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An epigenetic origin for the Passagem de Mariana gold deposit

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The gold-tourmaline quartz-vein deposit of Passagem de Mariana, in the southeastern part of the Quadrilátero Ferrífero, produced more than 60 tonne of gold, from the end of the 17th Century until 1954. The mine has not operated since 1985. Orebodies
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  An epigenetic srcin for the Passagem de Mariana gold deposit,Quadrilátero Ferrífero, Minas Gerais, Brazil D.S. Vial  a, ⁎ , B.P. Duarte  b , K. Fuzikawa  c , M.B.H. Vieira  d a  CVRD  —   Companhia Vale do Rio Doce, BR381, Km 459, Santa Luzia, MG, Brazil   b  Faculdade de Geologia da Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier, 524, Maracanã, Rio de Janeiro, RJ, Brazil  c CDTN-Centro de Desenvolvimento da Tecnologia Nuclear, Rua Mário Werneck, s/n, Campus UFMG, Pampulha, Belo Horizonte, MG, Brazil  d Companhia Vale do Rio Doce, BR262, Km 296, Santa Luzia, MG, Brazil  Received 10 December 2002; accepted 30 March 2005Available online 14 February 2007 Abstract The gold – tourmaline quartz – vein deposit of Passagem de Mariana, in the southeastern part of the Quadrilátero Ferrífero, produced more than 60 tonne of gold, from the end of the 17th Century until 1954. The mine has not operated since 1985.Orebodies are veins composed of white quartz ( N 60 vol.%), carbonate (ankerite), tourmaline, sericite and sulfides. Tourmaline(dravite), up to 10 vol.% of the vein, occurs as subhedral, coarse, commonly zoned crystals, and is concentrated along vein boundaries and on the edges of host rock inclusions in the veins. Tourmaline is present in all rock types in the mine, but thechemical composition of the host rocks determinates the intensity of tourmalinization, with the alteration being greater in sericitic phyllites, graphite – sericite phyllites, and calcareous rocks. The most abundant sulfide is arsenopyrite, which is normally associatedwith pyrite and pyrrhotite. Minor amounts of chalcopyrite, galena, löllingite, berthierite, and maldonite are present throughout thedeposit. Sulfides are concentrated at veins boundary or are dispersed in the veins. Arsenopyrite is associated, most commonly, withcalcareous rocks, and graphite – sericite phyllite. Pyrrhotite is usually found at the base of itabirites. Gold abundance is directly proportional to sulfide concentration. Hydrothermal alteration associated with the veins includes silicification, tourmalinization,and sulfidation. The mineralized zone is a shear zone associated with a bedding-parallel thrust fault that juxtaposes the itabirite(Lower Proterozoic Minas Supergroup) over other units. This shear zone/thrust fault extends for tens of km beyond the Passagemmine and hosts numerous gold deposits. The richest orebodies are along the itabirite footwall contact and within the graphite – sericite phyllite (Main orebody). Although many lithologic units were mineralized the graphite – sericite phyllite appears to have been most favorable for gold deposition.The area underwent three phases of deformation, D 1 , D 2  and D 3 . Mineral assemblages indicate upper-greenschist to lower-amphibolite conditions of regional metamorphism. Retrograde metamorphism, characterized by chloritization of biotite andchloritization and biotitization of garnet, developed locally. The gold-bearing veins crosscut the main foliation and lithologiccontacts at low angle and occur within, or are in contact with, all lithotypes. Field and laboratory data indicate that goldmineralization at Passagem de Mariana is epigenetic. Gold deposition occurred after the peak of metamorphism, within the late- to post-D 2  period of deformation, which is correlated with second set of structures of Trasamazonian age of Alkmim and Marshak[Alkmim, F.F., Marshak, S., 1998. Transamazonian Orogeny in the Southern São Francisco Craton Region, Minas Gerais, Brazil:evidence for Paleoproterozoic collision and collapse in the Quadrilátero Ferrífero. Precambrian Research 90, 29-58.], indicatingthat the gold mineralization occurred between 2.124 and 2.04 Ga. We choose to regard Passagem de Marina as an orogenic golddeposit as defined by Groves et al. [Groves, D. I., Goldfarb, R.J., Gebre-Mariam, M., Hagemann, S.G., Robert, F., 1998. Orogenic  Available online at www.sciencedirect.com Ore Geology Reviews 32 (2007) 596 – 613www.elsevier.com/locate/oregeorev ⁎  Corresponding author.  