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This institution reserves the right to refuse to accept a copying order if, in its judgment, fulfillment of the order would involve violation of copyright law. GEOTHIEZMAL RE!OuRCES, PRESmT AND FUTUREI: DlEMAND FOR POWEB, AND M LEixTISLATION IN THE STATE OF WYOMING Edwa,rd R. Decker, Depaxtment of Geology, University of Wyoming, Laramie, Wyoming 82070 INTRODUCTION This report briefly swnmarizes data on thermal springs and wells jyl the state of Wyoming, exclusive of Yellowstone Pnk, The presentation includes a map showing the general 1ocal;ion.s of the springs and wells outside the Park, and the lands in Wyondng that have been classified as being prospectively of geothermal value, The locations and geothermal data on the springs and wells are tabulated, and a short table of chemical analyses of spiry: waters is presented, Although them3, data constitute most of the material presented hereh, this report also swnroariees the present and future demands for electrical energy in Wyoming, The report also reviews legislation per- tainhg to exploration near thermal springs fi Yyoming, A list of state and federal agencies is included so that interested parties may obtain copies of pertinent legislation and information on the status of hdo KNOWN GEOTHEBMU RESOURCES AREA (KGRA) IN WYOMING Yellmstone Park is the only area in Wyoming that gresently qualifies as a KGRA. It is unlikely that this area will be released for the development of geothermal power, OTHER THERMAL AajEAs IN WYOMING Generalized geology of Uyomlng is sham in Figure 1, Figure 2 shows the locations of thermal springs and wells outside Yellowdone Park, and 178 the landrp in Uyomilng that nay be valuable prospectively for geothermal resourceds (after Godwin 49, (1971) ; Laraway (1971)). The thermal data aad more precise locations for each spring, spring area and well are listed in Table 1I together with comments references @ and updated general geology, Float of the data in Table 1. were taken from Waring (1965). Other data were mished by D.L, Blackstone, Jr, of the University of Wyoming and by J,D, Love of the United States Geological Survey, Table 2 lists all of the recent chemical analyses that I could find for the localities fia Table 1, I would like to thank DOEoWhite of the United States Geological Survey for the copies of the analyses of waters from the Auburn and Flaw Ranch Hot SprWgs, Regional Geology and General Comments on Springs (see Figures 1 and 2) With the exception of the thrust belt, the geology of Wyoming is characterized by north-south to northwest trending asymmetrical mountain, uplifts in which the Precaml$rian basement is exposed, Prior to Laramide deformation the baseanant was overlain by Paleosoic adMesoaoic marine sediments ranging up to 15,000 feet in thickness, Differential relief of the basement is as grea.t aa 35,000 feet, and in the intermontane basins late Cretaceous and Cenorzroic sediments have accumulated with thicknesses in excess of l5,OOO feet. In the thrust belt , Cretaceous and older rocks have been thrust from west to east, generally such that Cretaceous and older units are upon younger rocks. The Y ellowstone-Absaroka-Jackson =ea is the largest volcanic field in Wyoming, Volcanism in the Yellowstme-Absaroka regia started in the Eocene and continued to the Pleistocene (Love, 1968). According; to Love (1968) the Jackson Hole ax- did not subside during the first 20 million years of volcanism, despite the extrusion of more than 4x10 43kn of debris in the Yellowstone-Abaroka region. From the Miocene to the Pleistocene, however, subsidence of Jackson Hole was coincident with extensive activity throuaout the region (Love 1956 I 1968). The Leucite Hillsy the Rattlesnake Hills, and the Black Hills are other volcanic fields in Wyoming (see Figure 2)e Volcanism in the Leucite Hills has been dated as late Pliocene (Houston, 1963). The volcanic rocks in the Rattlesnake Hills are middle-to upper-Eocene ( ?) or younger , while flows and breccias irn the Black Hills are considered to be Oligocene (Houston I 1963) Twenty-four of the springs or spring-systems listed on Table 1 issue from folded or faulted Phanerozoic sediments. Of the remaining three, one issues from Precambrian granite, while the other two issue from Plio- cene and Pleistocene volcanic units, respectively, Five of the springs (Flagg Ranch, Jackson Lake, Kelley, Tetan Valley, and the Rattlesnake Hills) are close to (fi5 miles) late Tertiary eruptive centers; the others axe more than 10 miles from Tertiary volcanic