Figure I Generalized map of the Wilbur Mining ... - University of Utah

ABSTRiCT
Ttte igeology of .ore deposits in c;arbonate' rocks in
the eastern Great Basin gives );nsight into the
geology of present day geothermal reservoirs in
carbonate rocks. The Cove Etirt KGRA is geologically
similar to the Tintic mining district and
the geblogy of the Carlin mine area suggests a
cartxinate reservoir at the Beowawe KGHA. Carbonate
geothennal reservoir's are unique in that fluids
moving along fractares may leada calcite and, less
often, dolcroite and thereto increase poKJsity and
permeability.
IMTRQDUCTHa)
Geologists geherally recognize that most of
the: ore deposits of the •western U.S. are "fossilize3"
geothetmal systems. However, while ^ome
detailed attention has teen given to the use of
the "porphyry copper model" in geothermal explbration,
little attention has be^en given to other
types of ore deposits found in areas being eicplored
for geothermal reservoirs. Tlie purpose- of this
paper is to point out similarities between ore
deposits arid geoUiermal rfeservoirs in carbonate
rocks in the eastem Great Basin and to indicate
some of the unique problems_ and features of carbonate
geothermal reservoirs. Two major mining
districts and two *major geothennal prospects are
discussed telbw. "Hieir bdmparison is made possible
as a result of data from exploratory geothennal
wells having been purchased by the Departinent of
Enetgy ard made available throiqh the University of
Utah Research Institute (UURI).
The only"producing carbonate geothermal reservoirs
at this time are the Lardarello arid Mt.
Amiata fields in. Italy Vihere production is from
highly permeable, fractured carbonates^ capped- by
shaly fiysch facies which have beeti thrust over
the carbonates (Gelati, et al., 1975). While
space does not permit a
silver, copper and gold ores valued at oyer $568
million at th.e time of ptbductibn (Morris and
Mogensen, 1978). The ore bodies of, the district
consist of both massive, irregular replacements
and replacement -veins ih folded and faulted
Paleozoic limestones and dolan ites and open space
fillings in narrower fissure" veins in Paleozoic
quartzites arid Tertiary igneous rocks. The ore'
bodies are believed to have been deposited by
hydrothermal fluids following a period of major
vblcanism in the East Tintic Mountairis which took,
place iri the Oligocene, eridlng about 31.5: million
years ago. Itife vblcanic activity was centered a
few miles south of the preserit mining district and
in the early stages pfbduced a OTllapsed caldera
accaipanied by a thick welded tuff. A later conposite
cone which filled and coveted the caldera may
have attained a height of 13/000 ft - 16,000 ft.
Itie present day topography of the carbonate rbcks
may be very similar to that v^icii was for a long