4A=6@A7;::@7=?;4A;4@ hand, the churn-turbulent flow regime was distinguished by 0;=?;4A1>==@<4( steep parabolic gas holdup profiles with very wide variations in gas holdup versus time. For conditions relevant to column flotation, the maximum superficial gas velocity was determined for a column Two possible flow patterns were revealed in the simulated operating with an average bubble size of 1.5 mm and column in this study: the ‘Gulf Stream’ circulation pattern superficial liquid velocity equal to 0.38 cm/s. The maximum and an inverse circulation pattern. The latter was observed superficial gas velocity was found to be equal to 3.12 cm/s. only in the presence of fully developed saddle-shaped radial The corresponding maximum gas holdup value was 20.1%. gas holdup profiles.

         
 "!A22&   
 185 Investigation of flow regime transition in a column flotation cell using CFD

The CFD simulations in the present study assumed a @0@<@47@9 constant average bubble size for the flotation column. CLARK, N., ATKINSON, C., and FLEMMER, R. 1987. Turbulent circulation in bubble However, for the churn-turbulent regime, a bubble size columns. AIChE Journal, vol. 33, no. 3. pp. 515–518. distribution exists that could have an effect on the CLARK, N., VAN EGMOND, J., and NEBIOLO E. 1990. The drift-flux model applied to hydrodynamics of the column. CFD models coupled with a bubble columns and low velocity flows. International Journal of bubble population balance model should therefore be Multiphase Flow, vol. 16, no. 2. pp. 261–279. considered in future studies in order to account for bubble size distributions in the transition and churn-turbulent flow DOBBY, G., AMELUNXEN, R., and FINCH, J. 1985. Column flotation: Some plant experience and model development. Proceedings of the First IFAC regimes. Symposium on Automation for Mineral Resource Development, Brisbane, Australia, 9–11 July. IFAC Proceedings, vol. 18, no. 6. pp. 259–263. B74;*:@3/@5@4=9 FINCH, J.A. and DOBBY, G.S. 1990. Column Flotation. Pergamon, Oxford, UK. The authors would like to acknowledge the Centre for HILLS, J. 1974. Radial non-uniformity of velocity and voidage in a bubble International Cooperation at VU University Amsterdam (CIS- column. Transactions of the Institution of Chemical Engineers, vol. 52, VU) and the Copperbelt University (CBU) for providing the no. 1. pp. 1–9. scholarship and subsequent funding for this research through the Nuffic-HEART Project. We would also like to ITYOKUMBUL, M. 1992. A new modelling approach to flotation column desing . Minerals Engineering, vol. 5, no. 6. pp. 685–693. acknowledge the Process Engineering Department at Stellenbosch University for providing the necessary facilities KOBAYASI, K., IIDA, Y., and KANEGAE, N. 1970. Distribution of local void fraction that made this research possible. The CFD simulations in our of air-water two-phase flow in a vertical channel. Bulletin of JSME, studies were performed using the University of Stellenbosch's vol. 13, no. 62. pp. 1005–1012. Rhasatsha High Performance Computing (HPC) cluster: KOLEV, N.I. 2005. Multiphase Flow Dynamics 2: Thermal and Mechanical http://www.sun.ac.za/hpc Interactions. 2nd edn. Vol. 2. Springer, Berlin, Germany. LANGBERG, D. and JAMESON, G. 1992. The coexistence of the froth and liquid ;5@47:>=8<@ phases in a flotation column. Chemical Engineering Science, vol. 47, no. 17. pp. 345–355. CD Drag coefficient, dimensionless dB Bubble diameter, mm LIN. J., CHEN, M., and CHAO, B. 1985. A novel radioactive particle tracking facility for measurement of solids motion in gas fluidized beds. AIChE dBS Sauter mean bubble size Journal, vol. 31, no. 3. pp. 465–73. (FD) Drag force per unit volume, N/m3 LOCKETT, M. and KIRKPATRICK, R. 1975. Ideal bubbly flow and actual flow in g Gravitational acceleration, 9.81 m/s2 bubble columns. Transactions of the Institution of Chemical Engineers, Jg Superficial gas velocity, cm/s vol. 53. pp. 267–273. Jg,max Maximum superficial gas velocity MECKLENBURG, M.M. 1992. Hydrodynamic study of a downwards concurrent Jl Superficial liquid velocity bubble column. MEng dissertation, McGill University, Montreal, Canada. Turbulence kinetic energy, m2/s2 kE RUZICKA, M., ZAHRADNIK, J., DRAHOŠ, J., and THOMAS N. 2001. Homogeneous– P Pressure, Pa heterogeneous regime transition in bubble columns. Chemical Engineering Re Reynolds number, dimensionless Science, vol. 56, no. 15. pp. 4609–4626. Sk Mass source term for phase k, kg/m3-s SERIZAWA, A., KATAOKA, I., and MICHIYOSHI, I. 1975. Turbulence structure of air- u Reynolds averaged velocity, m/s water bubbly flow – II. local properties. International Journal of u' Velocity fluctuation, m/s Multiphase Flow, vol. 2, no. 3. pp. 235–246. SHAIKH, A. and AL-DAHHAN, M.H. 2007. A review on flow regime transition in <@@A:@==@<9 bubble columns. International Journal of Chemical Reactor Engineering, vol. 5, no. 1. https://doi.org/10.2202/1542-6580.1368 G Air volume fraction or gas holdup Volume fraction SHEN, G. 1994. Bubble swarm velocities in a flotation column. PhD dissertation, McGill University; Montreal, Canada. Turbulence dissipation rate, m2/s3 SUMMERS, A.J. 1995. A study of the operating variables of the Jameson cell. RT Rayleigh-Taylor instability wavelength MEng dissertation, McGill University, Montreal, Canada.  Viscosity, kg/m-s VIAL, C., PONCIN, S., WILD, G., and MIDOUX, N. 2001. A simple method for regime t Turbulent viscosity, kg/m-s identification and flow characterisation in bubble columns and airlift  Density, kg/m3 reactors. Chemical Engineering and Processing: Process Intensification, Surface tension (N/m) vol. 40, no. 2. pp. 135–151.
k Viscous stress tensor, Pa XU, M., FINCH, J., and URIBE-SALAS, A. 1991. Maximum gas and bubble surface rates in flotation columns. International Journal of Mineral Processing, 8.97

(2013) stated that mathematical models are & ><47?7 unable to capture the nonlinear relationship between several blasting-related parameters In an opencast mine explosives are used for fragmentation of rock. due to the complexity of the model input data. Inefficient use of explosive energy in an opencast operation produces excessive ground vibration, which is measured by peak particle velocity However, the difficulty involved in modelling (PPV). To mitigate ground vibration, it is essential to develop a model to complex blast vibration problems can be predict PPV. At present empirical models are used. These models are based removed by adopting an alternative soft on only a few input variables, hence they fail to take into account the computing modelling approach. One of the soft effects of the myriad factors that cause ground vibration. Due to lack of computing techniques is the artificial neural explicit knowledge about the complex mine blasting system the scope of network (ANN). Ragam and Nimaje (2018) application of mathematical and statistical modeling techniques is limited. developed an ANN model for predicting PPV The artificial neural network (ANN) technique is a learning algorithm that using six input variables. Kosti et al. (2013) can remove some of these limitations and can be applied to predict PPV. In stated that the conventional predictors fail to this paper an ANN model is developed for prediction of blast vibration provide acceptable prediction accuracy. They using 248 data records collected from three coal mines with diverse showed that a neural network model with four geomining conditions. The correlation coefficient between measured PPV and model output was found to be 0.96 and the average error percentage mine blast parameters as input could make 11.85. The ANN model output was compared with the output of three significantly more accurate on-site predictions. empirical models that are widely used for prediction of PPV. The Sayadi et al., (2013), using a database from correlation coefficient between the PPV predicted by an empirical model Teheran Cement Company limestone mines, and measured PPV data was 0.63 and the relative error percentage 38.47. found that a neural network resulted in This result demonstrates the superiority of the ANN model compared to maximum accuracy and minimum error. empirical blast models. By using site-specific structural discontinuities as Khandelwal and Singh (2009) developed an input the model performance can be further improved. Sensitivity analysis ANN model using 150 data records from an and 3D plotting were used to gain further knowledge about blast-induced Indian coal mine with site-specific rock ground vibration. characteristics and geomining setting. @ <:97 Khandewal and Singh (2007) built a ground artificial neural network, peak particle velocity, sensitivity analysis, vibration prediction model for a magnesite 3D plot. mine using four prediction variables with 20 data records. Kamali and Ataei (2010) predicted PPV in the structure of the Karoun III power plant and dam using an ANN. El Hafiz et al. (2010) evaluated ground vibration >=:<985=?<>A predictors using data from a single-station In an opencast coal mine explosives are used seismograph at a limestone quarry in Egypt. for fragmentation of coal and overburden. If ANN prediction models have been built for the explosive energy is not fully utilized it one Indian coal mine and one limestone mine. causes blast-induced ground vibration, which Using the findings of these initial studies, it is may damage nearby structures. Ground essential to enhance the application of ANN in vibration is expressed as peak particle velocity various mines in different Indian coal mining (PPV). During different stages of mine planning and operation, it is necessary to use a ground vibration prediction model for blast- hole design. Selection of the modelling technique is crucial. Mathematical and statistical modelling techniques have limited * application because of the lack of explicit Department of Mining Engineering, IIEST, India. † Department of Metallurgy, National Institute of knowledge about the complex mine blasting Technology, Raipur. system. Vogiatzi (2002) highlighted the © The Southern African Institute of Mining and problem of multicollinearity in case of Metallurgy, 2019. ISSN 2225-6253. Paper received statistical modeling techniques. Mutalib et al. Jun. 2018; revised paper received Oct. 2018.

         
)'"$-*A11!   
 187 Development of a blast-induced vibration prediction model using an artificial neural network regions. In this investigation we collected 248 data records Artificial neural network (ANN) models can overcome with 15 input variables from three mining regions. A some of the drawbacks of empirical models (Girish, 2007). combined database was built after randomization of the data. ANN is a nonlinear self-adaptive approach without any prior With the help of this database an ANN model was built and assumptions about the interrelations between series of input the final output obtained. The robustness of the model was variables. A back-propagation neural network (BPNN) is tested by using data from other mines and using the model to used as a learning algorithm for training a multilayer feed- predict PPV. Site-specific features, including fracture zones forward neural network. It provides a computationally due to the presence of underground workings and fault efficient method for changing the weights in a feed-forward planes, are expressed as a non-quantifiable variable by using network, with different activation function units. Dey et al. an ordinal scale. Tests were carried out to establish whether (2016) designed an ANN model that consists of number of the model prediction can be improved by using the non- inputs, a single output, and an intermediate hidden layer. quantifiable variable. Sensitivity analyses were performed by Training of the network is the process of learning when the using input and output connection weights of the model. error is calculated as the difference between the predicted Also, 3D plotting was done to understand the interplay output and actual output (target). As the error reaches a between two input variables, keeping the other variables user-defined error tolerance limit, the training is stopped; equal to the mean values. otherwise the weights are readjusted by back-propagation. All inputs to a node are weighted independently, summed #,,A2<9@6 with bias, and fed into logistic or other nonlinear functions. The output is then connected to all neurons of the next layer. Blast-induced ground vibration often damages structures Sivaprasad et al. (2006) and Hornik, Stinchcombe, and near a mine site. The intensity of mine blast-induced White (1989) stated that an ANN could act as a universal vibration must be predicted prior to blasting operations near approximation of nonlinear functions. Rahman et al. (2013) any important surface structure. PPV can be considered as noted that an ANN can be trained to identify nonlinear the representative indicator of ground vibration. It is a patterns between input and output values of opencast significant factor in control of structural damage (Bureau of blasting phenomena. Maqsood et al., (2002) affirmed that Indian Standards, 1973; Kahriman, 2002; Singh and Singh, ANNs do not require any prior knowledge of the system 2005; Bakhshandeh, Mozdianfard, and Siamaki, 2010; under consideration and are well suited for modellng Khandelwal and Singh 2009). Khandelwal, Kumar, and dynamic systems on a real-time basis. Huang and Foo Yellishetty (2011) observed that the empirical equations do (2002) and Scardi (2001) observed that an ANN can be used not include physicomechanical parameters of rock mass, blast either where no precise theoretical model is available, or design, and explosive type, which are relevant for the when uncertainty in input parameters complicates calculation of PPV. deterministic modelling. García, Rodríguez, and Tenorio The empirical method of PPV estimation is discussed (2011) observed that the ANN technique can also perform here. The basic relationship between the variables is V=KWa tasks based on training or initial experience, and does not Db, where W is the weight of explosive charge; D is the need an algorithm to solve a problem. This is because it can distance from the blast; V is the magnitude of vibration; and generate its own distribution of the weights of the links K, a, and b are constants whose values depend on the site- through learning. specific geomining conditions. V is expressed as PPV (mm/s). The prediction equation derived by the US Bureau of Mines is V=K (D/Q0.5)-b. A plot of PPV as a function of scaled distance (D/Q.05) on a log-log scale gives a straight line for mine Table II sites. To derive the values of K, a, and b for a particular site it is necessary to monitor test shots and plot PPV against scaled ;5=<:7A?>368@>5?>0A0:<8>9A.?(:;=?<> distance on a log-log scale. Ghasemi, Ataei, and &6A,< ;5=<:7A Hashemolhosseini (2013) observed that since only a limited number of variables are considered for deriving empirical 1 Rock types 2 Geological discontinuities equations, the PPV predictions are not accurate enough 3 Distance for demarcation of a safe zone around a mine blast site. 4 Explosive charge weight (Table I). The nature and intensity of blast-induced ground 5 Blast geometry 6 Rock mass properties vibration is dependent on many factors, the most important 7 Explosive types of which are shown in Table II.

Table I *24?:?5;6A4:@9?5=?<>A2<9@67A3<:A4:@9?5=?<>A<3A0:<8>9A.?(:;=?<>A

*24?:?5;6A2<9@67 <:286; &?=@A5<>7=;>=7A

Empirical models Empirical models Site constants USBM equation V = k(R/Q1/2)−b k = 239.56 & b = 1.166 Ambraseys and Hendron equation V = k(R/Q1/3)−b k = 1207.96 & b = 1.175 Langefors–Kihlstrom equation V=k(Q/(D2/3)b/2 k = 2.195 & b = 3.389 Indian Standard Predictor equation V=k(Q/(D2/3)b k = 2.195 & b = 1.694 188   
 )'"$-*A11!          
Development of a blast-induced vibration prediction model using an artificial neural network

Mohamad (2009) used several ANN models in the Assiut ;=;(;7@A limestone mine in Egypt and concluded that increasing the Mine blast-induced ground vibration (PPV) was recorded in number of input variables can improve the capability of an three mechanized coal mines. Study area I is located in the ANN to predict PPV. Monjezi, Ghafurikalajahi, and Bahrami Angul district in the state of Odisha. Study area II is located (2011) developed an ANN model to predict PPV at the in the Raniganj coalfield, Burdwan District, in the state of Siahbisheh pumped storage project in Iran, using the West Bengal. Study area III is located in the North Karanpura maximum charge per delay, the distance from the blasting coalfield, Chatra District in the state of Jharkhand. face to the monitoring point, stemming, and hole depth as PPV data was collected from 140 blasts: 50 blasts in input parameters and compared their results with empirical study area I, 36 in study area II, and 54 in study area III. The models and multivariate regression analysis. Using artificial blasting pattern is described in Table III. SME explosive and a intelligence approaches Khandelwal and Singh (2007), Nonel initiation system were used. Ground vibration was Mohamed (2011), Kamali and Ataei (2011), and Singh and recorded using BLASTMATE III, manufactured by Instantel, Singh (2005) predicted PPV using hole depth and diameter, Canada. Two instruments were stationed at distances of 40 m number of holes, burden, spacing, and the distance from the to 320 m from the blast site. PPV was recorded at different blast face as inputs. They concluded that the ANN is a more distances for each blast. Only those values above 1 mm/s accurate approach compared to regression analysis. Other were included in the database. Two hundred and forty-eight researchers predicted PPV based on ANN models in different data records were obtained from 140 blasts. projects. Amnieh, Mozdianfard, and Siamaki (2010), Input variables are presented in Table IV. These variables Amnieh, Siamaki, and Soltani (2012), and Alvarez et al. were selected based on the authors’ experience as well as a (2012) compared the results of both ANNs and empirical study of the relevant literature in the section ‘ANN model’. models with multiple linear regression (MLR) analysis to PPV data measured on the mine sites is described in Table V. establish the applicability of each method. A discussion on The ANN technique can detect similarities between these superiority of ANN modeling techniqueas is included in Appendix A. This subsection contains a brief discussion of the Table III conceptual framework in ANN model-building. Based on the discussions so far an ANN model is built by training the 6;7=?>0A4;==@:>A?>A<.@:(8:9@> network using input data from the study areas. Database Number of blasting rounds 140 development for model input is discussed in the next Number of observations 248 subsection. The training data constitutes 70% of the Diameter of drill-holes (mm) 150–160 database. The network is trained in supervised manner with Depth of holes(m) 3.50–6.50 Burden (m) 3.0–4.50 a back-propagation algorithm training a multilayered feed- Spacing (m) 3.5–5.0 forward network. Initially, training data is preprocessed by Explosive charge/hole (kg) 15.10–70.10 Maximum charge/delay (kg) 70.10 normalizing input and output data. A flow chart of the Maximum charge/round (kg) 7113.50 model-building process is shown in Figure 1.

