R. B. Schultz, 1991. "Metalliferous Black Shales: Accumulation of Carbon and Metals in Cratonic Basins", Sedimentary and Diagenetic Mineral Deposits: A Basin Analysis Approach to Exploration, Eric R. Force, J. James Eidel, J. Barry Maynard
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Black shales are frequently repositories for valuable metal constituents and represent a record of past anoxic water conditions. These metalliferous, carbon-rich units also record geochemical interactions of carbon, iron, sulfur, oxygen, and often phosphorus. Thus, although not ores at present, except for some small operations in China, metalliferous black shales have considerable importance for understanding processes of metal enrichment in sedimentary rocks.
Significant early work on black shales includes the appreciation of the importance of anoxic water conditions in their formation (Pettijohn, 1949), association with a distinctive biofacies, for example (Bulman, 1955), and the conclusion that, under modern conditions, these anoxic-water sediments are formed in basins restricted from free exchange with the open ocean, leading to stagnation in the bottom part of the water column (Strom, 1939). Such situations are rare in the modem, but the Lower Paleozoic and the Mesozoic rock records are indicative of more widespread anoxia when global climate was warmer and more equable.
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Sedimentary and Diagenetic Mineral Deposits: A Basin Analysis Approach to Exploration
Major oil companies have been utilizing techniques of quantitative basin analysis in exploration for a decade or more. Ore-forming processes in stratiform, sediment-hosted ore deposits commonly involve sedimentary processes, diagenesis, basinal brines, and paleohydrology. Like the maturation and migration of hydrocarbons, their formation is an integral part of basin history. Consequently, applying comprehensive basin analysis to mineral exploration is a logical and helpful approach to understanding sediment- hosted ore deposits and predicting their occurrence, location, and origin.
When the Society of Economic Geologists' Short Course Committee contacted the writer in 1985 to develop a short course on sedimentary processes of ore formation, ft seemed to me that such a course would provide an excellent opportunity to introduce the concept of comprehensive basin analysis as an exploration tool for sediment-hosted mineral deposits. As Sawkins pointed out (1990, p. 333), “Meaningful exploration in extensional tectonic paleo-environments will increasingly require the integration of surface, subsurface, and geophysical data, and enlightened programs of basin analysis similar to those practiced by the petroleum industry will be increasingly needed.”
Sediment-hosted ore deposits include sedimentary gold and other heavy mineral accumulations; evaporites; syngenetic to late diagenetic base metal and barite deposits in clastic and carbonate rocks, including epiclastic volcanic rocks; banded iron formations; Clinton-minette-type iron and manganese ores; unconformity-related and sandstonetype uranium deposits; and Mississippi Valley-type leadzinc deposits. Some sediment -hosted ore deposits were formed at various stages of basin history and are multistage. This short course focuses on (1) the types of basins in which major sediment - hosted ore deposits occur, and (2) the controls of basin types on ore-hosting sedimentary environments and ore-forming processes.
The precise role of sedimentary processes in the formation of ore deposits has been debated by geologists around the world; this debate has affected the manner and success of exploration program s . Skinner (1979, 1987) traced the origins of the polarization of thought on the genesis of ore deposits to Agricola, who expounded on lateral secretion and precipitation of metals from circulating ground waters, and to Descartes, who perceived the earth as an outgassing star and believed that metals were not derived from host rocks. The neptunist theories of Werner (1750-1817) may have evolved from Agricola and the plutonist theories of Hutton (1726-1797) from Descartes. L. C. Graton, whom the Graton-Sales volume Ore Deposits in the United States 1933-1967