PRESSURES AND TEMPERATURES FROM AQUEOUS FLUID INCLUSIONS IN SPHALERITE FROM MIDCONTINENT COUNTRY ROCKS

The present study was designed to accumulate a more complete set of thermometric data for aqueous fluids entrapped in trace occurrences of sphalerite in the country rocks of the Midwest than that of Coveney and Goebel (1983). Such data are vital to an understanding of the temperatures and compositions of fluids that once were pervasive in midcontinent country rocks, and therefore they provide basic information for evaluating any mechanisms to explain the origins of the Pb-Zn deposits of the Midwest, particularly in the cases of models involving the circulation of basinal brines. Concludes that, because measured gas bubble pressures normally amount to only a few atmospheres, significant pressure corrections are probably unnecessary for most midcontinent country rock-hosted inclusions. Thus, in most cases, fluid inclusion homogenization temperatures provide accurate minimum temperatures of entrapment.-from Authors