Provenance, mineralogy, geochemistry, geochronology and Pb isotope systematics of meta-siliciclastic rocks in the Mesoproterozoic Upper Vazante Sequence, Brazil: Implications for metal sources and base metal metallogeny
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The objective of this research is to investigate the origin and evolution of meta-siliciclastic rocks within the Mesoproterozoic Upper Vazante Sequence (1300 to 1100 Ma) in order to improve understanding of metal sources and metal mobility in the Vazante – Paracatu zinc mining district, Brazil. This was achieved through integrated study of the mineralogy, geochemistry, detrital zircon geochronology and whole-rock lead isotope compositions of meta-siliciclastic rocks occurring below and within carbonate strata that host pre-orogenic (1200 to 1000 Ma) and syn-orogenic (850 to 650 Ma) Zn – Pb silicate and sulfide orebodies. Lithogeochemistry of meta-siliciclastic rocks from the Serra do Garrote Formation (below carbonate rocks) and Serra do Poço Verde Formation (interbedded with carbonate rocks) indicates sediments were derived from andesitic to felsic, continental arc-related rocks. Detrital zircon U – Pb dates and provenance patterns suggest major sources of detrital material were Paleoproterozoic arc rocks, related to the Trans-Amazonian orogeny that built the Columbia Supercontinent (2.20 to 1.90 Ga). Deposition of these meta-siliciclastic rocks occurred between 1.30 and 1.20 Ga, during or after continental rifting related to continental breakup. Carbonaceous phyllites and phyllites from the Serra do Garrote Formation are enriched with respect to Zn and associated elements (e.g. Cd, Hg, In, Cu, V, U). Zn-enrichment is related to pre-orogenic hydrothermal sulfides that formed between 1200 and 665 Ma. Lithogeochemistry and whole-rock Pb isotope compositions of Zn-enriched phyllites suggest that metals were derived from upper crustal material and transported by U-bearing fluids. The lithogeochemical and Pb isotope signatures of siliciclastic-hosted mineralization, occurring underneath mineralized and un-mineralized carbonate strata, are similar to those from syn-orogenic carbonate-hosted Zn deposits. Although there is textural evidence that pre-orogenic sulfide mineralization was locally remobilized during the Brasiliano Orogeny, there is little evidence that measurable quantities of Zn were removed from the Serra do Garrote Formation during its evolution. The similar geochemical and isotopic signatures in the carbonate-hosted syn-orogenic orebodies and the Serra do Garrote pre-orogenic mineralization suggest that metals were derived from similar sources, such as the underlying basement that siliciclastic detritus originated from and upon which, the Upper Vazante Sequence was deposited.
URI for this recordhttp://hdl.handle.net/1974/27467
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