J. B. Maynard, 1991. "Copper: Product of Diagenesis in Rifted 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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Sediment-hosted copper deposits make up about a third of world production. They have also been the source of much controversy about the timing of ore formation. Syngenetic or early diagenetic models for the introduction of the copper to the sediments have long been popular and have been summarized recently by Mendelsohn (1989) and by Haynes and Bloom (1987a, b). Evidence is emerging, however, that for three major districts—the Kupferschiefer in Poland, White Pine in Michigan, and the African copper- belt—the dominant mineralization occurred during later diagenesis, after deposition of a considerable thickness of overlying strata. We will consider each of these areas in turn, then discuss the common features of their basin evolution.
The Permian of central and western Europe contains a series of unusual beds that have attracted scientific curiosity for many years (see Vaughan et al., 1989). The evaporites of the Zechstein sequence are prominent, as is a thin, carbon- rich, dolomitic shale beneath them known as the Kupfer- schiefer in continental Europe and the Marl Slate in England. Only a meter or so thick, this unit must mark some major event in the Permian evolution of the continent (see "Black Shales" in Chapter 6 for a discussion of anoxic events). It has been mined for copper since the Middle Ages in Germany. Most of these mines are long since abandoned, but recent discoveries in the Lubin district of Poland have added vast new reserves. Silver, lead, and zinc are recovered as well as copper, and there appears
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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