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Abstract

Fluid inclusions in ore and gangue minerals provide a wealth of data on the conditions of origin of these deposits with respect to density, temperature, rate of movement; salinity, and composition of the fluids that deposited the ores, at the site and time of deposition. Although some assumptions must be made that certainly cannot be strictly valid in every case, the available evidence indicates that, if care is used in inclusion sample selection and experimental technique, the exceptions to these assumptions will be few and of minor significance, and the accuracy of the results adequate for use in discussions of genesis.

From inclusion evidence alone, it is apparent that the ore fluids forming a number of these deposits were slow-moving, hot, dense, Na-Ca-Cl brines, containing abundant organic matter. The most striking feature is the uniformity of temperature, density, chemical composition, and salinity, over a wide range of stratiform-type deposits, including those in the Joplin, Southern Illinois, Southeast Missouri, East Tennessee, Derbyshire, North Pennine, and Santander districts, and in other smaller occurrences.

Although these data do not determine the origin or origins of these deposits, they place severe limitations on the possible mechanisms of ore transport and deposition. Origin by sedimentary-syngenetic, volcanic exhalative, simple magmatic-hydrothermal, and meteoric circulation processes seem to be precluded by the inclusion data; deposition from modified, deep-circulating, heated connate brines is compatible with these data, and is considered to be a satisfactory working hypothesis.

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