Geologic characteristics of sediment- and volcanic-hosted disseminated gold deposits - Search for an occurrence model
The current expansion of resource information, particularly on "disseminated" gold, and the improved technologies now available for resource investigations should place us in an enhanced position for developing a better predictive methodology for meeting one of the important responsibilities of the U.S. Geological Survey-to examine and assess the mineral resources of the geologic terranes composing the public (and privately owned) lands of the United States. The first step is systematic organization of these data. Geologic-occurrence models are an effective systematic method by which to organize large amounts of resource information into a logical sequence facilitating its use more effectively in meeting several industry and Survey objectives, which include the exploration for resources and the assessment of resource potential for land-use decisions. Such models also provide a scientific basis for metallogenesis research, which considers the observable features or attributes of ore occurrence and their "fit" into the Earth's resource puzzle. The use of models in making resource assessments/appraisals was addressed by Shawe (1981), who reported the results of a workshop on methods for resource appraisal of Wilderness and Conterminous United States Mineral Appraisal Program (CUSMAP; 1:250,000-scale quadrangles) areas. The Survey's main objective in the 1982 workshop was to evaluate the status of knowledge about disseminated or very fine grained gold deposits and, if possible, to develop an occurrence model(s).
This report on the workshop proceedings has three main objectives: (1) Education through the publication of a summary review and presentation of new thinking and observations about the scientific bases for those geologic processes and environments that foster disseminated gold-ore formation; (2) systematic organization of available geologic, geochemical, and geophysical information for a range of typical disseminated gold deposits (including recognition of gaps in those data); and (3) assessment of current understanding (as presented in objective 2) toward formulating an empirical ore-occurrence model for this type of deposit. As such, this volume represents a preliminary first step at classification and provides a source of pertinent background information.
Readers of this volume will soon discover, however, that full agreement has not yet been achieved in the interpretation of some of the geologic evidence. The resulting variations in tentative occurrence models for these controversial deposits ultimately will be resolved by filling the gaps in information that have already been identified. Thus, this volume does not report a U.S. Geological Survey consensus; the conclusions expressed in each chapter represent the particular interpretations of the various workshop participants.
Table of Contents
- Characteristics of disseminated gold occurrences
- Field examination of gold deposits and occurrences
- Status of the disseminated gold occurrence model
- Vein and disseminated gold-silver deposits of the Great Basin through space and time
- Silica minerals as indicators of conditions during gold deposition
- Geochemistry of hydrothermal transport and deposition of gold and sulfide minerals in Carlin-type gold deposits
- A model for the formation of carbonate-hosted disseminated gold deposits based on geologic, fluid-inclusion, geochemical, and stable-isotope studies of the Carlin and Cortez deposits, Nevada
- Characteristics of boiling-water-table and carbon dioxide models for epithermal gold deposition
- Geologic-geochemical features of hot-spring precious-metal deposits
- Geochronology of hydrothermal alteration and mineralization: Tertiary epithermal precious-metal deposits in the Great Basin
- Characteristics of bulk-minable gold-silver deposits in Cordilleran and island-arc settings
- Summary of Steamboat Springs geothermal area, Nevada, with attached road-log commentary
- Geologic discussion of the Borealis gold deposit, Mineral County, Nevada
- The geology of the Enfield Bell mine and the Jerritt Canyon district, Elko County, Nevada
- Discussion of the disseminated-gold-ore-occurrence model
|USGS Numbered Series
|Geologic characteristics of sediment- and volcanic-hosted disseminated gold deposits - Search for an occurrence model
|U.S. Government Printing Office
|v, 150 p.
|Arizona, California, Idaho, Nevada, Utah
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