E-mail address:  diogenes.vial@cvrd.com.br  (D.S. Vial).0169-1368/$ - see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.oregeorev.2005.03.017  gold deposits: A proposed classification in the context of their crustal distribution and relationship to other gold deposit types. OreGeology Reviews 13, 7-27.], i.e., an epigenetic, structurally-hosted lode – gold vein system in a deformed metamorphic terrane.© 2007 Elsevier B.V. All rights reserved.  Keywords:  Gold; Quartz vein; Arsenopyrite; Tourmaline; Passagem de Mariana; Quadrilátero Ferrífero; Brazil 1. Introduction The Passagem de Mariana gold mine is located in thevillage of Passagemde Mariana, 7 km eastof Ouro Preto,inthesoutheasternpartoftheQuadriláteroFerrífero(QF),Minas Gerais, Brazil (Fig. 1). The deposit produced at least 60 tonne of gold from sulfide – tourmaline – quartzveinsbetweentheendofthe17thCenturyand1954.After intermittent production from 1954 to 1985, the Compan-hia Minas da Passagem (CMP), owner of the property,halted mining operations. The mine is 409 m deep and isfloodedbelowthe315level(83mbelowsurface).Accessis via inclined shafts, 1400 m in length and dipping 15°,generally in an easterly direction (Fig. 2).A mineralized zone, which includes the Passagem deMariana mine, extends more than 23 km from Ouro Pretoto Antonio Pereira (Fig. 1). The following abandonedmines occur in this zone: Veloso, Palácio Velho or ChicoRey, Bom Jesus das Flores, Taquaral, Passagem deMariana, Mata Cavalo, Morro Redondo, Morro Santana,Rocinha, and Antonio Pereira (Fig. 1). The zone followsthebaseoftheitabiritesoftheProterozoicCauêFormation(Itabira Group). The main orebodies in the Passagem deMariana,Mata Cavalo,andMorroSantana mines occur at the base of the itabirite. Some orebodies occur within theitabirite inthe VelosoandAntonioPereira mines,whereassmaller orebodies occur within quartzites of the CaraçaGroup in the Rocinha and Ouro Preto mines. Mineraliza-tion in the Veloso mine formed quartz veins and massivearsenopyrite within itabirite, both along bedding.ThegeologyofthePassagemdeMarianagoldminehas been described by numerous authors (Hussak, 1898;Bensusan, 1910; Derby, 1911; Ferrand, 1913; Legraye,1937; Maia, 1944; Guimarães, 1965; Fleischer, 1971;Fleischer and Routhier, 1973; Vial, 1988; Vial et al., 1988;Duarte, 1991; Fleischer and Vial, 1991, and others). Thestratigraphy,structure,andgenesisofthedeposithavebeenthesubjectofmuchdebate.Amongthese,thegenesisoftheore remains the most contentious issue. Fleischer (1971)and Fleischer and Routhier (1973) proposed a syngeneticoriginfortheveindeposit,whereasanepigeneticoriginfor the deposit was favored by the other authors.The present contribution presents the results of studies by the authors, including sampling, chemicalassaying, underground mapping of 1700 m of workingsat 1:100 scale, as well as petrographical and fluidinclusion studies of both mineralized and barren veins.We propose to demonstrate the unquestionable epige-netic srcin of the deposit. 2. Regional geology The southeastern part of the QF is underlain bymetamorphosed Precambrian plutonic, volcanic, andsedimentary rocks comprising four major stratigraphicunits (Guimarães, 1965; Dorr, 1969). These are, fromoldest to youngest: (1) the Archean granitic and gneissic basement; (2) the Archean Rio das Velhas Supergroup;(3) the Lower Proterozoic Minas Supergroup; and (4)the Lower Proterozoic Itacolomi Group (Fig. 1).The Rio das Velhas Supergroup, a greenstone belt sequence, comprises two sub-groups in the region: the Nova Lima Group (metavolcanic rocks, metapelites, andiron-rich chemical metasedimentary rocks) and theMaquiné Group (metapsammites and metapelites). TheMinas Supergroup includes three groups: the CaraçaGroup (clastic metasedimentary rocks), the Itabira Group(chemical metasedimentary rocks), and the PiracicabaGroup (a rhythmic succession of clastic and chemicalmetasedimentary rocks). The Caraça Group includes theMoeda Formation (metaconglomerates, quartzite, andmetapelites) and the overlying Batatal Formation (car- bonaceous metapelites). The Itacolomi Group is made upof mature psammites (quartzites and conglomerates).The mine area is underlain by the Nova Lima, Caraça,and Itabira Groups (Fig. 1). The Nova Lima Group isrepresented by its upper portion, the Catarina MendesFormation,composedofintercalationsoffeldspar  – quartz – mica schist (metagraywacke), mica schist (metapelite),tourmalinite, calc-silicate rocks and tremolitite (metamarl),with rare paraconglomerate layers (Pinto and Silva, 1996;Zucchetti and Baltazar, 1998; Lobato et al., 2001). 