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Observations at several porphyry Cu deposits indicate that in those formed above source magma chambers emplaced to relatively shallow levels (roofs ∼3-4 km deep), zones of higher Cu grade are associated with the oldest intrusions of a central porphyry cluster, abundant early (A-type) quartz veins, secondary feldspar alteration, and usually high Fe/Fe + Cu, low S/Fe + Cu sulfide-oxide mineral assemblages. In deposits for which source magma chambers were deeper (roofs >5 km), porphyries closest in age to ore are spatially less directly related to mineralization. In these, higher Cu grades in early mineralization comprise swarms of veinlets with alteration halos that include sericite as well as secondary feldspar and biotite. Sulfide ± oxide assemblages are usually of lower Fe/Fe + Cu and higher S/Fe + Cu. These differences in deposit characteristics appear to correspond with a change from two-phase, chloride-bearing, aqueous fluids that would exsolve from magma at shallow depths, to one-phase fluids deeper. [ABSTRACT FROM AUTHOR]

Abstract: The Auph name="sbnd" />Zn low-sulfidation epithermal ore deposits of Troita, Trestia, and Magura (Apuseni Mountains, Romania) are spatially related to the Bolcana Cu-porphyry. In an attempt to demonstrate the connection between these mineralizations, a geometric study was made based on structural measurements and GOCAD© geomodeller 3D representation of deposits. This study indicates that a specific spatial distribution of the different Au and Pbof the epithermal deposits occurs around the Cu-porphyry, which cannot result from telescoped systems. To cite this article: O. Cardon et al., C. R. Geoscience 337 (2005). [Copyright &y& Elsevier]