THE SERRA VERDE CU-MO-AU DEPOSIT, CARAJÁS MINERAL PROVINCE, PARÁ STATE, BRAZIL

The Serra Verde Cu-Mo-Au deposit is located between the townships of Parauapebas and Curionópolis, Carajás Mineral Province, Brazil. This region is known for its large BIF-type Fe deposits (e.g., N4, N5) and its iron oxide Cu-Au systems (e.g., Salobo, Bahia-Alemão, Sossego, and Cristalino). The Carajás province represents a late Archean volcano-sedimentary basin that developed on a basement of Archean tonalitic and tronhjemitic high grade gneisses. Serra Verde is a small vein deposit with lenses of massive Cu-Mo-Au ore. The orebodies are situated in a N30W trending 45º-80ºSE dipping brittle fault in a meta-volcanosedimentary sequence that includes schists, gabbroic and mafic volcanic rocks. The deposit occurs near the contact of plutonic rocks that form part of the >2.53 Ga Estrela Granite Complex. Ore is constituted mainly by chalcopyrite, pyrrhotite, pyrite, molybdenite, and gold. Gangue mineralogy includes quartz, amphibole, apatite, tourmaline, and biotite. Sulfur isotope analysis on chalcopyrite from Serra Verde gave delta ³⁴S (CDT) values of 0.99 and 1.03 permil indicating a magmatic sulfur source. Oxygen isotope compositions of quartz in a matrix of massive chalcopyrite are 11.0 and 11.4 permil. These delta ¹⁸O (SMOW) values would be compatible with magmatic fluids assuming formation temperatures in excess of 350ºC. A Re-Os age of 2609 ± 13 Ma was determined for molybdenite from Serra Verde. The stable isotope data presented above are consistent with a magmatic-hydrothermal genetic model. Granitoid magmas of the Estrela Granite Complex are a possible metal, sulfur, and fluid source for the mineralization at Serra Verde.