Salient characters of the nickel-cobalt-native silver ore type as displayed in many parts of the world are reviewed. A primary origin for most of the native silver is indicated but downward enrichment appears to have developed rich ores in a few localities. In most districts where evidence of genetic relationship between ore deposition and igneous intrusion is available a derivation of the mineralizing solutions from acid magmas, mostly granitic, is indicated. The Ontario deposits are anomalous in forming an apparent exception to this rule as these deposits are associated with diabase sills. Evidence is presented indicating (a) that the causes of this association may be largely structural, and (b) that at Bruce Mines, Ontario, granite dikes cut the diabase flows and are in turn cut by the veins. It is concluded on this and other grounds that the mineralizing solutions in the Ontario districts may well have come from granitic rather than diabasic magmas.

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