?08:@A1-<9@6A36<A5/;:=

         
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 189 Development of a blast-induced vibration prediction model using an artificial neural network


 *$%+(+*,$()(+$(+$,&,+'"(,)%+) *$,

& '"(,)%+) *$ !*)' !*#+)' !&#* ()'#)%# !+'+ " !)+ " #*+)(+&'

1 Rock density (Rd) (gm/cc) 2.41 2.42 2.59 0.27 1.52 2.59 2 No. of holes (Nh) 61.60 57.00 60.00 36.73 1.00 142.00 3 Hole diameter (Hdia) (mm) 158.18 160.00 160.00 3.87 150.00 160.00 4 Hole depth (Hd) (m) 5.76 5.90 6.00 0.45 3.50 6.50 5 Burden (B) (m) 3.85 4.00 4.00 0.43 3.00 4.50 6 Spacing (S) (m) 4.45 4.50 5.00 0.55 3.50 5.00 7 Charge length (Cl) (m) 2.09 2.20 2.20 0.37 0.80 2.90 8 Stemming length (St) (m) 3.67 3.70 3.90 0.40 2.50 4.50 9 Max. explosive charge/delay (Ed) (kg) 52.34 55.10 60.10 9.45 15.10 70.10 10 Charge/round (Et) (kg) 3043.40 2813.50 2505.0 1923.38 45.10 7113.50 11 Monitoring point from face (DB) (m) 153.81 140.00 120.00 65.55 40.00 320.00 12 Young's modulus (E) (GPa) 14.40 15.25 15.25 3.31 2.21 15.65 13 Poisson’s ratio (P) 0.24 0.23 0.23 0.03 0.20 0.35 14 P-wave velocity (Vp) (m/s) 5450.68 5800.00 5800.0 968.41 1804.20 5999.10 15 Density of explosive (De) (gm/cc) 1.11 1.12 1.11 0.02 1.06 1.18

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1 PPV (mm/s) 10.38 8.11 26.36 7.20 1.249 33.84

the interactions between the inputs, because of the hidden 
units are able to handle extreme nonlinearity. The nature of *$(+',&,%*(%)+'+',*%&% )'*,&,(*, ,
+( these interactions is implicit in the values of the weights. ,+'"(, +##*',&#*$,&"("( Therefore multicollinearity in the input data is not an issue for training a neural network. Further discussion of this &,&, %)+'+',,(*$(+', *%) ,&%%* )(+&', aspect is presented in the review paper by Bhadesjia (1999). %"' ) &%+( &*++*'(,) "*

1 Tansig/ Trainlm 0.966 *$" ($,)'#,#+$"$$+&' Tansig/ Trainscg 0.924 The neural network toolbox of MATLAB 2015 was used to 2 Tansig/ Trainlm 0.968 build an ANN blast-induced vibration model. The ANN Tansig/ Trainscg 0.957 architecture (Table VIII) has fifteen input variables, one 3 Tansig/ Trainlm 0.975 hidden layer, and four nodes. Four nodes were selected since Tansig/ Trainscg 0.940 this gives a high R value (Table VII). The network was 4 Tansig/ Trainlm 0.943 trained up to maximum epoch of 1000 and the error goal was 5 Tansig/ Trainlm 0.959 set at 1e-7. In Figure 2 and Table IX the association between the PPV predicted by the model and the actual PPV measured in the field is 0.968, and the average relative error is 11.85. input variables. This property gives it excellent interpolation Therefore, the prediction capability of the model was deemed capability, especially when the input data is noisy (not to be good and the model ready for use. An attempt was exact). An ANN is capable of calculating arithematic and made to improve the model prediction by including non- logical functions, generalizing and transforming independent quantifiable variables. Diverse structural features were variables to dependent variables, parallel computations, observed during inspection of different mine sites. Some of nonlinear processing, handling of noisy data, function the quantifiable rock parameters are included in Table III as approximation, and pattern recognition (Sayadi et al., 2013). input to ANN models. Site-specific structural features are ANN can be applied to combat the problem of mostly non-quantifiable variables, therefore an ordinal scale multicollinearity in the data (Hermosilla and Carpio, 2005). of 1 to 3 is used. To cite an example, if the site has minimum The correlation coefficient is widely used in statistics but structural discontinuities then a value 1 is assigned, while 3 correlation is a measure of the linear association between represents highly fractured and faulted strata (Table XI). variables. If two variables are related in a nonlinear manner However, further research on use of non-quantifiable the correlation coefficient will not be able to do justice to the variables as model input is essential. By including the above strength of relationship (Makridakis, Wheelwright, and variable a marginal increase in R value from 0.968 to 0.975 Hyndman, 2005). The neural network is capable of capturing was obtained. The model performance was also compared 190   
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Development of a blast-induced vibration prediction model using an artificial neural network

Table VII #,,A2<9@6A4@:3<:2;>5@A( A.;: ?>0A>82(@:AA<3A><9@7A

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1 Tansig/ Trainlm 0.95 0.92 0.92 0.94 Tansig/ Trainscg 0.89 0.86 0.85 0.87 2 Tansig/ Trainlm 0.97 0.94 0.93 0.95 Tansig/ Trainscg 0.92 0.90 0.89 0.90 3 Tansig/ Trainlm 0.97 0.94 0.94 0.95 Tansig/ Trainscg 0.94 0.91 0.92 0.92 4 Tansig/ Trainlm 0.97 0.96 0.97 0.97 Tansig/ Trainscg 0.96 0.94 0.95 0.95 5 Tansig/ Trainlm 0.97 0.94 0.94 0.95 Tansig/ Trainscg 0.94 0.91 0.92 0.92

Table VIII with the multivariate linear regression model (Table IX) and results show the benefits of an ANN for enhancing accuracy ,@=<:A;:5/?=@5=8:@ in model prediction. Number of input variables 15 The robustness of the training was tested with different Number of nodes in hidden layer 4 initialized states of the network parameters for the given Number of hidden layers 1 Transfer function Hyperbolic tangent sigmoid transfer architecture while holding other training parameters and function (tansig) for hidden layer algorithms constant. Typical results for the 15-4-1 and Purelin for output layer architecture with the sigmodal transfer function and Levenberg-Marquardt training function retrained for five runs are presented in Table VI. The result shows significantly good convergence under repeated training with different initialized states, leading to a close variation in prediction performance. Twenty-eight new data records were used to examine the prediction performance of the ANN model. The output is compared with measured PPV in Table X. Also, the same database was used for predicting PPV by four empirical models (Table I). The reasons for selection of four out of several available empirical models are stated below. Scaled distance (maximum charge weight divided by the cube root or square root of actual distance) is used for deriving empirical formulae for Indian mines. The correlation ?08:@A
:;4/?5;6A:@4:@7@>=;=?<>A<3A;5=8;6A;>9A4:@9?5=@9A.;68@7A coefficients between the predicted and measured PPVs in case <3A) of the ANN and empirical model are 0.96 and 0.67 respectively (Table X). Other formulae, which are not Table IX included in Table II, are based on inelastic effects, which @:3<:2;>5@A<3A#,,A2<9@6A cause energy losses during blast wave propagation. Inelastic attenuation of elastic waves is dependent on the geotechnical  4@A<3A2<9@6 #,, -86=?.;:?;=@A6?>@;:A:@0:@77?<>A properties of the rocks. In case of other formulae, empirical constants are derived for specific geomining features and No. of observations 248 248 therefore they were not considered. Correlation coefficient 0.97 0.80 Av. relative error (%)* 11.85 16.01 &@>7?=?.?= A;>;6 7?7 Explicit knowledge about the interplay between different *The absolute error is the difference between the measured value and the true value. The relative error is defined as the absolute error relative to the variables responsible for blast-induced ground vibration is size of the measurement. largely lacking. To extract knowledge from the ANN model,

Table X @:3<:2;>5@A<3A#,,A;>9A@24?:?5;6A2<9@67A

-<9@6A4@:3<:2;>5@A #,, $& -A #2(:;7@ 7A;>9A+@>9:<>A ";>0@3<:7?/67=:<2A >9?;>A&=;>9;:97A4:@9?5=<:A@8;=?<>

No. of observations 28 28 28 28 28 Correlation coefficient 0.96 0.67 0.63 0.68 0.74 Av. relative error (%) 11.8 37.3 38.47 37.89 35.19

         
)'"$-*A11!   
 191 Development of a blast-induced vibration prediction model using an artificial neural network

Table XI &?=@%74@5?3?5A7=:85=8:;6A3@;=8:@7A<3A=/@A5;7@A7=89 A;:@;7A

@;=8:@7 ;7@A7=89 A;:@;A;7@A7=89 A;:@;A ;7@A7=89 A;:@;A

Presence of fractures Minor fracture planes Highly fractured due to presence Prominent fractures not found of underground working below opencast Faults Minor faults Three major faults of throw 80–240 m No major faults Structural discontinuities expressed in ordinal scale 1 3 2

?08:@A #5=8;6A 4:@9?5=@9A.;68@7A<3A)A87?>0A=:;?>?>0A=@7=A.;6?9;=?<>A;>9A;66A9;=;

output sensitivity analysis was carried out. Sensitivity and For Output O = 1 to o, where o = no. of outputs analysis is the method of studying a model by assessing the Weight of input variable j and hidden neuron i = Wji significance of each input variable on the model output. By Weight of output o and hidden neuron i = Woi this means it is possible to identify how different input Contribution of each input neuron to the output via variables influence the model output. A connection weight each hidden neuron is given by (Table XIII): approach was adopted. Calculation of the product of the raw Cji = |Woi| x |Wji| [1] input-hidden and hidden-output will assign weights between each input neuron and output neuron. Summation of the ii. Overall connection weight: the sum of the input- products across all hidden neurons is done for finding out hidden-output connection weights for each input connection weights. Olden and Jackson, (2002) observed that variable the sensitivity analysis approach can determine the iii. Relative importance (%) for each input variable significance of the variables in the neural network. Negative based on Garson’s algorithm connection weights represent inhibitory effects on neurons Garson, 1991 gave the procedure for partitioning the and decrease the value of the predicted response, whereas connection weights to determine the relative importance of positive connection weights represent excitatory effects on various inputs. The method essentially involves partitioning neurons and increase the value of the predicted response. the hidden-output connection weights of each hidden neuron The sensitivity of the network is given by connection weights into components associated with each input neuron. used in the network architecture by means of the following calculations. i. For each hidden neuron h, multiplying the absolute (i) Input-hidden-output connection weights: the value of the hidden-output layer connection weight product of input-hidden and hidden-output by the absolute value of the hidden input layer connection weights for each input and hidden connection weight. This is donefor each input neuron(Table XII); variable j. The following product Pji is obtained For Input I = 1 to j where j = no. of variables, hidden Table XIV: x neurons h= 1 to i, where i = no. of hidden neurons The product Pji = |Woi| |Wji [2] 192   
 )'"$-*A11!          
Development of a blast-induced vibration prediction model using an artificial neural network

Table XII Table XIV -;=:?A5<>=;?>?>0A?>48=%/?99@>A;>9A<8=48=%/?99@> :<985=A<3A/?99@>A?>48=%<8=48=A5<>>@5=?<>A@?0/=7

5<>>@5=?<>A@?0/=7 +?99@>A1 +?99@>A+?99@>A?%1 +?99@>A?

+?99@>A1 +?99@>A+?99@>A?%1 +?99@>A? IInput 1 P(1,1) P(1,2) P(1,i-1) P(1,i) (2,i) Input 2 P(2,1) P(2,2) P(2,i-1) P Input 1 W(1,1) W(1,2) W(1,i-1) W(1,i) (3,2) Input 3 P(3,1) P P(3,i-1) P(3,i) Input 2 W(2,1) W(2,2) W(21,i-1) W(2,i) Input 3 W(3,1) W(3,2) W(3,i-1) W(3,i) Input 4 P(4,1) P(4,2) P(4,i-1) P(4,i) Input 4 W(4,1) W(4,2) W(4,i-1) W(4,i) Input j-1 P(j-1,1) P(j-1,2) P(j-1,i-1) P(j-1,i) Input j-1 W(j-1,1) W(j-1,2) W(j-1,i-1) W(j-1,i) Input j P(j,1) P(j,2) P(j,i-1) P(j,i) Input j W(j,1) W(j,2) W(j-1,i-1) W(j,i) Output W(0,1) W(o,2) W(0,i-1) W(o,i)

Table XIII Table XV <>=:?(8=?<>A<3A@;5/A?>48=A>@8:<>A==:?(8=?<>A<3A@;5/A>@8:<>A=A>@8:<> <8=00A7?0>;6A<3A@;5/A/?99@>A>@8:<>

+?99@>A1 +?99@>A+?99@>A?%1+?99@>A? +?99@>A1 +?99@>A+?99@>A?%1 +?99@>A?

