Arc-Related Porphyry Molybdenum Deposit Model Chapter D of Mineral Deposit Models for Resource Assessment 0 1 CENTIMETER 0 0.5 INCH Scientific Investigations Report 2010–5070–D U.S. Department of the Interior U.S. Geological Survey COVER: Quartz-molybdenite vein cutting through potassically altered granite. Photograph by Ryan D. Taylor, U.S. Geological Survey. Arc-Related Porphyry Molybdenum Deposit Model By Ryan D. Taylor, Jane M. Hammarstrom, Nadine M. Piatak, and Robert R. Seal, II Chapter D of Mineral Deposit Model for Resource Assessment Scientific Investigations Report 2010–5070–D U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2012 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 http://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod To order this and other USGS information products, visit http://store.usgs.gov Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Taylor, R.D., Hammarstrom, J.M., Piatak, N.M., and Seal, R.R. II, 2012, Arc-related porphyry molybdenum deposit model, chap. D of Mineral deposit models for resource assessment: U.S. Geological Survey Scientific Investigations Report 2010–5070–D, 64 p. iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Deposit Type and Associated Commodities ..............................................................................................2 Name ......................................................................................................................................................2 Synonyms ...............................................................................................................................................2 Brief Description ...................................................................................................................................2 Associated Deposit Types ...................................................................................................................3 Primary Commodities ...........................................................................................................................3 Byproduct Commodities ......................................................................................................................3 Trace Constituents ................................................................................................................................3 Example Deposits..................................................................................................................................3 Historical Evolution of Descriptive and Genetic Knowledge and Concepts ........................................6 Regional Environment ...................................................................................................................................7 Geotectonic Environment ....................................................................................................................7 Temporal (Secular) Relations ..............................................................................................................7 Duration of Magmatic-Hydrothermal System ..................................................................................8 Relations to Structures ........................................................................................................................9 Relations to Igneous Rocks ...............................................................................................................10 Relations to Sedimentary Rocks ......................................................................................................10 Relations to Metamorphic Rocks .....................................................................................................10 Physical Description of Deposit ................................................................................................................11 Dimensions in Plan View ...................................................................................................................11 Size of Hydrothermal System Relative to Extent of Economically Mineralized Rock ..............11 Vertical Extent .....................................................................................................................................11 Form/Shape ..........................................................................................................................................11 Host Rocks ...........................................................................................................................................11 Structural Setting(s) and Controls ...................................................................................................11 Hypogene Ore Characteristics ..................................................................................................................12 Mineralogy ...........................................................................................................................................12 Mineral Assemblages ........................................................................................................................12 Paragenesis .........................................................................................................................................12 Zoning Patterns ...................................................................................................................................13 Ore Textures .........................................................................................................................................13 Grain Size .............................................................................................................................................14 Hypogene Gangue Characteristics ...........................................................................................................15 Mineralogy ...........................................................................................................................................15 Mineral Assemblages ........................................................................................................................15 Paragenesis .........................................................................................................................................15 Zoning Patterns ...................................................................................................................................15 Textures, Structures, and Grain Size ...............................................................................................15 iv Hydrothermal Alteration .............................................................................................................................16 Relations Between Alteration, Gangue, and Ore ..........................................................................16 Mineralogy ...........................................................................................................................................16 Mineral Assemblages ........................................................................................................................16 Lateral and Vertical Dimensions ......................................................................................................17 Selvages ...............................................................................................................................................17 Rock Matrix Alteration .......................................................................................................................18 Textures ................................................................................................................................................18 Zoning Patterns ...................................................................................................................................19 Supergene Ore Characteristics .................................................................................................................19 Supergene Gangue Characteristics .........................................................................................................19 Weathering/Supergene Processes ..........................................................................................................20 Geophysical Characteristics ......................................................................................................................20 Magnetic, Gravity, and Electrical Signatures ................................................................................21