The link between hydrothermal epigenetic copper mineralization and the Cac ° apava Granite of the Brasiliano Cycle in southern Brazil M.V.D. Remus a, *, L.A. Hartmann a , N.J. McNaughton b , D.I. Groves b , I.R. Fletcher b a Centro de Estudos em Petrologia e GeoquõÂmica, Instituto de Geocie Ãncias, Universidade Federal do Rio Grande do Sul, PO Box 15001, Porto Alegre RS 91501-970, Brazil b Centre for Strategic Mineral Deposits, University of Western Australia, Nedlands, WA 6907, Australia Accepted 31 January 2000 Abstract Base-metal deposits in the Cac ° apava do Sul Copper Province are hosted by both volcanosedimentary rocks of the Bom Jardim Group and by metamorphic rocks of the Passo Feio Formation, and show a spatial relationship to the Cac ° apava Granite. These associations have led to much controversy about the genesis of the base-metal deposits, which has been at least partly resolved by precise dating using SHRIMP (Sensitive High Resolution Ion Microprobe) U/Pb zircon studies combined with S, Pb, and Sr isotope trace studies. The Passo Feio Formation is Neoproterozoic in age and was derived from a complex continental source, as shown by the presence of xenocryst zircons of Archaean, Paleoproterozoic, and Neoproterozoic ages. It was metamorphosed at ca. 700 Ma. The syntectonic Cac ° apava Granite that intruded the supracrustal rocks of the Passo Feio Formation at 562 Ma was derived from an old sialic basement. Lead-isotope data are consistent with a 562 Ma age for the base-metal sulphide deposits sited in the Passo Feio Formation. The least-radiogenic compositions lie between the ®eld of the isotopic compositions of the Cac ° apava Granite and rocks of the Passo Feio Formation, suggesting that Pb in the sulphide deposits may have been derived from both sources. The Pb, like that in the Cac ° apava Granite and Passo Feio Formation, was derived from a primitive crustal source. Sulphur isotope data from the base-metal sulphide deposits in the Passo Feio Formation are compatible with a mixed sedimentary and magmatic source. The most logical model for ore genesis, based on the isotopic data and spatial relationships, is that magmatic metal-bearing ¯uids from Cac ° apava Granite leached metals from the Passo Feio Formation and that the deposited sulphides therefore show mixed isotopic signatures. However, there is also some isotopic evidence from the Cac ° apava Granite itself that suggests assimilation of S-bearing rocks of the Passo Feio Formation during emplacement. Thus, isotopic signatures could have been inherited from assimilated metal sulphides at this stage, and deposition could have been entirely from Cac ° apava Granite-derived magmatic ¯uids. Importantly, the inferred 562 2 8 Ma age for the deposits in the Passo Feio Formation is younger than the well-constrained age of 594 2 5 Ma for the CamaquaÄ/Santa Maria deposits. Thus, the epigenetic sulphides in the Passo Feio Formation cannot be the source of these deposits as previously suggested. Other isotopic data also argue against such a model. 7 2000 Elsevier Science Ltd. All rights reserved. Resumen Os depoÂsitos de metais-base da ProvõÂncia CuprõÂfera de Cac ° apava do Sul saÄo hospedados por rochas vulcanosedimentares do Grupo Bom Jardim e por rochas metamoÂr®cas da Formac ° aÄo Passo Feio, estando espacialmente associados ao Granito Journal of South American Earth Sciences 13 (2000) 191±216 0895-9811/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S0895-9811(00)00017-1 * Corresponding author. Fax: +55-51-319-1811. E-mail address: mremus@if.ufrgs.br (M.V.D. Remus).