Temperatures of mineralization by liquid inclusions, Cave-in-Rock fluorspar district, Illinois

Temperatures of vapor bubble disappearance of liquid inclusions in fluorite, sphalerite, and quartz from the Deardorff and Victory mines of the Cave-in-Rock fluorspar district were determined. Inclusions were studied in minerals of both principal stages of deposition indicated in the deposits. The data obtained indicate that ore deposition took place in the temperature range of 94 degrees C. to 142 degrees C., assuming a pressure correction of +13 degrees C., and that temperature oscillated during mineralization. Fluorite, the first mineral to be deposited in each stage, was deposited in the upper part of the temperature range, and sphalerite and quartz, which followed fluorite in each stage, were deposited at lower temperatures. Petroleum inclusions in fluorite show considerably lower temperatures of vapor bubble disappearance than aqueous inclusions, but petroleum inclusions cannot be used for temperature determinations, because pressure corrections cannot be estimated. The basic assumptions of the method are evaluated with respect to the deposits and it is concluded that no errors of first order magnitude are expected. The apparent variation in temperature during mineralization is tentatively interpreted as the result of 2 pulsations of hydrothermal solutions from a single source.