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.

11NTRODUCTION 2. THE OURO FINO SYNCLINE :GEOLUGICAL THE SE'ITING AND WEATHERING 'OF BIF The Quadrilatero Ferrifero (Iron Quadrangle) of Minas Gerais (Brazil) owes its name to an almost The Ouro Fino syncline is a small perched syncline, rectangular arrangement of huge banded iron- in which refolding has resulted in an acute axial formations or BIF @or, 1969 ; Hoppe et al., 1987). flexure (Fig. 1). The Caraça and Itabira groups The Quadrilatero Femfero is an area of about 7000 (lower and middle units of the Minas Supergroup) km2 of central Minas Gerais located approximately form the skeletal structure of the Serra do Ouro Fino 450 km north of Rio De Janeiro vig. 1). The area is (Table 1). The lower unit (Caraça group) consists of rich in mineral deposits@IF) of Au, Mn and AI (Abreu, Moeda and Batatal formationS.The middle unit 1973). The itabirites are in places gold bearing, (Itabira gronp) is represented by the Caue formation. and are enriched by decomposition (Siegers and These formations are the only units preserved in the Renger, 1985). syncline. The Moeda-formation is composed largely This paper reports a study of gold concentrations in of a clean white fine-grained quartzite and minor fresh and weathered itabirites and the factors amounts of sericitic Phyllite (Maxwell, 1972). The controlling gold mobility in the Ouro Fino syncline Batatal formation is a homogeneous dark-gray situated in the central part of the Quadrilatero graphitic argillite (Maxwell, 1972). The Caue Femfero. Gold in quartz veins is found in Caraça formation (lower Itabira group) is composed of group rocks associated with Precambrian banded itabirites (or SF),bedded metasedimentary rocks iron-formations (BE), and the BIF itself shows gold with altemating hematitehmgnetite and quartz layers. anomalies in the lateritic weathering proffie. There are The itabirites are deeply weathered (down to as two types of quartz veins. The first type cut the much as 200 m) and the different weathering itabirites and contain specularite but no gold. The horizons (Table 2) have been studied in detail second type are from the Batatal formation (Caraça (Ramanaidou, 1989). The first weathering stages group) and contain rare native gold particles. (Soft Itabirite, SI and Hematite B, HB) are Systematic fluid inclusion studies using isovolumemc ; their desilicificationis progressive but microthermometry and Raman spectrometry analyses important, and geothitisation is moderate. When have been carried out on different quartz veins desilicification is almost complete in the Hematite A crosscutting the Ouro Fino syncline series, in order horizon (HA), the primary oxides (hematite and to characterize the P-V-T-X conditions of the fluid magnetite) are destabilized. An epigenetic circulation in the fault network. replacement of the preexisting minerals occurs in 1 1I

I F ! "clay-like red product" a. product consists of sma hematite and goethite. Ir horizon (HGH) the goethi induration is strong lead destruction of the prima goethite-rich "cuirasse", ti weathering column. The plateau shows a res1 canga caps the HB or HA are marked by a deep and with a HGH horizon well I

3. GEOCHEMISTRY 1 PROFILE 3.1 .Raw data Atomic absorption analysi was used for the deter" 3). Fresh itabirites d; concentrations which ran laterites, the gold content level as in the BIF but m the bottom to the top of th horizons. Near the surfacl horizon, 30 to 40 ppb are values are obtained in the ("clay-Like red product") o .. -i . 3..2 - ¿3mtcteddata

-8' Using the density of thc possible to compare the gc of rocks in the different P 3). On the plateau, an en] Fig. 1 :Location of the Quadrilatem ferriffero (Don, 1969) the HB horizon and il weathering effect is not v leached. On the other k profile, when HGH horiz gold level seems erratic compared to the bed rock product, where the weath gold is the lowest. Thus, at the super: enrichments or depletic weathering of the itabiritt gold loss or gain from ont Hardened goethitic however difficult to horizon (HGH) concentrations (< 100 p ...... localization of the minerah Hematite A (HA) HA Though the gold in the E Hematite B (I3B) HB HB values are anomalous, a: ...... possible source of gold fc Soft itabirite (SI) SI SI veins. Itabirite IT o IT 4 . P-V-T-X CONDITIC FORMATION Systematic fluid incl1 microthermometry and R:

