OXYGEN ISOTOPE VARIATIONS Ln POLYMETAMORPHIC IRON ORES from the QUADRILÁTERO Ferrífero, BRAZIL

Total Page:16

File Type:pdf, Size:1020Kb

OXYGEN ISOTOPE VARIATIONS Ln POLYMETAMORPHIC IRON ORES from the QUADRILÁTERO Ferrífero, BRAZIL Revista Brasileira de Gecciências 12(1-3): 348-355, Mar.-Sel., 1982 - São Paulo OXYGEN ISOTOPE VARIATIONS lN POLYMETAMORPHIC IRON ORES FROM THE QUADRILÁTERO FERRíFERO, BRAZIL OEORO MÜLLER', ALFRED SCHUSTER' and JOACHIM HOEFS" ABSTRACT This study deals with the oxygen isotope variations in rich iron ore bodies and itabirites ofthe Iron Quadrangle (Quadrilátero Ferrífero), Brazil. The (5180 values of 136 quartz­ -iron oxide pairs have been determined and temperatures of formation have been calculated. The (5180 values of quartz vary distinctly between + 5°/ and + 20°/ , whereas 80/,0 of the iron oxide values fali in the small range between + 4°/ and -l}.s0/ . inlthat way the ô-value variations of the quartz-hematite pairs are dominantly ru~ed by the ,tuartz. The Quadrilátero Ferrifero can be divided into two different regions : in the large western zone of greenschist facies the quartz is distinctly more enriched in heavy oxygen than that from the smaller eastern amphibolite facies. The variation of oxygen isotope Fractionations between quartz and the iron oxides is obviou­ sly related to the complex deformation history of the iron ores. Sam pies with only primary schis­ tosity (SI) represent peak metamorphic conditions. ln the Ecregion these samples yield temperatures of formation > 700 "C and seem to correspond to orogenic events in the Archean basement 2,700 Ma ego. ln the w-rcgton o5l-temperatures betwecn 460 "C and 560 "C seem to represent peak metamorphic conditions .of the Proterozoic Minas metamorphism 2,000 Ma ago. lron ores which have been overprinted by later deformation events (052, 053) are selectively reset to lower isotopic temperatures. The more closely spaced the schistosity planes the larger the extent of a temperature lowering. The genetic processes which formed the rich iron ore bodies appear to be sedimentary-meta­ morphic rather than metasomatic events. Furthermore, there is no evidence for secondary leaching by weathering solutions with respect to the genesis of the blue dust ores. INTROOUCTION I Precipitation of banded quartz-iron metamorphosed 2.7 Ga ago in the Jequié Cycle, As is well formations - known as itabirites in Brazil ~ was a dominam known, this orogenic cycle forms a worldwide pattern process in the Late Archean and the Early Proterozoic (Moorbath, 1976) and is documented by Rb/Sr determina­ oceans, Among the problems associated with these forma­ tions in the Quadrilátero Ferrifero (Herz, 1970; Cordani tions is the genesis of hematite rich ores such as those found et al.. 1980). ln other regions of Central Brazil Hasui and in the Iron Quadrangle, Minas Gerais, Brazi!. Almeida (1970). Cordani et ai. (1973), Cordani and Iyer According to Dorr (1965) the high-grade metamorphic (1979), Brito Neves et ai. (1979), and Sighinolfi et ai. (1981) hematite-rich ores were enriched by synmetamorphic repla­ yie1d similar ages betwcen 2.7 and 2.8 Ga. cement of quartz in the host itabirite by hematite derived On top of this basement a series of older sediments (Rio from the iron formation itself. Dorr assumed that transport das Velhas) and of younger sediments (Minas) is deposited. of iron to and quartz from the sites of replacement was The rocks 'of these two series were metamorphosed some performed by high-temperature fluids. Dorr also proposes 2.0-1.8 Ga ago. ln the Quadrilátero Ferrífero, to the regional that the hard massive hematite ores were partially converted metamorphism of this orogenesis was given the local name to soft ores by the leaching aetion of surface waters during "Minas metarnorphism" since the Minas sediments are the Mesozoic and Tertiary time. If metasornatic solution of youngest deposits which recrystallized during this meta­ quartz and replacernent by iron oxides took place, huge morphic evenl. As shown by Hurley (1967) this orogenic quantities oftluids were required to dissolve immense masses