J. B. Maynard, 1991. "Shale-Hosted Deposits of PB, ZN, and BA: Syngenetic Deposition from Exhaled Brines in Deep Marine 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 deposits of lead and zinc can be divided into two end-member types: epigenetic in carbonate hosts and syngenetic in clastic hosts. The epigenetic (Mississippi Valley) type forms at temperatures of about 100-150°C from highly saline brines believed to be derived from the dewatering of sedimentary basins. Associated minerals are barite and fluorite. The clastic-hosted deposits form during deposition of the enclosing strata in relatively deep marine basins. Deposition seems to occur below wave base under conditions of low oxygen concentration in the bottom water. In some cases, free H<sub>2</sub>S was present in the water column in which case the basin is referred to as euxinic. Barite mineralization commonly accompanies Pb and Zn in these deposits, but fluorite is always absent. The Irish Pb- Zn-Ba-Ag deposits occupy an intermediate position, containing both epigenetic and syngenetic portions.
Barite may also be found alone, without base metal enrichment, in host rocks of similar lithology to those of the Pb,Zn-bearing deposits. The Pb,Zn-barren barite depos.its, however, differ in tectonic setting from the Pb,Zn-bearing deposits. A consideration of four examples from the Lower Paleozoic illustrates these two types of clastic-hosted mineralization. Well-studied examples from strata of other ages include the Proterozoic deposits of Australia (Gustafson and Williams, 1981; Lambert, 1983), which are very similar to those described here except for a general absence of barite, and the Carboniferous of Ireland (Samson and Russell, 1987), where barite is present in some deposits. The Irish deposits are distinctive in having extensive epigenetic mineralization
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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