Gold in the Neoproterozoic juvenile Bossoroca Volcanic Arc of southernmostBrazil: isotopic constraints on timing and sources

The Neoproterozoic Bossoroca juvenile Volcanic Are of southernmost Brazil c ontains are-related gold deposits. The Bossoroca gold deposit consists of v eins and stockworks of quartz-gold ores with minor pyrite, chalcopyrite, ga lena and tellurides. Carbonate, chlorite, sericite and tourmaline are the m ain gangue minerals. The ore shoots are contained in calc-alkaline pyroclas tic andesites and dacites with minor basalts and epiclastic rocks of the Ca mpestre Formation. SHRIMP U/Pb investigations of zircon show that the islan d-are volcanogenic sequence was formed ca 757 m.y. ago in the early Brasili ano Cycle and metamorphosed into transitional grsenschist/amphibolite facie s of low-pressure regional metamorphism at cn 700 Ma. Nearby. the post-tect onic Sao Sepe Granite was intruded into the volcanic are at ca 550 Ma. The mineralising fluids have been related either to metamorphism or to solution s derived from post-tectonic intrusive granites. Lead isotopic analyses, ca rried out on galena from the gold ore, on feldspar and total ruck from the associated volcanic pile, and also on feldspar and total rock from the Sao Sepe Granite, indicate that gold mineralisation is related to the volcanoge nic rocks, and that the deposit should be considered to be of an epizonal o rogenic type. (C) 1999 Elsevier Science Ltd. All rights reserved.