The purpose of this report is to make available fluid-inclusion information from drill holes in five geothermal areas: The Geysers and Long Valley caldera in northern California; Steamboat Springs, Nevada; the Ahuachapan field of El Salvador, Central America; and the Mutnovsky geothermal field, Kamchatka Peninsula, Russia. These data were produced at the request of various individuals to provide needed subsurface-temperature data for their investigations. The fluid-inclusion information presented in this report has not been previously published, and, since the author did not work in these geothermal areas, only a very minimal attempt is made at interpreting the data. Information on the location of the drill holes from which the core specimens originated ranges from very poor in the case of the Russian drill holes to very good for those in the USA.

Mineral specimens from drill-core samples in the five geothermal areas were utilized as cleavage chips, thin sections polished on a single side, or double polished thin sections (polished on both sides). Fluid inclusions from all three USA geothermal areas were found in either hydrothermal or primary quartz crystals. These fluid inclusions firstly were frozen and gradually thawed to determine the final melting-point temperatures (Tm) as the last piece of ice melted and secondly, were heated to the temperature at which the vapor phase disappeared to obtain homogenization temperatures (Tn). For the El Salvador and Russian core specimens the fluid inclusions were hosted in calcite, and the order of the two procedures was reversed because calcite is a much softer mineral than quartz and there is a greater danger of the fluid inclusions decrepitating as the ice expands during freezing.

A Chaixmeca microthermometry apparatus was used during studies of the Steamboat Springs and The Geysers fluid inclusions. For the remaining studies, a Linkam THM 600 heating/freezing stage and TMS 90 temperature control system were employed. Accuracy of the data generated from both instruments is similar, with values of about ±2°C for heating studies and about ±0.2°C for the freezing methods.