ABSTRACT: Implications of Oil in a Precious Metal Deposit, Alligator Ridge, Nevada

HULEN, JEFFREY B., University of Utah Research Institute, Salt Lake City, UT, JOHN W. COX, USMX, Inc., Reno, NV, and MICHAEL L. PINNELL, Pioneer Oil and Gas, Salt Lake City, UT

The Yankee gold deposit, in the Alligator Ridge mining district, is unique among Nevada's famous Carlin-type sediment-hosted precious-metal orebodies in hosting abundant "live"oil, both free-flowing and as large fluid inclusions in gold- and arsenic-bearing calcite veins. Detailed geologic mapping at Yankee, coupled with preliminary geochemical and petrographic studies, as well as reconnaissance fluid-inclusion microthermometry, suggests that the oil, derived from Devonian marine shales, migrated to its current entrapment site in a dilute (<3.5 wt.% NaCl equivalent), moderate-temperature geothermal system (Tn for primary oil and co-existing aqueous fluid inclusions average 103 degrees C [n = 185]). Migration pathways included faults and fractures as well as hydrothermal solution br ccias and decalcified, formerly calcareous siliciclastic strata. Although the oil-bearing calcite veins are highly gold-anomalous, the relationship of the gold to the petroleum remains to be determined. Clues to that relationship may be provided by the Blackburn and Grant Canyon oil fields -- both nearby in the Basin-and-Range province, and both producing oil from geologic settings not only similar to Yankee but including active moderate-temperature geothermal systems. Establishing a clear genetic connection between these unusual oil fields and the unique Yankee occurrence could lead to new models for oil and gold exploration in the western United States.

AAPG Search and Discovery Article #91016©1992 AAPG-SEPM-SEG-EMD Pacific Section Meeting, Sacramento, California, April 27-May 1, 1992 (2009)