The magmatic hydrothermal evolution of the San Pedro porphyry Cu-(Mo) deposit: Implications for the metallogenesis of the Permian magmatism in the western margin of Gondwana

ULRICH THOMAS; RUBINSTEIN NORA A.; GOMEZ ANABEL L. R.

RESOURCE GEOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2021 vol. 71 p. 93 - 104

1344-1698

The San Pedro porphyry Cu-(Mo) deposit, located in the San Rafael Massif(Argentina), is characterized by multiple stockwork vein generations developedin a subvolcanic intrusion with porphyry-type alteration and mineralization,as well as associated polymetallic veins. Previous works reveal that theintrusive rocks related to the San Pedro porphyry (263 Ma) show comparabletrace element signatures to giant porphyry deposits elsewhere (i.e., high Sr/Yand low Y). The fluid inclusions investigated in this study show that typicalearly, high-temperature magmatic fluids (up to 685°C; 81.3 wt% equiv. NaCl)evolved to lower-temperature, moderately saline fluids (up to 454°C; 52.4 wt%equiv. NaCl) due to fluid?rock interaction. The waning stage of the system ischaracterized by secondary, aqueous inclusions that represent dilution bymeteoric fluids (up to 390°C, 16.9 wt% equiv. NaCl). Fluid inclusions werestudied from two veinlet generations (A and B veinlets) related to potassicalteration and analyzed by LA-ICP-MS. The trace element signatures in thefluid inclusions suggest that there were two pulses of magmatic fluids that subsequentlyevolved under similar physicochemical conditions. The Cu concentrationin the earliest fluid is between 0.3 and 0.85 wt% and within theconcentrations found in other mineralized porphyry systems in the world.However, in contrast to economic porphyry systems, where a significantchange in Cu concentration during fluid evolution is observed, there is no distinctchange in the fluid Cu concentration at the San Pedro deposit, whichwould indicate that Cu and Mo precipitation was ineffective in the hydrothermalsystem