Apatite composition and the fugacities of HF and HC1 in metamorphic fluids

of apatites from two samples of amphibolite-facies schist from Connemara, Ireland, have been used to calculate the fugacity ratios fac0/fn2o and fnr/fa2o using the experi-mental data of Korzhinskiy. The results imply fugacities for both acids in the range 0.03 to 0.1 bars, but whereas for the lower grade rock fur>fncl, the migmatitic sample gives fHF~--fncl. An independent estimate of frlv/fnzo from the biotite composition i one sample is in accept-able agreement with the result obtained from apatite. KEVWORDS: apatite, halogens, metamorphic fluid, schist, Connemara, Ireland. MOST studies of metamorphic fluid composition are concerned only with the principal gas species present, but aqueous fluids in particular can also carry significant quantities of dissolved material