3. Mine geology 3.1. Stratigraphy Ten informal lithological units were identified duringunderground mapping of accessible workings. The rela-tionshipbetweenunitsissummarizedinFig.3.Eachunitis 597  D.S. Vial et al. / Ore Geology Reviews 32 (2007) 596   –  613  Fig. 1. (A) Regional geological map of the southeastern portion of the Quadrilátero Ferrífero (adapted from Balthasar and Zuchetti, this volume) withlocation of figure B. (B) Simplified geological map of the Passagem de Mariana gold district (after  Barbosa, 1969; Zucchetti and Baltazar, 1998).598  D.S. Vial et al. / Ore Geology Reviews 32 (2007) 596   –  613  a single rock type and may vary in mineralogical compo-sition at the mine scale. The units, from bottom to top, are:1) Brown quartz – carbonate –  biotite – sericite schist (QBS).2) White sericitic quartzite (QTZ).3) Gray banded calcareous rock (BCR).4) Silver-gray sericitic phyllite and dark-gray graph-ite – sericite phyllite (GSP).5) Sulfide-bearing banded quartz – carbonate rock(QCR).6) Light gray pyrrhotite- and quartz-rich rock (PQR).7) Amphibolite (AMP).8) Milky quartz with tourmaline and sulfides  —  oreveins (QTV).9) Pyrrhotite-bearing amphibole schist   —  Jopplingorebody (JOP).10) Dolomitic and amphibolitic itabirite (ITB).The only units that are continuous throughout themine are the quartz – carbonate –  biotitesericite schist   — QBS (at the base), and the itabirite (at the top). Their minimum thicknesses are 20 and 50 m respectively. Allother units occur as discontinuous restricted lensoid bodies with a combined thickness nowhere exceeding10 m. The quartz vein  –  QTV (ore) is hosted by all units below the itabirite  –  ITB, including quartz – carbonate –  biotite – sericite schist  – QBS. Late, vertical, barrenquartz veins transect all units. The irregular shape anddistribution of lithologic units was interpreted byFleischer and Routhier (1973) as being mainly theresult of facies controls during sedimentation. However,those investigators failed to recognize the structuralnature of most lithological contacts and the crosscuttingrelationships that are well exposed in the mine.Correlation of the ten mapped units with the regionalstratigraphy, coupled with structural studies is as follows:1) The itabirite  —  ITB belongs to the Itabira Group andthe quartz – carbonate –  biotite – sericite schist  – QBS tothe Catarina Mendes Formation of the Nova LimaGroup. Fig. 2. Mine plan (projected at surface) of the Passagem de Mariana gold mine showing the location of stopes, major orebodies, and geologicalsections of  Fig. 6A to J (from Companhia Minas da Passagem).599  D.S. Vial et al. / Ore Geology Reviews 32 (2007) 596   –  613  2) All other units, except those that are ore bearing(quartz vein  —  QTV and pyrrhotite-bearing amphi- bole schist   —  JOP), are imbricated tectonic sliversfrom the Nova Lima (quartz – carbonate –  biotite – sericite schist   —  QCR, amphibolite  —  AMP, and pyrrhotite- and quartz-rich rock  —  PQR) and Caraça(quartzite  —  QTZ, sericitic phyllite and graphite – sericite phyllite – GSP,and bandedcalcareous rock  — BCR) Groups.The graphite – sericite phyllite – GSP, which has beenconsidered by Fleischer (1971) as a typical lithotype of the Caraça Group (Batatal Formation) in the Passagemde Mariana gold mine, is very similar to graphitic phyllite that is widespread in the Nova Lima Group.There is no direct evidence to justify its correlationwith the Caraça Formation, but the inexistence of graphitic phyllite in the Nova Lima Group in theregion of the mine leads us to agree with theinterpretation of  Fleischer (1971). Amphibolite couldnot be correlated with the itibirite because it is anintrusive rock and shows crosscutting relationshipswith the itabirite. There are strong differences betweenamphibolitic itabirite and the amphibolite. Amphibo-litic itabirite is a banded magnetite – hematite rich rock,whereas amphibolite is a massive (low hematite – Fig. 3. Lithological sequence and schematic distribution of quartz veins (orebodies) in the Passagem de Mariana gold mine (after  Vial, 1988).600  D.S. Vial et al. / Ore Geology Reviews 32 (2007) 596   –  613
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