New Mexico Geological Society Annual Spring Meeting — Abstracts

Precious metal epithermal ore fluids are characterized by a combination of N₂ and CnNn. Total gas analyses of vein samples by mass spectrometry (MS) commonly yield 1 wt % hydrocarbons. Gas chromatography-mass spectrometry (GC-MS) analyses of inclusion gases have helped separate and confirm the presence of molecules tentatively identified earlier by MS. Organic species identified by each technique are:

MS: methane, ethane, benzene, toluene, mixed C_nH_n
GC-MS: methane, propane, butane, benzene, unidentified C_nH_n

Organic compourids occur in inclusion samples from several epithermal deposits, including Cochiti, Red River, and St. Cloud, New Mexico, and Creede, Colorado. Organics also are present in samples from Hansonburg, New Mexico, a Mississippi Valley-type deposit.

As seen through the microscope, organic liquids are difficult to recognize in fluid inclusions. These liquids may be dismissed as H₂S when they occur as globules on a vapor bubble. Hydrocarbons have been known to form separate inclusions due to immiscible segregation from host fluids. such organic inclusions resemble secondary inclusions and are easily overlooked. Quartz-vein samples from Creede contain organic liquids as droplets in ordinary primary aqueous inclusions.