cycle ean be detected in Venezuela, in lhe Guyana States l of quartz which would amount to more than 50 ,l " of the and in Brazil north of the Amazonas River and was named itabirite volume. Really, there is no evidence for quartz­ "Transarnazônico Cycle". -leaching in the country rocks, as schists, gneisses and 50 Fig. I shows a rough geologic sketch of the Quadrilátero on. If metasomatic fluids caused the formation of the hard Ferrífero which is divided into a low-grade western and a ores and surface watcr leaching produced the soft ores we high-grade metamorphic eastern region, The boundary bet­ should find different isotope fractionation values in -the ween the two zones is marked by the breakdown ofchloritoid different types. This was the idea to start our investigations. and the appearance of staurolite. With respect to the meta­ morphic grade Simmons (1968), Eichler (1968), Moore (1969), Schorscher (1975), and Lauenstein (1981) investiga­ GEOLOGV ANO PETROLOGV Table I shows a sim­ ted parageneses of coexisting silicates in sedimentary iron plified stratigraphic column of lhe Quadrilátero Ferrífero. ore bearing sequences of the Iron Quadrangle and found which is divided into four divisions by unconforrruties. mineral assemblages in the W-region which indicate meta­ name1y the Archean basement, the Proterozoic Rio das Ve­ morphic temperatures of greenschist facies whereas the lhas series, the Minas series and the Post-Cretaceous sedi­ E-region is marked by mineral parageneses of the arnphi­ ments. The rock sequences of the basement were strongly bolite facies. "Mineralogisch-Petrographisches Institut der Technischen Universitãt, C1austhal, Adolf Roemer Str. 2 A, D~3392 Clausthal-Zellerfeld, German Federal Republic **Geochemisches Institut der Universitãt Gôttingen, V.M. Goldschmidt Str. 1, D~3400 Gôttingen, German Federal Republic Revista Brasileira de Geocténctas, Volume 12 (1·3). 1982 349 Table 1 - Simp/ified stratigraphic column ofthe Quadrilátero Ferrí• Phases of fero (afier Dorr, 1969; Roeser and Müller, 1977; Guerra, 1979; deformation Phenomena of deformation Glõckner /98l) Age Series Lithology and orogenic cycles o, Canga, lacustrine and stream sands, c1ays, sands, alluvium and colluvium -', Minas" 12 _..... " - - --' /" _ !. !.2 ~o~ ~1 r kl Rio das Velhas sI Basement Figure 2 - Deformatíon and recrystallization history of the Iron Quadrangle metasedímentary rocks (after Guba, 1981) • ltacolomi after Glõckner, 1981, part of the Minas series Schorscher (1975) found in high-grade melamorphic ro­ cks ofthe eastern border zone the paragenesis: sillimanite + + quartz + garnet + cordierite and interpreted the break­ down of amphibole and the formation of c1inopyroxene in amphibolites as the beginning of a granulitization processo ln some areas of the Quadrilátero Ferrifero three phases ofrock deformation can be distinguished (Fig. 2) but mainly the folding of only two (D, and D,) were accompanied by strong recrystallization of minerals even if lhe relationships in delaiI may be more complex (Harder and Chamberlin, 1915; Dorr, 1964, 1965; Dorr and Barbosa, 1963; Eichler, 20· 00' 1968; Hackspacher, 1979; Rosiêre, 1981; Guba 1981). Samples which show only s occur as well in lhe sarne out­ t tacotom Serles uncJlVlded crops and mines as those which were affected by s, +s, + S,. Sometimes lhe distance between cornpact ores and strongly Minas Series wifh schistose samples çovers only a few meters. This is very Cauê Formalian importam for lhe understanding of the different t.-values and "isotopic temperatures of forrnation" in closely neigh­ bouring sam pies (Fig. 6). um Bosemenl SAMPLlNG AND ANALYSIS Mosl of lhe rocks in Central Brazil are overlain by a thick weathered cover, but Thrust taul f cuts la eo km due to large mining excavations and road a lot Df . fresh sam pies are available. 