Original paper

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

Damman, H.; Kars, Saskia M.; Touret, Jacques L.R.; Rieffe, E. Christiaan; Kramer, Johannes A.L.M.; Vis, Ronald D.; Pintea, Ioan

European Journal of Mineralogy Volume 8 Number 5 (1996), p. 1081 - 1096

33 references

published: Oct 30, 1996
manuscript accepted: Jun 20, 1996
manuscript received: May 15, 1995

DOI: 10.1127/ejm/8/5/1081

BibTeX file

ArtNo. ESP147050805015, Price: 29.00 €

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Abstract

Abstract The Rosia Poieni porphyry-Cu deposit is hosted 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 containing quartz and a great variety of ore minerals. Numerous fluid inclusions occur in quartz from the mineralized area. They belong to two synchronous types: vapor-rich fluids (V-type) and high-salinity brines (B-type) (relative abundance of both types 100/1000 to 1). The stable coexistence of both types at the scale of the host mineral indicates that they result from unmixing of a homogeneous fluid phase, issued from the magma during its crystallization (incipient boiling of the magmatic fluid, observed in remnants of melt inclusions). Brine inclusions (B-type) contain a number of solid 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 visible under the microscope at room temperature. Analysis by PIXE, supplemented by microscopic observation and SEM-EDS analysis on opened cavities, indicates the existence of 4 subtypes: Bl, containing all observed elements (mainly Na, K, Cl, Fe, but also a number of other elements such as Cu, Pb, Zn, Rb, Sr) and B2, differing from Bl by the absence of Rb, Sr and, in general, elements heavier than Fe. Coexisting with Bl and B2, 2 subtypes of vapor-rich inclusions (V-type) can be defined, which contain also metallic elements detectable by PIXE analysis: VI, containing 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 not correspond to accidental trapping of solid minerals from B-type inclusions. They witness the possibility of metal transport in the gazeous phase during two successive episodes of incipient boiling. The first one (Bl/V1) corresponds to the bulk of the formation of Cu mineralization, while the second one (B2/V2) leads to the transport of other metallic elements, notably Zn and Pb.

Keywords

PIXESEMfluid inclusionsporphyry Cu-deposits