730 "clay-like red product" alumina rich pockets. This Table 3 : Variation in gold content (absolute and product consists of small particles of secondary normalized at constant volume) in samples from the hematite and goethite. In the Hardened Goethitic alteration profies horizon (HGH) the goethitization is intense and the induration is strong leading sometimes to a total Sample Type Auppb Density ppb/lOOan: destruction of the primary bedding. A vesicular and I tabiri tes . goethite-rich "cuirasse", the so called canga caps the .._...... weathering column. 145 IT 4 3,27 13,08 The plateau shows a restricted evolution where the cPo7 IT 35 3,49 122,15 ..._.. canga caps the HB or HA horizons, while the slopes IT36 IT 68 3,1 2106 J marked by a deep and strong weathering column 123 IT 43 2,92 125,556 are with a HGH horizon well developed. IT1 IT 20 2,79 55,s .. CHBA3OO IT 60 2,24 134,4 . .. Profile 14 (upperslope) ...._. 3 . GEOCHEMISTRY IN THE WEATHERING PROFILE CHB91 SI 20 576 55,2 CHB92 SI 25 2,93 753 3.1 . Raw data CHB93 HB 17 2'44 41,48 CHB94 HB 35 23 873 Atomic absorption analysis (with a graphite furnace) ~ cc95 C 40 2,61 104,4 was used for the determination of gold content (Table Profile 1 (upperslo~e)-- 3). Fresh itabirites display anomalous gold HB 13 2,559 33,67 concentrations which range from 20 to 60 ppb. In laterites, the gold content remains at about the same 1~~~~0HA - 30 2 60 level as in the BIF but may vary significantly from 38 2,32 88,16 the bottom to the top of the hills, and in the different horizons. Near the surface (cuirasse) and in the HB 51 HA 45 2,06 92,7 horizon, 30 to 40 ppb are recorded, whereas lower 52 HA 45 3,02 135,9 values are obtained in the intermediate HA horizon 53 HA 20 2,17 43'4 ("clay-like red product") or in the HGH horizon. 55 HGH 35 3,m 107B 56 HGH 25 24 60 57 HGH 33 3,13 10329 3..2 - Corrected data CC58 C 32 237 82.24 Using the density of the different samples, it is Profile 4 (slope) possible to compare the gold level for a same volume 131 HA 8 2,99 23'92 of rocks in the different weathering horizons (Table 132 HA 39 1,92 74,88 3). On the plateau, an enrichment occurs mainly in 133 HGH 10 2,41 24,l the HB horizon and in the canga. When the 134 HGH 11 2,96 323 weathering effect is not very strong, the gold is not U,72 leached. On the other hand, on very weathered 135 HGH 28 1,49 profile, when HGH horizon is well developed, the 136 HGH 16 2,95 47,2 gold level seems erratic and we observe a loss 137 HGH 11 29 31,9 ng profiles on itabirites compared to the bed rock. In the pockets of the red 138 HGH 14 3,n 37,94 product, where the weathering effect is the highest, 139 C 10 2,12 21,2 gold is the lowest. Red products ateau (1) Plateau Thus, at the supergene stage, some gold 400 (2) enrichments or depletions could occur during RP 6 . - 1,7 10,2 weathering of the itabirites. The mechanisms of the 1O3 Rr 5 1,7 83 gold loss or gain from one of the lateritic horizon is however difficult to solve since the low concentrations (e 100 ppb) make impossible any have been carried out on different quartz veins localization of the mineralogical form of gold. crosscutting the Ouro Fino series, in order to Though the gold in the BIF is extremely low, these characterize the P-V-T-X conditions of the fluid values are anomalous, and are considered to be a circulation in the fault network. Two vein types have possible source of gold found in some of the quartz been identified : veins. -type 1- barren quartz-specularite veins which are frequent in the Ouro Fino syncline. The studied quartz vein from the Capanema mine croscut the 4 . P-V-T-X CONDITIONS OF QUARTZ VEIN itabirite series and do not show any ductile FORMATION deformation. They are centimetric to decimetxic in width, are partly weathered near the surface. They do Systematic fluid inclusion studies by using not show any gold concentration. Specularite mlcrothermometry and Raman spectrometry analysis crystallizes sometimes on cores of magnetite.

