Diverse Origins of Hydrothermal Ore Fluids

Abstract

Chemical, isotopic, and physical data from fluid inclusions, ore and gangue minerals, and active geothermal systems indicate the general characteristics and probable origins of the dominant ore-transporting waters of many systems. Evaluation of such data from a wide variety of mining districts and hot-spring systems indicate that five classes of waters, here called meteoric, ocean, "evolved conhate, " metamorphic, and magmatic, account in varying proportions for hydrothermal fluids. More than 40 localities are reviewed in this study, including: (1) 6 Hg systems involving metamorphic or "evolved-connate " waters; (2) 15 epithermal Au-Ag districts and 2 probably similar active hydrothermal systems involving meteorix: water and per-haps as much as 5 or 10 percent of magmatic water; (3) 10 ore districts and 2 active systems with abundant base metals--Ag, involving waters of diverse origins, including ocean, "evolved-connate, " meteoric, and magmatic, usually with salinities above 4 per-cent; and (4) 5 copper-molybdenum deposits, generally involving early dominance by magmatic water but with increasing proportions of meteoric water during sulfide and postsulfide stages. Individual constituents, including the metals, CI, S, and CO2, may come from the same or different sources than the dominant water. Igneous intrusions frequently pro-vide the energy and perhaps the S and C of the ore deposits, but a magmatic origin of the metals, H20, and other constituents is commonly assumed uncritically. Ore deposition may require favorable combinations of circumstances that differ from place to place, but with some combinations being especially favorable. No simple model of origin is likely to explain all or even most metalliferous ore deposits.