Abstract

The Selbaie Cu–Zn deposit is located in the northeastern portion of the northern Archean Abitibi volcanic belt. It is one of the most important base metal deposits in Canada. It includes stratiform pyrite levels in the volcanites and shallow-water sediments, stockworks in a rhyodacitic breccia, and a copper-rich vein, in a caldera context. The study of the regional alteration distribution is based on a database of more than 2300 chemical sample analyses using the NORMAT normative mineral alteration index. This method allows independent analysis of the numerous lithologic variations in the Selbaie district. Five facies are distinguished in a vast sodium-depleted zone, from the core to the periphery of the hydrothermal system: chlorite–pyrophyllite in the mineralized zones, chlorite–sericite, sericite, sericite–orthoclase and orthoclase at the periphery. The carbonates also show zoning, with ankerite–dolomite at the periphery and siderite–magnesite at the core. With NORMAT, it is possible to highlight overprinted alterations. The zoning observed at Selbaie corresponds to the overprinting of a system showing sulphide ore and acid-type epithermal deposit characteristics, with abundant pyrophyllite, very likely related to a deeper porphyritic system

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