A rich end-cut of high-grade silver from the O'Brien Mine in Coleman Township showing thick silver mineralization. It is an "end cut" with some pink erythrite on the uncut surface.
The O'Brien mine was discovered in 1903 and started production almost immediately. It was the longest continuously operating mine in the Cobalt area. It was developed through 5 shafts, the deepest being 345ft; and over 16 miles of drifts, cross-cuts, and raises. Total production was approx. 41 million oz. Ag; 3 million lbs. Co; 200,000 lbs. Ni; 500,000 lbs. Cu; and 64 oz. of gold*.