N[sub 2]-Ar-He compositions in fluid inclusions: Indicators of fluid source
- New Mexico Tech, Socorro, NM (United States)
- Los Alamos National Laboratory, NM (United States)
A quadrupole mass spectrometer was used to measure bulk samples of conservative gas species N[sub 2], Ar, and He in fluid inclusions from a variety of hydrothermal systems. Analysis of these tracer elements help determine (1) if gases extracted by bulk inclusion analysis can provide accurate measurement of N[sub 2]-Ar-He in active and fossil geothermal systems, (2) if hydrothermal fluids associated with paleogeothermal systems in a continental setting follow N[sub 2]-Ar-He systematics similar to those in the western Pacific Rim active geothermal systems, specifically New Zealand, and (3) whether different deposit types systematically vary with regard to N[sub 2]-Ar-He. The N[sub 2]-Ar-He ratios of fluid inclusion volatiles released from recently deposited minerals from the Valles system are similar to those of present day Valles thermal waters. Those inclusion samples from deep within the Valles system, below a regional aquitard, increase in N[sub 2]. Compositions for inclusions from the Questa and Copper Flat-porphyry deposits are N[sub 2]-rich, similar to those of arc-related volcanic gases, whereas those from Taylor Creek Sn deposit appear to be mixtures of magmatic and crustal components. N[sub 2]-Ar-He ratios of the Precambrian Tribag deposit suggest a basalt source, but significant levels of self-generated He from U and Th in the inclusion fluids are also possible. Inclusions from two epithermal deposits with low-salinity inclusions have N[sub 2]-Ar-He ratios trending towards air-saturated meteoric waters (ASW), and those inclusions with higher salinities indicate minor to no ASW component. The N[sub 2]-Ar-He ratios in Fresnillo and Cochiti inclusions, which have magmatic helium isotopic ratios, indicate additions of magmatic gases to meteoric fluids. Inclusions from sediment-hosted deposits that contain hydrocarbon-bearing brines are He-rich, as are meteoric waters with a long residence time in the crust.
- OSTI ID:
- 7198660
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 58:3; ISSN GCACAK; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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