Deposits in the Beardmore-Geraldton Greenstone Belt
Both Beardmore and Geraldton have past producing gold mines of notable high-grade. The MacLeod-Cockshutt Mine, and the Central Patricia and Pickle Crow mines in Pickle Lake are non-stratiform deposits. Non-stratiform deposits contain sulfide-rich alteration zones immediately adjacent to late structures and are similar to mesothermal vein-type gold deposits. Late quartz veins and/or shear zones are present in most known BIF-hosted gold deposits. The distributions of gold-bearing veins and sulfide-rich zones are commonly controlled by fold structures. Major faults of regional scale have been recognized near many non-stratiform deposits. Irregular, massive lenses of sulfides and quartz occur in a folded series of greywacke and iron formation in the Hard Rock and MacLeod-Cockshutt mines (Horwood and Pye, 1951). These massive replacement lenses (up to 65%, sulfides) cut the folded iron formation and are related to quartz-carbonate veins up to 0.6 m wide. Veins are usually barren of gold mineralization except where they contain sulfides, consisting primarily of pyrite, arsenopyrite and pyrrhotite.