The Cipoeiro gold deposit,Gurupi Belt,Brazil: Geology,chlorite geochemistry,and stable isotope study |
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| Institution: | 1. CPRM, Geological Survey of Brazil, Av. Dr. Freitas, 3645, Belém-PA CEP: 66095-110, Brazil;2. Programa de Pós-Graduação em Geologia e Geoquímica, Universidade Federal do Pará (UFPA), Caixa postal 8608, Belém-PA CEP: 66075-110, Brazil;3. GPGE, Grupo de Pesquisa em Geologia Econômica, UFPA, Brazil;4. Conj. Satélite Tv., WE10 casa 586, Coqueiro, Belém-PA CEP: 66670-240, Brazil;5. Université de Nice, Département de Géologie, UMR 7329 GEOAZUR, Parc Valrose (Batiment Sciences Naturelles), Nice 06108, France;6. Western Australian Argon Isotope Facility, Department of Applied Geology & JdL-CMS, Curtin University, Perth WA6845, Australia;7. Research School of Earth Sciences, The Australian National University, Mills Road, Canberra 0200, Australia;1. MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, People''s Republic of China;2. National Research Center of Geoanalysis, Beijing 100037, People''s Republic of China;3. South Jiangxi Geological Survey Party of JBEDGMR, Ganzhou 341000, People''s Republic of China;1. MNR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;2. Radiogenic Isotope Facility, School of Earth and Environment Sciences, University of Queensland, Brisbane, QLD 4072, Australia;3. Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, School of Earth Sciences, Guilin University of Technology, Guilin 541004, China;1. Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University in Prague, Prague, Czech Republic;2. Aurea, Jílové u Prahy, Czech Republic;3. Czech Geological Survey, Brno, Czech Republic;4. Czech Geological Survey, Prague, Czech Republic |
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| Abstract: | The Cipoeiro gold deposit, located in the Gurupi Belt, northern Brazil, is hosted by tonalites of 2148 Ma. The deposit is controlled by splays related to the major strike-slip Tentugal shear zone, and at the deposit scale, the mineralization is confined to ductile–brittle shear zones. Mineralization style comprises thick quartz veins and narrow and discontinuous quartz-carbonate veinlets associated with disseminations in altered host rocks. The postmetamorphic hydrothermal paragenesis is composed of quartz, calcite, chlorite, white mica (phengite), pyrite, and minor albite. Electron microprobe analysis of chlorites reveals a relatively uniform chemical composition at depths of more than 100 m. The chlorites are characterized by (Fe + Mg) ratios between 0.37 and 0.47 and AlIV ranging between 2.22 and 2.59 a.p.f.u. and are classified as Fe-chlinochlore. Temperatures calculated by applying the AlIV contents of chlorites yield a relatively narrow interval of 305 ± 15°C. Stable isotope (O, H, C, S) compositions have been determined in silicate, carbonate, and sulfide minerals. The δ18O and δD values of the mineralizing fluid range from +2.4 to +5.7 and from ?43‰ to ?20‰, respectively, and are interpreted as having a metamorphic origin. The δ13C values of fluid CO2 are in the range ?10.7‰ to ?3.9‰, whereas the fluid δ34S is around 0‰. Carbon and sulfur compositions are not diagnostic of their sources, compatible as they are with mantle, magmatic, or average crustal reservoirs. The hydrothermal paragenesis, chlorite–pyrite coexistence, temperature of ore formation, and sulfur isotope evidence indicate relatively reduced fO2 conditions for the mineralizing fluid. Geologic, chemical, and isotopic characteristics of the Cipoeiro deposit are compatible with the class of orogenic gold deposits. |
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