Productora Cu-Au-Mo deposit – a porphyry-related magmatic-hydrothermal breccia complex with local magnetite-apatite and porphyry mineralisation

The Productora Cu-Au-Mo deposit is hosted by a hydrothermal breccia complex in the Coastal Cordillara of Region III, northern Chile. Hydrothermal breccias, tectonic breccias, veins and alteration assemblages observed on two cross sections at Productora have been separated into five paragenetic stages. Stage 1 produced quartz – pyrite cemented hydrothermal breccia with muscovite alteration. Stage 2 formed a chaotic matrix-supported tectonic breccia with kaolinite–muscovite-pyrite alteration. Stage 3 tourmaline-pyrite-chalcopyrite± magnetite±biotite-cemented hydrothermal breccias are associated with K-feldspar±albite alteration. Stage 4 veins contain chalcopyrite±pyrite±sericite, illite, epidote and chlorite, and stage 5 veins contain calcite. The Productora hydrothermal system crosscuts earlier-formed sodic-calcic alteration and magnetite-apatite mineralisation and pre-dates porphyry mineralisation.

Based on textural, mineralogical, stable (S) and radiogenic (Sr, Nd) isotope data, the Productora breccia complex is inferred to be a magmatic-hydrothermal breccia complex formed as a result of explosive volatile fluid release at depths causing brecciation and alteration of the overlying rock mass. Metal-bearing fluids were of magmatic affinity and evolved under oxidising conditions. Despite sharing many similarities with the Andean IOCG clan (strong structural control, regional sodic-calcic alteration, local U), fluid evolution at the Productora Cu-Au-Mo deposit is consistent with that of a porphyry magmatic hydrothermal breccia (sulphur-rich, acid alteration assemblages and relatively low magnetite, <5 wt%). The Productora camp provides an excellent example of the close spatial association of Mesozoic magnetite-apatite, porphyry (Alice) and magmatic-hydrothermal breccia mineralisation styles, a relationship seen throughout the Coastal Cordillera of northern Chile.