TERTIARY-AGED FE OXIDE-CU-AU MINERALIZATION AT THE ARIZARO PROSPECT, SALTA PROVINCE, NORTHWEST ARGENTINA

The Arizaro iron oxide-Cu-Au prospect is located adjacent to the Salar de Arizaro in the western portion of the Salta Province, Argentina which contains in excess of 1km of evaporites. The prospect is hosted in a mid-late Tertiary volcanic-intrusive complex of andesitic composition. These igneous rocks intrude and unconformably overlie Paleozoic (?) granitic basement and Cretaceous-early Tertiary red beds. Alteration at Arizaro is zoned from distal epidote-calcite alteration inwards to actinolite-biotite-magnetite-potassium feldspar alteration (calcic-potassic) and to a central core of intense potassium feldspar-biotite-magnetite alteration (potassic). The potassic alteration zone is further subdivided into biotite- and potassium feldspar-rich zones. Calcic-potassic alteration is observed to cut potassic alteration. Weak hydrolytic alteration occurs on the periphery of the system and overprints other alteration types. Alteration minerals associated with both potassic and calcic-potassic alteration formed dominantly by replacement of wallrock. Magnetite is common as veins, vein stockworks, breccia zones and disseminations throughout both potassic and calcic-potassic zones. Chalcopyrite is the only sulfide observed at Arizaro. It dominantly occurs as extremely fine grains intergrown or replacing both disseminated and veinlet magnetite. Iron sulfides are not present. Gold occurs with copper but has not been observed megascopically or in thin section. Copper and gold values are generally highest in the potassically altered zone. Mineralized zones display a distinct northwest, northeast and north-northeast trend. Northwest trends are parallel to regional, high angle structures.