73 1 - type 2- quartz veins containing rare native gold of the vapours is estimated to be very low from the itabirites and other metan panicles, mostly located in metamorphic series rare observation of ice melting near 0.0"C in some those characterized by spe surrounding the itabirites. Small and old scrapes inclusions. acting as buffers (graphite-: attest of local investigations for gold. The weathering series from the Batatal gol makes difficult the identification of the primary The fluid compositions, especially in type c sulphide assemblages which are partially to totally inclusions are rather unusual : low pH at room 6. CONCLUSIONS transformed into iron oxydes and/ or hydroxydes. temperature, sulfate rich aqueous solutions, some of them being mixed with volatiles (C02). The This study has shown that : Type 1 veins display three kind of inclusions. Most coexistence of aqueous vapours together with - Itabirite which consis inclusions are scaterred within the quartz and no hypersaline fluids are probably indicative of boiling magnetite or quartz layers 1 chronology could be established. No definite planes process which probably lead the crystallization of the content as a source rock. ' of fluid inclusions have been recognized. This quartz -hematite assemblage. The observed levels (down to 2OOm) by suggest that most fluids are contemporaneous of the compositions reveal highly oxydizing conditions, transforms the initial min( crystallization or recrystallization of the quartz. and temperatures above 200-300°C. It is actually oxides and hydroxidr a) two-fluid phase aqueous inclusions : the Tm difficult to propose any source for such fluids redistribution of gold ma H20 are mostly in the -8.5;-10S°C, whilst the (evaporites ?). depletions (down to 5 r temperature of first melting is low around -60°C.The However, the two successi Th (L-V)L range from 63 to 137°C. Type 2 quartz veins contain volatile rich fluids the itabirite, noted HB,HA b) sulfate rich inclusions mostly borne by fluid inclusion trails. Each trail is ferruginous cuirasse so-CB Two types are distinguished : characterized by rather homogeneous phase contents have gold contem - hypersaline CO2 -rich inclusions : they are relationships at room temperature. Especially, the 8-45 ppbrange. multiphase and contain : water filling which varies from nearly O up to 70% in It is highly probable tha - one or more solids : a solid hexagonal in shape the whole set of inclusions, is nearly constant within lateritization is necessa representing about 10% of the total volume of the a given fluid inclusion plane. Textutal relationships concentrations, such as fi inclusion, identified by Raman spectroscopy as a suggest repeated fracturing, with the trapping of reworking of the weathe sulphate (barite, or celestite, ?). Other solids are fluids characterized by increasing amounts of water. waters followed by a diffi difficult to identify. Tm of the hexagonal solid is Tm CO2 ranges from -56.7 to 57.2"C with a gravity of the transporte( around 140 rt 15 OC. maximum at -56.8"C. Tm H20 when H20 is present such process would neei - a vapour phase dominated by CO2 accompanied is in the -1.5 ; -11.5"C range with a maximum which were not canied OUI by small amounts of N2. ThC02(L or V) is in the lo- around -2.7"C. ThCo2 (L-V)L shows rather constant - the systematic fluid inc 17.8"C range with a maximum between 7" and 14°C. values within a given trail, but varies