Ag/Au total production ratio and Au-Ag minerals from three types of Japanese deposits, which have produced both gold and silver, are summarized. These deposits include, Au-Ag vein (Type 1-A), base metal (Cu, Pb, Zn, Mn, (Sn), (W), (Bi), (Mo), (Sb)) vein (Type 1-B), and Au rich disseminated-type ones (Type 2).
Generally, base metal rich deposits (Type 1-B) are characterized by that, (1) the Ag/Au total production ratio is high, (2) dominant Ag minerals are Se poor argentite and sometimes Ag sulfosalts (pyrargyrite, polybasite, argentian tetrahedrite), (3) Se and Te-bearing Au-Ag minerals are absent, and (4) Sn, W, and Bi minerals are sometimes found. In contrast, Au-Ag rich deposits (Type 1-A and Type 2) have the following features; (1) the Ag/Au total production ratio is low, (2) dominant Ag minerals in Type 1-A are Ag-Se-S minerals (naumannite, aguilarite, and Sebearing argentite), and Ag sulfosalts (polybasite, pyrargyrite, argentian tetrahedrite), (3) Hg, As, Sb, and Te minerals are occasionally found, (4) in Type 2, Ag minerals except Au-Ag series minerals are rare.
The above differences in the mineralogical characteristics of the Au-Ag rich and base metal rich deposits are considered to be resulted from the differences in chemical nature of ore fluids (sulfur and oxygen activities, CO
2 concentration, pH and temperature), depositional mechanism and depth of formation. The relationship between Ag/ Au total production ratio and kinds of metals concentrated to the deposits found in the Japanese deposits is also observed in epithermal Au-Ag vein-type deposits in western U.S.A. and active geothermal systems accompanied by precipitations of base metal and precious metals.
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