STABLE ISOTOPE GEOCHEMISTRY OF MARBLE-HOSTED ZN DEPOSITS, CENTRAL METASEDIMENTARY BELT, GRENVILLE PROVINCE, ONTARIO

The Central Metasedimentary Belt of Ontario is underlain by Mesoproterozoic supracrustal rocks and intruded by 1.2 to 1.0 Ga plutonic suites. Marble in the supracrustal package hosts several stratiform sphalerite deposits that have not been extensively studied. The purpose of this study is to constrain the origin of these deposits using carbon and oxygen isotope ratios of marble host rocks and ores. Samples were examined from the Long Lake zinc mine, the Slave Lake deposit, and the Wilkinson zinc prospect in the Sharbot Lake domain, and also from the Thirty Island Lake deposit in the Frontenac terrane. Samples from these sites share similar mineralogies: Host rocks typically contain calcite + diopside, with variable chondrodite and graphite while ore samples contain sphalerite + pyrite with other sulphides. Samples from Thirty Island Lake are comparable to normal Grenville marble (δ¹³C= -1.20±1.32‰ PDB, δ¹⁸O= 24.55±0.94‰ SMOW, n=7), as are those from Slave Lake (δ¹³C= 3.35±0.27‰, δ¹⁸O= 24.12±3.12‰, n=5). Long Lake has consistently lower values (δ¹³C= 1.35±0.76‰, δ¹⁸O= 15.95±1.00‰, n=11). Wilkinson samples have the most variability (δ¹³C= 2.13±1.26‰ and δ¹⁸O= 20.41±5.05‰, n=7). Preliminary isotope results show distinct isotope trends in the two terranes. Taken together, Sharbot Lake domain samples define a positive trend between carbon and oxygen isotopes, suggesting water-rock interaction and hydrothermal alteration. In contrast, the Thirty Island Lake deposit (Frontenac terrane) has isotope systematics similar to the Balmat-Edwards Zn-Pb deposits (Whelan et al., AJS 1990).