Input 1 C(1,1) C(1,2) C(1,i-1) C(1,i) Input 1 Q(1,1) Q(1,2) Q(1,i-1) Q(1,i) Input 2 C(2,1)C(2,2) C(2,i-1) C(2,i) Input 2 Q(2,1) Q(2,2) Q(2,i-1) Q(2,i) Input 3 C(3,1) C(3,2) C(3,i-1) C(3,i) Input 3 Q(3,1) Q(3,2) Q(3,i-1)Q(3,i) Input 4 C(4,1) C(4,2) C(4,i-1) C(4,i) Input 4 Q(4,1) Q(4,2) Q(4,i-1)Q(4,i) Input j-1 C(j-1,1) C(j-1,2) C(j-1,i-1) C(j-1,i) Input j-1 Q(j-1,1) Q(j-1,2) Q(j-1,i-1) Q(j-1,i) Input j C(j,1) C(j,2) C(j-1,i-1) C(j,i) Input j Q(j,1) Q(j,2) Q(j,i-1) Q(j,i)

Table XVI &82A<3A?>48=A>@8:<>A:@6;=?.@A5<>=:?(8=?<>A<3A@;5/A/?99@>A>@8:<>A

+?99@>A1 +?99@>A+?99@>A?%1 +?99@>A? &82A&

Input 1 Q(1,1) Q(1,2) Q(1,i-1) Q(1,i) S1 = (Q(1,1) + Q(1,2) +..+ Q(1,i) Input 2 Q(2,1) Q(2,2) Q(2,i-1) Q(2,i) S2 = (Q(2,1) + Q(2,2) +..+ Q(2,i) Input 3 Q(3,1) Q(3,2) Q(3,i-1) Q(3,i) S3 = (Q(3,1) + Q(3,2) +..+ Q(3,i) Input 4 Q(4,1) Q(4,2) Q(4,i-1) Q(4,i) S4 = (Q(4,1) + Q(4,2) +..+ Q(4,i) Input j-1 Q(j-1,1) Q(j-1,2) Q(j-1,i-1) Q(j-1,i) Sj = (Q(j-1,1) + Q(j-1,2) +..+ Q(j-1,i) Input j Q(j,1) Q(j,2) Q(j,i-1) Q(j,i) Sj = (Q(j,1) + Q(j,2) +..+ Q(j,i)

ii. For each hidden neuron,Pjiis divided by sum for all the input variables to obtain Qji (Table XV). For example for Hidden neuron1, Q(1,1)= P(1,1)/ (P(1,1) + P(2,1)+………+ P(j,1)) Pji [3] i.e. Qji = ∑Pji (iii) For each input neuron sum the product Sj formed from the previous computation Qji (Table XVI). Sj = ∑ Qji [4]

iv. Sj is divided by the sum for all the input variables and expressed in terms of percentage, which gives the relative importance or distribution of all output weights attributable to the given input variable. Relative Importance Percentage = Sj/ ∑Sj [5] ?08:@A #:5/?=@5=8:@A<3A#,,A>@=<: ><6@90@A0;?>A( A7@>7?=?.?= A;>;6 7?7 Weights are plotted on the y axis (Figure 4), which gives a measure of sensitivity from least to highest sensitivity. The sensitive to the above variables. A negative sign indicates an graph shows that the maximum charge per delay and inverse relationship with blast-induced ground vibration. distance from the face have the highest sensitivity. This Other variables with moderate sensitivity are the blast design implies that blast-induced ground vibration (PPV) is highly parameters like spacing, burden, and depth. It is common

         
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 193 Development of a blast-induced vibration prediction model using an artificial neural network knowledge that some of the variables are related to blast- A database was prepared with the input variables varying at induced ground vibration but the degree of sensitivity of regular intervals within the range of values collected from the these variables is definitely knowledge gained from the mines. For one value of a variable there will be ten values of model output. The details of sensitivity analysis are given in the other variable. Keeping the remaining variables at their Table XVII and graphically represented in Figures 4 and 5. mean values, the selected variables were varied at regular intervals. A 3D plot (Figure 7) was constructed using area to A46<==?>0AA represent two input variables, distance of the monitoring Three-dimensional shaded graphs were drawn to study the station and charge per delay, and showing the model output responses of blast-induced ground vibration to the changes PPV. The following conclusions can be drawn from the plot. in various input variables. Out of the fifteen variables, only (a) PPV is more sensitive to changes in distance values of two variables were changed at a time, and the between the blast site and the monitoring station at remaining variables were kept constant at their mean values. distances greater than 150 m. In this manner a two-way interaction of variables or (b) PPV is more sensitive to charge per delay when sensitivity is created. The purpose is to study how ground distance between the blast site and the monitoring vibration is sensitive to the changes of these input variables. station is less than 150 m.

Table XVII <>>@5=?<>A@?0/=7A;>9A:@6;=?.@A?24<:=;>5@A3<:A=/@A>@8:;6A>@=<:A2<9@66?>0A

,;2@A<3A.;:?;(6@7A <>>@5 =?<>A@?0/=7 @6; =?.@A?24<:=;>5@A

No. of holes Nh 0.5 6.08 Hole diameter (m) Hdia -0.5 6.15 Hole depth (m) Hd 0.4 4.85 Burden (m) B 0.3 3.45 Spacing (m) S 0.5 5.97 Charge length (m) Cl 0 0.0 4 Stemming length (m) St -0.1 1.4 Max. explosive charge/hole (kg) Ed 2.4 29 .25 Charge per round (kg) Et -0.05 0 .88 Density of explosive (g/cm2) De 0.05 0.45 Young's modulus (GPa) E 0.4 4.6 3 Poisson's ratio P -0.3 3.5 3 P-wave velocity (m/s) Vp -0.2 2.3 3 Rock density (g/ cm2) Rd 0.05 0.64 Distance of monitoring point from face (m) DB -2.5 30.33

* Variables shown in Figure 4

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Development of a blast-induced vibration prediction model using an artificial neural network

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<>5687?<> artificial neural network. International Journal of Rock Mechanics and Mining Sciences, vol. 55. pp.108–16. An ANN model was developed using fifteen variables AMBRASEYS, N.R. and HENDRON, A.J. 1968. Dynamic behavior of rock masses. covering blast design, rock characteristics, and the distance Rock Mechanics in Engineering Practices. Wiley, London. pp. 203–207. between the blast site and monitoring station as input AMNIEH, H.B., MOZDIANFARD, M.R., and SIAMAKI, A. 2010. Predicting of blasting variables. The ANN model was found to perform better than vibration in Sarcheshmeh copper mine by neural network. Safety Science, the conventional models. Thus far, application of the ANN vol. 48, no. 3. pp. 319–25. AMNIEH, H.B., SIAMAKI, A., and SOLTANI, S. 2012. Design of blasting pattern in modelling technique to predict blast-induced ground vibration proportion to the peak particle velocity (PPV): artificial neural networks is limited and the number of input variables taken into approach. Safety Science, vol. 50, no. 9. pp. 1913–1916. consideration is small. In this research an attempt was made ARMAGHANI, D.J., HAJIHASSANI, M., MARTO, A., and MOHAMAD, E.T. 2015. Ground to train the model at three coal mining sites across India, vibration prediction in quarry blasting through an artificial neural network which are being operated under highly diverse geological and optimized by imperialist competitive algorithm. Bulletein of Engineering mining conditions. The predictive capability of the model was Geology and Environment, vol. 74, no. 3. pp. 873–886. further tested with a new set of data. An attempt was made ARMAGHANI, J.D., HAJIHASSANI, M., MOHAMAD, T.E., MARTO, A., and NOORANI, S.A. 2013. Blasting-induced flyrock and ground vibrationprediction through an to gain knowledge about ground vibration by analysis of the expert artificial neural network based onparticle swarm optimization. model output. The findings will help engineers to design Arabian Journal of Geoscience. doi:10.1007/s12517-013-1174-0 optimum blasting patterns for their mines. The paper BADAL, K.K. 2010. Blast vibration studies in surface mines.BS Thesis. provides a basis for future research on identification of some Department of Mining Engineering, National Institute of Technology significant variables that can further enhance the Rourkela. performance of the prediction model. Also, the applicability of BAHRAMI, A., MONJEZI, M., GOSHTASBI, K., and GHAZVINIAN, A. 2011. Prediction of rock fragmentation due to blasting using artificial neural network. the model can be further expanded by extensively training Engineering with Computers, vol. 27, no. 2. pp 177–181. the model using data from different opencast coal mining BAKHSHANDEH, A.H., MOZDIANFARD, M.R., and SIAMAKI, A. 2010. Predicting of sites. blasting vibrations in Sarcheshmeh copper mine by neural network. Safety Science, vol. 48, no. 3, pp. 319–325. @3@:@>5@7A BAKHSHANDEH, A.H., SIAMAKI, A., and MOHAMADI, S.S. 2012. Design of blasting pattern in proportion to the peak particle velocity (PPV): Artificial neural AK, H. and KONUK, A. 2008. The effect of discontinuity frequency on ground networks approach. Safety Science, vol. 50, no. 9. pp. 1913–1916. vibrations produced from bench blasting - a case study. Soil Dynamics BHADESHIA, H.D.K.H. 1990. Neural networks in materials science. ISIJ and Earthquake Engineering, vol. 28, no. 9. pp. 686–694. International, vol. 39. pp. 966–979 ALVAREZ, V.A.E., GONZALES, N.C., LOPEZ, G.F., and ALVAREZ, F.M.I. 2012. BUREAU OF INDIAN STANDARDS (BIS) 1973. Criteria for safety and design of Predicting blasting propagation velocity and vibration frequency using structures subject to underground blast. New Delhi, India.

         
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Predicting blast-induced ground vibration using various types of neural pp. 227–31. networks. Soil Dynamics & Earthquake Engineering, vol. 30. pp. 1233–1236. RAMCHANDRA , K. and SINGH , T.N. 2001. A computational approach for prediction of rock fragmentation. Mining Engineering Journal. pp. 16–25. MONJEZI , M., GHAFURIKALAJAHI, M., and BAHRAMI, A. 2011. Prediction of blast- induced ground vibration using artificial neural networks. Tunneling and RAGAM, P. and NIMAJE, D.S. 2018. Evaluation and prediction of blast induced Underground Space Technology, vol. 46, no. 7. pp. 1214–1222. peak particle velocity using artificial neural network: case study. Noise & MONJEZI, M., MEHRDANESH, A., MALEK, A., and KHANDELWAL, M. 2013a. Vibration Worldwide, vol. 49, no. 3. pp. 111–119. Evaluation of effect of blast design parameters on flyrock using artificial RAHMAN, N.H.A., LEE, M.H., LATIF, M.T., and SUHARTONO, S. 2013. Forecasting neural networks. Neural Computing and Applications, vol. 23, no. 2. of air pollution index with artificial neural network. Jurnal Teknologi pp 349–356. (Science and Engineering), vol. 63, no. 2. pp. 59–64. MONJEZI, M., AHMADI, Z., VARJANI, A.Y., and KHANDELWAL, M. 2013b. Backbreak https://ukm.pure.elsevier.com/en/publications/forecasting-of-air- prediction in the Chadormalu iron mine using artificial neural network. pollution-index-with-artificial-neural-network Neural Computing and Applications, vol. 23, no. 3-4. pp. 1101–1107. SAYADI, A., MONJEZI, M., TALEBI, N., and KHANDELWAL, M. 2013. A comparative MONJEZI, M., BAHRAMI, A., VARJANI, A.Y., and SAYADI, A.R. 2011 Prediction and study on the application of various artificial neural networks to controlling of flyrock in blasting operation using artificial neural network. simultaneous prediction of rock fragmentation and back break. Journal of Arabian Journal of Geosciences, vol. 4, no. 3-4. pp. 421–425. 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SINGH, T.N., KANCHAN, R., SAIGAL, K., and VERMA, A.K. 2004b. Prediction of TAWADROUS, A.S. and KATSABANI, P.D. 2005. Prediction of surface blast patterns p – wave velocity and anisotropic property of rock using artificial neural in limestone quarries using artificial neural networks. Fragblast, vol. 9, technique. Journal of Scientific & Industrial Research, vol. 63. pp. 32–38. no. 4. pp. 233-242. https://doi.org/10.1080/13855140600761863 SINGH, T.N. and SINGH, V. 2005. An intelligent approach to prediction and TAWADROUS, A.S. 2006. Evaluation of artificial neural networks as a reliable control ground vibration in mines. Geotechnical and Geological tool in blast design. International Society of Explosives Engineers, vol. 1. Engineering, vol. 23. pp. 249–262. pp. 1–12. SIVAPRASAD, P.V., MANDAL, S., VENUGOPAL, S., and RAJ, B. 2006. Artificial neural TRIVEDI, R. SINGH, T.N., and RAINA, A.K. 2014. Prediction of blast-induced network modeling of the tensile properties of indigenously developed flyrock in Indian limestone mines using neural networks. Journal of Rock 15Cr-15Ni-2.2Mo-Ti modified austenitic stainless steel. Transactions of Mechanics and Geotechnical Engineering, vol. 6, no. 5. pp. 447–454. the Indian Institute of Metals, vol. 59. no. 4. pp. 437–445. TRIVEDI, R., SINGH, T.N., MUDGAL, K., and GUPTA, N. 2014. Application of artificial neural network for blast performance evaluation. International SINGH, T.N., SINGH, A. and SINGH, C.S. 1994. Prediction of ground vibration Journal of Research in Engineering and Technology, vol. 3, no. 5. induced by blasting. Indian Mining Engineering Journal, vol. 33. https://www.researchgate.net/profile/Neel_Gupta/publication/273301349 p. 31–34. _APPLICATION_OF_ARTIFICIAL_NEURAL_NETWORK_FOR_BLAST_PERF SINGH, T.N. 2004a. Artificial neural network approach for prediction and ORMANCE_EVALUATION/links/5617df9108ae88df90e03c23/APPLICATI control of ground vibrations in mines. Mining Technology, Sec A, ON-OF-ARTIFICIAL-NEURAL-NETWORK-FOR-BLAST-PERFORMANCE- vol. 113, no. 4. pp. 251–6. EVALUATION.pdf SINGH, V.K., SINGH, D., and SINGH, T.N. 2001. A computational approach for VOGIATZI, E. 2002. Problems in regression analysis and their corrections. prediction of rock fragmentation. Mining Engineering Journal. pp. 16–25. http://www.oocities.org/qecon2002/founda10.html SISKIND, D.E., STAGG, M.S., KOPP, J.W., and DOWDING, C.H.1980.Structure YANG, Y. and ZHANG, Q. 1997. A hierarchical analysis for rock engineering response and damage produced by ground vibration from surface mine using artificial neural networks. Rock Mechanics and Rock Engineering, blasting. U.S. Department of the Interior, Bureau of Mines. vol. 30. pp. 207–22. TANG, H., SHI, Y., LI, H., LI, J., WANG, X., and JIANG, P. 2007. Prediction of peak ZHU, H.B. and WU, L. 2005. Application of gray correlation analysis and velocity of blasting vibration based on neural network. Chinese Journal of artificial neural network in rock mass blasting. Journal of Coal Science Rock Mechanics and Engineering, vol. 26, suppl. 1. pp. 3533–3539. and Engineering, vol. 11, no.1. pp. 44–47.

