Descriptive models for epithermal gold-silver deposits. Chapter Q of mineral deposit models for resource assessment / Описательные модели для эпитермальных золото-серебряных месторождений. Глава Q о моделях месторождений полезных ископаемых для оценки ПИ

This report constitutes a new descriptive model for epithermal gold-silver deposits. It summarizes characteristics of known deposits, including their geological, geophysical, geochemical, and geoenvironmental aspects. Models concerning the genesis of epithermal gold-silver deposits are discussed. How descriptive and genetic aspects of the model can be applied to mineral exploration and resource assessment of undiscovered deposits is described.

Finally, areas where additional research is needed to better understand the genesis of these deposits are identified. An extensive summary table outlining the characteristics of about 100 epithermal gold-silver deposits is included as an appendix; this summary table includes most of the world’s largest epithermal gold-silver deposits, and many smaller, well-studied deposits.
Epithermal gold-silver deposits are shallowly formed vein, stockwork, disseminated, and replacement deposits that are mined primarily for their gold and silver contents; some deposits also contain substantial resources of lead, zinc, copper, and (or) mercury. Although many epithermal deposits are known for their high gold grades (bonanza ores with more than 1 troy ounce [31.10348 grams of gold per short ton] [34.3 parts per million]) amenable to mining by underground methods, many bulk tonnage deposits with as little as 1 part per million (ppm) gold or less are presently being exploited by open-pit mining.
Many deposit subtypes have been defined and alternative classification schemes developed for epithermal gold-silver deposits; these subtypes and classification schemes reflect variations in metal contents, gangue and ore minerals, or inferred composition of ore-forming hydrothermal fluids. In this descriptive model, epithermal gold-silver deposits are separated into low-, intermediate-, and high-sulfidation subtypes to reflect the most frequently used classification scheme. A variant of low-sulfidation deposits associated with alkaline igneous rocks is not discussed in this model. <...>