Vanadium mineralization at Los Chihuidos sediment hosted stratiform Cu deposit

RAINOLDI A. L.; FRANCHINI M.; BEAUFORT D.; PATRIER P.; GIUSIANO A.; PONS M. J.; CESARETTI N.

Salta

Simposio; 15th Quadrennial IAGOD International Association on the Genesis of Ore Deposits Symposium; 2018

15th Quadrennial IAGOD International Association on the Genesis of Ore Deposits-SEGEMAR

Sediment-hosted stratiform copper (SSC) deposits represent the main metalliferous resource of the Neuquén Basin (Argentina). These deposits are spatially linked to oil and gas reservoirs and contain minor amounts of V, U and Ag. Los Chihuidos deposit outstands because contains major amounts of vanadium compared with the other SSC deposits of the basin. The Los Chihuidos deposit (37°50?30"S; 69°27?W) is located in the central part of the Neuquén Basin, near the Sierra Chata gas reservoir, and it is hosted in the Huincul Formation (Late Cenomanian-Early Turonian) of the Neuquén Group. The Neuquén Group represents a red bed sequence, but at the site of mineralization, the rocks are bleached. Bleaching resulted in colorful outcrops variations with the original red sandstone interbedded with white sandstone, whereas gray and brown sandstones are subordinated to the contact between the formers. The highest anomalies of V are always located below zones with high Cu grades, but at regional-scale, V is always present at the contact between the red and the overlying bleached sandstone, where gray sandstones occur. Uranium anomalies are more erratic, always associated with vanadium anomalies and characterized by the presence of U-V supergene minerals (i.e. carnotite group). The main differences between the sandstones with different colors are due to variations in the porosity and in the mineralogy of the authigenic minerals. This contribution presents the first mineralogical study of the vanadium-rich zones at Los Chihuidos, and discusses plausible sources of vanadium and the mechanisms for the metal precipitation, which has important implications for understanding the formation of vanadium mineralization in the SSC deposits of the Neuquén Basin.