#44@>9?A# @.?@A<3A;.;?6;(6@A6?=@:;=8:@A<>A=/@A784@:?<:?= A<3A#,,7A<.@:A<=/@:A2<9@66?>0A=@5/>?8@7A?>A4:@9?5=?>0A2?>@ (6;7=%?>985@9A0:<8>9A.?(:;=?<> The empirical method for prediction of blast-induced vibration has been adopted by many researchers in the form of predictor equations. Predictor equations are site-specific and indirectly related to the physical, mechanical, and geological properties of the rock mass as blast-induced ground vibration is a function of various controllable and uncontrollable parameters. Rock parameters for the blasting face and propagation media for blast vibration waves are uncontrollable parameters, whereas blast design parameters like hole diameter, hole depth, column length of explosive charge, total number of blast-holes, burden, spacing, explosive charge per delay, total explosive charge in a blasting round, and initiation system are controllable parameters. For a blasting engineer it is essential to gain knowledge, which is otherwise very limited, about the interplay between the several blast variables, since a blasting engineer will have to design, by trial and error, an optimum blast-hole pattern to achieve a high powder factor and optimum fragmentation. In commonly used empirical models this knowledge base is not available as it is primarily based on two variables. ANN models are claimed to be better than empirical models. Also, in the case of empirical models it is not possible to predict PPV for new blast sites unless test shot are fired and the results are used for deriving two site constants. Some of the empirical predictors are highlighted in Table A.1

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1 Duvall and Petkof (1959) v = k(R/Q1/2)−b 12 Kahriman et al. (2006) v = 0.561D−1.432 2/3 b/2 b −α 2 Langefors and Kihlstrom (1963) v = k(Q/R ) 13 Rai and Singh (2004) v = kR− Qmaxe 3 Ambraseys and Hendron (1968) v = k(R/Q1/3)−b 14 Nicholson (2005) v = 0.438D−1.52 −1.63 2 b 4 Nicholls et al. (1971) v = 0.362D 15 Rai et al. (2005) Qmax = k(vD ) 5 IS 6922 (1973) v = k(Q2/3/R)1.25 16 Ozer (2008) (sandstone) v = 0.257D−1.03 6 Siskind et al. (1980) v = 0.828D−1.32 17 Ozer (2008) (shale) v = 6.31D−1.9 7 Ghosh and Daemen (1983) v = k(R/Q1/2)−be−αR 18 Ozer (2008) (limestone) v = 3.02D−1.69 8 Pal Roy (1991) v = n + k(R/Q1/2)−1 19 Ak et al. (2009) v = 1.367D−1.59 9 CMRI (1993) v = n + k(R/Q1/2)−1 20 Badal (2010) v = 0.29D−1.296 10 Kahriman (2002) v = 1.91D−1.13 21 Mesec et al. (2010) v = 0.508D−1.37 11 Kahriman (2004) v = 0.34D−1.79

v is the PPV (m/s); D is the scaled distance (m/kg1/2), which is defined as the distance R (m) divided by the square root of explosive charge mass Q (kg) net equivalent charge weight, i.e. D = R/Q1/2; k and b are site-specific constants. Generally, site constants k and b are determined by regression analysis of blasting results. Peak particle velocity (PPV) is a function of the borehole pressure, confinement, charge weight, distance from blast area, manner of decay of compressive waves through the rock mass, and the firing sequence of adjacent holes. In the case of empirical predictors there is no uniformity in the predicted result since different predictors give different values of PPV for various amounts of allowable charge per delay in the same operating area. (Dowding, 1985; Khandelwal and Singh, 2007; Monjezi et al., 2011). Moreover, empirical methods are unable to incorporate the numerous factors that affect the PPV and their complex interrelationships, hence the need for other techniques, including artificial neural networks (Khandelwal, 2010). Table A.2 highlights some of the applications of the ANN technique for modelling some of the detrimental effects of blasting. 198   
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Development of a blast-induced vibration prediction model using an artificial neural network

Table A.2 #,,A2<9@67

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Iphar, Yavuz, and Ak (2008) ANFIS DI, C PPV 44 R2 = 0.98 Bakhshandeh, Mozdianfard, and Siamaki (2010) ANN ST, DI ,C ,N PPV 29 R2 = 0.99 Monjezi et al. (2011a) ANN HD, ST, DI, C PPV 182 R2 = 0.95 Khandelwal, Kumar, and Yellishetty (2011) ANN DI, C PPV 130 R2 = 0.92 2 Mohamed (2011) ANN, FIS DI, C PPV 162 R ANN=0.94; 2 R FIS=0.90 Fisne, Kuju, and Hudaverdi (2011) FIS DI, C PPV 33 R2 = 0.92 Li, Yan, and Zhang (2012) SVM DI, C PPV 37 R2 = 0.89 2 Mohamadnejad et al. (2012) SVM, ANN DI, C PPV 37 R SVM=0.89; 2 R ANN=0.85 Ghasemi, Ataei, and Hashemolhosseini (2013) FIS B, S, ST, N, C, DI PPV 120 R2 = 0.95 Monjezi et al. (2013a) ANN C, DI, TC PPV 20 R2 = 0.93 Armaghani et al. (2013) ANN-PSO S, B, ST, PF, C, D, N, RD, SD PPV 44 R2 = 0.94 Hajihassani et al. (2014b) ANN-ICA BS, ST, PF, C, DI, Vp, E PPV 95 R2 = 0.98 Ghoraba et al. (2015) ANN BS, DI, C, ST, HL PPV 115 R2 = 0.98 Khandelwal and Singh (2005) ANN DI, C AOp 56 R2 = 0.96 2 Mohamed (2011) ANN, FIS DI, C AOp 162 R FIS=0.92; 2 R ANN=0.86 Khandelwal and Kankar (2011) SVM DI, C AOp 75 R2 = 0.85 Bakhshandeh, Siamaki, and Mohamadi (2012) ANN HD, S, B, N, D, ST, PF AOp 38 R2 = 0.93 Hajihassani et al. (2015) ANN-PSO HD, S, B, ST, PF, N, DI, C, RQD AOp 62 R2 = 0.86 Monjezi et al. (2010) ANN HD, BS, ST, PF, SD, N, C, RD Flyrock 250 R2 = 0.98 Rezaei et al. (2011) FIS HD, S, B, ST, PF, SD, RD, C Flyrock 490 R2 = 0.98 Monjezi et al. (2011) ANN HD, BS, ST, PF, D, SD, C, B Flyrock 192 R2 = 0.97 Monjezi et al. (2012) ANN-GA HD, S, B, ST, PF, SD, D, C, RMR Flyrock 195 R2 = 0.89 2 Ghasemi et al. (2012) SVM, ANN HL, S, B, ST, PF, SD, D Flyrock 245 R SVM=0.97; 2 R ANN=0.92 Mohamad et al. (2013) ANN HD, BS, ST, PF, C, D, N, RD, SD Flyrock 39 R2 = 0.97 Armaghani et al. (2013) ANN-PSO S, B, ST, PF, C, D, N, RD, SD Flyrock 44 R2 = 0.94 Monjezi et al. (2013b) ANN HD, S, B, D, C Flyrock 310 R2 = 0.98 Khandelwal and Monjezi (2013) SVM HL, S, B, ST, PF, SD Flyrock 187 R2 = 0.95 Marto et al. (2014) ANN-ICA RD, HD, BS, ST, PF, C, Rn Flyrock 113 R2 = 0.98 Trivedi, Singh, and Raina, (2014) ANN B, ST, qI, q, σc, RQD Flyrock 95 R2 = 0.98 2 Ghasemi et al. (2014) ANN, FIS HL, S, B, ST, PF, C Flyrock 230 R FIS=0.94; 2 R ANN=0.96 2 Armaghani et al. (2015) ANN, BS, ST, PF, C, DI PPV, Aop, 166 R ANFIS=0.77; 2 ANFIS Flyrock R ANN=0.94 2 R ANFIS=0.86; 2 R ANN=0.95 2 R ANFIS=0.83; 2 R ANN=0.96

B Blastability index q Specific charge B Burden qI Linear charge concentration BS Burden to spacing RD Rock density C Maximum charge per delay RMR Rock mass rating D Hole diameter RQD Rock quality designation DI Distance from the blasting face S Spacing E Young’s modulus Sb Subdrilling GA Genetic algorithm SD Specific drilling HD Hole depth ST Stemming HL Hole length SVM Support vector machine ICA Imperialist competitive algorithm TC Total charge N Number of row Vp P-wave velocity PF Powder factor σc Unconfined compressive strength PSO Particle swarm optimization

Khandelwal and Singh (2006) applied an ANN for predicting ground vibration by including relevant parameters for rock mass, explosive characteristics, and blast design. The ANN was trained by 150 data-sets with 458 epochs and 20 testing data-sets. The ANN was found to be superior to a conventional statistical relationship. The correlation coefficient determined by ANN for PPV was higher than that determined by statistical analysis. Khandelwal and Singh (2007) investigated the prediction of PPV at a magnesite mine in a tectonically active hilly terrain in the Himalayan region in India. This study established that the feed-forward back-propagation neural network approach seems to be the better option for predicting PPV in order to protect surrounding environment and structures. Khandelwal and Singh (2009) predicted PPV in a coal mine in India based on ten input parameters using an ANN technique. The network architecture was a three-layer, feed-forward back-propagation neural network with 15 hidden neurons. Input parameters were trained using 154 experimental and monitored blast records. Comparison of the results by using correlation and mean absolute error (MAE) for monitored and predicted values of PPV showed that that ANN results for the PPV were very close to the field data-sets compared to the conventional predictors and MVRA predictions. Monjezi et al. (2010) predicted blast-induced ground vibration using various types of neural networks such as multi-layer perceptron neural network (MLPNN), radial-basis function neural network (RBFNN), and general regression neural network (GRNN) at Sarcheshmeh copper mine, Iran. MLPNN gave the best results, with a root mean square error and correlation coefficient of 0.03 and 0.954 respectively. ANN, multivariate regression analysis (MVRA), and empirical, analysis were used by Kamali and Ataei (2010) to predict the blast-induced PPV at the Karoun III power plant and dam.

         
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 199 Development of a blast-induced vibration prediction model using an artificial neural network

Table A.2 #,,A2<9@67A5<>=?>8@9

The best model was the ANN, since its outputs were highly correlated to the measured and observed data. Tang et al. (2007) developed a back- propagation neural network model to predict the peak velocity of blast vibration. They considered the charge hole diameter, distance, depth, column distance between charge holes, line of least resistance, maximum charge of single hole, maximum charge weight per delay, stemming length, total charge, magnitude of relative altitude and explosive distance as input parameters and found the predicted results from the ANN closer to the measured values than those from empirical predictors. Singh and Singh (1995) studied the blast-induced ground vibration at Dharapani magnesite mine, Pitthoragarh Himalaya in India and predicted PPV using neural networks. The artificial intelligence method of simulating and predicting ground vibration due to blasting is accurate, reliable, practical, user-oriented, and easy to operate as well as useful for engineers (Lianjon, Guojian, and Yingxian, 2002). Neural network models provide descriptive and predictive capabilities and, for this reason, have been applied through the range of rock parameter identification and engineering activities (Hudson and Hudson, 1997). A number of conventional statistical, empirical equations and ANN systems have been employed by various researchers to predict rock fragmentation, ground vibration and air blast prior to blasting operations. However, the ANN is preferred over the other predictive techniques due to its ability to incorporate the numerous factors affecting the outcome of a blast among other advantages. The ANN model generated is site specific, the input parameters can be expanded to include mechanical and geotechnical rock parameters such as rock strength, RQD, rock hardness, number of joints etc. to provide the ANN model a wider application. The artificial intelligence method of simulating and predicting blasting is accurate, reliable, practical, user-oriented, and easy to operate as well as useful for engineers (Lianjon, Guojian, and Yingxian, 2002). Cai and Zhao (1997) discussed ANN applications and incorporated the numerous factors that affect the PPV and their complex interrelationships. Chakraborty et al. (2004) underlined the effectiveness of multilayer perceptron (MLP) networks for estimation of blasting vibration and proposed a fusion network that combines several MLPs and on-line feature selection technique to obtain more reliable and accurate estimations compared with the empirical predictors. Mohamed (2009) used three different variations of ANN for prediction of PPV due to blast-induced ground vibrations and observed that the ANN using a large number of inputs parameters gave better prediction of PPV than an ANN using one or two inputs parameters. Also, the ANN model with two input parameters provided better results than the model with one input parameter. That is to say, increasing the number of input variables improves the ability of the ANN to learn and to predict more precisely. Singh (2005) attempted to predict the ground vibration in Indian coal measure rocks using ANN and confirmed that the network provided better results than a conventional multivariate regression method. PPV is generally used to assess potential blast vibration damage to structures on surface, but this parameter cannot fully explain the effect on structures situated far from the point of blasting and which can be damaged even at very low PPVs. (Ramchandar and Singh, 2001; Singh, Singh and Singh, 1994). The longer wavelength and smaller amplitude of these vibrations damage structures more severely than higher amplitude, shorter wavelength vibrations (Perrson, 1997). Maity and Saha (2004) used a neural network to assess damage in structures due to variation of static parameters. Using ANN, P-wave velocity and anisotropic property of rocks were investigated by Singh et al. (2004a). Lu (2005) studied the blast- induced ground shocks using an ANN at underground mines. Singh and Singh (2005) studied the dynamic constants of rock mass with a neural network and neuro-fuzzy system. This literature review provides a broad overview of the wide application of the ANN modelling technique. The observations quoted by several researchers, as discussed above, establish the superiority of ANN as modelling technique in predicting blast-induced ground vibration .

SAMCODES CONFERENCE 2019 Best Practice An Industry Standard for Mining Professionals in South Africa 8–9 October 2019 Birchwood Hotel & OR Tambo Conference Centre, Johannesburg

OBJECTIVES The conference provides Competent Persons and Competent Valuators the opportunity to prepare and present details of recognised standards and in- dustry benchmarks in all aspects of the SAMREC and SAMVAL Codes. These contributions will be collated into a Companion Volume to provide a guideline and industry standard for the public reporting of Exploration Results, Mineral Resources and Mineral Reserves and the Valuation of Mineral Projects. The conference will provide a wide range of information pertaining to industry best practice including aspects of a various geological deposit types, commodities, permitting and legal obligations, resource estimation, mining engineering methodologies, metallurgical and process arrange- ments, engineering/infrastructure design, social and environmental factors etc for SAMREC Code reporting. Other papers will cover the application of the various methods of valuation and where and when they should be applied in accordance with the SAMVAL Code.

For further information contact: Camielah Jardine, Head of Conferencing, SAIMM, E-mail: [email protected], Website: http://www.saimm.co.za 200   
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http://dx.doi.org/10.17159/2411-9717/2019/v119n2a12 Changes in subsidence-field surface movement in shallow-seam coal mining

by X-J. Liu* and Z-B. Cheng†

hygiene, and economic development. Deterioration of the ecological environment in    mining areas has a long history and is very Intensive mining of shallow coal seams tends to result in severe harmful (Lu, 2015). subsidence of the ground surface. Surface subsidence is a complex Surface subsidence is an extremely dynamic spatiotemporal process that constantly changes as mining important control index for underground advances. With Liangshuijing coal mine as a case study, 3DEC numerical software was used to simulate the development of the moving subsidence excavations. Many experts and scholars have field from open-off cut to full subsidence on the working face. The results devoted resources to the research and demonstrate that the formation of a subsidence field is directly related to remediation of damage caused by coal mining the coal seam depth H and the extent of the mine workings. Taking the from the surveying, numerical simulation, advance distance of the working face as the unit of scale, the process of mathematical, mechanical, geological, and surface subsidence can be divided into four stages: micro-change (H/π), mining engineering points of view. These the development of surface subsidence (2H/π), the formation of a studies have revealed general laws of mining π π movement subsidence field (3H/ ), and dynamic balance (4H/ ). The subsidence (Hu, 2012). The most prominent changing movement of a subsidence field can be fully described by the characteristic of these is that surface characteristics of surface subsidence value, curve slope, and the inflection subsidence has an obvious time-dependency, position. The results provide important technical support for predicting surface subsidence and the temporal–spatial evolution features of mining and may continue for several months, or even subsidence. years, from the start to the end of surface movements. Since the 1970s, with the wide    application of computer methods, numerical coal seam, subsidence, surface movement, mining. simulation has been increasingly applied in the calculation of mining subsidence and the analysis of subsidence mechanisms, and many experts and scholars have undertaken research in this field, such as Dahl and Choi (1981).
    The West German scholar Kratzsch (1974) China’s coal output was about 3.52 Gt in 2017 summarized methods of predicting coal mining (China National Coal Association, 2018), subsidence in his book ’Mining Damage and making it the largest coal producer in the Protection’. Ma and Yang (2001) researched world, accounting for almost half of total world the spatial and temporal effects of rock coal production. Coal production and movement using the discrete element method. distribution play a vital role in the energy Cui and Deng (2017) carried out a real-time industry of China. However, entire overlying displacement analysis of surface movement strata, from coal seam to surface, are disturbed and deformation for the main section of a coal as a result of long-term, high-intensity and mine, and studied mining subsidence utilizing large-scale mining, causing surface a rheological model. subsidence. This results in groundwater loss, Surface subsidence continually changes surface desertification, vegetation loss, and during the exploitation of a mining face; mud-rock flows. These issues have become topics of common concern throughout society. According to related research results (Liu 2008), the area of surface subsidence caused by coal mining in China has reached about 600 * State Key Laboratory of Water Resource 000 ha, some 0.2 ha (and up to 0.42 ha) of Protection and Utilization in Coal Mining, surface subsidence for every 10 000 t of coal Beijing, China. produced. Surface subsidence disasters not † Department of Ground Engineering, School of Engineering, University of Warwick, Coventry, only damage buildings, water conservancy, United Kingdom. transportation infrastructure, and farmland, © The Southern African Institute of Mining and but also cause adverse effects on individual Metallurgy, 2019. ISSN 2225-6253. Paper received and community lifestyles, environmental Nov. 2017; revised paper received Aug. 2018.