fields (Figure 2), The correla- tion between thermal spring activity and Tertiary volcanism outside the Yellowstone-Jackson-Absaroka, area is obscure; for example, I could not find evidence for hot springs in the Leucite Hills, an area where lavas have been dated at 1.25 million years (Houston, 1963) Uses of Geothermal Resources in Wyaming Geothermal resources in IJyaming have been used for hot waters at resorts and sanitariums, and for irrigation (Table 1) The Wyoming Geological Survey and other state agencies have received inquiries abolrt the geothermal resources of Wyaming, hnrt there is no evidence for active exploration, Cursory Evrtluat ion of Areas Out side Y ellowstone Park be employed in the evEllucltiaa of geothermal resource areas. The application of some of these criteria to areas in Wyoming outside Yellow- stone Park is bribfly summiarkzed blow: 1, None of the springs listed in Table 1 are characterized by geyser activity, In addition, there is little evidence for significant amounts of siliceous sinter at each locality, while sevedrml of the areas are characterized by large deposits of travertine (Table 1). For the springs with large discbrge, these data imply low reservoir tempemhres (Godwin & a.I 1971; White, 1970). 2, The analyses listed in Table 2 were discussed with J.I. Drevsr and H,P, Eugster, geochemists presently at the University of Wyoming, My impressions of their comments are8 a) that the compositions are not inconsistent with low4emperatme (dlOO°C) reqwtiqme, between meteoric waters and marine sediments or volcanic rocks; and b) thatl although the compositions may no;t be emplayed for accwrate geothermometry, they may imply that reservoir temperatures are not abnormally high. White (1970) infers that the si02 content of sample #2 (Table 2) from Thermopolis Hot springs ahso implies hm temperatures (\(lls°C) in the underlying reservoirt 3, Several of the springs are chaxacterised by moderate tempdares (total measured range 23.%62.2*C). Although the surface data nay provide pstinmtes for minirum subsurface temperatures, those springs with mxinum tempratures of 23 to 29OC could reflect the result of waters circulating to depths of 1 to 2 km in axeas with normre1 geo- thermal gradients (25OC/km) Other data in Wyoming suggest that some of the other springs are not associated with shallow "gecsthsrmnrl reservoirs", For example, heat flow determinatiana at Cooke City and Nye Basin, Montana and Meeteetse, Wyoming sange from 1.3 to 1.8 HFU' (Blackwell, 1969; Sass & trl, , 1971) I suggesting that the anomalous regional flux ( 6-10 m; after White (1965) ; brier (1969)) in Yellowstone Park does not extend very far to the east and northeast. Considered together, the geothermal data in the Absaroka region (Figure 2) suggest that the DeMaris Hot Spin@ wy bs related in part to above- average, but not abnormal regional flux and gradients, The high gradients in areas around Thennopolis, Alcova, and the Battlesnake Hills (Figure 2) suggest that 60 to 7OoC waters could occur between 1 and 2 km depths near these springs while the regional flu may not be ahomally high (see Blackwell (1969)). 4, The high bottomahole temperature (135OC) in the Carter Cole well, the thermal springs near Doughs, and Blacbell% (1969) "estimated" heat flows (1,8-2,0 HF'U) in the Salt Creek and Lance Creek of1 fields, suggest that the Powder River Basin may be chazaderiaed by above- average flux, This Bone of high flux (?) may extend into the Black Hills to the northeast; Blackwell (1969) and Sass & &, (1971) calm- laked heat flows of 1.9 HFU near Lead, South Dakota, and recent studies (Deck=, unpublished) west of Speaxfish, South Dakota tend to confirm high regional flw (1,g-2.4 HF'U). These values of flux are not high enough to suggest shallow geothermal reservoirs, lnrt above-average 2 1, 1HFU = 1 heat flw unit = 1 microcal/cm sec, 182 heat flow would imply that the Basin could be a source of hot waters, In sumnvLrly, the available data imply that some of the thermal areas in Wyoming outs3de of Yellowstone National Park are not characrterhed by reservoir tempemtwes appropriate for the development of steam directly as a result of shallow (2 km) drillbg, Howevert the present information on every mea is inadequate for proper evaluation; therefore, more rigorous geochemical, geophysical and geological studies should be initiated at each locality, A better knowleae of the heat flow pattern in eastern Wyoming also is needed, since the Powder River Basin is expected to be a mjor source of a large increase in demand for water irJ.