Abstract
The pre-Cambrian rocks of the northern Black Hills which have been mapped and studied by the staff of the Homestake Mining Company comprise sedimentary formations with a total stratigraphic thickness of about 20,000 feet. The oldest formations, the Poorman and Homestake, are dominantly ankeritic carbonate and iron-magnesium carbonate respectively. The younger formations, the Ellison, Northwestern, Grizzly, and Flag Rock, are dominantly argillaceous rocks with some quartzites and other rock types. Pre-Cambrian intrusive rocks, originally gabbroic, cut the pre-Cambrian sedimentary rocks; and the whole succession is overlain unconformably by the Cambrian Deadwood formation, and everything is cut by Tertiary intrusive rocks.
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