Hydrogen movement into and out of fluid inclusions in quartz: Experimental evidence and geologic implications

Details Hydrogen movement into and out of fluid inclusions in quartz: Experimental evidence and geologic implications Hydrogen movement into and out of fluid inclusions in quartz: Experimental evidence and geologic implications

Jan 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994gecoa..58..141m&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 58, Issue 1, pp.141-148

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13

Scientific paper

Natural chalcopyrite-bearing fluid inclusions from the Red Mountain, Arizona, porphyry copper prospect have been used to experimentally document the movement of hydrogen into and out of fluid inclusions in quartz. Chalcopyrite daughter minerals in inclusions do not dissolve during heating studies of "as collected" quartz vein material. However, after the samples were held at an elevated (but unknown) hydrogen pressure in a cold-seal-type pressure vessel at 600°C and 2.5 kbar for seven days, chalcopyrite daughter crystals in fluid inclusions dissolve easily and completely during subsequent heating. The presence of hydrogen in the re-equilibrated inclusions was confirmed by both Raman microprobe and quadrupole mass spectrometric analyses of the inclusions. Repeated heating of re-equilibrated inclusions to measure the dissolution temperature of chalcopyrite (Tm Cpy) results in a considerably higher Tm Cpy during each successive run until, eventually, the chalcopyrite no longer dissolves when heated to the upper limit of the heating stage. This behavior is interpreted to indicate that hydrogen which had diffused into inclusions during re-equilibration experiments diffused out of the inclusions during microthermometric analyses. The dissolution of chalcopyrite following re-equilibration and its failure to dissolve before re-equilibration are consistent with proposed solubility models for chalcopyrite in aqueous solutions. The rapid movement of hydrogen into inclusions is also consistent with experimentally determined diffusion rates for hydrogen through quartz. These results reinforce conclusions reached by earlier workers who suggested that the failure of some fluid inclusion daughter minerals to dissolve during heating is a result of hydrogen loss. These results also support earlier workers who have suggested that unexpectedly low D values obtained from inclusion fluids were produced by the preferential movement of hydrogen (relative to deuterium) into fluid inclusions. Finally, these results suggest that f o 2 conditions inferred from Raman or other microanalytical data obtained from fluid inclusions may not represent f O 2 conditions present at the time of trapping.

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