Genesis of polymetallic mineralization and the metallogeny of the Paleoproterozoic Cobalt Embayment, northern Ontario.

摘要

The recent discoveries of gold-rich and uranium-bearing, polymetallic mineralization in a geological setting akin to that of the historical Cobalt Ag-Co veins has: (i) clearly demonstrated the potential of the Cobalt Embayment to host hydrothermal mineral deposits enriched in economic metals other than silver; and (ii) prompted a re-evaluation of the metallogeny of this important Paleoproterozoic basin, which covers an area of 60,000 km 2 in northern Ontario. This re-evaluation has integrated field mapping, ore mineralogy, petrography, and stable and radiogenic isotope studies in order to assess the petrogenetic similarities of the regionally distributed hydrothermal mineralization whose main characteristics are its: (1) Occurrence in steeply-dipping, discordant calcite-quartz vein systems; (2) Location in Early Proterozoic host rocks, most importantly the Nipissing Diabase and the upper Huronian sedimentary rocks; (3) Spatial association with periodically reactivated, regional fault systems; and (4) Polymetallic (Cu, Co, Ni, Fe, As, Au, Ag, +/-U) ore assemblage.;Radiogenic and stable isotope results confirm the occurrence of at least two basin-wide mineralizing events that occurred in the Early Proterozoic (ca. 2220 and ca. 1700 Ma). In addition, the integrated field and geochemical data suggest a petrogenetic model for vein mineralization in which oxidized basin fluids reacted with localized reductants along major regional fault systems that were reactivated both during and post-intrusion of the Nipissing Diabase. Such features are suggestive of a hydrothermal system in which the polymetallic veins may represent a peripheral element of a previously unrecognized unconformity-associated mineralization at depth. This model represents the development of a new mineral exploration model for the Proterozoic rocks of the Cobalt Embayment.;Keywords. Cobalt Embayment, gold, uranium, polymetallic, ore deposits, unconformity-associated, Proterozoic, carbon, oxygen, lead, strontium, stable isotopes, radiogenic isotopes, Merico-Ethel, Elk Lake, Brett property.