greatly from by using microthermomeq Tm CO2 in the -56.6" -56.8"C range indicate the trail to trail :it ranges from -1 1.5"C to + 29.8"C, with analysis have shown th. presence of dominating C02, which is confirmed by maxima at -7"C, +3"C, +17"C, and + 27°C. Most compositions characterize I Raman spectroscopy ; inclusions decrepitate at temperatures ranging from veins crocutting the Ourc quartz-specularite veins ( a liquid phase where SO4 2- is the dominant 180 to 320°C. Some global homogenization to the - vapour phase have been obtained in the 320-400°C kinds of fluids, with ion identified by Raman spectroscopy, while HS04- range. Raman spectroscopy reveals the presence of compositionsCO2 such as hypt ions are detected but in much lower concentrations. CH4 , H2S, (C2H6 and N2) in the volatile phase. rich fluid inclusion: TmH20 is in the -4.3'; -57°C range. The presence of CH4 reveals much lower f02 than conditions (T min.= 200-: A11 studied inclusions decrepitated at for type 1 veins. (when recalculated at suc1 temperatures ranging from 160 to 280°C sulfate rich solutions) incompatible with gold h-ar - bisulfate rich inclusions, are two-fluid phase 5. CONDITIONS OF GOLD MOBILITY IN THE On the contrary, the qu: inclusions characterized by the presence of an OURO FINO SERIES AT THE HYDROTHERMAL native gold particles, most unidentified small solid.TH Most Tm H20 ranges from - STAGE series smunding the itabi 1.5 to -4.5 OC. Some &-V)L are recorded around C-H-O-N-S rich fluids v. 230°C whilst most inclusions decrepitate at Itabirites constitute the most probable source rocks. water. These fluids indicai temperatures up to 290°C. for gold anomalies encountered in this area. At the and probable equilibrium I Considering the polyatomic species which can hydrothermal stage, gold deposition seems to be most fluids described in F. identified by Raman spectroscopy, the liquid phase restricted to the veins characterized by the presence al., 1990, Alvarenga et al.. contains both SO4'- and HS04- ions in rather similar of carbonic fluids (type2) characterized by rather low concentrations. f02 and moderate pH, whilst no gold deposition Thanks to a calibration by using experimental characterizes the studied quartz-specularite veins REFERENCES solutions (Moissette et al., 1990), (SO4--) was which are characterized by high f02 (f02 greater estimated to be around 0.32 k 0.05 molal, and pH than that fur4 by the Hematite-magnetitebuffer) and Abrcu S.F.A. 1973. Reci around -0.3 * 0.2 at 25°C in such inclusions. It is nearly neud pH at 250"-300 "C. 2nd Ed., Vol. 2, Sa0 Pau probably the first Occurrence of such acid fluids in Consideration of thermodynamical data on gold Alvarenga J.M. S, Cathc natural fluid inclusions. solubility gives a relatively good explanation to the 1990.Chronology and different behaviour of gold in such contrasted C02-H20 and H20 ri~ -c) aqueous vapours : the vapour phase occupies conditions. Gold was probably easily transported in inmetamorphic quartz. around 80-90 % of the inclusion. No volatile species highly saline and oxydizing solutions and could not dismct, Brazil. Min. Mal has been identified by Raman spectroscopy. No TH be deposited before any changes in the surrounding Boiron M.C., Cathelineau could be obtained due to decrepitation. The salinity physical-chemical conditions (f02 or pH). Such A. 1990. Fluids in herc changes could occur at the contact zones between french variscan belt. Mi

