Occurrence Model for Magmatic Sulfide-Rich Nickel- Copper-(Platinum-Group Element) Deposits Related to Mafic and Ultramafic Dike-Sill Complexes Scientific Investigations Report 2010–5070–I U.S. Department of the Interior U.S. Geological Survey COVER. Ferrar dikes and sills intruding Beacon sandstones, Finger Mountain, Dry Valleys, Antarctica. Photograph by Dean Peterson, Duluth Metals Limited. Occurrence Model for Magmatic Sulfide- Rich Nickel-Copper-(Platinum-Group Element) Deposits Related to Mafic and Ultramafic Dike-Sill Complexes By Klaus J. Schulz, Laurel G. Woodruff, Suzanne W. Nicholson, Robert R. Seal II, Nadine M. Piatak, Val W. Chandler, and John L. Mars Chapter I of Mineral Deposit Models for Resource Assessment Scientific Investigations Report 2010–5070–I U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior SALLY JEWELL, Secretary U.S. Geological Survey Suzette Kimball, Acting Director U.S. Geological Survey, Reston, Virginia: 2014 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, 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: Schulz, K.J., Woodruff, L.G., Nicholson, S.W., Seal, R.R., II, Piatak, N.M., Chandler, V.W., and Mars, J.L., 2014, Occurrence model for magmatic sulfide-rich nickel-copper-(platinum-group element) deposits related to mafic and ultramafic dike-sill complexes: U.S. Geological Survey Scientific Investigations Report 2010–5070–I, 80 p., http://dx.doi.org/10.3133/sir20105070I. ISSN 2328-0328 (online) iii Contents 1. Introduction Overview..........................................................................................................................................................1 Scope ...............................................................................................................................................................1 Purpose............................................................................................................................................................3 2. Deposit Type and Associated Deposits Name and Synonyms.....................................................................................................................................3 Brief Deposit Description .............................................................................................................................3 Associated Deposit Types ............................................................................................................................4 Primary and Byproduct Commodities .........................................................................................................4 Example Deposits...........................................................................................................................................4 3. Historical Evolution of Descriptive and Genetic Knowledge and Concepts 4. Regional Environment Geotectonic Environment ...........................................................................................................................10 Temporal (Secular) Relations .....................................................................................................................11 Duration of Magmatic-Hydrothermal System and/or Mineralizing Processes .................................11 Relations to Structures ...............................................................................................................................11 Relations to Igneous Rocks ........................................................................................................................12 Relations to Sedimentary Rocks ...............................................................................................................12 Relations to Metamorphic Rocks ..............................................................................................................12 5. Physical Description of Deposits Size and Shape of Deposits .......................................................................................................................13 Size of Mineralizing System Relative to Extent of Economically Mineralized Rock .........................15 Host Rocks ....................................................................................................................................................16 Structural Setting(s) and Controls ............................................................................................................16 6. Geophysical Signatures Introduction...................................................................................................................................................16 Magnetic Signature .....................................................................................................................................17 Gravity Signature .........................................................................................................................................17 Electrical Signature .....................................................................................................................................20 Electromagnetic (EM) Signature ...............................................................................................................21 Seismic Signature ........................................................................................................................................23 Spectral Characteristics ............................................................................................................................24 7. Hypogene and Supergene Ore Characteristics Hypogene Ore Characteristics ..................................................................................................................31 Mineralogy and Mineral Assemblages ...........................................................................................31 Paragenesis .........................................................................................................................................32 Zoning Patterns ...................................................................................................................................34 Textures and Structures ....................................................................................................................35 Grain Sizes ...........................................................................................................................................36 Supergene Ore Characteristics .................................................................................................................37 8. Hypogene Gangue Characteristics Mineralogy and Mineral Assemblages ....................................................................................................37 Paragenesis .................................................................................................................................................37 iv 9. Geochemical Characteristics of Ores Trace Elements and Element Associations ............................................................................................38 Metal Normalizations and Ratios .............................................................................................................38 Stable Isotopes.............................................................................................................................................41 Sulfur Isotopes ...................................................................................................................................41 Oxygen Isotopes..................................................................................................................................42 Radiogenic Isotopes ....................................................................................................................................44 Rhenium-Osmium Isotopes ...............................................................................................................44 Rubidium-Strontium, Samarium-Neodymium, and Lead Isotopes .............................................45 10. Petrology of Associated Igneous Rocks Rock Names ..................................................................................................................................................46 Forms of Igneous Rocks and Rock Associations ...................................................................................46 Mineralogy ....................................................................................................................................................46 Textures, Structures, and Grain Size ........................................................................................................48 Petrochemistry .............................................................................................................................................49