375 samples of 3-5 kg weíght Fou/l were laken in lhe Iron Quadrangle (Fig. I) and supplemented Figure 1 - Rough geologic sketch after Dorr et at. (/969) and map by five samples frorn the Southern Serra do Espinhaço. of samplíng points. Dashed Une = "staurolite in" after Schorscher, Amidsl 380 sarnples, 143 (see Table 2) were selected for 1975 .. Roeser, 1977; Glõckner, 1981,' and own observattons near mineral separation through jaw crushing, pulverizing in a Ouro Preto. W = greenschist facíes area; E = amphibolite and gra­ disc mill, sieving. magnetíc separation in series of different nulite facies area; partially retrograde recrystallízed steps and fractionations, enrichment of specularite and tale 350 Revista Brasileira de Geociências, Volume 12 (1-3), 1982 Table 2 - Raw-materia! classtfícatton of investígated ítabirítes and rich ores • c ~"9i,"n ,,59 Nwnber Nome Fe(%) Physlcal propertles ofsamples 1:' i I I I i I I ",flfl" ',r;=;l",,'fl, Quartz-itabirite <30 Compact and hard or " arenaceous or dusty b. E-region weak . 2 n" 77 Itabirite 30-50 Compact and hard or (sensu stricto) arenaceous or dusty we~ ak, partially carbonace- o ous and silicate-bearing 30 n Rich itabirite 51-63 Compact and hard or dusty weak 29 " Iron Quodrongle n" 136 Hard hematite >63 Lumpy, hard, coarse ore ± magnetite grained, blueish-gray, magnetite ore sometimes very coarse grained 39 4 Soft hematite >63 fine flaky, platy, soft ore sliding,"blue dust" 39 Hydrothermal Variable Very coarse grained 4 veins on a vibrating table, heavy liquid separation, grinding in an Fig. 4 summarizes lhe ó"O-values of 136 hematite and agate mortar for separating the finest intergrowth, and in magnetite samples coexisting with the above mentioned alI cases stereo-microscopical selection of pure mineral quartzo The iron oxide samples range between + 10"/00 and ~ , concentrates by hand picking. 3,5°/00 ln contrast to quartz the iron oxides do not show Minerais used in the oxygen isotope investigations were: any regional differenccs. quartz, hematite. magnetite. martite and a few concentrates n of tale, , w- region Initially, sampies with small amounts of martite and mag­ n= 59 netite were separated from the main constituent hematite and measured separately. Since the concentrates of martite, magnetite and hematite did not show any difference in .,1"0 to that of the total iron oxide fractions, this cornplicated and time consuming procedure was considered unnecessary.
Recommended publications
  • Symposium on the Stratigraphy of the Series in the Quadrilatero Ferrifero, Gerais, Brazil
    SYMPOSIUM ON THE STRATIGRAPHY OF THE MINAS SERIES IN THE QUADRILATERO FERRIFERO, MINAS GERAIS, BRAZIL (*) by Ceologists of the joint DNPM-USGS team INTRODUCTION by JOHN VAN N. DORR II Tha ten short papers in this symposium define and describe eight new formations in the Minas series and redefine a formation set up many years ago. They thus give a summary of the stratigraphy of the Minas series. The purpose of the symposium is twofold. The first purpose is to present in succinct form for the use of the many geologists doing economic research in the area some of the stratigraphic results of twelve years of joint mapping by geologists of the Departamento Nacional da Producao Mineral and the United States Geological Survey in the Quadrilatero Fer­ rifero of Minas Gerais, Brazil. The second purpose is to formally intro­ duce into the geologic literature the stratigraphic names which will be used in puhlicatiorrs now being prepared as a result of this long campaign of mapping. The Minas series was first defined by Derby (Derby, 1906) as including the schistose rocks resting unconformably on the coarsely cryE­ talline "Archean" basement complex. This definition was accepted by Harder and Chamberlin (Harder and Chamberlin, 1915), 'who subdivided the Minas series into five units, the Caraca quartzite, the Batatal schist, the Itabira formation, the Piracicaba formation, and the Itacolomi quartzite. Guimarjies (Cuimarfies, 1931) recognized a major unconformity between Harder and Chamberlin's Piracicaba formation and the Itacolomi quartzite and moved th~ Itacolomi to series rank. Rynearson, Pomerene, and Dorr (Rynearson, et aI, 1954) recognized a major unconformity between Harder and Chamberlin's Caraca quartzite and the underlying schistose rocks, and separated the rocks below this major unconformity into a sepa­ rate series.