         
 
  
 201 Changes in subsidence-field surface movement in shallow-seam coal mining

The maximum surface subsidence occurs in the middle of the goaf. Therefore, the surface displacement curve, which is shown in Figure 2, can be obtained by taking the distance of advance of the working face as the X axis and the central axis (Y axis) of the surface subsidence basin as a vertical section. Surface subsidence changes as the coal seam is mined, "6-,.7
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 VOLUME 119          
Changes in subsidence-field surface movement in shallow-seam coal mining

subsidence behind the goaf is no longer affected by mining and is stable on the goaf side. Moreover, if the deviation of the inflection point of curve S1 is equal to the mining height (M), a moving subsidence field in front of the goaf is gradually formed until the advance distance increases to 4H/π, at which time a basin begins to form. If the advance distance exceeds 4H/π, the dynamic balance stage (IV) is established, represented by the curves W10, W11, and W12. The moving subsidence "6-,.7
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VOLUME 119          
  
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Roof Aeolian sand 20 2635 33 32 2 38 1 Mild clay 36 1370 8 7.3 0.4 20 0.3 Medium -coarse grained sandstones 20 2635 20 10 0.1 18 0.1 Medium -grained sandstone 24 2560 10 10 0.4 19 0.6 Fine-grained sandstones 7 2635 10 10 0.8 20 0.9 Coal seam 4-2 coal seam 3 2220 8 4 0.1 15 0.4 Floor Siltstone 10 2560 8 4 0.1 15 0.04

employed in the numerical simulation model are shown in the side of the goaf. Therefore, to discuss changes in the Table I. The Mohr–Coulomb failure criterion was adopted. inflection point of the subsidence curve in detail, the front According to Peng (2006), there is a critical value of the side of the advancing goaf was defined as the front inflection working face width (B) that is linearly related to mining point of the surface subsidence curve; similarly, the back and depth (H) when the ground surface is fully subsided. lateral side of the advancing goaf were defined as the back Therefore: B = 100 + 1.048H = 212 m. Because the length of and lateral inflection points, respectively. Changes in the this model was 500 m and the width of the boundary coal inflection point of the surface subsidence curve as the pillars on both sides was 80 m, the advance distance was working face advances are shown in Figure 6. 340 m, which is approximately π times the mining depth (H). The red curve in Figure 6 indicates the change of the From the above result, it can be seen that the length of the inflection point in front of the goaf with advance of the working face was larger than the critical length of full working face. Overall, the location of the inflection point at mining. the side of the goaf showed an approximately linear relationship with the advance distance of the working face ,.+407
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 VOLUME 119          
Changes in subsidence-field surface movement in shallow-seam coal mining working face. The starting position of the inflection point was Figure 7. These curves show that the peak value of ten times the mining height on the side of the coal body subsidence bore little relation to the length of the working behind the open-off cut. As the working face advanced, the face and the amount of subsidence increased with advance of inflection point became offset to the side of the goaf. When the mining distance. The peak value of surface subsidence no movement of the subsidence field remained at the stage of longer increased and began to stabilize when the advance micro-change and development (i.e., the advance distance distance reached 4H/π and movement of the subsidence field was less than 2H/π), the location of the inflection point was occurred. Similarly, the subsidence increased with working always stable at the side of the coal body; its location face mining in the stages of micro-change and development transfers to the side of the goaf during the stage of to the back and front boundary points of the excavation. movement of the stress field. Finally, when the advance However, the back boundary point was static, so the distance exceeded 4H/π, the inflection point position subsidence increased to a certain extent and was then no stabilized at 3 m on the side of the goaf in the dynamic longer influenced by mining when the advance distance equilibrium stage. exceeded 2H/π, which meant that the initial subsidence field The blue curve shows changes of the inflection point had formed. For the front boundary point, the next value lateral to the goaf with advance of the working face. Because fluctuated and the subsidence value was always lower than the length of the working face was much larger than the that of the rear value because of moving abutment pressure. advance distance in the initial stage, the deflection velocity of Regarding the lateral boundary settlement, there was no the lateral region was obviously greater than that of the front change when the advance distance reached 160 m, which and back, thus the inflection point was transferred from the was less than the empirically calculated critical value of about coal body to the goaf in the micro-change stage, and then to 240 m, because the length of working face (240 m) was deep in the goaf in the development stage. Finally, the larger than 4H/π. Therefore, if the size of the excavation is location of the inflection point returned some distance and less than 2H/π, the ground surface does not form a stabilized at 7 m, which can be calculated by the formula movement subsidence field; if the excavation size is less than (πBM)/(2H). 4H/π, a movement subsidence field can form. However, the working face can reach the full mining extent and the moving       stress field can enter the dynamic balance stage without the 
    advance distance reaching the length of the working face The process of surface subsidence caused by underground once the excavation size exceeds 4H/π. mining is a complex space-time phenomenon. In theory, the amount of subsidence is equal to the increase in underground        space; in fact, surface subsidence does not have the same The distribution and process of change of a surface subsidence value at different positions of the goaf due to the continuous curve caused by coal seam mining can be represented by the advance of the working face. The changes in the amount of slope of the subsidence curve. The changes in slope of the subsidence of the boundary point and the maximum surface subsidence boundary curve about the working face are subsidence of the surface are shown in Figure 7 from the shown in Figure 8 for the open-off cut to an advance distance open-off cut to a position at which the advance distance of of the working face equal to its length. the working face is equal to its length (L=B). The slopes on the front, back, and lateral side of the goaf The maximum subsidence of the surface caused by can indicate changes in the surface subsidence curve. The excavation is shown as the green and pink curves in curve obviously underwent fluctuation, which meant that

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VOLUME 119          
  
 205 Changes in subsidence-field surface movement in shallow-seam coal mining

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* surface subsidence exhibited a non-uniform velocity working face, and advance distance are designated H, B, and variation as the working face advanced. When the width of L, respectively, the distance of the micro-change stage varies the working face exceeded 4H/π, the slope of the lateral from zero to H/π, that of the development of surface surface subsidence curve always increased until it stabilized. subsidence varies from H/π to 2H/π, the formation of the The slope of the subsidence curve is affected by mining moving subsidence field varies from 2H/π to 4H/π, and the and can fluctuate in the micro-variable stage. It then range of the dynamic balance stage exceeds 4H/π. The width constantly increases in the development stage, finally of the basin that is formed by surface subsidence is the reaching a peak value before decreasing again during the maximum value of both (B – H) and B/2 or (L − 4H/π). stage of subsidence field formation. The slope therefore These results can provide scientific guidance for green mining displays significant variation when the advance distance is and ecological mitigation and control. 2H/π. With continuous advance of the working face, the slope decreased until the advance distance equalled 4H/π, at 80'52&(7)-*753 which point the slope tended to stabilize. The slope of the This research is funded by the National Key Basic Research subsidence curve on the front side of the surface rises sharply Program (2016YFC0501100). The authors are grateful to from the open-off cut, reaches a peak value when the their State Key Laboratory of Water Resource Protection and advance distance is 2H/π, then drops continuously until the Utilization in Coal Mining for their help and Kathryn Sole, advance is 4H/π where it reaches a local minimum; however, PhD, for editing the English. it begins to increase again during the full mining stage. In summary, the slope of the front subsidence curve is in a 7+7.75071 weak fluctuation and cannot be stabilized due to the China National Coal Association. 2018. Annual report on China's coal industry influence of the working face excavation. The slope of the in 2017. surface subsidence curve at the back of the goaf is always Choi, D.S. and Dahl, H.D. 1981. Measurement and prediction of mine greater than that of the lateral side, which indicates that the subsidence over room and pillar in three dimensions. Proceedings of the slope in the advancing direction is always larger than that of Workshop on Subsidence due to Underground Mining. Peng, S.S. (ed.). inclination. West Virginia University, Morgantown, WV. pp. 34–47. Cui, X.M, and Deng, K.Z. 2017. Research review of predicting theory and method for coal mining subsidence. Coal Science and Technology, vol. 45. 250(,1625 pp. 160–169. Surface subsidence is a gradual process of formation and Hu, H.F. 2012. Research on surface subsidence regularity and prediction under development, the characteristics of which are related to burial composite media with different thickness rations of loose bedrock. PhD depth and the dimensions of the excavation. The distances of thesis, Taiyuan University of Technology. influence of the movement subsidence field at the front of the Kratzch, H 1983. Mining Subsidence Engineering. Springer-Verlag, Berlin, coal body and the side of goaf are H/π and 2H/π, Heidelberg. respectively. The width of the basin can be calculated by Liu, Z. 2008. Research on the deformation rule of surface movement caused by π mining under the conditions of thick alluvium and hard solid rock. reducing the working face advance distance by 4H/ . Master's thesis, Xi`an University of Science and Technology. According to the ratio of burial depth to advance distance and Lu, T.T. 2015. Surface change detection using InSAR technology. Master's the characteristics of the movement subsidence field, the thesis, Chang'an University. evolution of the surface subsidence curve can be divided into Ma, F.H. and Yang, F. 2001. Research on numerical simulation of stratum four stages: the micro-change stage, the development of subsidence. Journal of Liaoning Technical University Natural Science, vol. surface subsidence, formation of a moving subsidence field, 20. pp. 257–261. and dynamic balance. When the burial depth, width of the Peng, S.S. 2011. Longwall Mining, 2nd edn. Science Press, Beijing. 206   
 VOLUME 119          
http://dx.doi.org/10.17159/2411-9717/2019/v119n2a13 Recycling pre-oxidized chromite fines in the oxidative sintered pellet production process

by S.P. du Preez*, J.P. Beukes*, D. Paktunc†, P.G. van Zyl*, and A. Jordaan*

According to this review, FeCr is principally produced in (i) conventional open/semi-closed    submerged arc furnaces (SAFs) that are The chromium (Cr) content of stainless steel originates from recycled scrap mainly fed with lumpy (typically 6–150 mm) and/or ferrochrome (FeCr), which is produced mainly by the carbothermic chromite ore, fluxes. and reductants, (ii) reduction of chromite ore. The oxidative sintered pellet production process closed SAFs that are fed with oxidative is one of the most widely applied FeCr processes. The supplier of this sintered chromite pellets, as well as lumpy technology specifies that recycling of chromite-containing dust collected reductants and fluxes, (iii) closed SAFs fed from the pellet sintering off-gas and fines screened out from the sintered with prereduced chromite pellets, as well as pellets (collectively referred to as pre-oxidized chromite fines) should be lumpy reductants and fluxes, and (iv) closed limited to a maximum of 4 wt% of the total pellet composition. However, direct current (DC) arc furnaces fed with fine the results presented in this paper suggest that recycling of such fines up to a limit of 32 wt% of the total pellet composition may improve the (typically
6 mm) chromite ore, fluxes, and compressive and abrasion strengths of the cured pellet. In addition, reductants. Of particular interest for the present electron microprobe and quantitative X-ray diffraction (XRD) analyses paper is the oxidative sintered pellet process, demonstrate that chromite grains present in the pre-oxidized chromite which is commercially known as the Outotec fines consist, at least partially, of crystalline phases/compounds that will steel belt sintering process (Outotec, 2017). improve the metallurgical efficiency and specific electricity consumption Various authors have previously described (i.e. MWh/ton FeCr produced) of the smelting process. the oxidative sintered pellet production process    (Riekkola-Vanhanen, 1999; Beukes, Dawson, Chromite, ferrochrome, ferrochromium, pre-oxidation, oxidative sintering, and van Zyl, 2010; Basson and Daavittila, recycling. 2013). Chromite fines (typically
1mm) are wet milled together with a small percentage of a carbonaceous material that serves as an energy source during sintering. The grain size specification that must be obtained during milling is typically a d80 of 74 μm (80%
    passing size of 74 μm). Ceramic filters are Stainless steel is a vital modern-day alloy that used to dewater the milled slurry to a moisture is well-known for its corrosion resistance, content of below 9%. A fine clay binder which is mainly due to the inclusion of (usually refined bentonite) is then mixed into chromium (Cr) (ICDA, 2013). Stainless steel is the moist filter cake with a high-intensity mostly produced from recycled scrap and mixer, and the moist mixture is pelletized in a ferrochrome (FeCr), a relatively crude alloy of pelletizing drum. The newly formed pellets are Cr and iron (Fe). FeCr is predominantly screened on a roller screen. Oversized pellets produced by the carbothermic reduction of are broken down and recycled, together with chromite, a mineral belonging to the spinel undersized pellets. This leads to fairly group characterized by the unit formula homogeneously sized green (uncured) pellets [(Mg,Fe2+)(Al,Cr,Fe3+)2O4] (Haggerty, 1991; with an average diameter of approximately Paktunc and Cabri, 1995; Tathavakar, Antony, 12 mm. The green pellets are then layered on a and Jha, 2005). Although Cr can occur in 82 different minerals, chromite is the only source of new Cr units that can be exploited in commercial volumes (Motzer and Engineers, 2004). Approximately 95% of mined chromite is used in the production of various FeCr * Chemical Resource Beneficiation (CRB), North- grades, of which high-carbon and charge West University, Potchefstroom, South Africa. † CanmetMINING, Natural Resources Canada, grade FeCr are the most common (ICDA, Ottawa, Canada. 2013). © The Southern African Institute of Mining and Beukes et al., (2017) recently presented a Metallurgy, 2019. ISSN 2225-6253. Paper received review of FeCr production processes. Dec. 2017; revised paper received Aug. 2018.

         
 
