Sediment- hosted copper deposits in the Cretaceous

JOSEFINA PONS; RAINOLDI ANA; FRANCHINI MARTA; ADOLFO GIUSIANO

Upsala

Congreso; 12th SGA Biennial Meeting; 2013

Geological Survey of Sweden

The Tordillos and the Sapo Sur prospects are two examples of sediment-hosted Cu (V-U) deposits located in the Dorsal de Huincul and Dorso de los Chihuidos Highs, respectively. Both deposits are located near hydrocarbon fields and are hosted in thepaleochannels red bed sequences of the Huincul Formation (Late Cenomanian-Early Turonian, Neuquén Group). During the eodiagenesis the precipitation of hematite gave the red coloration to the sedimentary rocks. With progressive burial precipitated pore-filling kaolinite and quartz and albite overgrowths following by calcite,   mineralization is hosted in these pervasively bleached rocks impregnated with bitumen. The bleaching was produced by the interaction of the reducing hydrocarbons with the authigenic minerals. The synchronic oxidation of hydrocarbons locally produced carbonates precipitation.  Copper mineralization is interstitial, occludes the primary        and secondary porosity of the rocks and fractures. It consists of chalcocite (CuS)>chalcopyrite and bornite partially replaced by supergene minerals (chrysocolla > brochantite> malachite > azurite traces > covellite (Cu1- S) > complex oxides of Cu, Mn and Ba-copper wad >     cuprite > tenorite, volborthite, and traces of U-V minerals, carnotite, franchevillite?). Hypogene sulfurs selectively replace information has enabled an interpretation of the source of sulphur and the hydrothermal fluid-flow processes that favoured the formation of these deposit.