Ross Lawrence Sherlock MSc thesis abstract
Historic drill core form the Shuniah Mine and more recent drill core from the Keystone and Porcupine Mines have provided the basis for a study of these past silver-producing veins as a function of depth. Precipitation was initiated from a boiling fluid at temperatures in excess of 370EC. Cooling of the fluid and precipitation of calcite and sulfides followed generally at 100EC. Several episodes of deposition separated by fracturing events are evidenced. From fluid boiling temperatures the depth of emplacement for the veins is 1 km with the pressure regime alternating between hydrostatic and lithostatic. The ore-depositing solutions appear, therefore, to have arisen from depth and deposited their ores in proximity to diabase sills, which cap the various vein systems, in response to hydrologic factors.
Stable isotope studies reveal that carbon in vein calcite was possibly derived from oxidation of amorphous carbon in the Gunflint and Rove Formations (*13 C=-33 per mil), which host the silver lodes. Calcite as well, does not occur at great depth in the vein systems. *18O in calcite increases with depth, from calculated negative to positive values, suggesting that the ore-depositing fluid was a basinal-type brine that become increasingly mixed with meteoric water towards the surface. Fluid salinities are low to moderate, but invariably undersaturated, also supporting mixing. The dominant salts are NaCl, MgCl2 and to a lesser extent CaCl2.
Ross is currently the Exploration Manager for Gold Fields Canada
A copy of the thesis can be downloaded here