--> The Application of Petroleum Surface Geochemical Methods to Detecting Mississippi Valley and Carlin Type Ore Bodies, by S. A. Tedesco; #90986 (1994).

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Abstract: The Application of Petroleum Surface Geochemical Methods to Detecting Mississippi Valley and Carlin Type Ore bodies

Steven A. Tedesco

The application of surface geochemical methods to finding petroleum is based on the detection of hydrocarbons in the soil that have leaked from a petroleum reservoir at depth. Mineral deposits like the Carlin type deposits in Nevada and Mississippi Valley Type (MVT) deposits in the Central United States have petroleum associated with them that is either a product of or directly related to their formation. The inter-relationship of basinal brines, petroleum and gold in Nevada's Basin and Range Province has only recently been recognized. However, the formation and origin of MVT deposits from "oil field brines" or basinal brines carrying petroleum, lead and zinc that have been expelled to the basin margin has long been recognized. Both types of mineral deposits, early in their history we e found by surface exposures. As these deposits were exhausted, a variety of methods were used to find new ones. In the case of MVT deposits random drilling has generally been found the most successful. The Carlin type deposits close to or at the surface can be detected by soil changes but as exploration moves away from the rim of a basin into areas of greater overburden, random drilling becomes the only option. Therefore, if petroleum surface geochemical methods can be applied, this should provide a target for drilling, substantially reducing exploration risk and cost.

MVT deposits are formed by first the brecciation of the country rock, typically along a strike-slip/wrench fault system which extends from the basement along the basement margin. Later an episode(s) of dolomitization of the breccia occurs followed by subsequent episode(s) of deposition of spalerite(Zn), galena (Pb) and petroleum. Carlin type deposits are similar in

that a breccia is formed, with subsequent alteration and deposition of gold and petroleum. MVT deposits that have produced hydrocarbons economically are known in the petroleum industry as "dolomite chimneys." The most notable fields that produce from these chimneys are Albion-Scipio (161+ MMbbls) and Stoney Point (8.4 MMbbls) of the Michigan Basin, the Wood-Hancock Complex (215+ MMbbls) in Northwestern Ohio, Hilham (1.1 MMbbls) in Ontario and the Fergusen 9372 well (335,000 barrels) in South-Central Kentucky. In these deposits Zn and Pb are minor constituents whereas they are economically recovered from chimneys or breccias at the Elmwood Mine in Central Tennessee, Viburnum trend in Southeastern Missouri and Galena District in Northwestern Illinois.

Surface geochemical methods which detect hydrocarbons can be used effectively to find mineral deposits of the MVT and Carlin types. The model for development of these orebodies involves the same mechanisms that form dolomite chimneys that are petroleum productive. In fact, petroleum might precede the ore deposit creating the proper chemical conditions to precipitate the minerals. Several mines that produce from MVT and Carlin deposits report minor petroleum seeps, bitumen in the ore body and petroleum hydrocarbons. The methods used to test the effectiveness of petroleum surface geochemical techniques detecting hydrocarbon leakage from these ore bodies was iodine and soil gas. Five test areas were chosen: (1) three gold mines in northern and central Nevada; (2) the Gainesboro and Dodso Branch zinc deposits in Central Tennessee; (3) the Buick Mine area of the Viburnum trend in Southeastern Missouri; (4) the Crandon deposit in Northern Wisconsin and (5) the gold district in the Cripple Creek area. The Crandon and Cripple Creek areas were chosen because petroleum hydrocarbons are not known to be associated with the ore bodies and the host rocks are considered non-petroliferous. The results will be discussed in detail.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994