New Mexico Geological Society Annual Spring Meeting — Abstracts

Fluid inclusions in samples from epithermal ore veins were analyzed by mass spectrometry to determine the volatile compounds present and their relative amounts. Identification of the organic constituents was of primary concern. Epithermal ore fluids were characterized by a combination of N₂ and organics. A typical gas analysis from the St. Cloud-U.S. Treasury mine yielded the following values (in weight per cent): H₂O, 94.690; CO₂ , 2.856; SO₂, 1.102; N₂, 0.869; organics, 0.481; and H₂, 0.002. An analysis from the Cochiti-Bland mine contained: H₂O, 98.121; SO₂, 1.211; CO₂, 0.326; CO, 0.153; N₂, 0.117; organics, 0.042; H₂S, 0.027; and CS₂, 0.002. Organic content ranged from 1.203 wt.% to 0.006 wt. %. Compounds up to C₆ were present and tentatively identified as short straight-chain alkanes (methane, propane, butane, pentane), cycloalkanes (possibly cyclopentane, methycyclopentane, cyclohexane), and aromatics (benzene, toluene). These compounds correspond with literature reports of the types of organics present in subsurface brines. The significance of organic compounds and their role in ore deposition has not yet been determined.