    [Show full text]
  • Geology and Mineral Resources of the Pico De Itabirito District Minas Gerais, Brazil
    Geology and Mineral Resources of the Pico de Itabirito District Minas Gerais, Brazil GEOLOGICAL SURVEY PROFESSIONAL PAPER 341-F Prepared in cooperation with the Departamento Nacional da Producao Mineral of Brazil under the auspices of the Agency for International Development of the United States Department of State Geology and Mineral Resources of the Pico de Itabirito District Minas Gerais, Brazil By ROBERTS M. WALLACE GEOLOGY AND MINERAL RESOURCES OF PARTS OF MINAS GERAIS, BRAZIL GEOLOGICAL SURVEY PROFESSIONAL PAPER 341-F Prepared in cooperation with the Departamento Nacional da Producao Mineral of Brazil under the au-spices of the Agency for International Development of the United States Department of State UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1965 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page Page Abstract_ _---_-_---___-__________________________ Fl Metamorphism_ ____________________________________ F34 Introduction. ______________________________________ 2 Geologic history____________________________________ 35 Purpose of the survey.__________________________ 3 Economic geology______---_---__-_-_----_---------- 36 History of investigations_______________________ 3 Iron ores.__--_-------------------------------- 37 Present work_________________________________ 3 High-grade hematite______-__-_-------_-- 37 Coordinate system for locations________________
    [Show full text]
  • The Statherian Itabirite-Bearing Sequence from the Morro Escuro Ridge, Santa Maria De Itabira, Minas Gerais, Brazil
    Journal of South American Earth Sciences 58 (2015) 33e53 Contents lists available at ScienceDirect Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames The Statherian itabirite-bearing sequence from the Morro Escuro Ridge, Santa Maria de Itabira, Minas Gerais, Brazil * Flavia Cristina Silveira Braga a, , Carlos Alberto Rosiere b,Glaucia Nascimento Queiroga c, Vassily Khoury Rolim d,Joao~ Orestes Schneider Santos e, Neal Jesse McNaughton f a Graduate Program, Instituto de Geoci^encias, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil b Instituto de Geoci^encias, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil c Departamento de Geologia, Universidade Federal de Ouro Preto, Ouro Preto, MG, Brazil d Graduate Program, Instituto de Geoci^encias, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil e Centre for Exploration Targeting, University of Western Australia, Perth, Australia f Curtin University of Technology, Perth, Australia article info abstract Article history: The itabirite-bearing metasedimentary sequence from Morro Escuro Ridge comprises the basal units Received 8 June 2014 of the Espinhaço Supergroup and makes up a small tectonic inlier developed during one of the Bra- Accepted 18 December 2014 siliano orogenic events (800-500 Ma), amongst horses of the Archean TTG gneisses, including sheared Available online 27 December 2014 granites of the anorogenic Borrachudos Suite (~1700 Ma). The metasedimentary rocks are comprised of low-to intermediate-amphibolite facies schists, quartzites, conglomerates and banded iron for- Keywords: mation (itabirite) correlatable with the sequences of the Serro Group, which underlies the meta- Morro Escuro Ridge sedimentary rocks of the Espinhaço Supergroup in the Serra da Serpentina Ridge.
