PRESNELL, RICARDO, Kennecott Exploration Company, Salt Lake City, UT

ABSTRACT: The Association of Gold and Hydrocarbons in Sediment-Hosted Disseminated Gold Deposits

Large (>100,000 oz) sediment-hosted disseminated gold deposits (SHDG) are found at or near the crest of anticlines. Many SHDG are within or closely associated with tectonic windows, which are the erosional remnants of fold culminations. The Carlin and Cortez SHDG trends are defined by the alignment of windows. This window alignment delineates large anticlinoria of Mesozoic age.

Fold culminations form hydrocarbon traps in the Canadian Rockies and the overthrust belt of Idaho, Wyoming, and Utah. The structural similarity and the presence of degraded hydrocarbons in SHDG suggest that these fold culminations are paleohydrocarbon traps. An anticline trapping model for gold-bearing hydrothermal fluids akin to hydrocarbon structural trapping can account for the anticline, SHDG deposit, and hydrocarbon association.

The strong empirical relationship between large SHDG and anticlinoria suggests that trapping and/or concentrating of gold-bearing hydrothermal fluids can produce a large SHDG. Due to buoyancy, hydrothermal fluids will flow up the fold limbs to the anticlinal crests where they will flow longitudinally along faults and fractures until they are trapped in fold culminations. Once trapped, a variety of mechanisms can deposit the gold. The 200-300 degrees C hydrothermal fluids would remobilize and mature the previously trapped hydrocarbons.

Recent work in SHDG is beginning to show that they are orogenic deposits, perhaps derived from metaliferous black shales during tectonism. The black shales also may be the source for the hydrocarbons. As is the case with hydrocarbon deposits, many SHDG are in or adjacent to sedimentary basins. Also, fluid transport mechanisms may be similar.

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