Spencer R. Titley, 1989. "Regional Variation of Silver and Gold Ratios in Vein Ores of Arizona", The Geology of Gold Deposits: The Perspective in 1988, Reid R. Keays, W. R. H. Ramsay, David I. Groves
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An analysis of silver and gold production from Arizona vein-related mining districts reveals order-of-magnitude contrasts in ratios of precious metal values that correspond in a striking way to two geologically distinct blocks of crust. The contrasts in metal content transgress epochs of mineralization and other traditional controls of mineralization as well as inferred processes and environments of metal deposition. Comparison of produced silver to gold ratios in districts with those ratios representative of lithologies of contiguous or subjacent Proterozoic crust reveals that the metal ratios mimic those values in the Precambrian rocks. Deep plumbing systems in vein districts sample a significant thickness of Proterozoic rocks, and the mineralizing process appears to have resulted in metals inherited in deposits in the same proportions in which they occur within the crustal setting of ore formation.