Fluid inclusion investigation of the mid-Tertiary Helen Rae gold mine, Nogal district, New Mexico
Andrew R. Campbell, James A. Porter, and Scott E. Douglass
The Nogal mining district contains porphyry-type primary deposits, breccia pipes, and precious-and base-metal veins. The Helen Rae deposit is a precious-metal vein containing quartz, calcite, pyrite, sphalerite, galena and native gold. Quartz is paragenetically early and is followed by sulfides, which compose only about 2 wt% of the vein material. Gold deposition followed the sulfides and gold grains exhibit rims that have been depleted in silver, presumably by supergene leaching. The final hypogene mineral to be formed is carbonate. Primary fluid inclusions in quartz were found both with, and without, solid crystals in the inclusions. The inclusions have average values for homogenization temperature (Th) of 200°C and average salinities of 16 eq wt% NaCI. Inclusions in calcite have very low salinities of 0 to 3 wt% NaCI and Th values from 146°C to 165°C.ð18O values of quartz range from 6.0 to I3.5%c with corresponding ð180 H2O values from —4.4 to 3.1%o. Two calcite samples have values of 23.6 and 24.2%c, with corresponding ð18O H2O values of 0.7 and I.3%o. The lightest water values are associated with barren quartz or late calcite veins and the heaviest values are from the mineralized veins. The fluid inclusion and isotope evidence suggest that two fluids were involved in ore mineralization. The high salinities of the mineralizing fluid are unusual for gold mineralization, perhaps providing evidence for the involvement of fluids from the porphyry systems in the district.
- Campbell, Andrew R.; Porter, James A.; Douglass, Scott E., 1991, Fluid inclusion investigation of the mid-Tertiary Helen Rae gold mine, Nogal district, New Mexico, in: Geology of the Sierra Blanca, Sacramento and Capitan Ranges, New Mexico, Barker, James M.; Kues, Barry S.; Austin, George S.; Lucas, Spencer, G., New Mexico Geological Society, Guidebook, 42nd Field Conference, pp. 317-321.