A Deposit Model for Mississippi Valley-Type Lead-Zinc Ores Chapter A of Mineral Deposit Models for Resource Assessment 2 cm Sample of spheroidal sphalerite with dendritic sphalerite, galena, and iron sulfides (pyrite plus marcasite) from the Pomorzany mine. Note the “up direction” is indicated by “snow-on-the-roof” texture of galena and Scientificsphalerite Investigations alnong colloform Report layers of2010–5070–A light-colored spahlerite. Hydrothermal sulfide clasts in the left center of the sample are encrusted by sphalerire and iron sulfides. Size of sample is 20x13 cm. Photo by David Leach. U.S. Department of the Interior U.S. Geological Survey COVER: Sample of spheroidal sphalerite with dendritic sphalerite, galena, and iron sulfides (pyrite plus mar- casite) from Pomorzany mine. Note the “up direction” is indicated by “snow-on-the-roof” texture of galena and sphalerite along colloform layers of light-colored sphalerite. Hydrothermal sulfide clasts in the left center of the sample are encrusted by sphalerite and iron sulfides. Size of sample is 20x13 centimeters. (Photograph by David L. Leach, U.S. Geological Survey.) A Deposit Model for Mississippi Valley- Type Lead-Zinc Ores By David L. Leach, Ryan D. Taylor, David L. Fey, Sharon F. Diehl, and Richard W. Saltus Chapter A of Mineral Deposit Models for Resource Assessment Scientific Investigations Report 2010–5070–A 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: 2010 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: Leach, D.L., Taylor, R.D., Fey, D.L., Diehl, S.F., and Saltus, R.W., 2010, A deposit model for Mississippi Valley-Type lead-zinc ores, chap. A of Mineral deposit models for resource assessment: U.S. Geological Survey Scientific Investi- gations Report 2010–5070–A, 52 p. iii Contents Abstract ..........................................................................................................................................................1 Introduction....................................................................................................................................................1 Purpose and Scope .............................................................................................................................3 Deposit Type and Associated Commodities .............................................................................................3 Name .....................................................................................................................................................3 Synonyms ..............................................................................................................................................3 Brief Description ..................................................................................................................................3 Associated and Transitional Deposit Types ....................................................................................4 SEDEX ...........................................................................................................................................4 Sandstone-Lead ..........................................................................................................................4 Sandstone-Hosted Lead Deposits ...........................................................................................4 Fracture Controlled Pb-Zn and Fluorite-Barite Deposits .....................................................4 Distal Pb-Zn Skarn and Igneous Related Pb-Zn Mantos Deposits .....................................4 Primary Commodities ..........................................................................................................................4 Byproduct Commodities .....................................................................................................................4 Trace Constituents ...............................................................................................................................5 Example Deposits.................................................................................................................................5 MVT Metallogenic Provinces ...................................................................................................5 MVT Districts ...............................................................................................................................5 Important Deposits .....................................................................................................................5 Historical Evolution of Descriptive and Genetic Knowledge and Concepts .......................................5 Regional Environment ..................................................................................................................................6 Geotectonic Environment ...................................................................................................................6 Temporal (Secular) Relations .............................................................................................................6 Duration of Magmatic-Hydrothermal System and/or Mineralizing Processes .........................6 Relation to Structures .........................................................................................................................7 Relations to Igneous Rocks ................................................................................................................7 Relations to Sedimentary Rocks .......................................................................................................7 Relations to Metamorphic Rocks ......................................................................................................7 Physical Description of Deposits ...............................................................................................................8 Dimensions in Plan View ....................................................................................................................8 Size of Hydrothermal System Relative to Extent of Economically Mineralized Rock ...............8 Vertical Extent ......................................................................................................................................8 Form and Shape ...................................................................................................................................8 Host Rocks ..........................................................................................................................................10 Structural Setting(s) and Controls ..................................................................................................10 Use of Geophysics in Resource Assessment for Mississippi Valley-Type Deposits .......................12 Hypogene Ore Characteristics .................................................................................................................13 Mineralogy and Mineral Assemblages ..........................................................................................13 Paragenesis ........................................................................................................................................13 Zoning Patterns ..................................................................................................................................13 Textures, Structures, and Grain Size ..............................................................................................15 iv Hypogene Gangue Characteristics...........................................................................................................15 Mineralogy and Mineral Assemblages ...........................................................................................15 Paragenesis and Zoning Patterns ....................................................................................................16 Hydrothermal Alteration .............................................................................................................................16 Dissolution and Hydrothermal Brecciation ....................................................................................16 Dolomite and Calcite Alteration .......................................................................................................16 Silicification .........................................................................................................................................16 Clay, Mica, and Feldspar Diagenesis ..............................................................................................16 Supergene Ore and Gangue Characteristics ..........................................................................................16