Geological research carried out on the structural and lithostratigraphic relation between base-metal mineralization and medium-grade metamorphic rocks led to elucidation of their genesis. The massive and disseminated sulfide ores are localized in rhyolitic metaepiclastics and in overlying biotite-muscovite–micaschists of leptino-amphibolitic formation (SM2) of Somes series (Upper Precambrian-Lower Cambrian), highly retrograded and crossed by laramide microgranites. The Somes metamorphites are developed as a horst between Vladeasa graben and Transilvania basin. Syngenetic, concordant, metamorphosed mineralization was formed by sulfide precipitation, fed by submarine hydrothermal activity. It is genetically associated to rhyolitic volcanism of island-arc stage evolution and belongs to metamorphosed hydrothermal volcano-sedimentary type. The following subtypes were identified taking into account the mineral assemblage and the lithostratigraphic and tectonic control:
1. syngenetic, stratiform, concordant, massive/disseminated Zn-Pb +/Cu, Au, Ag ore, consisting of pyrite (25-30%), arsenopyrite (7-10%), sphalerite (3.8-4.6%), galena (0,6-3,7%) pyrrhotite (0.6%),chalcopyrite (0.4-0.8%), tetraedrite, siderite, quartz, sericite, situated in the upper part of quartz-feldspar schists, at the boundary with the biotite-muscovite-micaschists. In the Alunis valley there are 2 bends which unify on the strike. The boundary is sharp at the bottom and clear or gradual at the top, by euhedral arsenopyrite dissemination. On the strike, the massive ore passes to pyrite-arsenopyrite disseminated ore. The banded massive ore, sometimes brecciated at the bottom, consists of broken porphyroblasts of pyrite and arsenopyrite, sometimes of 0.3-0.9 mm in size, associated with quartz, “cemented” by soft sulfides, included in siderite. The sphalerite contains coherent and incoherent exsolutions of pyrrhotite and chalcopyrite. The gold is included in the crystal lattice of sulphides. Galena, with tetraedrite exsolutions, has high contents of Ag. The Au:Ag ratio is about 1:10.
2. syngenetic, lenticular of Fe (siderite, magnetite) and Cu-Au ores (pyrite, arsenopyrite, chalcopyrite, pyrrhotite, quartz, sericite), in quartzose sequences of biotitemuscovite micaschists, overlying the quartz-feldspar schists. In Negru brook area, there are 3 lenses of massive pyritic ore which unify into one in the depth. In Gingineasa area, there are 2 orebodies, one of siderite and magnetite assemblage, at the lower part of the sequence, and another one of banded massive sulfide, mainly pyrite, arsenopyrite and chalcopyrite, at the top. Both are localized in highly retrograded biotite-muscovite-micaschists, with interbedded amphibolite of ten meters in thickness, crossed by crenulation cleavage and transposed on a cross fault plane. In banded iron ore, the magnetite grains have a core of siderite and they were probably formed during increasing O2/CO2 ratio. On a fault plane which cut the banded sulfide lenses, secondary pyrrhotite was formed as nests by conversion of pyrite during tectonic deformation.
3. metamorphosed hydrothermal sulfide ore, hosted by cross faults, consisting of siderite, as large porphiroblasts, pyrite, arsenopyrite, pyrrhotite, chalcopyrite and quartz, developed nearby the syngenetic, stratiform massive ore, or cross cutting them.
4. hydrothermal sulfide ore, formed by remobilizations and recrystallizations during synmetamorphic deformations and Laramide tectonic phase of Alpine cycle, in shape of discordant veinlets of galena in iron ore; of arsenopyrite on ”ac” fissures; of arsenopyrite, pyrite, chalcopyrite, siderite, and quartz (Agastau valley); as small lenses of arsenopyrite, pyrite and sphalerite (Cetatuia valley); as nests of steely galena, including large crystals of arsenopyrite (Alunis brook); as parallel vein, with the massive pyritic ore, consisting mainly of sphalerite and subordinate amount of pyrite, chalcopyrite, galena and fragments of iron ore and breccia column (Leurdis brook, mining works) made of sphalerite, pyrrhotite, galena, arsenopyrite, pyrite, siderite, quartz and fragments of micaschist, strongly affected by chloritization. The breccia body was produced by a Laramide igneous body intrusion, highly affected by argillic alteration.The massive and disseminated sulfide ore has the same genesis as the sulphde ore deposits of the Tulghes Group, Eastern Carpathians.