Sedimentary Exhalative (Sedex) Zinc-Lead-Silver Deposit Model Chapter N of Mineral Deposit Models for Resource Assessment Scientific Investigations Report 2010–5070–N U.S. Department of the Interior U.S. Geological Survey Zn Pb Fe 7 MILLIMETERS Cover. Polymictic sedimentary conglomerate overlying rhythmically laminated high-grade sphalerite and galena ore from the I 3/4 horizon in McArthur River (HYC) deposit, Australia. Inset shows scanning micro x-ray fluorescence (XRF) map of zinc (Zn), lead (Pb), and iron (Fe) concentrations. Deformation and partial truncation of fine, chemically graded laminae at contact with conglomeratic base of the overlying turbidite and intralaminar deformation together indicate deposition and modification through sea-floor processes, suggesting ore was deposited syndepositionally as a chemical sediment on the sea floor. Sedimentary Exhalative (Sedex) Zinc-Lead-Silver Deposit Model By Poul Emsbo, Robert R. Seal, George N. Breit, Sharon F. Diehl, and Anjana K. Shah Chapter N of Mineral Deposit Models for Resource Assessment Scientific Investigations Report 2010–5070–N U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior SALLY JEWELL, Secretary U.S. Geological Survey Suzette M. Kimball, Director U.S. Geological Survey, Reston, Virginia: 2016 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://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: Emsbo, Poul, Seal, R.R., Breit, G.N., Diehl, S.F., and Shah, A.K., 2016, Sedimentary exhalative (sedex) zinc-lead-silver deposit model: U.S. Geological Survey Scientific Investigations Report 2010–5070–N, 57 p., http://dx.doi.org/10.3133/ sir20105070N. ISSN 2328-0328 (online) iii Contents Introduction.....................................................................................................................................................1 Scope ......................................................................................................................................................1 Purpose...................................................................................................................................................1 Deposit Type and Associated Commodities ..............................................................................................1 Name .......................................................................................................................................................1 Synonyms ...............................................................................................................................................1 Brief Description ...................................................................................................................................1 Deposit Model—Clarification and Exclusions ........................................................................2 Irish-Type Deposits .............................................................................................................2 Broken Hill-Type Deposits .................................................................................................5 Volcanogenic Massive Sulfide Deposits ........................................................................5 Associated Deposit Types ..........................................................................................................5 Mississippi Valley-Type and Irish-Type Deposits .........................................................5 Sedex Barite ........................................................................................................................5 Sediment-Hosted Manganese, Iron, Phosphate, and Metalliferous Black Shales .........................................................................................................6 Primary Commodities ...........................................................................................................................6 Byproduct Commodities ......................................................................................................................6 Trace Constituents ................................................................................................................................6 Example Deposits..................................................................................................................................6 Historical Evolution of Descriptive and Genetic Knowledge and Concepts ........................................6 Regional Environment ...................................................................................................................................7 Geotectonic Environment ....................................................................................................................7 Relations to Structures ........................................................................................................................7 Relations to Sedimentary Rocks ........................................................................................................7 Temporal (Secular) Relations ..............................................................................................................8 Duration of Hydrothermal System and (or) Mineralizing Processes .........................................10 Relations to Igneous Rocks ...............................................................................................................11 Relations to Metamorphic Rocks .....................................................................................................11 Physical Description of Deposit ................................................................................................................11 Dimensions in Plan View ...................................................................................................................11 Vertical Extent .....................................................................................................................................11 Form/Shape ..........................................................................................................................................11 Host Rocks ...........................................................................................................................................15 Structural Setting and Controls ........................................................................................................15 Geophysical Characteristics ......................................................................................................................15 Magnetic Signature ............................................................................................................................15 Gravity Signature ................................................................................................................................19 Electrical Signature ............................................................................................................................20 Radiometric Signature .......................................................................................................................20 iv Hypogene Ore/Gangue Characteristics ...................................................................................................20 Mineralogy ...........................................................................................................................................20 Paragenesis .........................................................................................................................................22 Zoning Patterns ...................................................................................................................................22 Textures, Structures, and Grain Size ...............................................................................................22 Relations Between Alteration, Gangue, and Ore ...................................................................................22 Mineralogy ...........................................................................................................................................22 Zoning Patterns ...................................................................................................................................24 Weathering/Supergene Processes ..........................................................................................................24 Geochemical Characteristics ....................................................................................................................24 Trace Elements and Element Associations ....................................................................................24 Zoning Patterns ...................................................................................................................................25 Fluid-Inclusion Thermometry