Mineral-Deposit Model for Lithium-Cesium- Tantalum Pegmatites Chapter O of Mineral Deposit Models for Resource Assessment Scientific Investigations Report 2010–5070–O U.S. Department of the Interior U.S. Geological Survey Cover. Giant crystals of beryl from the Bumpus pegmatite mine in Maine. The vintage 1927 photograph is from Perham (1986), used with permission. Mineral-Deposit Model for Lithium-Cesium- Tantalum Pegmatites By Dwight C. Bradley, Andrew D. McCauley, and Lisa M. Stillings Chapter O of Mineral Deposit Models for Resource Assessment Scientific Investigations Report 2010–5070–O 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: 2017 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: Bradley, D.C., McCauley, A.D., and Stillings, L.M., 2017, Mineral-deposit model for lithium-cesium-tantalum pegmatites: U.S. Geological Survey Scientific Investigations Report 2010–5070–O, 48 p., https://doi.org/10.3133/sir20105070O. ISSN 2328-0328 (online) iii Contents Abstract ..........................................................................................................................................................1 1.0. Introduction ........................................................................................................................................2 2.0. Deposit Type and Associated Commodities.................................................................................2 2.1. Name ........................................................................................................................................2 2.2. Nomenclature and Synonyms ..............................................................................................2 2.3. Brief Description ..................................................................................................................10 2.4. Associated Deposit Types...................................................................................................11 2.5. Primary and By-Product Commodities .............................................................................12 2.6. Trace Constituents ...............................................................................................................12 2.7. Example Deposits ................................................................................................................12 3.0. History of Pegmatite Research .....................................................................................................13 4.0. Regional Environment ....................................................................................................................14 4.1. Tectonic Environment ..........................................................................................................14 4.2. Temporal (Secular) Relations .............................................................................................15 4.3. Duration of Magmatic System and (or) Mineralizing Process .....................................15 4.4. Relation to Structures ..........................................................................................................15 4.5. Relations to Igneous Rocks ................................................................................................18 4.6. Relations to Sedimentary Rocks ........................................................................................18 4.7. Relations to Metamorphic Rocks ......................................................................................18 5.0. Physical Description of Deposits ................................................................................................18 5.1. Dimensions, Form, and Shape ............................................................................................18 5.2. Host Rocks .............................................................................................................................18 6.0. Geophysical Characteristics ........................................................................................................18 7.0. Hypogene Ore Characteristics .....................................................................................................19 7.1. Mineralogy and Mineral Assemblages ............................................................................19 7.2. Zoning Patterns ....................................................................................................................21 7.3. Paragenesis ..........................................................................................................................23 7.4. Textures, Structure, and Grain Size...................................................................................23 8.0. Hypogene Gangue Characteristics ..............................................................................................24 8.1. Mineralogy and Mineral Assemblages ............................................................................25 9.0. Hydrothermal Alteration ................................................................................................................26 10.0. Supergene Ore and Gangue Characteristics .............................................................................26 11.0. Geochemical Characteristics .......................................................................................................26 11.1. Trace Elements and Element Associations ....................................................................26 11.2. Fluid Inclusion and Melt Inclusion Thermometry and Chemistry ...............................26 11.3. Stable Isotope Geochemistry ...........................................................................................27 11.4. Petrology of Associated Igneous Rocks ........................................................................27 11.5. LCT Pegmatite Geochronology ........................................................................................27 11.6. Environment of Mineralization .........................................................................................28 12.0. Theory of Pegmatite Origin ...........................................................................................................28 12.1. Ore Deposit System Affiliation .........................................................................................29 12.2. Sources of Metals ..............................................................................................................29 12.3. Sources of Melt Fluxes ......................................................................................................29 12.4. Chemical Transport and Differentiation..........................................................................30 12.5. Nature of Geological Traps that Trigger Ore Precipitation ..........................................30 iv 13.0. Geological Exploration and Assessment Guide .......................................................................30 13.1. Regional-Scale Favorability ..............................................................................................30 13.2. District-Scale Vectors .......................................................................................................30 13.3. Alteration Haloes ................................................................................................................31 13.4. Geophysical Guidelines .....................................................................................................32 14.0. Geoenvironmental Features and Anthropogenic Mining Effects ..........................................32 14.1. Soil and Sediment Signatures Prior to Mining ..............................................................32 14.2. Drainage Signatures from Mining of LCT Pegmatites ..................................................32 14.3. Climate Effects on Geoenvironmental Signatures ........................................................33 14.4. Mining Methods ................................................................................................................33 14.5. Ore-Processing Methods .................................................................................................33 14.6. Metal Mobility from Solid Mine Waste ...........................................................................33 15.0. Knowledge Gaps and Future Research Directions ..................................................................34 16.0. Acknowledgments ..........................................................................................................................36 References Cited..........................................................................................................................................36