    [Show full text]
  • Oxide Chemistry and Fluid Inclusion Constraints on the Formation of Itabirite-Hosted Iron Ore Deposits at the Eastern Border of the Southern Espinhaço Range, Brazil
    This is a repository copy of Oxide chemistry and fluid inclusion constraints on the formation of itabirite-hosted iron ore deposits at the eastern border of the southern Espinhaço Range, Brazil. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/129313/ Version: Accepted Version Article: Gomes, SD, Berger, S, Figueiredo e Silva, RC et al. (5 more authors) (2018) Oxide chemistry and fluid inclusion constraints on the formation of itabirite-hosted iron ore deposits at the eastern border of the southern Espinhaço Range, Brazil. Ore Geology Reviews, 95. pp. 821-848. ISSN 0169-1368 https://doi.org/10.1016/j.oregeorev.2018.03.025 © 2018 Elsevier B.V. This is an author produced version of a paper published in Ore Geology Reviews. Uploaded in accordance with the publisher's self-archiving policy. This manuscript version is made available under the Creative Commons CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ Reuse This article is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs (CC BY-NC-ND) licence. This licence only allows you to download this work and share it with others as long as you credit the authors, but you can’t change the article in any way or use it commercially. More information and the full terms of the licence here: https://creativecommons.org/licenses/ Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request.
    [Show full text]
  • Proposal for an Environmentally Sustainable Beneficiation Route For
    minerals Article Proposal for an Environmentally Sustainable Beneficiation Route for the Amphibolitic Itabirite from the Quadrilátero Ferrífero-Brazil Gizele Maria Campos Gonçalves 1 and Rosa Malena Fernandes Lima 2,* 1 Mine Planning at Brucutu Mine—Vale, São Gonçalo do Rio Abaixo, Rio de Janeiro CEP 35.935-000, Brazil; [email protected] 2 Mining Engineering Department, School of Mines, Federal University of Ouro Preto, Ouro Preto 35400-000, Brazil * Correspondence: [email protected] Received: 27 July 2020; Accepted: 4 October 2020; Published: 10 October 2020 Abstract: The high world demand for iron ores opposed to the rapid exhaustion of high-grade deposits from the main producing regions around the world has motivated the search and/or improvement of beneficiation routes, which enable the economic use of iron formations previously considered marginal ores, which have the potential to considerably increase mineable reserves due to their large volume. In this study, a sample of amphibolitic itabirite from the eastern region of the Quadrilátero Ferrífero, minas Gerais, Brazil was characterized, aiming at its use in the industrial pelletizing circuit. The main physical characteristics of this ore are moisture = 10% and specific weight = 3710 kg/m3. The ore has a high grade of loss on ignition—LOI (6.7%) and P (0.14%). Through X-ray diffractometry (XRD), optical microscopy and scanning electron microscope—SEM, the ore was found to consist of 64.5% goethite (amphibolitic, alveolar, massive and earthy); 6.8% hematite (martitic, granular and lamellar) and 0.9% magnetite. The main gangue mineral is quartz (25.5%). Based on the results of concentration tests (magnetic and flotation) performed with the studied sample, the magnetic concentration route of deslimed sample followed by the addition of slimes in magnetic concentrate can be incorporated into the pelletizing process.
