The Cerro Maricunga (Fenix) porphyry-style gold deposit, Maricunga belt, northern Chile

The Cerro Maricunga (Fenix) gold deposit is located in the Maricunga gold belt of northern Chile, within the remnant edifice of the Miocene Ojo de Maricunga volcano. The low-grade gold resource (411 Mt at 0.38 g/t Au, measured + indicated; 0.15 g/t Au cut-off) occurs in a diatreme system of multiply brecciated (sub)volcanic andesitic rocks. The deposit is within a large halo of smectite ± illite ± kaolinite alteration and mostly lacks the high-sulfidation association common to other Maricunga-style Au(-Cu) porphyry-epithermal deposits in the belt. Very limited silicification is veinlet-controlled. The gold mineralization is almost entirely in mm to cm-wide banded quartz veinlets (white to black color tints). The sulfide content (<0.1 vol%) of the hydrothermal system is very low and consists of a cryptic bornite-pyrite-chalcopyrite-chalcocite (plus locally molybdenite) assemblage with subordinate gold content. Supergene gold is insignificant. Primary gold is mainly in nanoparticles in the dehydrated and porous silica matrix of the banded quartz veinlets. The Re-Os model age on a molybdenite concentrate is 17.9 ± 0.4 Ma, concordant with the U-Pb zircon age of the diatreme system. The geochemical signature of the ore deposit is simple, with enrichment of Au and Cu only, whereas neighboring deposits have the typical epithermal enrichment of Mo-As-Sb-Bi-Hg-Te-Re. The Cerro Maricunga (Fenix) gold deposit represents the low-grade root zones of an eroded sulfide-poor porphyry system. High-to moderate-temperature hydrothermal magnetite connects the system to its deeper porphyry source. • Gold at the Cerro Maricunga (Fenix) deposit is largely related to the dark bands in banded quartz veinlets. • Re-Os model age on a molybdenite concentrate is 17.9 ± 0.4 Ma concordant with the U-Pb zircon age of the diatreme system. • Geochemical signature of the ore deposit is simple, with enrichment of Au and Cu only. • Cerro Maricunga (Fenix) gold deposit represents the low-grade root zones of an eroded sulfide-poor porphyry system.