Evolução paragenética e dos fluidos no depósito Epitermal Cupro-Aurífero Golden Hill, Camaguey, Cuba

Abstract

The Cu-Au mineralization at the Golden Hill deposit in the Las Tunas Province, Eastern Cuba, is characterized by brecciahosted massive and semi-massive sulfide bodies confined to the Crucero Contramaestre Formation in the Cretaceous Volcanic Arc. The deposit is enveloped by a silicic, argillic and advanced argillic alteration assemblage and the Cu-Au orebodies are particularly associated with the latter, typical of high sulfidation epithermal deposits. Within the advanced argillic alteration zone, two stages of alteration were defined on the basis of the mineralogical and textural associations: (i) Stage I with quartz–kaolinite–alunite–zunyite–diaspore, disseminated pyrite, enargite and, probably, sub-microscopic Au; (ii) Stage II with quartz – natroalunite – pyrophyllite, closely related to pyrite – enargite – luzonite – famatinite and Au. Barite commonly occurs filling fractures and cavities and may have been introduced late during Stage II. These assemblages indicate that, in both stages, the advanced argillic alteration and the Cu-Au mineralization took place under conditions of low pH ( 10 -32.8 bar) and high SO 4 - /H 2 S ratios, with f S 2 > 10 -9.7 bar and f S 2 > 10 -8.7 bar for stages I and II, respectively. Additionally, temperatures for the stage I were constrained between 250°C and 275°C, based on the coexistence of alunite-woodhouseite and quartz-kaolinite-diaspore, whereas for stage II they varied from 188°C and 330°C, according to the total homogenization temperatures of fluid inclusions in quartz and the stability of pyrophyllite-bearing assemblages. Fluid inclusion investigations, restricted to stage II quartz and barite, revealed that part of the advanced argillic alteration and the Cu-Au mineralization took place in the presence of CO 2 - poor (< 0.85 molal), low, but variable, salinity (0,5 – 9,3 wt% eq. NaCl) aqueous solutions. The presence of CO 2 and the ample interval of salinity and total homogenization values of the inclusion fluids, together with Wand Bi-Mo-bearing minerals in Stage II, are evidence to envisage the hydrothermal system of the Golden Hill deposit as a result of a progressive interaction of more diluted and lower temperature surface fluids, with more saline and higher temperature magmatic solutions. This would imply in possibilities of the occurrence of shallow epizonal intrusions, which are generally considered important sites for porphyry Cu-Au mineralization.