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Mining Practice in the Kimberley Division of De Beers Consolidated Mines Limited by J

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Mining Practice in the Kimberley Division of De Beers Consolidated Mines Limited by J Mining practice in the Kimberley Division of De Beers Consolidated Mines Limited by J. V. CLEASBY*. B.Se.. A.R.S.M. (Fellow). H. J. WRIGHT*. B.Se.. M.Se.. (Fellow). and M. T. G. DAVIES*. B.Se. (Visitor) SYNOPSIS T his paper highlights the changes that are taking place at De Beers Consolidated Mines Limited in mining methods, mechanization, and employment practices. De Beers has four underground mines in Kimberley itself (Dutoitspan, Bultfontein, De Beers, and Wesselton), and two open-cast mines outside Kimberley (Finsch and Koffiefontein). Emphasis is placed on the new method envisaged for Koffiefontein when it becomes an underground mine. The paper also includes notes on chemical drilling and on winding practices. SAMEVATTING Hierdie referaat laat die klem val op die veranderinge wat by De Beers Consolidated Mines Beperk aan die gang is wat betref mynboumetodes, meganisering en indiensnemingspraktyke. De Beers het vier ondergrondse myne in Kimberley self (Dutoitspan, Bultfontein, De Beers en Wesselton) en twee oopgroefmyne buite Kimberley (Finsch en Koffiefontein). Die nuwe metode wat vir Koffiefontein beoog word wanneer dit 'n ondergrondse myn word, word veral benadruk. Die referaat sluit ook aantekeninge oor chemiese boorwerk en oor wenasgebruike in. INTRODUCTION tains the head office of the De 1891. Finsch Mine was a more Beers Company, and the diamond- recent discovery by A. T. Fincham The Kimberley Division of De sorting and trading companies for in 1961. Beers Consolidated Mines Limited goods produced in Southern Africa, The 'Big Hole' remains as a is composed of four underground which are newly housed in a building monument to the Kimberley Mine, mines in Kimberley itself (Dutoits- specially designed for the purpose. which was closed in 1913, and today pan, Bultfontein, De Beers, and Diamonds were first discovered is a great South Mrican tourist Wesselton) and two open-cast mines in the Kimberley area at Hopetown attraction, second only to the Kruger outside Kimberley (Finsch and in 1866 on the banks of the Orange National Park. De Beers have built Koffiefontein). Fig. 1 is a map of River. This and later finds triggered a museum at the edge of the 'Big the Kimberley district showing the the start of the great 'diamond Hole', which preserves buildings, location of these min'3s. Finsch is rush'. In 1870 the Jagersfontein mining equipment, shops, and goods 150 km west of Kimberley and (now closed) and Dutoitspan pipes from the early Kimberley days. Koffiefontein is 80 km south of were discovered, followed by those Finsch and Koffiefontein Mines Kimberley. Kimberley also con- at Bultfontein, De Beers, and Kim- are both open-pit bench mines and berley (now closed) in 1871, Koffie- are fully self-contained, with their *De Beers Consolidated Mines Limited. fontein in 1880, and Wesselton in own treatment plants, housing, ser- '::Q L I'r ".. 1MB LEY .00~n. Outoitspan Mint . W llon Mint N01 TO SCALE. Jag.rslontein Mint . Fig. I-Map showing the location of the mines of De Beers Consolidated Mines Limited in the Kimberley area JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY DECEMBER 1975 247 B 24T ,UHE Of SECTION 1 1 l05m.Level 24M 2'l5mLe'. 385mLe", 620 met" "," '!2:i!!L1.mL- 24M 620m'-"o! 24M , B 50 o 50 'QOm"" Fig. 2-Plans and section showing the downward taper of the upper part, and the irregularity of the lower part, of a typical Kimberley pipe vices, etc. The four mines in Kim- Wesselton, De Beers, and Dutoits- generally sharp, indicating that berley feed ore by conveyor to a pan pipes (Fig. 2). earlier intrusions were completely central treatment plant and enjoy From surface to approximately consolidated prior to the intrusion joint services. These mines utilize 100 m, the wallrocks around the of later material. At Finsch and the block-caving method of mining, Kimberley group of pipes consist of Koffiefontein Mines only one major which has almost entirely replaced black and grey shalcs of the Karoo phase of intrusion is apparent at the the previous method of chambering. System, containing numerous and present levels of exposure, but, as The combined tonnage of ore pro- generally concordant dolcrite sills. in the Kimberley pipes, included duced by the Kimberley Mines is The shales overlie a variable thick- fragments of earlier kimberlite indi- 15000 t per day, Koffiefontein ness (300 to 1000 m) of Ventersdorp cate a more complex intrusive 12 000 t per day, and Finsch 13 000 t lavas with intervening quartzite history. per day. horizons. The Ventersdorp rock rests Most varieties of kimberlite are uncomfortably on Basement characteristically hygroscopic, GEOLOGY granite-gneiss. The Ventersdorp swelling and crumbling when wet The Kimberley pipes are approxi- System is not present at Koffie- owing to the absorption of water by mately circular or oval in shape, fontein, where Karoo shales, with clay