Predominant alteration shows zoning related to distance from fractures. Adjacent to fractures, illite (sericite), quartz, and pyrite replace all feldspars, chlorite, and mixed-layer illite-montmorillonite; the chlorite and illite-montmorillonite represent alteration of primary hornblende, biotite, and calcic plagioclase, farther from fractures. Less prominent changes, related to depth, include local replacement of calcic cores of plagioclase by albite or calcite at 200 feet or more, and by K-feldspar above 300 feet. The minerals are those that theoretically would be expected at the temperatures and water compositions in the drill holes, which suggests that present waters are producing the observed alteration, and resemble an ore-forming fluid.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.