PIXE AND SEM ANALYSES OF FLUID INCLUSIONS IN QUARTZ CRYSTALS FROM THEK-ALTERATION ZONE OF THE ROSIA-POIENI PORPHYRY-CU DEPOSIT, APUSENI MOUNTAINS, ROMANIA

The Rosia Poieni porphyry-Cu deposit is hosted by two Neogene shallow intrusions, an andesite and a slightly younger porphyritic microdiorit e. The ore mineralization occurs in a central K-alteration zone, as a dense network of hydrothermal veins containing quartz and a great vari ety of ore minerals. Numerous fluid inclusions occur in quartz from th e mineralized area. They belong to two synchronous types: vapor-rich f luids (V-type) and high-salinity brines (B-type) (relative abundance o f both types 100/1000 to 1). The stable coexistence of both types at t he scale of the host mineral indicates that they result from unmixing of a homogeneous fluid phase, issued from the magma during its crystal lization (incipient boiling of the magmatic fluid, observed in remnant s of melt inclusions). Brine inclusions (B-type) contain a number of s olid phases (daughter or captured minerals): halite, sylvite, hydrated (K)-Fe-chloride, K-feldspar, hematite and undetermined ore minerals, anhydrite, rutile, etc. In most cases, V-type inclusions are entirely gazeous, only in few of them a narrow rim of low-salinity H2O is visib le under the microscope at room temperature. Analysis by PIXE, supplem ented by microscopic observation and SEM-EDS analysis on opened caviti es, indicates the existence of 4 subtypes: B1, containing all observed elements (mainly Na, K, Cl, Fe, but also a number of other elements s uch as Cu, Pb, Zn, Rb, Sr) and B2, differing from B1 by the absence of Rb, Sr and, in general, elements heavier than Fe. Coexisting with B1 and B2, 2 subtypes of vapor-rich inclusions (V-type) can be defined, w hich contain also metallic elements detectable by PIXE analysis: V1, c ontaining Cu and Fe, and V2, in which other elements (e.g. Zn, Pb, Br, Rb and Sr) occur. Metallic elements in the vapor-rich inclusions do n ot correspond to accidental trapping of solid minerals from B-type inc lusions. They witness the possibility of metal transport in the gazeou s phase during two successive episodes of incipient boiling. The first one (B1/V1) corresponds to the bulk of the formation of Cu mineraliza tion, while the second one (B2/V2) leads to the transport of other met allic elements, notably Zn and Pb.