Milton C. Graves

Hydrocarbon involvement in the genesis of ore deposits; an example in Cretaceous stratabound (manto-type) copper deposits of central Chile

The analysis of the empirical association of organic carbon in its various forms (e.g., oil, gas, coal) with a variety of ore-deposit types can be a rewarding exercise in the formulation of genetic models and exploration. In many ore provinces, organic matter, residing in its source rocks, migrating in the form of hydrocarbons, or in transient, permanent, leaking, or degrading reservoirs, is likely to have interacted with ground waters, with hydrothermal solutions of diverse origin, or with magmas. After a brief review of these associations, we describe the ubiquitous occurrence of remnant petroleum in two representative “manto-type” stratabound copper deposits in Chile and suggest its possible genetic role and exploration significance. Overmature petroleum (solid bitumen, pyrobitumen) is found in association with copper ores in the southern orebodies of the El Soldado copper deposit in central Chile. Textures indicate that petroleum occupied the host-rock porosity before copper mineralization. Isotopic d...