  
 207 Recycling pre-oxidized chromite fines in the oxidative sintered pellet production process perforated steel belt, which carries the pellets through a homogeneous, representative sample, a bulk sample of multi-compartment sintering furnace. The perforated steel approximately 320 kg was taken by manually collecting belt is protected against excessive temperatures by a layer of shovel loads of material at various points and various heights previously sintered pellets below the green pellets. The of the ore stockpile. The bulk sample was then split at the temperature of the pellet bed gradually increases as it passes laboratory of the FeCr producer three times with a riffle-type through the sintering furnace, reaching a maximum of sample splitter to yield a sample of approximately 80 kg, approximately 1400 to 1500°C. Sintered pellets are then which was transported to the laboratories at the Chemical cooled by air blown through the pellet bed from below. Resource Beneficiation (CRB) unit, North-West University. Thereafter, the sintered pellets are discharged and screened There, the sample mass required for a specific experiment to remove < 6 mm material, but screening at a smaller was obtained by splitting the sample further using a vibrating aperture has also been observed by the authors during plant feeder that fed a rotating tray of containers. Previously, visits at FeCr producers applying this process. The overall Glastonbury et al., (2015) presented a detailed process produces porous and mechanically strong pellets characterization of this case study ore, therefore such a suitable for SAF smelting (Riekkola-Vanhanen, 1999), which characterization is not repeated here. In short, the ore results in improved SAF stability and metallurgical efficiency, contained 44.19 wt% Cr2O3, 24.68 wt% FeO, 14.71 wt% as well as lower energy consumption compared with Al2O3, wt% 10.31 MgO, and 2.96 wt% SiO2, and had a Cr/Fe conventional SAF smelting of lumpy ore (Basson and ratio of 1.58 (Glastonbury et al., 2015). This composition is Daavittila, 2013). representative of a typical South African metallurgical grade The suppliers of the steel belt sintering technology chromite ore (Cramer, Basson, and Nelson, 2004). It has to indicated that chromite-containing dusts collected from the be considered that a substantial fraction of the chromite pellet sintering scrubber and fines screened out from the smelted outside South Africa originates from South Africa. In sintered pellets can be re-introduced into the moist material 2012 for instance, 28% of the chromite ore consumed in the mixture that is pelletized (Basson and Daavittila, 2013). rest of the world originated from South Africa (Kleynhans et However, it is specified that the addition must be limited to a al., 2016). Therefore, the results generated from the case maximum of 4 wt% of the total pellet composition, since this study ore are of international relevance. material is believed to adversely affect pellet quality (Basson A sample of chromite fines screened out from industrially and Daavittila, 2013). The fundamental reasoning behind produced sintered pellets was obtained from a large FeCr this limitation is not stated in the public peer-reviewed producer in South Africa that utilizes the oxidative sintered domain. A recent personal communication indicated that pellet production process. In this paper, this material is specifically, pellet strength deteriorates with increasing referred to as ‘pre-oxidized chromite’. This material was content of recycled pre-oxidized fines (Päätalo, 2018). This sampled in a similar manner as the ore. Refined bentonite can be countered by increasing the clay binder and carbon (binder) and coke fines (carbon fuel source), which were contents in the green pellets. However, an increased carbon used to produce oxidative sintered pellets at the content could lead to higher sintering temperatures, which aforementioned FeCr producer, were also obtained. may result in a shorter operational life of the steel sintering Kleynhans et al., (2012, 2017) previously presented full belt (Päätalo, 2018). characterizations of the bentonite and coke fines (sample Co5 The authors were approached by a FeCr producer at in Kleynhans et al., 2017), therefore this information is not which the generation of pre-oxidized fines, originating from repeated here. the sintering scrubber and screening of the sintered pellets, exceeds the 4 wt% limitation. This has resulted in the          accumulation of pre-oxidized fine chromite stockpiles. Pre- Material for pelletization experiments was prepared by dry oxidized chromite requires less energy to metallize compared milling a 50 g mixture, consisting of 1.5 wt% coke, with to normal chromite (Kapure et al., 2010). Furthermore, the chromite the balance, for 2 minutes in a Siebtechnik reduction of oxidative sintered pellets requires less energy laboratory disc mill. Prior to milling, all materials were dried (Zhao and Hayes, 2010) and pre-oxidation of chromite fines in an oven overnight at 75°C to enable accurate and significantly improves prereduction (solid-state reduction) of repeatable batching of the mixtures. A tungsten carbide chromite (Kleynhans et al., 2016, 2017). Considering these grinding chamber was used to avoid possible Fe energy-related benefits, the authors believe that all pre- contamination. This milling procedure yielded a particle size oxidized fine chromite should be recycled on-site at FeCr distribution with a d80 of 75 μm, which is similar to the producers. With this in mind, the possible recycling of pre- industrial particle size specification, i.e. d80 of 74 μm (Basson oxidized chromite fines into oxidative sintered pellets beyond and Daavittila, 2013; Glastonbury et al., 2015). After milling, the current limitation of 4 wt% pellet composition was refined bentonite was added to obtain a mixture with a investigated, considering both fundamental and practical composition of 97.52 wt% ore, 1.49 wt% coke, and 0.99 wt% aspects. bentonite. The pelletization mixture was then vigorously blended for 15 minutes using a laboratory-scale Eirich-type 478564-1943/9)87.2/1 mixer. As-received pre-oxidized chromite was then added to the pelletization mixture to obtain mixtures containing 4, 8,    16, 32, and 64 wt% pre-oxidized chromite. No additional A metallurgical grade chromite ore sample was received from coke or bentonite was added to these mixtures to compensate a large FeCr producer in South Africa, which served as the for the addition of pre-oxidized chromite, since this is also case study ore in this investigation. To obtain a the practice in industry. 208   
 VOLUME 119          
Recycling pre-oxidized chromite fines in the oxidative sintered pellet production process

Green pellets containing the various percentages of pre- ambient atmosphere. The sintering process also took place in oxidized chromite were generated using a laboratory-scale an ambient gaseous environment and no dwelling time was disk pelletizer. The laboratory disk pelletizer consisted of a allowed at the maximum temperature, in order to mimic the 600 mm diameter flat steel disk with a 150 mm deep rim. The industrial process as closely as possible. entire disk and rim were pressed from a single steel plate and the connection area between the disk and rim was rounded to      limit material build-up. The pelletizer rotated at a speed of Scanning electron microscopy (SEM) equipped with energy 40 r/min and a constant angle of 60° to the horizontal was dispersive X-ray spectroscopy (EDS) was used to perform maintained in all experiments. Fine water spray was surface characterization of the sintered pellets in secondary introduced to the mixture with a handheld spray bottle to electron mode. An FEI Quanta 250 FEG instrument initiate pellet nucleation, i.e. formation of micro-pellets. incorporating an Oxford X-map EDS system operating at Thereafter, the micro-pellets were grown by continuously 15 kV and a working distance of 10 mm was used. Pellets wetting of their surfaces with water spray and introducing were split in half and mounted on aluminium stubs, or were new, dry feed until the desired pellet diameter was achieved. set in resin and polished with a SS20 Spectrum System Material build-ups on the bottom, side, and pelletizer corner Grinder polisher before being mounted on the stubs. The (connecting area between disk and rim) were continuously polished resin-embedded samples were coated with carbon in loosened with a fit-for-purpose handheld scraper to facilitate an Emscope TB 500 carbon coater prior to SEM analysis. the inclusion of this material into the pellets. This scraper Resin-embedded polished pellets were imaged in had a flat edge to remove material build-up from the disk and backscattered electron mode, and un-embedded pellets in the rim, as well as a rounded point to remove material build- secondary electron mode. up from the corner. Pellets with a diameter of > 11 and Crystalline phase analysis of bulk samples was performed < 13 mm were collected by screening. Care was taken to by X-ray diffraction (XRD) using two methods: ensure a consistent pellet moisture content, with all pellets A Rigaku D/MAX 2500 rotating-anode powder used in further experiments containing 5.5 ± 0.7 wt% diffractometer with Cu K
radiation at 50 kV, 260 mA, moisture. Pellet moisture contents were determined with an a step-scan of 0.02º, and a scan rate at 1/min in 2 ADAM PMB 53 moisture balance. Green pellets were allowed hours from 5 to 70º. Phase identification was to dry in an ambient atmosphere after collection before performed using JADE v.3.9 with the ICDD and ICSD oxidative sintering experiments proceeded. diffraction databases         A Röntgen diffraction system (PW3040/60 X’Pert Pro) and a back-loading preparation method to determine As previously stated, Basson and Daavittila (2013) indicated the crystalline phases, and their percentages, present in that industrially produced oxidative sintered pellets are size-partitioned samples and milled mixtures. heated to maximum temperatures of between 1400 and 1500°C. Glastonbury et al., (2015) mimicked the industrially The samples were scanned using X-rays generated by a applied process on the laboratory scale, with a temperature copper (Cu) K
X-ray tube. Measurements were carried out profile that attained a maximum temperature of 1400°C. between variable divergence and fixed receiving slits. Phases However, these authors did not verify how deep into the were identified using X’PertHighscore plus software. Phase pellets oxidation proceeded. Zhao and Hayes (2010) proved refinement was performed using the Rietveld method (Hill that only the outer chromite grains of industrially produced and Howard, 1987). oxidative sintered pellets are partially oxidized, while the Further analysis was undertaken by mounting cross- chromite grains deeper into the pellets are not oxidized. Heat sectioned polished pellets on glass slides and carbon-coating transfer to pellets in laboratory conditions, where small them prior to electron microprobe analysis (EMPA). Analysis amounts of pellets are sintered in batches with very effective was performed using a JEOL JXA-8900 electron microprobe furnaces, will be significantly superior to that in industrial fitted with five wavelength-dispersive spectrometers at an furnaces, where very large quantities are treated accelerating voltage of 20 kV and beam current of 26 nA. continuously. Therefore, rather than blindly selecting a maximum sintering temperature, or applying the temperature           profile used by Glastonbury et al., (2015), the authors tested The compressive strengths of sintered pellets were various maximum temperatures. A Lenton Elite camber determined using an Ametek Lloyd Instruments LRXplus furnace (UK, Model BRF 15/5) with a programmable 5 kN strength tester. NEXYGENPlus material test and data temperature controller was used for sintering. The analysis software was used to capture and process the temperature probe of this furnace was situated inside the generated data, as well as to control and monitor all aspects heating chamber, which ensured that the recorded of the system. The speed of the compression plates was kept temperature and the actual pellet temperatures correlated to 10 mm/min during compressive strength tests in order to well. Prior to oxidative sintering, the pellets (in a 99.7% apply an increasing force on the prepared pellets. The Al2O3 ceramic crucible) and furnace were pre-heated to 100 maximum load to induce pellet breakage was recorded. and 900°C, respectively. A pellet batch (consisting of 25 Standard deviations were calculated based on 10 pellets) was then placed in the furnace and the temperature experimental repetitions. was ramped up from 900°C to the designated maximum The abrasion resistance apparatus used in this study was temperature at a rate of approximately 17°C/min. Once the based on a downscaled version of the European Standard EN designated maximum temperature was reached, the pellets 15051 rotating drum, as described by Schneider and Jensen were removed from the furnace and allowed to cool in the (2008). The same drum was utilized in previous studies

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 209 Recycling pre-oxidized chromite fines in the oxidative sintered pellet production process

(Kleynhans et al., 2012, 2016; Neizel et al., 2013; randomly selected from each prepared pellet batch, revealed Glastonbury et al., 2015). During each experiment, 10 that the outer chromite grains of pellets sintered at < 1200ºC sintered pellets were abraded at 40 r/min rotational speed for did not indicate signs of oxidation, while oxidation 64 minutes. The pellets were screened at time intervals of. 1, penetrated deep into pellets sintered at > 1200ºC. A sintering 2, 4, 8, 16, 32, and 64 minutes using a sieve with an profile with a maximum temperature of 1200ºC was therefore aperture of 6.5 mm. This aperture was chosen since < 6 mm applied within the context of this paper, to mimic the material is generally classified as fines, which have to be industrially applied oxidative sintered pellets process. limited in SAF feed material (Basson and Daavittila, 2013). Figure 1 presents backscattered electron SEM micrographs The oversized materials ( 6.5 mm) were weighed and of a cross-sectioned polished pellet containing zero wt% returned to the drum, together with the fines ( 6.5 mm), for pre-oxidized chromite, which was sintered at a maximum further abrasion until the full abrasion time, i.e. 64 minutes, temperature of 1200ºC. Oxidation-induced differences was reached. Standard deviations were calculated based on (alteration being indicated by the lighter greyscale patterns) three experimental repetitions. were evident between the outer chromite grains and grains toward the centre of the pellet (Figure 1a). The higher <81(-71943/9/610(11623 magnification micrograph of the outer chromite grains (Figure 1b) clearly shows an oxidation-induced altered phase                that formed on the rim of such grains, while the chromite   grains toward the pellet centre were unaffected (Figure 1c). As previously stated, Zhao and Hayes (2010) showed that Similar oxidation-induced phase patterns have been observed only the outer chromite grains of industrially produced during investigations considering pre-oxidation of chromite oxidative sintered pellets are partially oxidized, while the prior to direct reduction (Kapure et al., 2010), laboratory grains deeper into the pellet cores remain unoxidized. oxidative sintering of chromite pellets (Glastonbury et al., Therefore, it was critical to establish the maximum 2015), and industrially produced oxidative sintered chromite temperature for the proposed laboratory sintering profile (see pellets (Zhao and Hayes, 2010). Pellet oxidative sintering section). Consequently, batches of pellets were cured with sintering profiles that had maximum         temperatures from 1000 to 1500ºC. SEM examination of In order to gain insight into the recycling of pre-oxidized three cross-sectioned, polished sintered pellets, which were chromite fines, it is vital to understand the mechanism(s) at

#6*(589 40 10477858/98-8075239 9)6052*54,.192+94905211$18076238/943/9,2-61.8/9,8--879023746363*98529'79,58$2&6/68/90.52)67891637858/94794 )4&6)()978),8547(5892+9 9 &6/47623$63/(08/9/6++85830819"63/60478/9%97.89-6*.7859*58104-89,4778531!9458986/8379%87'88397.892(78590.52)678 *54631943/9*54631972'45/97.890837589"4!9.8189/6++858308194589%877859188396397.89.6*.859)4*36+604762396)4*8192+97.892(78590.52)6789*546319"%!943/9*54631 72'45/97.8908375892+97.89,8--879"0! 210   
 VOLUME 119          
Recycling pre-oxidized chromite fines in the oxidative sintered pellet production process

Table I   9"'7!92+9/6++85837954639-2047623943/954639458419419'8--9419 *#8943/95#8954762192+97.8 75431+25)476239,52/(0719"0.52)678943/9   ,.418!96394958,581837476891637858/9,8--879")4&6)()916378563* 78),8547(5892+9 !9023746363*9329,58$2&6/68/90.52)67896&97299434-1819'8589023/(078/963916)6-45 -20476231943/94584192+9%87'8839+2(5972986*.79,45760-819'67.97.894854*81943/91743/45/9/86476231963/60478/

54639999999999999546394584 '7 9547621

-2047623 5  -  #8 #8  * 6 
  3 6 * 5 #8#8

Centre Interior 47.25 15.78 19.77 6.13 9.90 0.70 0.36 0.23 0.12 0.30 1.64 (chromite) ±0.77 ±0.71 ±0.58 ±1.26 ±0.33 ±0.08 ±0.03 ±0.02 ±0.01 Outer Interior 48.49 15.39 15.39 6.75 12.65 0.72 0.36 0.32 0.13 0.46 1.99 ±0.76 ±0.92 ±1.12 ±1.02 ±0.69 ±0.06 ±0.03 ±0.05 ±0.02

Outer Rim (M2O3 48.30 16.47 0.21 33.15 0.31 0.79 0.41 0.01 0.01 0.01 1.42 layer phase) ±1.06 ±1.65 ±0.15 ±1.67 ±0.09 ±0.07 ±0.03 ±0.01 ±0.01

play during the oxidative sintered pellet production process. enrichment at the expense of Fe2+ in grains at the outer layer. Oxidation-induced alteration, which is indicated by lighter Fe2+ occupies the tetrahedral sites in normal (untreated) greyscale patterns in the SEM micrographs in Figure 1b, was chromite spinel. High-temperature oxidative treatment of evident on the rims of the outer chromite grains of sintered chromite caused Fe2+ to oxidize and diffuse towards the grain pellets containing no pre-oxidized chromite. EMPA was rim, generating tetrahedral site vacancies within the particle subsequently used to determine the chemical compositions of interior. Vacancy formation occurs according to the following the transformation products. However, access to the EMPA reaction (Lindsley, 1991; Tathavakar, Antony, and Jha., was limited, therefore only one pellet, sintered according to 2005) the optimum sintering profile, was analysed. SEM micrographs of all three of the randomly selected pellets from [1] the batch sintered at 1200ºC indicated the same phase 2- transformations at the rim of the pellets (see Mimicking the where O 0 represents oxygen anions in the cubic closed industrial applied oxidative sintering process section), which packed lattice, Vcat is the cation vacancies, and h a ‘hole’, proved that the randomly selected pellet analysed with EMPA respectively. Vcat + 2h collectively represent mobile point was representative. The results of the EMPA are shown in defects, from which mass transfer occurs. These tetrahedral Table I. The areas analysed are indicated as ‘grain location’ vacancies were filled by Mg2+ (originating from the particle and ‘grain area’, with ‘location’ referring to the position of rim) via a Mg-Fe exchange reaction, which resulted in the the chromite grain within the pellet (i.e. centre or outer observed 0.31 wt% MgO content at the grain rim in the pellet grains), and ‘grain area’ referring to the zone within a outer layer. specific grain (i.e. interior or rim of a specific grain, which is The Fe2+ that migrated to the grain rim in the pellet outer also indicated in Figure 1b). The Cr/Fe and Mg/Fe elemental layer was subsequently oxidized to Fe3+, or alternatively the ratios, with Fe = Fe2+ + Fe3+, as determined by EMPA, are Fe2+ was oxidized to Fe3+ which then migrated to the surface also presented in Table I. – currently it is impossible to say with certainty which occurs As is evident from Table I, the interiors of grains at the first. The generalized oxidative spinel phase decomposition is centre and outer layer of the pellets had appreciably different described by Equation [2] (Alper, 1970; Tathavakar, Antony, MgO and FeO contents, whereas no appreciable differences and Jha, 2005) between trivalent cations (primarily Cr3+, Al3+, and Fe3+, indicated as Cr2O3, Al2O3, and Fe2O3, respectively) occupying [2] the octahedral sites in chromite were observed. In contrast, relatively large differences in FeO, Fe2O3, and MgO contents The products of complete oxidative decomposition of were evident for grain interiors and rims located in the outer chromite (Mg,Fe)[Al,Cr,Fe]2O4 at elevated temperatures are layer of pellets. free oxides of the various species, as indicated by Equation Grain interiors in the centre of pellets had an MgO [2]. However, in this study complete oxidative decomposition content of 9.90 wt%, compared to 12.65 wt% at the outer was not the intention, nor was it achieved. The products of layer. The FeO content of grain interiors at the centre and chromite oxidation are strongly dependent on temperature, outer layer of pellets were 19.77 and 15.93 wt%, respectively. oxygen partial pressure, and the chemical composition of the Consequently, the Mg/Fe ratios for grain interiors at the pellet chromite. In the presence of oxygen, Fe2+ will be oxidized to outer layer were higher (0.46) than for grains at the pellet Fe3+ at sufficiently high temperatures. This explains the centre (0.30). The Mg/Fe ratio difference of grain interiors as decrease in FeO content of 15.39% to 0.21% and increase in a function of location within the pellet was indicative of Mg2+ Fe2O3 content of 6.75 to 33.15% from the grain interior to

