Mineralogía de skarn y fluidos asociados a los yacimientos de Cu-Zn-Ni-Co de La Esperanza, Sonora, México

the la esperanza deposits in sonora contain a metallic cu-zn-ni-co paragenesis, which is singular in the metallogenetic setting of northwestern mexico. the mineralization is related to a contact metamorphic halo developed between a 89-90 ma porphyry and late paleozoic carbonated rocks. these skarn-type deposits, are characterized by a prograde stage represented by calcic garnet and pyoxene, and a retrograde stage contaning calcite, epidote, quartz, chlorite, feldspar and sulfides. ore minerals are chalcopyrite, sphalerite, pyrite, siegenite (ni,co)3s4, hematite, and magnetite. fluid inclusions data from garnet (prograde skarn) indicate a fluid with 12.8-20.2% nacl eq. and homogenization temperatures (th) of 480-680 °c. fluid inclusions in quartz and calcite from the retrograde stage indicate a fluid with 12.8-18.6% nacl eq. and th of 180-190 °c. primary fluid inclusions in quartz phenocrystals of the porphyry, indicate a supersaturated fluid, with 36-44% nacl eq. and total th of 270-370 °c. chemical compositions of garnet and th values suggest that the prograde skarn formed at high temperature, between 500 and 680 °c and fluid pressures lower than 600 bar. th in quartz and calcite are consistent with a retrograde stage at temperature and pressure lower than 380 °c and 50 bar, respectively. fluids in garnet, quartz and calcite come from the same source, of magmatic origin, mixed during a late mineralizing stage with meteoric waters. fluid inclusion data of quartz of the porphyry are related to early magmatic fluids previous to the the skarn formation.