    [Show full text]
  • Microporosity of BIF Hosted Massive Hematite Ore, Iron Quadrangle, Brazil
    Anais da Academia Brasileira de Ciências (2002) 74(1): 113–126 (Annals of the Brazilian Academy of Sciences) ISSN 0001-3765 www.scielo.br/aabc Microporosity of BIF hosted massive hematite ore, Iron Quadrangle, Brazil CÉSAR A.C. VARAJÃO1, ARY BRUAND,2 ERICK R. RAMANAIDOU3 and ROBERT J. GILKES4 1DEGEO, Escola de Minas, Universidade Federal de Ouro Preto, Campus Morro do Cruzeiro, 35400 Ouro Preto, Brazil 2ISTO, Université d’Orléans, Géosciences, BP 6759, 45067 Orléans Cedex 2 – France 3CSIRO – Division of Exploration and Mining, Private Bag. P.O., Wembley – WA 6014 – Australia 4Soil Science and Plant Nutrition, The University of Western Australia, Nedlands, WA 6907, Australia Manuscript received on September 27, 2000; accepted for publication on September 6, 2001; presented by A.J. Melfi ABSTRACT Massive hematite ore (MHO) is a special high-grade iron ore, used as lump ore in the process of obtaining direct reduction iron (DRI). The influence of porosity on the reducibility of MHO from the Capitão do Mato Mine (Iron Quadrangle, Brazil) was investigated using optical and scanning electron microscopes on drill core and open pit samples. Hematite is the main component of the samples and occurs as granular crystals (10 µm), microplates (1 µm) and euhedral martite (10 to 30 µm). Quartz, maghemite, kenomagnetite and goethite are minor components. Primary micropores (Å to 1 µm) are associated with microplaty crystals that fill cavities between granular hematite. Secondary micropores (Å to 5 µm) related to euhedral martite crystals, are the most important. The total porosity of weathered samples, measured using nitrogen adsorption and mercury injection, attains values up to 11%, whereas unweathered samples have a porosity less than 2.5%.
    [Show full text]
  • From Fresh Itabirites and Carbonates to Weathered Iron Ore: Mineral
    minerals Article From Fresh Itabirites and Carbonates to Weathered Iron Ore: Mineral Composition, Density and Porosity of Different Fresh and Altered Rocks from the Quadrilátero Ferrífero, Brazil Diniz Ribeiro 1,*, Israel Moraes 1, Rogerio Kwitko-Ribeiro 2, Deivid Braga 1, Carlos Spier 3 and Pedro Santos 4 1 Vale S.A., Iron Resource Management, Escritório de Águas Claras, Nova Lima, MG 34.006-200, Brazil; [email protected] (I.M.); [email protected] (D.B.) 2 Vale S.A., Mineral Technology, Centro de Desenvolvimento Mineral, Santa Luzia, MG 33.040-900, Brazil; [email protected] 3 School of Earth and Environmental Sciences, The University of Queensland, Saint Lucia, QLD 4072, Australia; [email protected] 4 Independent Consultant, Itabira, MG 35.900-360, Brazil; [email protected] * Correspondence: [email protected] Abstract: The weathering of Paleoproterozoic itabirites (metamorphic-banded iron formations) and dolomites from the Cauê and Gandarela Formations in the Quadrilátero Ferrífero (QF), Brazil, produces supergene iron ore with different mineralogical, chemical, and physical properties. In this work, we present a methodology to assess the changes in chemical and physical features of those rocks during weathering, via quantitative analyses of mineral assemblages. These mineral assemblages were calculated from chemical analyses of fresh and weathered samples collected from drill holes drilled in different iron ore deposits in the QF. In general, the number of mineral species found in fresh or/and weathered itabirite is restricted, which helps the quantification of the mass and volumes of minerals by normative calculation in a large dataset of drilling and channel samples.
    [Show full text]
  • Gold Mobility During Hydrothermal and Supergene Alteration of BIF (Itabirites), Ouro Fino Syncline, Brazil
    BW/LGOLD'91, E.A.Ladeira (ed.)O 1991 Bakema, Rotterdam. ISBN906191 1958 Gold mobility during hydrothermal and supergene alteration of BIF (Itabirites), Ouro Fino syncline, Brazil E. Ramanaidou CSIRO, Division of Exploration Geosciences, Wembley, WA., Australia di Laboratoire de Pétrologie de la Surface, Université de Poitiers, France J. M.Cathelineau, Dubessy & M.Le Gleuher CREW and GS CNRS-CREGU,Vandoeuvre les Nancy. France J. J.Trescases Laboratoire de Pétrologie de la Surface, Université de Poitiers, France Abstract : The Precambrian banded iron formation from the Quadrilatero Femfero and from the Ouro Fino syncline (Minas Gerais, Brazil) display some gold showings as quartz veins, and some gold anomalies in the surficial alteration facies.Fresh and altered rocks as well as quartz veins crosscutting the Ouro Fino series have been sampled in order to understand the factors controlling gold mobility in the itabirite series during hydrothermal vein formation, and during laterite formation. Fresh itabirites display rather high gold concentrations which range from 30 to 40 ppb. In laterites, the gold content remains relatively high but may vary significantly from the bottom to the top of the hills, and within the different horizons from 20 to 60 ppb Thus, fresh and altered itabirites may have constituted significant source rocks for gold. Systematic fluid inclusion studies by using microthermometry and Raman spectrometry analysis have been carried out on different types of quartz veins. At the hydrothermal stage, gold deposition seems to be restricted to the veins characterized by the presence of C-H-O-S fluids characterized by rather low f02 (around that kedby the Ni- Ni0 oxygen buffer) whilst no gold was found in the quartz-specularite veins characterized by high fO2 (f02 greater than that fixed by the Hematite-magnetite buffer) and sulfate rich solutions.
