Geochemical Orientation Over Grant Canyon and Bacon Flat Oil Fields, Nevada The Grant Canyon and Bacon Flat oil fields produce prolifically from the remnants of detached Devonian dolomites that cap a rectangular, faulted horst block. The Grant Canyon reservoir is approximately 1300 feet thick and covers an area of 500 acres. The Bacon Flat reservoir covers about 160 acres and with an approximate thickness of 1100 feet. The reservoirs are covered by 5000 to 6000 feet of Neogene “valley fill” deposits of volcanics, conglomerates, sands and clays. The oil, which was generated within the last 5 million years from the Mississippian Chainman shales, migrated into overlying Devonian reservoirs in the horst blocks. The Grant Canyon and Bacon Flat reservoirs have produced a total of about 20 million barrels of oil to date. DIRECT GEOCHEMICAL conducted orientation soil surveys at 1/5- to 1/10-mile sample intervals over the Grant Canyon and Bacon Flat oil fields to develop geochemical models for oil exploration elsewhere in Nevada. The soil samples were analyzed for C1-C6 hydrocarbons and 26 major and trace elements. The data were incorporated in a database for multivariate statistical analysis and an evaluation of absolute concentration and ratios. As indicated in Figure 1, high discriminant scores (oil probabilities) are spatially associated with production at Grant Canyon and along the fault leading to Bacon Flat. Normal hexane is anomalous mainly on the western margin of the Grant Canyon Field. Magnesium is also anomalous over and adjacent to the Grant Canyon field, and this increase in magnesium could be related to low temperature hydrothermal alternation of overburden by ascending geothermal fluids (Figure 2).

Figure 1. Percent normal hexane Z-scores superimposed on Grant Canyon oil probability (Grant Canyon and Bacon Flat Fields, Nevada).

Figure 2. Magnesium Z-scores superimposed on Grant Canyon oil probability (Grant Canyon and Bacon Flat Fields, Nevada).

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