Field and Stable Isotopic Characteristics of Carbonate Alteration Zones, Timmins Area

Abstract

<p> Hydrothermal carbonate was introduced into igneous rock in the Timmins area during an early, sea water alteration event when calcite (δ13C = 0 to -3o/oo) filled the primary porosity of basalt flows and during a later hydrothermal event when mafic and ultramafic igneous rock were altered into a zoned sequence consisting of an inner zone of ferroan or magnesian carbonate flanked by calcite- and chlorite-rich assemblages. The younger intense carbonate alteration event predated or was synchronous with regional metamorphism and deformation and was focused along structurally induced, permeable zones. Gold was introduced during and after the intense carbonate alteration.</p> <p> Away from carbonaceous sediments, δ13C-values of the ferroan carbonate are very uniform (-3.5 to -5o/oo) regardless of stratigraphic position, size, or gold tenor of the alteration zone. As carbonaceous sediments are approached, 13C of the ferroan carbonate becomes upto 4o/oo heavier. The 13C of the CO2 and δ18O and δD of the water components of the hydrothermal fluid are estimated to have been -3 to -6, +5 to +10, and -40 to -60o/oo respectively. The geological controls on the distribution of carbonate alteration, and the stable isotopic values of the hydrothermal components suggest that the H2O-CO2 hydrothermal fluid was of magmatic origin, a result of mantle degassing.</p>