Precious metal deposits
Precious metals, including gold (Au), silver (Ag) and platinum group metals (PGM’s) have all been and are currently being mined in Northwestern Ontario. Greenstone itself has hosted a number of high grade gold mines in its past and current exploration at the Hardrock Project in Geraldton is promising.
Precious metal deposits tend to be smaller, higher grade and low tonnage as the value and demand of the mineral being extracted tends to be very high.
Hydrothermal solutions are brines derived from water mixing with soluble minerals at depth. These brines/fluids at great pressures and temperatures can dissolve other minerals and in particular native minerals like gold and silver. The brines themselves have a multitude of sources, from surface waters to fluids released from Magmas, as such its composition can vary greatly even with a small area.
As the solutions of brines and dissolved minerals it moves through rocks, cracks and voids in rocks. When the solution changes its pressure, temperature or has a reaction with another rock whereby it can no longer stay liquid or keep the minerals dissolved, the minerals are precipitated out and/ore the fluids solidify.
The solidified solution typically forms quartz veins with the dissolved minerals solidifying within them.
Due to the relatively narrow nature of veins, only precious metals tend to be mined this way. Gold and Silver will appear in the vein in its native form in small amounts irregularly distributed within the vein.