732 iated to be very low from the itabirites and other metamorphic series, especially DOIT J.V.N.11 1969. Physiographic, stratigraphic . melting near O.O°C in some those characterized by specific mineral assemblages and structural development of the Quadrilatero acting as buffers (graphite-sulphide rich metamorphic Femfero, Minas Gerais, Brazil. U.S.G.S. Prof. series from the Batatal group for instance). Paper. MIA, 110 p. tions, especially in type c Hoppe A., Schobbenhaus C & Detlef H.G.W. 1987. unusual : low pH at room 6. CONCLUSIONS Precambrian Iron Formations in Brazil. Precambrian :h aqueous solutions, some of Iron Formations. Editors Peter. W. Uitterdijk Nith volatiles (C02). The This study has shown that : Appel. Teophrastus Publications. JUS vapours together with - Itabirite which consists of alteming hematite- Ladeira E.A. 1980. Metallogenesis of gold at the xobably indicative of boiling magnetite or quartz layers have a relatively high gold Morro Velho mine and in Nova Lima district, . lead the crystallization of the content as a source rock. When affected in surfcial Quadrilatero Femfero, Minas Gerais, Brazil. 'Univ. :semblage. The observed levels (down to 2OOm) by a lateritic alteration, which West Ontario. Unpubl. Ph. D. Thesis. 272 p. Iighly oxydizing conditions, transforms the initial mineralogy into complex iron Maxwell C.H. 1972. Geology and ore deposits of ve 200-30O0C. It is actually oxides and hydroxide assemblages, some the Alegria district, Minas Gerais, Brazil. U.S.G.S. my source for such fluids redistribution of gold may occur with some local Prof. Paper. 341J. 72 p. depletions (down to 5 ppb in the red product). Moisette, A., Dubessy J, Cathelineau M., C' However, the two successive lateritic horizons above Ramanaïdou E. & Le Gleuher M. 1990 Fluids with contain volatile rich fluids the itabirite, noted KB, HA,which are overlain by the high acidity evidenced by Raman micro- inclusion trails. Each trail is ferruginous cuirasse so-called "canga"disp1ay gold spectrometric analysis of sulfate and bisulfate ions ther homogeneous phase contents have gold contents which remain within the in fluid inclusions from a gold showing (Brazil). temperature. Especially, the 8-45 ppb range. IAGOD symposium. Ottawa (Canada). Abstract from nearly O up to 70% in It is highly probable that further process than the p.Al8. 2s lateritization is necessary to get higher grade Ramanaidou E. 1989. Genese d'un gisement ons, is nearly constant within plane. Textutal relationships concentrations, such as for instance a mechanical lateritique. Evolution supergene des itabirites uring, with the trapping of reworking of the weathered profiles by surficial Proterozoiques de la mine de fer de Capanema ncreasing amounts of water. waters followed by a differential sedimentation by (Minas Gerais, Brazil). These Doct. Poitiers 183 p. om -56.7 to 57.2OC with a gravity of the transported products. The study of Siegers A. & Renger F. 1985. Gold mining in 'm H20 when H20 is present such process would need specific investigations Brazil. Enmetall., 38,7/8.351-358. 'C range with a maximum which were not carried out in our study. L-V)L shows rather constant - the systematic fluid inclusion studies canied out rail, but varies greatly from by using microthermometry and Raman spectrometry xn -1 1.5OC to + 29.8OC, with analysis have shown that rather different fluid , +17OC, and + 27°C. Most compositions characterize the barren and mineralized t temperatures ranging from veins crocutting the Ouro Fino series. The barren obal homogenization to the quartz-specularite veins (type 1) display different I obtained in the 320-400°C kinds of fluids, with, especially, unusual opy reveals the presence of compositions such as hypersaline, sulfate rich and i N2) in the volatile phase. CO2 rich fluid inclusions. The physical-chemical :veals much lower f02 than conditions (T min.= 200-300"C, pH nearly neutral (when recalculated at such temperatures, high f02. sulfate rich solutions) seem to have been incompatible with gold transport or deposition. ?OLD MOBILITY IN THE On the contrary, the quartz veins containing rare TTHEHYDROTHERMAL native gold particles, mostly located in metamorphic series surrounding the itabirites, are characterized by C-H-O-N-Srich fluids with varying amounts of most probable source rocks water. These fluids indicative of relatively low f02, luntered in this area. At the and probable equilibrium with graphite are similar to Id deposition seems to be most fluids described in Au-quartz veins (Boiron et laracterized by the presence d., 1990. Alvarenga et al., 1990). I characterized by rather low whilst no gold deposition *dquartz-specularite veins REFERENCES by high f02 (f02 greater natite-magnetite buffer) and Abreu S.F.A. 1973. Recursos minerais do Brasil, -300OC. 2nd Ed., Vol. 2, Sao Paulo (E. Blucher). nodynamical data on gold Alvarenga J.M. S, Cathelineau M. & Dubessy J. Ay good explanation to the 1990.Chronology and orientation of N2-CH4, gold in such contrasted C02-H20 and H20 rich fluid inclusion trails in )bably easily transported in intrametamorphicquartz veins from the Cuiaba gold ing solutions and could not district, Brazil. Min. Mag. 54,245-255. changes in the surrounding Boiron M.C., Cathelineau M., Dubessy J. & Bastou1 itions (f02 or pH). Such A. 1990. Fluids in hercynian Au-veins from the che contact zones between french variscan belt. Min. Mag., 54.231-243..

