Although the Pine Point ore is relatively poor in useable fluid inclusions, some sphalerite crystals from replacements, vugs, and from " colloform" crusts were found to contain primary or pseudosecondary liquid-gas inclusions adequate for study. Most (132 of 133) of these had low freezing temperatures, indicating exceedingly saline brines. The 112 inclusions suitable for filling-temperature determination homogenized at +51° to +97° C. A very small pressure correction must be added to obtain the trapping temperature.Dolomite crystals from some of the same vugs contain large numbers of primary inclusions, many of which have leaked. The twenty-three that presumably have not leaked had filling temperatures of 90°-100° C, but somewhat lower salinities. Inclusions in late calcite appeared to have similar gas-liquid ratios, but had still lower salinities.The significance of these data lies in the limitations they place on the choice of possible mechanisms of origin of these large deposits. This choice, in turn, may influence the success in prospecting for blind ore bodies. There is general agreement that the deposits are of Mississippi Valley type. Although the high salinities may reflect solution of salts from evaporites, as are now found to the south, the elevated temperatures seem to require deep circulation, perhaps through known faults in the underlying Pre-cambrian. The densities of these brines, even at their elevated temperatures, are well above that of fresh, cold surface water, thus restricting the possible modes of circulation during ore deposition.