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 211 Recycling pre-oxidized chromite fines in the oxidative sintered pellet production process

#6*(589.898++80792+9,58$2&6/68/90.52)6789+63819023783792390(58/9,8--87902),581168917583*7.9.89855259%451963/6047897.891743/45/9/8647623192+9 8&,856)8374-958,8471

#6*(589.898++80792+9,58$2&6/68/90.52)6789+63819023783792390(58/9,8--8794%541623917583*7.9.89855259%451963/6047897.891743/45/9/8647623192+97.588 8&,856)8374-958,8471

the rim of the pellet outer layer. Ultimately, this results in the vacancies present in the maghaemite structure (Hellwege and exsolution of a Fe2O3-rich sesquioxide phase along the Hellwege, 1970). chromite grain rims and cleavage planes, as shown in Figure Furthermore, chromite oxidation resulted in variations in 1b and identified in Table I. Such Widmänstatten the Cr/Fe ratio at the grain interiors and rims as a function of intergrowths of sesquioxide phase (M2O3, with M grain location within the pellet. The unoxidized chromite had representing a series of trivalent ions such as Cr3+, Al3+, and a Cr/Fe ratio of 1.64, which correlated well with typical Cr/Fe Fe3+) during chromite oxidation, have been identified by ratios of South African chromite ore originating from the various authors (Tathavakar, Antony, and Jha, 2005; Kapure Middle Group 1 and 2 seams of the Bushveld Complex et al., 2010; Zhao and Hayes, 2010; Glastonbury et al., (Basson, Curr, and Gericke, 2007; Kleynhans, 2011). 2015). It is believed that the sesquioxide Fe2O3 phase is Chromite near the grain rim in the outer layer of sintered initially present as metastable, intermediate maghemite pellets had a Cr/Fe ratio of 1.42 as opposed to 1.99 near the ( -Fe2O3) exsolved precipitate, which forms by changing an grain interior, which resulted from Fe diffusion from the ABC packing into an ABAB packing by dislocations along the grain interior towards the grain rim. (111) chromite spinel plane. The maghemite phase then decomposes to the more stable hematite (Fe2O3) phase at     
       elevated temperatures (> 600ºC) in the presence of oxygen Quantitative Rietveld refined XRD analysis was performed

(PO2 = 0.2 atm.) (Tathavakar et al., 2005; Pan, Yang, and on the as-received pre-oxidized chromite fines. The phases Zhu, 2015). The presence of Al3+ cations increases the found (in order of decreasing abundance) were chromite oxidative decomposition temperature as they can occupy 39.9 wt%, chromian spinel 42.9 wt%, haematite 5.1 wt%, 212   
 VOLUME 119          
Recycling pre-oxidized chromite fines in the oxidative sintered pellet production process and enstatite 12.0 wt%. The chromite phase represents containing pre-oxidized chromite fines contained a larger residual chromite. The chromian spinel chromite formed at proportion of ultrafine particles, as is evident from a 1200ºC in the presence of oxygen. Tathavakar et al., (2015) comparison of Figures 4a and 4b. These ultrafine particles stated that South African chromite decomposes into two filled interparticle gaps and improved particle contact, which spinel phases upon heating, i.e. (Mg1-x,Fex)(Cr1-y,Aly)2O4 enhanced cured pellet strength. The presence of the ultrafine and (Fe1-a,Mga)(Cr1-b,Alb)2O4. The two observed chromite particles in the pre-oxidized chromite fines can be related to phases, i.e. chromite and chromian spinel, were in agreement the phase/chemical nature thereof. EMPA indicated that with phases detected by Tathavakar, Antony, and Jha sesquioxide Fe2O3 phases were formed in outer layer pellet (2015). Furthermore, the detection of hematite (Fe2O3) chromite grains (see Mechanism of chromite oxidation indicated that free Fe2O3, which formed as described in the section, Table I) during pellet oxidative sintering. section Mechanism of chromite oxidation, was present in the Quantitative Rietveld refined XRD analysis even indicated the pre-oxidized chromite fines. The enstatite phase likely presence of haematite (XRD characterization of pre-oxidized originated from siliceous gangue minerals, clay that was chromite fines section) in the pre-oxidized chromite fines. added as a pellet binder, and ash from the coke (in-pellet Zhao and Hayes (2010), who also investigated oxidative carbon fuel source). sintered chromite pellets, found that the phase transformation responsible for Fe2O3 formation resulted in a            shear mechanism (i.e. crystal stress/strain build-up) that can If pre-oxidized chromite fines were to be recycled into cause crystalline mechanical break-up, thereby generating oxidative sintered pellets beyond the current limitation of the ultrafine particles observed in the pre-oxidized chromite 4 wt% (Basson and Daavittila, 2013), such pellets must be fines (Figure 4b). physically strong enough to prevent fines formation. Figures In addition to the particle size-related enhancement of 2 and 3 present the cured compressive and abrasion cured pellet strength, particle surface morphology was also resistance strengths of pellets containing 4, 8, 16, 32, and considered. Surface SEM micrographs of pellets containing 64 wt% pre-oxidized chromite fines, compared to pellets zero and 16 wt% pre-oxidized chromite fines pellets are containing zero wt% pre-oxidized chromite fines (indicated presented in Figures 5a and 5b, respectively. The most by the y-axis). notable difference in surface morphology is the enhanced From Figures 2 and 3, it is evident that pellet interparticle sintering of the cured sintered pellets containing compressive and abrasion resistance strengths remained the pre-oxidized chromite fines. This suggests that some same, or improved, compared to the base case (zero wt% pre- additional degree of melting occurred during sintering, oxidized chromite fines) as the pre-oxidized chromite fines probably due to the presence of pre-oxidized chromite fines. content increased from 4 to 32 wt%. However, pellets Obviously, this can at least in part be attributed to the better containing 64 wt% pre-oxidized chromite fines were interparticle contact and reduced interparticle voids, but it substantially weaker. It thus seems feasible to include up to was also important to investigate the chemical nature of the 32 wt% pre-oxidized chromite fines in oxidative sintered interparticle bonding. SEM-EDS analyses of the areas pellet mixtures without adversely affecting cured pellet highlighted with the white blocks in Figures 5a and 5b strengths. However, it is unlikely that such large additions indicated similar chemical compositions. This suggests that would ever be required. the siliceous gangue minerals, clay as the pellet binder, and There might be various reasons why the cured sintered ash from the coke (in-pellet carbon fuel source) jointly pellets containing pre-oxidized chromite fines (at least up to contributed to binding the particles together via the 32 wt% containing pellets) were stronger than the base case. formation of a molten phase. Figure 6a present a SEM However, the most obvious is that the cured sintered pellets micrograph of a typical pre-oxidized chromite fines particle,

#6*(589 40 10477858/98-8075239 9)6052*54,.192+94905211$18076238/90(58/9,8--879023746363*9"4!98529'7943/9"%!99'79,58$2&6/68/90.52)6789+6381

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 213 Recycling pre-oxidized chromite fines in the oxidative sintered pellet production process

#6*(5898023/4598-8075239 9)6052*54,.192+97.89,45760-89)25,.2-2*6819'67.91(5+4089+847(58192+9,8--8719023746363*9"4!9852943/9"%!9 9'79 ,58$2&6/68/90.52)6789+63819023746363*9,8--8719.89'.6789%2&81963/604789458419434-18/9%9 $

#6*(589 8023/4598-8075239 9)6052*54,.192+9497,604-9,58$2&6/68/90.52)6789+63819,45760-894797'29)4*36+604762319.89'.6789%2&9.6*.-6*.71943 4-()63216-60478$7,89,45760-897.479834%-81963785,45760-89%63/63*9/(897297.89+25)4762392+949)2-7839,.418

while the white box in Figure 6b indicate the presence of a therefore recommend that pre-oxidized chromite fines can be aluminosilicate type particle (SEM-EDS composition of recycled in excess of the current 4 wt% limitation, but only 4.0 wt% Al, 8.0 wt% Si, 7.7 wt% Mg, and 0.5 wt% Ca). after considering the following aspects. Considering that the interparticle bridges in the samples with An appropriate techno-economic study should be and without the pre-oxidized chromite fines were conducted to assess the financial viability of the compositionally similar, the difference in their sintered changes to the process. compressive and abrasion strengths can most likely be Practical implications, such as equipment attributed to the presence of more ultrafine particles in the modifications, as well as equipment and/or process pre-oxidized chromite fines. licensing/warranty issues. For instance, the crushing of oversized green pellets and the operational lifetime of 230-(16231 the steel sintering belt were not considered in this The findings presented in this paper suggest that pre- paper. Currently, oversized green pellets are crushed oxidized chromite fines, originating from the oxidative pellet with a roller before the moist material is recycled to the sintering scrubber, and fines screened out from oxidative pelletizing drum. This roller might be damaged by sintered pellets may be re-introduced into the moist material larger hard particles in the pre-oxidized chromite fines mixture that is pelletized in excess of the current 4 wt% limit if this material is mixed with the moist material that is indicated by the technology supplier. EMPA and quantitative pelletized. This can be avoided by replacing the roller XRD analysis verified the formation of Fe2O3-rich by a more robust crushing device, or alternatively sesquioxide phases and/or liberated Fe2O3. Such phases will milling the pre-oxidized chromite fines with the ore and metallize at lower temperatures during smelting compared to carbonaceous material to prevent roller damage. As normal chromite; hence possibly enhancing metallurgical previously mentioned, increased recycling of pre- efficiency and reducing electricity consumption. The authors oxidized chromite fines might also require higher 214   
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Recycling pre-oxidized chromite fines in the oxidative sintered pellet production process

carbon additions in the green pellets, which could be HILL, R., and HOWARD, C. 1987. Quantitative phase analysis from neutron shorten the operational lifetime of the steel sintering powder diffraction data using the Rietveld method. Journal of Applied belt. However, our results indicate that increased Crystallography, vol. 20, no. 6. pp. 467–474. https://doi.org/10.1107/S0021889887086199 recycling of pre-oxidized chromite fines up to a very high percentage does not adversely influence sintered ICDA. 2013. Statistical Bulletin 2013 Edition. International Chromium pellet strength. Such decisions (how to introduce Development Association, Paris, France. larger, hard pre-oxidized particles and the effect of KAPURE, G., TATHAVADKAR, V., RAO, C.B., RAO, S.M., and RAJU, K.S. 2010. Coal increased recycling of pre-oxidized fines on the steel based direct reduction of preoxidized chromite ore at high temperature. sintering belt) will be guided by the techno-economic Proceedings of the 12th International Ferroalloys Congress (INFACON study of the process alteration options, and additionally XII), Helsinki, Finland. Vartiainen, A. (ed). Outotec Oyj. pp. 293–301. by equipment and/or process licensing/warranty KLEYNHANS, E.L.J. 2011. Unique challenges of clay binders in a pelletised issues. However, the possible metallurgical and energy chromite pre-reduction process – a case study. MSc dissertation, North- benefits associated with recycling of pre-oxidized West University, Potchefstroom, South Africa.

chromite fines, which have up to now largely been KLEYNHANS, E.L.J., BEUKES, J.P., VAN ZYL, P.G., KESTENS, P.H.I., and LANGA, J.M. ignored, should also be considered. 2012. Unique challenges of clay binders in a pelletised chromite pre- reduction process. Minerals Engineering, vol. 34. pp. 55–62. https://doi.org/10.1016/j.mineng.2012.03.021 0 32'-8/*8)8371 KLEYNHANS, E.L.J., NEIZEL, B.W., BEUKES, J.P., and VAN ZYL, P.G. 2016. Utilisation The authors thank Sarel Naude from the Department of of pre-oxidised ore in the pelletised chromite pre-reduction process. Mechanical Engineering for assistance during sample Minerals Engineering, vol. 92. pp. 114–124. preparation. Thanks are also given to Derek Smith and https://doi.org/10.1016/j.mineng.2016.03.005 Dominique Duguay at CANMET for XRD and electron KLEYNHANS, E.L.J., BEUKES, J.P, VAN ZYL, P.G, and FICK, J.I.J. 2017. Techno- microprobe analyses, respectively. The financial assistance of economic feasibility of a pre-oxidation process to enhance prereduction of the National Research Foundation (NRF) towards the PhD chromite. Journal of the Southern African Institute of Mining and study of S.P. du Preez (grant number 101345) is hereby Metallurgy, vol. 117, no. 5. pp. 457–468. acknowledged. Opinions expressed and conclusions arrived http://dx.doi.org/10.17159/2411-9717/2017/v117n5a8 at, are those of the authors and are not necessarily to be LINDSLEY, D.H. 1991. Reviews in Mineralogy. Mineralogical Society of America. attributed to the NRF. Washington DC. Vol. 25. pp. 323–350.

MOTZER, W.E., and ENGINEERS, T. 2004. Chemistry, geochemistry, and geology of <8+8583081 chromium and chromium compounds. Chromium(VI) Handbook. Guetin, J., Jacobs, J.A, and Avakian, C.P. (eds.). CRC Press. Boca Raton, FL. ALPER, A.M. 1970. High Temperature Oxides, Academic Press, New York. pp. 23–91. BASSON, J., CURR, T., and GERICKE, W. 2007. South Africa's ferroalloys industry- NEIZEL, B.W., BEUKES, J.P, VAN ZYL, P.G., and DAWSON, N.F. 2013. Why is CaCO present status and future outlook. Proceedings of the 11th International 3 not used as an additive in the pelletised chromite pre-reduction process? Ferroalloys Congress (INFACON XI). Das, R.K. and Sundaresan, T.S. (eds). Indian Ferro Alloys Producers Association, New Delhi. pp. 3–24. Minerals Engineering, vol. 45. pp. 115–120. http://dx.doi.org/10.1016/j.mineng.2013.02.015 BASSON, J., and DAAVITTILA, J. 2013. High carbon ferrochrome technology. Handbook of Ferroalloys: Theory and Technology. Gasik, M. (ed.). OUTOTEC. 2017. Outotec® steel belt sintering plant. Elsevier Science, UK. Chapter 9. pp. 317–363. https://www.outotec.com/products/sintering-and-pelletizing/steel-belt- http://dx.doi.org/10.1016/B978-0-08-097753-9.00009-5 sintering-plant [accessed 24 October 2017].

