The Productora Cu-Au-Mo Deposit, Chile

Productora, located in the coastal range of Region III, northern Chile, is a magmatic-hydrothermal, tourmaline breccia hosted, structurally controlled, Mesozoic Cu-Au-Mo deposit. It is hosted by a thick sequence of Jurassic rhyodacite volcanics which have been intruded by two stocks; the Cachiyuyito tonalite and Ruta-5 granodiorite, and by several phases of basaltandesite dykes. There are two major fault orientations; north trending and northwest trending sets, which control the mineralised breccias and locally upgrade mineralisation respectively. Alteration is widespread, complex and pervasive. Hypogene alteration assemblages transition from distal magnetite-amphibole, to sodic-calcic, to sodic, to phyllic, to proximal potassic. Lower temperature advanced argillic assemblages are juxtaposed next to proximal high-temperature assemblages indicating significant vertical offset on local faults. There is strong evidence for magmatic hydrothermal processes but the subordinate iron-oxide content and lack of an intimately associated igneous intrusion mean the deposit does not easily fall into the IOCG or porphyry deposit class. Overall, current data suggests that the deposit is more compatible with the porphyry model. The mineralisation and potassic alteration zonation may be attributed to cooling hydrothermal fluids, and the halo of sodic and magnetite alteration attributed to heating of regional brines.