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Alkalic-Type Epithermal Gold Deposit Model Alkalic-Type Epithermal Gold Deposit Model Chapter R of Mineral Deposit Models for Resource Assessment Scientific Investigations Report 2010–5070–R U.S. Department of the Interior U.S. Geological Survey Cover. Photographs of alkalic-type epithermal gold deposits and ores. Upper left: Cripple Creek, Colorado—One of the largest alkalic-type epithermal gold deposits in the world showing the Cresson open pit looking southwest. Note the green funnel-shaped area along the pit wall is lamprophyre of the Cresson Pipe, a common alkaline rock type in these deposits. The Cresson Pipe was mined by historic underground methods and produced some of the richest ores in the district. The holes that are visible along several benches in the pit (bottom portion of photograph) are historic underground mine levels. (Photograph by Karen Kelley, USGS, April, 2002). Upper right: High-grade gold ore from the Porgera deposit in Papua New Guinea showing native gold intergrown with gold-silver telluride minerals (silvery) and pyrite. (Photograph by Jeremy Richards, University of Alberta, Canada, 2013, used with permission). Lower left: Mayflower Mine, Montana—High-grade hessite, petzite, benleonardite, and coloradoite in limestone. (Photograph by Paul Spry, Iowa State University, 1995, used with permission). Lower right: View of north rim of Navilawa Caldera, which hosts the Banana Creek prospect, Fiji, from the portal of the Tuvatu prospect. (Photograph by Paul Spry, Iowa State University, 2007, used with permission). Alkalic-Type Epithermal Gold Deposit Model By Karen D. Kelley, Paul G. Spry, Virginia T. McLemore, David L. Fey, and Eric D. Anderson Chapter R of Mineral Deposit Models for Resource Assessment Scientific Investigations Report 2010–5070–R U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DAVID BERNHARDT, Secretary U.S. Geological Survey James F. Reilly II, Director U.S. Geological Survey, Reston, Virginia: 2020 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit https://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov/. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Kelley, K.D., Spry, P.G., McLemore, V.T., Fey, D.L., and Anderson, E.D., 2020, Alkalic-type epithermal gold deposit model: U.S. Geological Survey Scientific Investigations Report 2010–5070–R, 74 p., https://doi.org/ 10.3133/ sir20105070R. ISSN 2328-0328 (online) iii Acknowledgments We thank Antonio Arribas (University of Texas, El Paso) and Jeremy Richards (University of Alberta, Canada, deceased in 2019) who provided photographs, and Eric Jensen (EMX Royalty Corporation), who provided stimulating discussions about alkalic-type epithermal gold deposits. Ed du Bray (Emeritus, U.S. Geological Survey) and Jim Saunders (Consultant) reviewed the manuscript, which greatly improved the content. v Contents Acknowledgments ........................................................................................................................................iii Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Deposit Type and Associated Commodities ............................................................................................17 Name .....................................................................................................................................................17 Synonyms .............................................................................................................................................17 Brief Description ���������������������������������������������������������������������������������������������������������������������������������17 Associated Deposit Types .................................................................................................................18 Primary Commodities .........................................................................................................................18 Byproduct Commodities ....................................................................................................................18 Trace Constituents ..............................................................................................................................18 Example Deposits................................................................................................................................19 Historical Evolution of Descriptive and Genetic Knowledge and Concepts .............................19 Regional Environment .................................................................................................................................20 Geotectonic Environment ..................................................................................................................20 Temporal (Secular) Relations ............................................................................................................20 Duration of Magmatic-Hydrothermal System and (or) Mineralizing Processes ......................20 Relations to Structures ......................................................................................................................21 Relations to Igneous Rocks ...............................................................................................................21 Relations to Sedimentary Rocks ......................................................................................................23 Relations to Metamorphic Rocks .....................................................................................................23 Physical Description of Deposit ................................................................................................................23 Dimensions in Plan View ...................................................................................................................23 Vertical Extent �������������������������������������������������������������������������������������������������������������������������������������23 Form/Shape ..........................................................................................................................................25 Host Rocks ...........................................................................................................................................25 Structural Setting(s) and Controls ...................................................................................................27 Geophysical Characteristics ......................................................................................................................27 Hypogene and Supergene Ore Characteristics ......................................................................................33 Mineralogy and Mineral Assemblages ...........................................................................................33 Paragenesis .........................................................................................................................................37 Zoning Patterns �����������������������������������������������������������������������������������������������������������������������������������39 Textures and Grain Size .....................................................................................................................39 Hypogene and Supergene Gangue Characteristics ..............................................................................41 Mineralogy, Mineral Assemblages, and Paragenesis ..................................................................41 Textures and Grain Size .....................................................................................................................42 Geochemical Characteristics ....................................................................................................................42 Trace Elements and Element Associations ....................................................................................42 Zoning Patterns �����������������������������������������������������������������������������������������������������������������������������������43 Fluid-Inclusion Microthermometry .................................................................................................43 Stable Isotope Geochemistry ....................................................................................................................44 Oxygen and Hydrogen ........................................................................................................................44 Sulfur and Carbon ...............................................................................................................................44 vi Tellurium ...............................................................................................................................................44
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