No abstract

v i i The investigations of the Wood River area reported herein were done by the Idaho Department of Water Resources Geothermal Section for the purpose of evaluating the geothermal potential of the area. Pre-Tertiary sediments of the Milligen and Wood River Formations consisting primarily of argillite, quartzite, shale and dolomite are, for the most part, exposed throughout the area and are cut locally by outliers of the Idaho Batholith. At some locations, Tertiary-age Challis Volcanics overlay these formations. Structurally the area is complex with major folding and faulting visible in many exposures. Many of the stream drainages appear to be fault controlled. Hydrologic studies indicate hot spring occurrences are related to major structural trends, as rock permeabilities are generally low. Geochemical studies using stable isotopes of hydrogen and oxygen indicate the thermal water in the Wood River region to be depleted by about 10 O/oo in D and by 1 to 2 O/oo in 180 relative to cold water. This suggests the water could be meteoric water that fell during the late Pleistocene. The geologic data, as well as the chemical data, indicate the geothermal waters are heated at depth, and subsequently migrate along permeable structural zones. In almost all cases the chemical data suggest slightly different thermal histories and recharge areas f o r t h e water issuing from the hot springs. Sustained use of the thermal water at any of the identified springs is probably limited to flow rates approximating the existing spring discharge.