BEUKES, J.P., DAWSON, N.F., and VAN ZYL, P.G. 2010. Theoretical and practical PÄÄTALO, M. 2018. Head of Research and Development, Outokumpu, Finland. aspects of Cr(VI) in the South African ferrochrome industry. Journal of the Personal communication. Southern African Institute of Mining and Metallurgy, vol. 110, no. 12. pp. 743–750. PAKTUNC, A.D., and CABRI, L. 1995. A proton-and electron-microprobe study of gallium, nickel and zinc distribution in chromian spinel. Lithos, vol. 35, BEUKES, J.P., DU PREEZ, S.P., VAN ZYL, P.G., PAKTUNC, D., FABRITIUS, T., PÄÄTALO, no. 3. pp. 261–282. https://doi.org/10.1016/0024-4937(95)99071-4 M., and CRAMER, M. 2017. Review of Cr (VI) environmental practices in the chromite mining and smelting industry–relevance to development of PAN, J., YANG, C., and ZHU, D. 2015. Solid state reduction of preoxidized the Ring of Fire, Canada. Journal of Cleaner Production, vol. 165. pp. 874– chromite-iron ore pellets by coal. ISIJ International, vol. 55, no. 4. 889. https://doi.org/10.1016/j.jclepro.2017.07.176 pp. 727–735. http://doi.org/10.2355/isijinternational.55.727

CRAMER, L.A., BASSON, J., and NELSON, L.R. 2004. The impact of platinum RIEKKOLA-VANHANEN, M. 1999. Finnish expert report on best available production from UG2 ore on ferrochrome production in South Africa. techniques in ferrochromium production. Helsinki. Journal of the South African Institute of Mining and Metallurgy, vol. 104, no. 9. pp 517–527. SCHNEIDER, T., and JENSEN, K.A. 2008. Combined single-drop and rotating drum dustiness test of fine to nanosize powders using a small drum. Annals of GLASTONBURY, R.I., BEUKES, J.P, VAN ZYL, P.G, SADIKI, L.N, JORDAAN, A., CAMPBELL, Occupational Hygiene, vol. 52, no. 1. pp. 23–34. Q.P, STEWART, H.M, and DAWSON, N.F. 2015. Comparison of physical https://doi.org/10.1093/annhyg/mem059 properties of oxidative sintered pellets produced with UG2 or metallurgical-grade South African chromite: A case study. Journal of the TATHAVAKAR, V.D., ANTONY, M., and JHA, A. 2005. The physical chemistry of Southern African Institute of Mining and Metallurgy, vol. 115, no. 8. pp. thermal decomposition of South African chromite minerals. Metallurgical 699–706. http://dx.doi.org/10.17159/2411-9717/2015/V115N8A6 and Materials Transactions B, vol. 36, no. 1. pp. 75–84.

HAGGERTY, S.E. 1991. Oxide mineralogy of the upper mantle. Reviews in https://doi.org/10.1007/s11663-005-0008-1 Mineralogy and Geochemistry, vol. 25, no. 1. pp. 355–416. ZHAO, B. and HAYES, P. 2010. Effects of oxidation on the microstructure and HELLWEGE, K.H., and HELLWEGE, A.H. 1970. Landolt–Bornsten Numerical Data reduction of chromite pellets. Proceedings of the 12th International Ferro and Functional Relation in Science and Technology. Springer-Verlag. b52, Alloys Congress (INFACON XII), Helsinki, Finland. Vartiainen, A. (ed). a18-a20. Outotec Oyj. pp. 263–273.

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 215 NINTH INTERNATIONAL CONFERENCE ON DEEP AND HIGH STRESS MINING 2019 24–25 JUNE 2019 - CONFERENCE 26 JUNE 2019 - SARES 2019 27 JUNE 2019 - TECHNICAL VISIT MISTY HILLS CONFERENCE CENTRE, MULDERSDRIFT, JOHANNESBURG, SOUTH AFRICA

BACKGROUND The Ninth International Conference on Deep and High Stress Mining (Deep Mining 2019) will be held at the Misty Hills Conference Centre, Muldersdrift, Johannesburg on 24 and 25 June 2019. Conferences in this series have previously been hosted in Australia, South Africa, Canada, and Chile. Around the world, mines are getting deeper and the challenges of stress damage, squeezing ground, and rockbursts are ever- present and increasing. Mining methods and support systems have evolved slowly to improve the management of excavation damage and safety of personnel, but damage still occurs and personnel are injured. Techniques for modelling and monitoring have been adapted and enhanced to help us understand rock mass behaviour under high stress. Many efficacious dynamic support products have been developed, but our understanding of the demand and capacity of support systems remains uncertain.

OBJECTIVE To create an international forum for discussing the challenges associated with deep and high stress mining and to present advances in technology.

WHO SHOULD ATTEND Sponsors Rock engineering practitioners Mining engineers Researchers Academics Geotechnical engineers Hydraulic fracturing engineers High stress mining engineers Waste repository engineers Rock engineers Petroleum engineers Tunnelling engineers

For further information contact: Camielah Jardine, Head of Conferencing, SAIMM, Tel: +27 11 834-1273/7, Fax: +27 11 833-8156 or +27 11 838-5923 E-mail: [email protected], Website: http://www.saimm.co.za NATIONAL & INTERNATIONAL ACTIVITIES

2019

11–13 March 2019 — 7th Sulphur and Sulphuric Acid 2019 5–7 August 2019 — The Southern African Institute of Mining Conference and Metallurgy in collaboration with the Zululand Branch is Swakopmund Hotel, Swakopmund, Namibia organising The Eleventh International Heavy Minerals Contact: Camielah Jardine Conference Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 ‘Renewed focus on Process and Optimization’ E-mail: [email protected], Website: http://www.saimm.co.za The Vineyard, Cape Town, South Africa 2–3 April 2019 — Global Mining Standards and Guidelines Contact: Yolanda Ndimande Group Forum 2019 Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 Wits Club, University of the Witwatersrand, Johannesburg, South E-mail: [email protected], Website: http://www.saimm.co.za Africa 18–21 August 2019 — Copper 2019 Contact: Yolanda Ndimande Vancouver Convention Centre, Canada Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 Contact: Brigitte Farah E-mail: [email protected], Website: http://www.saimm.co.za Tel: +1 514-939-2710 (ext. 1329), E-mail: [email protected] 22–23 May 2019 — Mine Planner’s Colloquium 2019 Website: http://com.metsoc.org ‘Skills for the future – yours and your mine’s’ 19–22 Augusts 2019 — Southern African Coal Processing Glenhove Conference Centre, Melrose Estate, Johannesburg Society 2019 Conference and Networking Opportunity Contact: Camielah Jardine Graceland Hotel Casino and Country Club, Secunda Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 Contact: Johan de Korte E-mail: [email protected], Website: http://www.saimm.co.za Tel: 079 872-6403 E-mail: [email protected] 27–29 May 2019 — The 9th International Conference on Website: http://www.sacoalprep.co.za Sustainable Development in the Minerals Industry Park Royal Darling Harbour, Sydney , Australia 28–29 August 2019 — International Mine Health and Safety Contact: Georgios Barakos Conference 2019 Tel: +49(0)3731 39 3602, Fax: +49(0)3731 39 2087 ‘Beyond Zero Harm’ E-mail: [email protected] Johannesburg Website: http://sdimi.ausimm.com/ Contact: Camielah Jardine Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 5–6 June 2019 — New Technology Conference and Trade Show E-mail: [email protected], Website: http://www.saimm.co.za ‘Embracing the Fourth Industrial Revolution in the Minerals Industry’ 11–12 September 2019 — Surface Mining 2019 Conference Driving competitiveness through people, processes and technology ‘Better · cheaper · safer’ in a modernised environment Glenhove Conference Centre, Melrose Estate, Johannesburg The Canvas Riversands, Fourways, Johannesburg, South Africa Contact: Camielah Jardine Contact: Yolanda Ndimande Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: [email protected], Website: http://www.saimm.co.za E-mail: [email protected], Website: http://www.saimm.co.za 8–9 October 2019 — SAMCODES Conference 2019 24–27 June 2019 — Ninth International Conference on Deep Best Practice and High Stress Mining 2019 ‘An Industry Standard for Mining Professionals in South Africa’ Misty Hills Conference Centre, Muldersdrift, Johannesburg Birchwood Hotel & OR Tambo Conference Centre, Johannesburg Contact: Camielah Jardine Contact: Camielah Jardine Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: [email protected], Website: http://www.saimm.co.za E-mail: [email protected], Website: http://www.saimm.co.za 4–5 July 2019 — Smart Mining, Smart Environment, Smart 16–17 October 2019 — Tailing Storage Conference 2019 Society ‘Investing in a Sustainable Future’ ‘Implementing change now, for the mine of the future’ Birchwood Hotel & OR Tambo Conference Centre, Johannesburg Midrand Contact: Camielah Jardine Contact: Yolanda Ndimande Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: [email protected], Website: http://www.saimm.co.za E-mail: [email protected], Website: http://www.saimm.co.za 13–15 November 2019 — XIX International Coal Preparation 31 July–1 August 2019 — Entrepreneurship in Mining Congress & Expo 2019 Conference 2019 New Delhi, India The Canvas Riversands, Fourways, Johannesburg, South Africa Contact: Coal Preparation Society of India Contact: Camielah Jardine Tel/Fax: +91-11-26136416, 4166 1820 Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: cpsidelhi. [email protected], [email protected]. E-mail: [email protected], Website: http://www.saimm.co.za [email protected], [email protected]

         
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 vii  
Ukwazi Mining Solutions (Pty) Ltd Umgeni Water Webber Wentzel Weir Minerals Africa Worley Parsons RSA (Pty) Ltd Murray and Roberts Cementation Nalco Africa (Pty) Ltd Ltd Namakwa Sands(Pty) Ltd Ncamiso Trading (Pty) (Pty) Limited New Concept Mining - Zondereinde Northam Platinum Ltd OPTRON (Pty) Ltd PANalytical (Pty) Ltd Paterson & Cooke Consulting Engineers (Pty) Ltd Perkinelmer Polysius A Division Of Thyssenkrupp Industrial Sol Precious Metals Refiners Rand Refinery Limited Redpath Mining (South Africa) (Pty) Ltd Rocbolt Technologies Rosond (Pty) Ltd Royal Bafokeng Platinum Roytec Global (Pty) Ltd RungePincockMinarco Limited Rustenburg Platinum Mines Limited Salene Mining (Pty) Ltd Sandvik Mining and Construction Delmas (Pty) Ltd Sandvik Mining and Construction RSA(Pty) Ltd SANIRE Schauenburg (Pty) Ltd Sebilo Resources (Pty) Ltd SENET (Pty) Ltd Senmin International (Pty) Ltd Smec South Africa Sound Mining Solution (Pty) Ltd SRK Consulting SA (Pty) Ltd Technology Innovation Agency Time Mining and Processing (Pty) Ltd Timrite Pty Ltd Tomra (Pty) Ltd          66666 ! 6-- # %  $ Company Affiliates Company Expectra 2004 (Pty) Ltd Exxaro Coal (Pty) Ltd Exxaro Resources Limited Filtaquip (Pty) Ltd Ltd FLSmidth Minerals (Pty) Ltd Fluor Daniel SA (Pty) Franki Africa (Pty) Ltd-JHB Fraser Alexander (Pty) Ltd G H H Mining Machines (Pty) Ltd Geobrugg Southern Africa (Pty) Ltd Glencore Hall Core Drilling (Pty) Ltd Hatch (Pty) Ltd Herrenknecht AG HPE Hydro Power Equipment (Pty) Ltd Immersive Technologies IMS Engineering (Pty) Ltd Ivanhoe Mines SA Joy Global Inc.(Africa) Kudumane Manganese Resources Leco Africa (Pty) Limited Longyear South Africa (Pty) Ltd Lonmin Plc Lull Storm Trading (Pty) Ltd Maccaferri SA (Pty) Ltd Magnetech (Pty) Ltd MAGOTTEAUX (PTY) LTD Maptek (Pty) Ltd MBE Minerals SA Pty Ltd MCC Contracts (Pty) Ltd MD Mineral Technologies SA (Pty) Ltd MDM Technical Africa (Pty) Ltd Metalock Engineering RSA (Pty)Ltd Metorex Limited Metso Minerals (South Africa) Pty Ltd Minerals Council of South Africa Minerals Operations Executive (Pty) Ltd MineRP Holding (Pty) Ltd Mintek MIP Process Technologies (Pty) Limited Modular Mining Systems Africa (Pty) Ltd MSA Group (Pty) Ltd Multotec (Pty) Ltd   
 The following organizations have been admitted to the Institute as Company Affiliates to the Institute as have been admitted organizations The following viii 3M South Africa (Pty) Limited 3M South Africa (Pty) AECOM SA (Pty) Ltd Limited AEL Mining Services Air Liquide (PTY) Ltd Africa (Pty) Ltd Alexander Proudfoot AMEC Foster Wheeler Africa (Pty) Ltd AMIRA International ANDRITZ Delkor(Pty) Ltd Anglo Operations Proprietary Limited Anglogold Ashanti Ltd Arcus Gibb (Pty) Ltd Atlas Copco Holdings South Africa (Pty) Limited Aurecon South Africa (Pty) Ltd Aveng Engineering Aveng Mining Shafts and Underground Axis House Pty Ltd Bafokeng Rasimone Platinum Mine Barloworld Equipment -Mining BASF Holdings SA (Pty) Ltd BCL Limited Becker Mining (Pty) Ltd BedRock Mining Support Pty Ltd BHP Billiton Energy Coal SA Ltd Blue Cube Systems (Pty) Ltd Bluhm Burton Engineering Pty Ltd Bouygues Travaux Publics CDM Group CGG Services SA Coalmin Process Technologies CC Concor Opencast Mining Concor Technicrete Council for Geoscience Library CRONIMET Mining Processing SA Pty Ltd CSIR Natural Resources and the Environment (NRE) Data Mine SA Department of Water Affairs and Forestry Digby Wells and Associates DRA Mineral Projects (Pty) Ltd DTP Mining - Bouygues Construction Duraset Elbroc Mining Products (Pty) Ltd eThekwini Municipality The Southern African Institute of Mining and Metallurgy       
    2019

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11–12 March 2019 Conference 13 March 2019 Technical Visit (Swakop Uranium)

Swakopmund Hotel, Swakopmund, Namibia

BACKGROUND

The production of SO2 and sulphuric acid remains a pertinent topic in the Southern African mining and metallurgical industry, especially in view of the strong demand for, and increasing prices of, vital base metals such as cobalt and copper. The electric car revolution is well underway and demand for cobalt is rocketing. New sulphuric acid plants are being built, comprising both smelters and sulphur burners, as the demand for metals increases. However, these projects take time to plan and construct, and in the interim sulphuric acid is being sourced from far afield, sometimes more than 2000 km away from the place that it is required. The need for sulphuric acid ‘sinks’ such as phosphate fertilizer plants is also becoming apparent. All of the above factors create both opportunities and issues and supply chain challenges. To ensure that you stay abreast of developments in the industry, the Southern African Institute of Mining and Metallurgy invites you to participate in a conference on the production, utilization, and conversion of sulphur, sulphuric acid, and SO2 abatement in metallurgical and other processes, to be held in March 2019 in Namibia.

OBJECTIVES WHO SHOULD ATTEND > To expose delegates to issues The Conference will be of value to: relating to the generation and > Metallurgical and chemical engineers handling of sulphur, sulphuric acid, working in the minerals and metals and SO2 abatement in the processing and chemical industries metallurgical and other industries. > Metallurgical/chemical/plant management > Provide an opportunity to producers > Project managers and consumers of sulphur and sulphuric acid and related products to > Research and development personnel be introduced to new technologies > Academics and students and equipment in the field. > Technology providers and engineering firms > Enable participants to share > Equipment and system providers information about and experience in > Relevant legislators the application of such technologies. > Environmentalists > Provide an opportunity for role players in the industry to discuss > Consultants common problems and their solutions EXHIBITION/SPONSORSHIP There are a number of sponsorship opportunities available. Companies wishing to sponsor or exhibit should contact the Conference Co-ordinator. SPONSORS

For further information contact: Camielah Jardine Head of Conferencing, SAIMM, P O Box 61127, Marshalltown 2107 Tel: (011) 834-1273/7 Fax: (011) 833-8156 or (011) 838-5923 E-mail: [email protected] Website: http://www.saimm.co.za