Paragenesis, fluid flow and structural controls on bitumen vein deposits and bitumen-hosted ore deposits, Andean Cordillera
Three bitumen-hosted ore deposits from Peru, Argentina and Chile are described. These deposits (now abandoned) contain diverse mineral assemblages and were mined for vanadium (Minasragra, Peru), uranium (Cerro Huemul, Argentina) and copper (Copiapó, Chile). Highly integrated geological and geochemical studies have enabled the construction of paragenetic sequences and genetic models for these deposits. The Minasragra deposit was a bitumen-hosted vanadium orebody located within the Central Peruvian Andes. It was characterised by a highly unusual and world-unique mineral assemblage which included the vanadium sulphide mineral, patronite. Paragenesis is divided into four distinct phases and deposit genesis is linked to the extreme alteration of an in situ vanadium and sulphur-rich bitumen vein catalyzed by the intrusion of a high-level dyke suite. Cerro Huemul is a bitumen-hosted sandstone-type U-Cu deposit located within continental facies in the Neuquén Basin. Petrographic studies of bitumens and ore species coupled with fluid inclusion analysis enable reconstruction of fluid flow through this sandstone unit. Mineralization is divided into three paragenetic stages and is integrated into a regional and deposit-specific genetic model for ore deposition. The Copiapó study focuses on an extensive andesite lava horizon of Lower Cretaceous age which contains a diverse suite of copper sulphide minerals in intimate association with solid bitumen. Petrographic studies of ore and bitumen species enable the construction of paragenetic sequence which is divided into three mineralizing stages. All three bitumen-ore deposits formed due to the presence of solid bitumen and each case study investigates the role that bitumen played in the mineralizing process. Collectively these studies provide detailed insight into mineralization processes at bitumen-hosted ore deposits and highlight the versatility of bitumens to economically-concentrate a wide range of metals and minerals. A synopsis of the formation of all bitumen-type deposits (solid bitumen veins and bitumen-hosted ore bodies) is presented and ideas regarding the potential of mineral exploration for organo-metallic deposits within the Andean Cordillera are outlined.