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Scientific Investigation Report 2010–5070–F

Occurrence Model for Volcanogenic Beryllium Deposits

By Nora K. Foley, Albert H. Hofstra, David A. Lindsey, Robert R. Seal, II, Brian Jaskula, and Nadine M. Piatak

Chapter F of Mineral Deposit Models for Resource Assessment

Thumbnail of and link to report PDF (11.1 MB)Abstract

Current global and domestic mineral resources of beryllium (Be) for industrial uses are dominated by ores produced from deposits of the volcanogenic Be type. Beryllium deposits of this type can form where hydrothermal fluids interact with fluorine and lithophile-element (uranium, thorium, rubidium, lithium, beryllium, cesium, tantalum, rare earth elements, and tin) enriched volcanic rocks that contain a highly reactive lithic component, such as carbonate clasts. Volcanic and hypabyssal high-silica biotite-bearing topaz rhyolite constitutes the most well-recognized igneous suite associated with such Be deposits. The exemplar setting is an extensional tectonic environment, such as that characterized by the Basin and Range Province, where younger topaz-bearing igneous rock sequences overlie older dolomite, quartzite, shale, and limestone sequences. Mined deposits and related mineralized rocks at Spor Mountain, Utah, make up a unique economic deposit of volcanogenic Be having extensive production and proven and probable reserves. Proven reserves in Utah, as reported by the U.S. Geological Survey National Mineral Information Center, total about 15,900 tons of Be that are present in the mineral bertrandite (Be4Si2O7(OH)2). At the type locality for volcanogenic Be, Spor Mountain, the tuffaceous breccias and stratified tuffs that host the Be ore formed as a result of explosive volcanism that brought carbonate and other lithic fragments to the surface through vent structures that cut the underlying dolomitic Paleozoic sedimentary rock sequences. The tuffaceous sediments and lithic clasts are thought to make up phreatomagmatic base surge deposits. Hydrothermal fluids leached Be from volcanic glass in the tuff and redeposited the Be as bertrandite upon reaction of the hydrothermal fluid with carbonate clasts in lithic-rich sections of tuff. The localization of the deposits in tuff above fluorite-mineralized faults in carbonate rocks, together with isotopic evidence for the involvement of magmatic water in an otherwise meteoric water-dominated hydrothermal system, indicate that magmatic volatiles contributed to mineralization. At the type locality, hydrothermal alteration of dolomite clasts formed layered nodules of calcite, opal, fluorite, and bertrandite, the latter occurring finely intergrown with fluorite. Alteration assemblages and elemental enrichments in the tuff and surrounding volcanic rocks include regional diagenetic clays and potassium feldspar and distinctive hydrothermal halos of anomalous fluorine, lithium, molybdenum, niobium, tin, and tantalum, and intense potassium feldspathization with sericite and lithium-smectite in the immediate vicinity of Be ore. Formation of volcanogenic Be deposits is due to the coincidence of multiple factors that include an appropriate Be-bearing source rock, a subjacent pluton that supplied volatiles and heat to drive convection of meteoric groundwater, a depositional site characterized by the intersection of normal faults with permeable tuff below a less permeable cap rock, a fluorine-rich ore fluid that facilitated Be transport (for example, BeF42– complex), and the existence of a chemical trap that caused fluorite and bertrandite to precipitate at the former site of carbonate lithic clasts in the tuff.

First posted January 4, 2013

For additional information contact:
Director, Central Mineral and Environmental Resources Science Center
U.S. Geological Survey
Box 25046, Mail Stop 973
Denver, CO 80225
http://minerals.cr.usgs.gov/

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Suggested citation:

Foley, N.K., Hofstra, A.H., Lindsey, D.A., Seal, R.R., II, Jaskula, Brian, and Piatak, N.M., 2012, Occurrence model for volcanogenic beryllium deposits, chap. F of Mineral deposit models for resource assessment: U.S. Geological Survey Scientific Investigations Report 2010–5070–F, 43 p.



Contents

Abstract

Introduction

Deposit Type and Associated Commodities

Historical Evolution of Descriptive and Genetic Knowledge and Concepts

Regional Environment

Physical Description of Deposit

Hypogene Ore and Gangue Characteristics

Hydrothermal Alteration

Supergene Ore Characteristics and Processes

Geochemical Characteristics

Petrology of Associated Igneous Rocks

Petrology of Associated Sedimentary Rocks

Petrology of Associated Metamorphic Rocks

Theory of Deposit Formation

Geoenvironmental Features and Anthropogenic Mining Effects

Exploration and Resource Assessment Guides

Acknowledgments

References Cited


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