    [Show full text]
  • Holistic Pre-Feasibility Study of Comminution Routes for a Brazilian Itabirite Ore
    minerals Article Holistic Pre-Feasibility Study of Comminution Routes for a Brazilian Itabirite Ore Juliana Segura-Salazar 1,2 , Natasha de S. L. Santos 1,3 and Luís Marcelo Tavares 1,* 1 Department of Metallurgical and Materials Engineering, Universidade Federal do Rio de Janeiro—COPPE/UFRJ, Cx. Postal 68505, Rio de Janeiro CEP 21941-972, Brazil; [email protected] (J.S.-S.); [email protected] (N.d.S.L.S.) 2 Department of Earth Science and Engineering, Royal School of Mines, Imperial College London, South Kensington Campus, London SW7 2AZ, UK 3 BHP Chile Inc., Cerro El Plomo 6000, Las Condes, Santiago 7560623, Chile * Correspondence: [email protected] Abstract: Comminution is an essential step in processing itabirite ores, given the need to liberate silica and other contaminants from the iron minerals for downstream concentration and then pellet feed production. In general, these ores in Brazil are not particularly hard to crush and grind, but both capital (CAPEx) and operating (OPEx) expenditures in this stage of preparation can be critical for the project, in particular due to uncertainties in iron ore prices. Several circuits have been designed and are in operation for this type of ore in Brazil; however, it is not yet clear which technologies are more cost-effective and in which configuration they should be applied. This work critically analyzes four comminution circuits for an undisclosed case study. For these circuits, CAPEx, OPEx, and some environmental sustainability indices, as well as qualitative technical criteria, were used in the comparisons. This work concludes that two of these process routes, especially those based on more energy-efficient technologies (and one of these still rarely explored even at bench-scale), have demonstrated to be very attractive from multiple standpoints.
    [Show full text]
  • Geology and Ore Deposits of the Itabira District Minas Gerais, Brazil
    Geology and Ore Deposits of the Itabira District Minas Gerais, Brazil GEOLOGICAL SURVEY PROFESSIONAL PAPER 341-C Prepared in cooperation with the Departamento Nacional da Producao Mineral of Br axil under the auspices of the International Cooperation Administration of the United States Geology and Ore Deposits of the Itabira District Minas Gerais, Brazil By JOHN VAN N. DORR 20 and ALUIZIO LICINIO de MIRANDA BARBOSA GEOLOGY AND MINERAL RESOURCES OF PARTS OF MINAS GERAIS, BRAZIL GEOLOGICAL SURVEY PROFESSIONAL PAPER 341-C Prepared in cooperation with the Departamento Nacional da Producao Mineral of Brazil under the auspices of the International Cooperation Administration of the United States UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1963 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, D.C. CONTENTS Page Page Abstract.__________________________________________ Cl Geology of the Itabira district Continued Introduction.______________________________________ 2 Structure Continued Acknowledgments....- _ _________________________ 3 Folds in other rocks_____-_--______-_________ C51 History_ _ ____________________________________ 4 Faults____________-___---_____---__-____- 51 Fieldwork and maps.___________________________ 6 Metamorphism. ________________________________ 52 General geology of the Quadrilatero Ferrifero___________ 6 Regional metamorphism_____________---_-__- 52 Topography
    [Show full text]
  • And Sial, A.N., 2007. Geochemistry and Genesis of the Banded Iron
