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Records show discovery of, perhaps, 40,000 gold and silver deposits in western United States. Mine descriptions give dates of operation and allow correlations with history. These mine histories commonly indicate that the properties have further potential. Many of the prospects left 50, 75, and even 100 years ago are of interest today because of new geological concepts. Simple veins of yesterday may be the exposed parts of larger entities. The old ore controls, structures, or zones may be tied to larger lineaments, elements, or zones. In younger deposits, corollaries are often made with geothermal fields. Lineations and cross lineations require further consideration. Connections with plate tectonics come easily.
As an example of the increase in size of useful parameters, the line of segmentation portrayed in coast ranges of northern California and Oregon might be looked upon as lines marking transverse zones of extension. Better known zones of extension are parts of the very large fault network centering around the San Andreas and Garlock faults, and parts of the Imperial Valley region south of the Salton Sea, a well known geothermal area. Corollaries with such areas are sought, for example, along lines marked by the Antler and Sevier tectonic belts in Nevada.
In other western areas, pillow lavas occur in close proximity with gold occurrences which stimulates thinking along lines of spreading centers and submarine springs.
The old gold and silver deposits appear to fit readily into a framework, in which treatment of prospects as segments within a geothermal model is helpful. Conversely, with the growth of geothermal development, the view of activity will be incomplete without consideration of the potential by-products, precious metals.
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