In the early history of the development of many ore deposits, especially those of silver and of copper, masses of rich sulphide ore are encountered which lie below the limit of surface decomposition, and which are very often soon passed through in mining and found to give place more or less abruptly to comparatively poor and base sulphide ores. In other cases “bonanzas” are encountered, which in many instances consist of rich ores of a mineralogic character wholly unlike the main mass of the mineral deposit; or sometimes fissures in a low grade ore are filled by a rich ore. Such masses are believed to be generally of later origin than the original vein filling, and as they enrich the vein they are designated as sulphide enrichments.
This paper is an attempt to explain the genesis of such bodies of sulphide ores as enrichments formed by . . .