Association of pyrobitumen with copper mineralization from the Uchumi and Talcuna districts, central Chile

摘要

Pyrobitumen has been shown to be an essential component in formation of some Chilean manto-type (strata-bound) copper deposits and its presence has been observed in a number of other deposits but has received limited investigation. In this paper we present paragenetic and geochemical data from two central Chilean manto-type deposits from the Uchumi and Talcuna districts where solid pyrobitumen (residual petroleum) is intimately associated with copper sulfides. Pyrobitumen in the Uchumi deposit occurs in pore space within the host conglomerates and is adjacent to a granitoid stock; pyrobitumen predates bornite-chalcocite mineralization and may have reduced subsequent mineralizing fluids. Pyrobitumen from the Manto Delirio deposit, Talcuna District, fills the cores of early sphalerite veins and was partially replaced by later Cu-As mineralization; pyrobitumen is petrographically intergrown with Cu-Fe sulfides and light delta~(13)C values of gangue calcite indicates the interaction of pyrobitumen with the mineralizing fluid. The presence of pyrobitumen within the ores of other manto-type copper deposits in the Lower Cretaceous basin of Chile suggests that degraded petroleum reservoirs, in particular if biodegradation generated authigenic pyrite, can be important controls for metallic mineralization derived from hydrothermal solutions of different sources.