Nature and origin of the protolith succession to the Paleoproterozoic Serra do Navio manganese deposit,Amapa Province,Brazil |
| |
| Institution: | 1. Paleoproterozoic Mineralization Research Group, Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, South Africa;2. CAE Mining-Datamine, 8 Bentley Office Park, Corner Bevan & Wessels Road Rivonia, 2128, Johannesburg, South Africa;3. Department of Mineralogy, Technische Universität Bergakademie Freiberg, 09596 Freiberg, Saxony, Germany;4. Department of Geology, North-West University, Potchefstroom Campus, Private Bag, x6001, 2520 Potchefstroom, South Africa;1. Department of Physics and Earth Sciences, Jacobs University Bremen, Campus Ring 1, 28759 Bremen, Germany;2. Instituto de Geociências, Universidade de Brasília, Campus Universitário Darcy Ribeiro, CEP 70910-900 Brasília, DF, Brazil;3. Instituto de Geociências, Universidade de São Paulo, Rua do Lago 562, 05508-080 São Paulo, SP, Brazil;1. Geology Department, Rhodes University, Makhanda/Grahamstown 6140, South Africa;2. Department of Earth Sciences, Utrecht University, Princetonlaan 8A, 3584CB, the Netherlands;3. Department of Geological Sciences, University of Cape Town, Rondebosch 7700, South Africa;1. Council for Geoscience, P Bag X112, Pretoria, 0001, South Africa;2. Department of Geology, University of Fort Hare, Private bag X1314, Alice 5700, South Africa;1. Department of Geology, University of Johannesburg, Auckland Park 2006, Johannesburg, South Africa;2. LGCA, UMR 5025, Université Joseph Fourier, 1381 rue de la Piscine, BP 53, F-38041 Grenoble Cedex 09, France;3. Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Università di Bologna, Via Zamboni 67, 40126 Bologna, Italy;1. Federal University of Paraná State, Polytechnic Center, Geology Department, 81531-980 Curitiba, Brazil;2. University of Montpellier 2, Geosciences of Montpellier, cc. 060, 34095 Montpellier, cedex 5, France;1. Graduate Program in Geology, Brasilia University, Geoscience Institute, Darcy Riberio University Campus, 70910-900 Brasília, Federal District, Brazil;2. Brasilia University, Geoscience Institute, Darcy Riberio University Campus, 70910-900 Brasília, Federal District, Brazil |
| |
| Abstract: | Until its closure in 1997, the Serra do Navio deposit, located in Amapá Province, Brazil, was one of the most important sources of high-grade manganese ore to the North American market. The high-grade manganese oxide ores were derived by lateritic weathering from metasedimentary manganese protoliths of the Serra do Navio Formation. The local geological context and nature of this protolith succession are not well understood, due to poor surface outcrop conditions, and intense deformation. However, based on similar age, regional tectonic setting and lithology the Paleoproterozoic volcanosedimentary succession that includes the Serra do Navio Formation is widely believed to be similar in origin and laterally equivalent to the Birimian Supergroup in West Africa. For the present investigation several diamond drill cores intersecting the protolith succession were studied. Detailed petrographic and whole rock geochemical studies permit distinction of two fundamental lithological groups comprising of a total of five lithotypes. Biotite schist and graphitic schist lithotypes are interpreted as former metapelites. A greywacke or pyroclastic protolith cannot be excluded for the biotite schist, whereas the graphitic schist certainly originated as a sulfide-rich carbonaceous mudstone. Rhodochrosite marble, Mn-calcite marble and Mn-silicate rock are grouped together as manganiferous carbonate rocks. Manganese lutite constitutes the most probable protolith for rhodochrosite marble, whereas Mn-calcite marble was derived from Mn-rich marl and Mn-silicate rock from variable mixtures of Mn-rich marl and chert.The sedimentary succession at the Serra do Navio deposit is similar to that encountered at many other black shale and chert-hosted Mn carbonate deposits. A metallogenetic model is proposed, predicting deposition of manganese and closely associated chert in intra-arc basins, in environments that were bypassed by distal siliciclastic (carbonaceous mud) and proximal pyroclastic/siliciclastic detritus. Positive Ce anomalies and δ13CVPDB values of − 4.3 to − 9.4 per mill suggest that manganiferous carbonates derived during suboxic diagenesis from sedimentary Mn4+ oxyhydroxide precipitates. Metamorphic alteration of manganese carbonate–chert assemblages resulted in the formation of Mn-silicates, most importantly rhodonite and tephroite; porphyroblastic spessartine formed where Mn-carbonate reacted with aluminous clay minerals. Microthermometric studies of fluid inclusions in spessartine porphyroblasts suggests that peak metamorphic conditions reached the upper greenschist facies (1–2 kbars and 400–500 °C). Retrograde metamorphism is marked by partial re-carbonation, expressed by the formation of small volumes of rhodochrosite, and Mn-calcite that are closely associated with quartz, chlorite and minor amounts of sulfides related to post-metamorphic veinlets. It is this metamorphosed succession that sourced the high-grade manganese oxide ores during prolonged lateritic weathering. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