    Precambrian Research 152 (2007) 170–206 Geochemistry and genesis of the banded iron formations of the Caueˆ Formation, Quadrilatero´ Ferr´ıfero, Minas Gerais, Brazil Carlos A. Spier ∗, Sonia M.B. de Oliveira, Alcides N. Sial, Francisco J. Rios Minera¸c˜oes Brasileiras Reunidas—MBR, Av. de Liga¸c˜ao 3580, Nova Lima, 34000-000, Minas Gerais, Brazil Received 5 August 2004; received in revised form 28 September 2006; accepted 9 October 2006 Abstract The Caueˆ Formation of the Paleoproterozoic Minas Supergroup hosts banded iron formations (BIFs), locally called itabirites, deposited in shallow marine passive margin settings. Two major compositional types of itabirite, dolomitic and quartz itabirites, are found in the northwestern part of QF. The former consists of alternating dolomite-rich and hematite-rich bands, whereas the latter is formed with alternating quartz-rich and hematite-rich bands. Accessory minerals are chlorite, sericite, and apatite in both types. Dolomitic and quartz itabirites have a very simple chemical composition. In the dolomitic itabirite, Fe2O3 plus CaO, MgO, and LOI range from 95.8 to 97.8%, while in the quartz itabirite, Fe2O3 plus SiO2 range from 94.4 to 99.6%. Both itabirites are highly oxidized and present Fe3+/(Fe2+ +Fe3+) ratios higher than 0.98, by far superior than the average ratios of Paleoproterozoic BIFs. Trace element concentrations in itabirites are very low, ranging from <10 to 55 ppm. Dolomite shows negative ␦13C values varying from −2.5 to −0.8‰ versus PDB, while the oxygen isotope data display ␦18O values varying from −12.4 to −8.5‰ versus PDB.
    [Show full text]
  • Influence of Hematite Particle Morphology on Friable Itabirite Concentration in Humphreys Spiral Concentrator Influência Da
    Brazilian Journal of Development 17721 ISSN: 2525-8761 Influence of hematite particle morphology on friable itabirite concentration in Humphreys spiral concentrator Influência da morfologia da hematita presente em itabirito friável na concentração por espiral concentradora Humphreys DOI:10.34117/bjdv7n2-424 Recebimento dos originais: 18/01/2020 Aceitação para publicação: 21/02/2021 Fábio de São José PhD in Mineral Engineering Mining and Construction Department, Federal Center for Technological Education of Minas Gerais, Araxá, Brazil Av. Min. Olavo Drummond, 25 - Amazonas, Araxá - Minas Gerais Email: [email protected] João Paulo Sousa Coelho Master in Mineral Engineering Mining Engineering Department, Federal University of Ouro Preto, Ouro Preto, Brazil Campus Morro do Cruzeiro, Bauxita, Ouro Preto - Minas Gerais Email: [email protected] Carlos Alberto Pereira PhD in Mineral Engineering Mining Engineering Department, Federal University of Ouro Preto, Ouro Preto, Brazil Campus Morro do Cruzeiro, Bauxita, Ouro Preto - Minas Gerais Email: [email protected] ABSTRACT The depletion of hematitic mineral deposits and the growing content of itabirites in the iron ores mined in the Quadrilátero Ferrífero - Brazil calls for further studies in an effort to adjust the actual technologies, due to the different behaviors of the different mineral species present in the new ore. Currently, little is known about the fundamentals of particle separation in Humphreys spiral, as far as the different particles morphologies. Therefore, the performance of a spiral concentrator was evaluated by a sequence of friable itabirite tests at an industrial scale. The smallest iron content and smaller metallurgical recovery attained in the tests owe to a small particle size in sample (33.67% < 106 µm and d80 ≈ 675 µm) and a greater content of tabular hematite.
    [Show full text]