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A newly released book, Life Cycle of the Phosphoria Formation: From Deposition to the Post-Mining Environment, is the final product of a large, multidisciplinary project funded by the U.S. Geological Survey (USGS)'s Mineral Resources Program and headed by USGS scientist James Hein (Western Coastal and Marine Geology Team, Menlo Park, CA).
The project was a collaboration among numerous groups, including the USGS, the Bureau of Land Management, the U.S. Fish and Wildlife Service, the U.S. Forest Service, the Bureau of Indian Affairs, and the Idaho Department of Environmental Quality. More information about the project and a complete list of collaborators are available at the Western U.S. Phosphate Project Web site.
Project scientists studied the 350,000-km2 Western U.S. Phosphate Field, which includes the world's largest phosphate deposit, the Phosphoria Formation. They addressed such issues as the nature of the Phosphoria sea, resource-reserve estimates, the mineralogical-geochemical-tectonic evolution of the deposit, and present-day contaminant issues associated with the release of selenium from waste-rock dumps produced during mining.
This last issue involved studies of surface and ground water, soil, biota, and rock. Selenium contamination has killed livestock in the area. Vanadium was also mined from this deposit until 1999, and the deposit was once considered a potential source for uranium.
The 5-year program tied together geology, geochemistry, water resources, and biology into an integrative approach to understand an important U.S. mineral resourcephosphateand the consequences of its recovery. This type of approach and the knowledge it yields are essential prerequisites for the environmentally sound mining of ores that are critical to the functioning of modern society.
Many aspects of this work have direct application to understanding phosphate deposits in the modern marine environment. Although no exact modern analog exists for the depositional setting of the Phosphoria Formation, certain similarities are noticeable in various modern marine environments.
The Phosphoria Formation was deposited off the west coast of North America (Pangea) 250 million years ago. The depositional environment was a very wide continental shelf that sloped down to a basin about 200 to 600 m deep.
Phosphates were deposited on the shelf, ramp, and basin. Islands to the west (visualize the Southern California Borderland) created a semiclosed basin open to the north and south. Phosphate was derived from organic matter produced during upwelling, but the most important factor for the concentration of phosphate was the lack of dilution by terrigenous and carbonate debris. Terrigenous input was prohibited by low relief and an arid climate to the east, and the formation of marine carbonate was minimized by water temperature and oceanographic conditions.
The Phosphoria Formation is a world-class deposit, and knowledge gained from its study can be applied to many other deposits worldwide. This book will be of interest to environmental geologists and biologists, economic geologists, mineralogists, sedimentologists, oceanographers, geochemists, and others from industry, Federal, State, and local government agencies, and academia.
The full reference for the book is Hein, J.R., ed., 2004, Life cycle of the Phosphoria Formation; from deposition to the post-mining environment: Amsterdam, Elsevier, 635 p. [includes CD].
in this issue:
New Book on the Phosphoria Formation
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