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Book Chapter

The Geobiology of Sediment-Hosted Mineral Deposits

By
Clint Scott
Clint Scott
U.S. Geological Survey, National Center, MS 954, Reston, Virginia 20192
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Karen D. Kelley
Karen D. Kelley
U.S. Geological Survey, Box 25046, MS 973, Denver, Colorado 80225
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John F. Slack
John F. Slack
U.S. Geological Survey, National Center, MS 954, Reston, Virginia 20192
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Published:
January 01, 2014

Abstract

The role of biological processes in the formation of sediment-hosted ore deposits has long been recognized. In this review, we focus on the biogeochemical cycling of C, Mn, Fe, and S as they relate to the formation of sediment-hosted Mn and Fe deposits, metalliferous black shales, clastic-dominated (CD) Pb-Zn deposits, and phosphorites. Biological mediation of ore-forming processes occurs over large spans of space and time. The most important step is oxygenic photosynthesis, a biological innovation dating from the Archean Eon that releases free oxygen into the surface oceans and atmosphere and delivers chemical potential, in the form of reduced carbon, to the seafloor. Photosynthetic oxygen is available to precipitate dissolved Fe2+ and Mn2+, and therefore it augments the formation of sedimentary Mn and Fe deposits, and drives oxidative weathering of exposed crust, thereby delivering sulfate and transition metals to the ocean. Where reduced carbon accumulates in the deep oceans and on the seafloor, bacterial sulfate reduction produces hydrogen sulfide thereby facilitating the formation of metalliferous black shales, sediment-hosted Pb and Zn sulfide deposits, and phosphorites. Thus, an understanding of major biogeochemical processes and how they have evolved over time is required in order to refine genetic models for sediment-hosted ore deposits and to guide future mineral exploration.

A close secular relationship between deposit formation and trends in major biogeochemical cycles provides a potentially powerful tool for mineral resource assessment. Sedimentary basins that formed during a time that is known to lack deposits of a particular metal can be eliminated during exploration programs, whereas others of permissive ages should be considered priorities. For example, sedimentary basins older than ca. 1.8 Ga are unlikely to contain large CD Pb-Zn deposits, and basins that formed between 1.6 and 0.6 Ga are not prospective for phosphorites. Recent technological advances in the application of nanometer-, micron-, and bulk-scale analytical techniques allow for imaging of complex biological structures and have provided new insights into the role of bacteria, not only in direct formation of mineral deposits, but also in leaching of metals from ore and mineralized rocks. Future exploration for, and exploitation of, mineral deposits may include offshore or land-based, low-grade, high-tonnage targets; understanding the role of bacteria in mineral growth, mineral dissolution, and redox transformations will aid in predicting where such deposits exist, and how metal extraction from ores can be enhanced.

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Contents

Special Publications of the Society of Economic Geologists

Building Exploration Capability for the 21st Century

Karen D. Kelley
Karen D. Kelley
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Howard C. Golden
Howard C. Golden
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Society of Economic Geologists
Volume
18
ISBN electronic:
9781629499291
Publication date:
January 01, 2014

GeoRef

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