733 Ladeira. Eduardo A. (ed.) 906191 1958 Batugina,I.M. & I. M.Petukhov 9061919487 Brazil Gold '91- The economics,geology. geochemistry and gen- Geodynamic zoning of mineral deposits for planning and esis of gold deposits - Proceedings of the symposium Brazil Gold exploitation of mines '91,Belo Horizonte, MG, 13-17.05.1991 (Russiantranslations series, 77) (No rights India) 1991.25cm,844pp..Hfl.165/$95.00/f50 1990.25 cm. 169 pp.. Hfl.95 /550.00/f30 Gold and gold deposits are one of the main focuses of pure and This book describes the principal aspects. objectives and prob- applied research in geological science at the present time. At the lems, as well as the method of geodynamic zoning in areas of Intemational SymposiumBrazil Gold '91,participants from 23 mineral deposits and mine fields. Data are given from investiga- counmes and with a wide variety of research interests joined to tions of the physico-mechanical properties of the rock massif and present and discuss their latest contributions on the economics, conditions of formation, nature and energy of rockburst. The geo- geology, geochemistryand exploration of gold deposits. dynamic system of blocks has been taken as the basis of stress The proceedings of Brazil Gold '91 encompass 117 papers which conditions of the virgin rockmass and methods of its assessment are distributed in five sections: Regional studies; Petrology and are enumerated. Problems concerning the practicd application of . geochemistry; Geology and case studie of gold deposits: Struc- geodynamic zoning of mineral deposits are discussed in terms of tural geology of gold deposits and dishicts;.and Mineral explora- ensuring safe working conditions in coal and metal mines. tion. They will be very useful for professional geologists, geophy- sicists and mining engineers concemed with precious metal de- Fytas. K..L.Collins & R.K.Smghal (eds.) 90 6191 7603 . posits, whether working in research and development, industry, or Computer applications in the mineral industry- Proceedings mineral exploration. It will certainly also be an essential source for of thefirst Canadian conference,Quebec, 7-9 March 1988 both undergraduateand graduate students in economic and 1988.25cm,784pp.,Hfl.185/$100.00/f58 applied geology. Mme planning &scheduling: Mine evaluation; Mineral processing; Orebody modeIlimgJGeostatistics; Geotechnical applications; Mme wansport; Monitoring; Expert systems; Mine ventilation; moM THE SAME PUBLISHER: Exploration; Maintenance management 88 papers. Foster. R.E (ed.) 906191504X Jain. S.K. 90 6191 485 X Gold 82: The geology, geochemistry and genesis of gold depos- Ore processing its - Proceedings of the symposium GoId'82. University of Zim- (Indian edition series, 15) (No rights India) babwe, 24 - 28 May I982 1987.24 cm, 530 pp., Hfl.95 /%50.00/UO (Geological Society of Zimbabwe Special Publications, 1) Fundamental priciples & industrial asp&History &economics: 1984.25 m.764pp..Hfl.195 /%I10.00/€62, Pre-treatment & liberation of minerais; Comminution of m, the This work covers theme gold from explorationmethods to the Suing &classification; Gravity concentration: Flotation: Magne- genesis of gold on deposits. All the papers nad at the htema- tic & electrical separation; Solid-fluid separation. tional symposium organized by the Geological Society of Zim- babwe an included in the proceedings. Many contributions arc by Plotnikov, N.I. & 1.1. Roginets 9061919002 invited lecturers frmn Canada,Austmlia. South Africa and else- Hydrogeology of ore deposits where. They include some of the foremost research workers in this (Russian translations series, 72) (No rights India) field. 1989.21 cm. 298 pp., Hfl.95 /$50.00/€30 Gened hydrological conditions; Study of hydrological conditions Kesse. G.O. 906191 5899 at stage of exploitation of ore deposits; Analysis of influence of The mineral and rock resources of Ghana exploitation of ore deposits on changes in the geological environ- 1985,25cm,624pp.,H8.245/$138.00/f70 ment. Importance of minetals. Ghana: Geography, physiography, geology &geohydrology;Mined resources of Ghana: background; Ghose, A.K. (ed.) 906191 498 1 MetaIlic & non-metallic minerals: Bulk constmction materials; Strategies for exploitation of mineral resources in developing Radioactive minerals, Petroleum &other fossil fuels: Minor countries - Proceedings of the international symposium, Dhan- minerals: Minerals in concentrates: Tables of summary of mineral badp6-8 November 1986 & rock resources in Ghana: Legislation afFecting mineral conces- (Indian edition series, 16) (No rights India) sions &mining industry; Index. Author: Director Geological Sur- 1987,30cm.286pp.,Hfl.l25/$70.00/€39 vey Department of Ghana Mineral development strategiesin developing countries: Smallscalemining worldwide; Mined development in LDCS; Lateritisation processes 90 6191 202 4 Ecological disturbances; Pehuleum strategies: Offshire oil poUu- Proceedings of the international seminar, Trivandrum,India, I I - tion: etc. 28 papers from Australia, Brazil, India, Indonesia 14 December 1979 (No rights India) Pakistan. UK & USA. 1981.28 cm,458pp., Hfl.225/$125.00/€71 Geomorphic & genetic aspeas; Distribution in space & time, & 906191 615 1 global tectonics or palaeoenvironmental controls; Geochemical. The development science and art of minerals surveying geophysical & other exploration techniques for minddeposits Proceedings of the 6th international congress of the Intemational associated with laterite; Relation to agriculture, geohydrology & Sociery for Mine Surveying, Harrogate, 9- 13 September 1985 geotechnique. 51 papers. 1985,25cm, 1098pp.,2vols,HR.27$/S150.00/f87

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PROCEEDINGS OF THE SYMPOSIUM BRAZIL GOLD'9 1 BELOHORIZONTE/MG/13- 17MAY 1991 BRAZIL GOLD'91 The Economics, Geology, Geochemistry and Genesis of Gold Deposits

Edited by E.A.LADEIRA Department of Geology, Institute of Geosciences, Universidade Federal de Minas Gerais, Belo Horizonte - MG

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Published for the Associação Organizadora do Brazil Gold, Belo Horizonte, Brazil by A.A. BALKEMA /ROTTERDAM / BROOKFIELD / 1991