Trap Spring field was discovered in 1976, becoming the second commercial oil field in Nevada. The first, Eagle Springs, was discovered in 1955 and is about 6 mi east of Trap Spring. Currant, a third, noncommercial, one-well field, was found in 1978 and is about 7 mi north of Eagle Springs. Trap Spring field is productive from Oligocene welded ash-flow tuffs, and Currant produced from the Eocene Sheep Pass Formation. Production at Eagle Springs is from both of these units plus some production from the Ely Limestone (Pennsylvanian). Possible sources of oil for these fields are beds within the nonmarine Sheep Pass Formation and the marine black shales of the Chainman Formation (Mississippian). Prior to discovery of Currant field, the origin of the Eagle Springs and Trap Spring oils was problematical, and a wide range of source rock and postgeneration alteration possibilities were considered. The n-C15+ chromatograph of the Currant oil shows unusually high peaks of pristane and phytane and a slight even-carbon preference in the n-C18 to n-C26 range. These factors are indicative of a recently generated oil from a source rock in a carbonate-evaporative sequence. The geochemical data and geologic conditions support the hypothesis that the oil produced at the Currant well was generated in the Sheep Pass Formation. The n-C15+. distribution of Trap Spring oil differs significantly from that of the Currant oil and is more typical of oil generated in source rock deposited in a marine environment. The most likely source of this oil is the Chainman Formation. The origin of the oil from Eagle Springs remains unclear as it has chemical affinities to both Trap Spring and Currant oils. It is possible that the Eagle Springs oil is a mixture of oil generated in the Sheep Pass Formation and Chainman Shale.

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