ORE GENESIS CONSTRAINTS ON THE IDAHO COBALT BELT FROM FLUID INCLUSION GAS, NOBLE GAS ISOTOPE, AND ION RATIO ANALYSES—A DISCUSSION

Abstract

Sir: In their paper, “Ore genesis constraints on the Idaho cobalt belt from fluid inclusion gas, noble gas isotope, and ion ratio analyses,” Landis and Hofstra (2012) report on the analysis of hydrogen gas within fluid inclusions using mass spectrometry. They indicate surprisingly high hydrogen contents in fluid inclusions (~25,000 ppm) in this and their other, previous work that they reference. But it is highly unlikely that hydrogen is really that common in geofluids and even less likely that it could remain trapped in fluid inclusions for geological time periods because hydrogen diffuses easily through most materials, including quartz. The laser Raman method for analysis of gas contents of fluid inclusions can also measure hydrogen contents, but such analyses never find the presence of hydrogen within inclusions. The only detection of hydrogen in fluid inclusions by laser Raman that I am aware of was by Dubessy et al. (1988) and the hydrogen was present due to radiolytic dissociation of water within inclusions in a uranium deposit. These contradictions in the measurement of hydrogen in fluid inclusions are most likely a problem within the method of mass spectrometric analysis for hydrogen in aqueous fluids, as occur in fluid …