minerals in the rocks. This and are deeply eroded volcanic intervening dolerite sills, rest directly characteristic makes wet drilling of necks, which, at the present land on granite-gneiss at a depth of kimberlite extremely difficult, and surface, have average diameters approximately 250 m. The wall- additional complications arise from ranging from approximately 230 to rocks at Finsch consist of 130 m the generally incompetent, low- 500 m. The upper parts of all the of banded ironstone separated from strength characteristics of kimber- pipes decrease in area with increas- the underlying dolomite, limestone, lite, compounded by the abundance ing depth, the average dip of the dolomitic shale, and chert of the of structural discontinuities (shear contacts being approximately 80°. Dolomite Stage by a sequence of planes and fractures). These features At depths of more than 500 m, this passage beds approximately 25 m make kimberlite difficult to support regular decrease in area is not thick. The passage beds consist of but are an advantage during block- always maintained, and the pipes colourful, rhythmic alternations of cave mining operations since they assume highly irregular forms. The thin dolomitic, siliceous, and iron- facilitate collapse and break-up of contact between the pipe and the rich layers. ground within the caves. wall-rock varies in inclination rapidly Several stages of intrusion have The occurrence of diamonds in over short vertical intervals, and a resulted in the presence of separate these pipes and separate intrusions marked effect of the kimberlite columns of kimberlite and kimber- within individual pipes ranges from intrusion by structures in the wall- lite breccias within the four Kim- approximately I part in 8 million rock is evident. This irregularity berley pipes. Internal contacts be- to less than I part in 100 million. at depth is most pronounced at the tween these separate phases are The distribution of diamonds is 248 DECEMBER 1975 JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY extremely complex. At any level irregularly over successive depth axial hole of the drill steel effectively in the pipes, the grade of separate zones. In general, however, both allays dust, water alone cannot be intrusions may be similar or may the grade and the average size of used during the drilling of kimber- vary by a factor of five or more. diamonds decrease with depth. lite because it coagulates the dust Similarly, pronounced changes in particles into a thick clay that CHEMICAL DRILLING horizontal grade may occur within causes the drill steel to stick in the a single intrusive phase. Vertical The problem of dust during drill- hole. In addition, the roof, side- variations of grades within indi- ing operations has long been one walls, and footwall are weakened by vidual intrusions may be relatively of the biggest single mining hazards. water and therefore become difficult limited, may change in more or Unlike other mining operations, to keep safe. Fortunately, however, less linear fashion, or may vary where water flushing through the there is no free silica in kimberlite, HrJndJe t Lock c/'usfmenf ,~~ 1)o$~ed Nu/-. ~ d/ , ~ ;:, ~'& FRONT VIEW OF DRill BIT. --. -- ' -\ -0-.-~ '--- --. , ., / I MOb/FIE/) NEWMAN H£ND£R VALVE , - !\ , FOR CJ.lEMICAl /JRllLlNG. j \ , ~ ! \ Del,)jl at: ShanktLip Seal, 70 .- -------- --- --------------- -------- Of --:~--m] ~.# ',""; :;~ss Jm I. DETAIL Or 25""... /-IE){ DRILL S/-IANK, Fig. 3-- The valve, drill bit, drill-steel shank, and lip seal used in chemical drilling JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY DECEMBER 1975 249 and thus the dust hazard is much in the shank of the drill steel to Jeto bottom-dump skips are used smaller than in some mines. Most allow the water tube to penetrate at De Beers and Bultfontein Mines, of the drilling in kimberlite has into the steel for approximately and Sala bottom-dump skips at hitherto been dry, but mining regu- 58 mm (Fig. 3). The head of the Wesselton Mine. lations introduced in 1965 called drill steel has two holes drilled The man and material winders for a dust count of less than 500 adjacent to the T.O. insert that on the Bultfontein and De Beers particles per millilitre. Attempts intersect the axial hole to ensure main shafts (and, from 1976, the were made as far back as 1949 to proper wetting and reduce blockages. Wesselton main shaft) are automatic suppress the dust, and various types Encouraging results have been elevators with a payload of 5000 of dust-extraction filters, mobile achieved with standard non-vented kg and a speed of 7,5 m/s, and are dust cars, and chamber dust cars rock drills. Special permission was designed for a maximum winding were used with a fair measure of obtained from the Mines Depart- depth of 975 m. In operation, they success. However, it was eventually ment for an experiment, the ad- are identical to an automatic eleva- found that greater efficiency could vantages being tor in a building, no driver or opera- be obtained from the use of a (1) less leakage due to increased tor being required.
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