--> Abstract: Hydrothermal Systematics, Alteration, and Mineralization in the Grant Canyon, Bacon Flat, and Blackburn Oil Fields, Nevada-Intriguing Parallels with Carlin-Type Gold Deposits, by J. B. Hulen and D. L. Nielson; #90993 (1993).

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HULEN, JEFFREY B., and DENNIS L. NIELSON, University of Utah Research Institute, Salt Lake City, UT

ABSTRACT: Hydrothermal Systematics, Alteration, and Mineralization in the Grant Canyon, Bacon Flat, and Blackburn Oil Fields, Nevada-Intriguing Parallels with Carlin-Type Gold Deposits

Nevada's three known thermally active oil reservoirs-Blackburn, Bacon Flat, and Grant Canyon-share a surprisingly long list of essential attributes with the Carlin-type, low-grade, sediment-hosted gold deposits, particularly those of the Alligator Ridge mining district. Like these rich precious-metal ore bodies, the three fields (1) are hosted by Paleozoic carbonate and calcareous siliciclastic strata; (2) occur in structural or structural/stratigraphic traps sealed beneath shales or hydrothermally argillized and silicified tuffs and epiclastic debris, (3) have undergone intense fracturing and brecciation, as well as massive hydrothermal decalcification as major porosity-creating processes; (4) occupy rocks partly altered to or veined by the secondary-mineral assemblage quartz-kaolin- arite-pyrite-marcasite; (5) have a direct geothermal connection; and (6) are enriched in the elements arsenic, antimony, mercury, thallium, and even contain significant traces of gold-up to 50 ppb in altered Mississippian Chainman Shale in the Blackburn field. Moreover, measured temperatures, as well as late-stage, fluid-inclusion homogenization temperatures (Th), at the fields-all in the range 100-135 degrees C-fall within the fluid-inclusion Th span of 90-165 degrees C recorded for multiple Alligator Ridge deposits. Fracture-controlled live oil and oil-bearing fluid inclusions in some of the Alligator Ridge ores provide further evidence of genetic similarities with the oil reservoirs. We suggest that the three oil fields could represent either weakly mineralized analogs of the gold dep sits or an incipient phase in their evolution ultimately leading to ore mineralization.

AAPG Search and Discovery Article #90993©1993 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah, September 12-15, 1993.