PIXE and SEM analyses of fluid inclusions in quartz crystals from the K-alteration zone of the Rosia Poieni porphyry-Cu deposit, Apuseni Mountains, Rumania

This Romanian porphyry-Cu deposit is h osted by two Neogene shallow intrusions, an andesite and a slightly younger porphyritic microdiorite; the ore mineralization occurs in a central K-alteration zone, as a dense network of hydrothermal veins with quartz and a great variety of ore minerals. The numerous fluid inclusions in the quartz belong to two synchronous types: vapour-rich fluids and very much rarer high-salinity brines. They result from the unmixing of a homogeneous fluid phase derived from the magma during crystallization; the vapour type are entirely gaseous, but the brine inclusions contain solid phases (halite, sylvite, hydrated (K)-Fe chlorite, K-feldspar, hematite, anhydrite, rutile and various ore minerals). Analyses by PIXE and SEM are reported and show that metallic elements in the vapour-rich inclusions do not correspond with accidental trapping of solid minerals from brine inclusions, but witness the possibility of metal transport in the gaseous phase during two successive episodes of incipient boiling.