HYDROGEN MOVEMENT INTO AND OUT OF FLUID INCLUSIONS IN QUARTZ - EXPERIMENTAL-EVIDENCE AND GEOLOGIC IMPLICATIONS

Natural chalcopyrite-bearing fluid inclusions from the Red Mountain, A rizona, porphyry copper prospect have been used to experimentally docu ment the movement of hydrogen into and out of fluid inclusions in quar tz. Chalcopyrite daughter minerals in inclusions do not dissolve durin g heating studies of ''as collected'' quartz vein material. However, a fter the samples were held at an elevated (but unknown) hydrogen press ure in a cold-seal-type pressure vessel at 600-degrees-C and 2.5 kbar for seven days, chalcopyrite daughter crystals in fluid inclusions dis solve easily and completely during subsequent heating. The presence of hydrogen in the re-equilibrated inclusions was confirmed by both Rama n microprobe and quadrupole mass spectrometric analyses of the inclusi ons. Repeated heating of re-equilibrated inclusions to measure the dis solution temperature of chalcopyrite (Tm Cpy) results in a considerabl y higher Tm Cpy during each successive run until, eventually, the chal copyrite no longer dissolves when heated to the upper limit of the hea ting stage. This behavior is interpreted to indicate that hydrogen whi ch had diffused into inclusions during re-equilibration experiments di ffused out of the inclusions during microthermometric analyses The dis solution of chalcopyrite following re-equilibration and its failure to dissolve before re-equilibration are consistent with proposed solubil ity models for chalcopyrite in aqueous solutions. The rapid movement o f hydrogen into inclusions is also consistent with experimentally dete rmined diffusion.rates for hydrogen through quartz. These results rein force conclusions reached by earlier workers who suggested that the fa ilure of some fluid inclusion daughter minerals to dissolve during hea ting is a result of hydrogen loss. These results also support earlier workers who have suggested that unexpectedly low deltaD values obtaine d from inclusion fluids were produced by the preferential movement of hydrogen (relative to deuterium) into fluid inclusions. Finally, these results suggest that f(O2) conditions inferred from Raman or other mi croanalytical data obtained from fluid inclusions may not represent f( O2) conditions present at the time of trapping.