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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 64 (1980)

Issue: 5. (May)

First Page: 767

Last Page: 767

Title: Oil and Metals in Ordovician and Devonian Kerogenous Marine Strata of Central Nevada: ABSTRACT

Author(s): Forrest G. Poole, George A. Desborough

Article Type: Meeting abstract

Abstract:

Kerogen-rich mudstone, siltstone, dolomite, and chert units as much as 50 m thick in the Vinini (Ordovician) and Woodruff (Devonian) formations contain potential resources of syncrude oil, V, Zn, Mo, Se, Ag, and Cr. Most kerogenous rocks originally consisted of organic-rich siliceous muds, slimes, and oozes. Organic matter is mostly amorphous, flaky, and stringy sapropel composed of planktonic organisms. The strata are within strongly deformed eugeosynclinal Paleozoic marine rocks of the Roberts Mountains allochthon.

Many fresh black rocks are low-grade oil shales which, upon pyrolysis, yield < 40 l of oil per metric ton of rock; some thin layers yield as much as 125 l per metric ton. In these rocks, solid bitumen and liquid oil commonly fill voids and microfractures. Such early-phase hydrocarbons probably were released during diagenesis and formed without any major thermal degradation of the kerogen. Geochemical data suggest that the organic matter is thermochemically immature to mature and has not been subjected to temperatures above 60°C since deposition. Hydrocarbon contents (< 100 to 5,400 ppm) and organic carbon contents (< 1 to 25 weight %) vary widely.

V, Mo, Se, Ag, and Cr in fresh black rocks occur chiefly in organic matter; Zn occurs as sphalerite and Ni in iron sulfides. Concentrations are as much as 5,000 ppm V, 18,000 ppm Zn, 1,000 ppm Mo, 100 ppm Se, 20 ppm Ag, 150 ppm Ni, and 600 ppm Cr in unoxidized rocks. Enrichment of V and Se and depletion of Zn, Mo, Ni, and organic matter occur in oxidized rocks.

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