VEIN TYPE AG-(AU)-PB, ZN, CU-(W,SN) MINERALIZATION IN THE SOUTHERN KREUZECK MOUNTAINS, CARINTHIA PROVINCE, AUSTRIA

The Early Paleozoic Altkristallin of the Kreuzeck Mountains is well-kn own for its mostly small gold, silver, copper, lead, zinc, antimony, a nd mercury deposits. A detailed investigation of silver(-gold)-base me tal mineralizations (Plattach, Niedermulleralm, Grakofel and Drassnitz ) is presented in this paper. The deposits are structurally controlled . Faults and shear zones penetrate garnet-mica schists, gneisses (part ly at Grakofel), and amphibolites (partly at Drassnitz). In places the mineralization occurs at the sheared contact between quartz porphyrit e dykes (K/Ar ages of 30-40 Ma) and country rocks (e.g. at Niedermulle ralm). The precious metal mineralization occurs as bundles of quartz v eins, which were mined over a distance of 150-200 m along strike and d ip. The depositional textures such as vugs, symmetrical banding, cocka de and colloform structures clearly indicate open space filling. The m ineral parageneses of Plattach, Niedermiilleralm and Grakofel ores are similar to each other, but distinctly different from that of the Dras snitz deposit. The first mentioned deposits are characterized by abund ant silver sulfosalts such as freibergite (21.7-36.3 wt.% Ag), pyrargy rite, miargyrite, diaphorite (Pb1.7-1.8Ag2.9-3.2Sb2.8-3.0S8), owyheeit e (Ag2.69Pb9.44Sb10.38S28) and stephanite, as well as sphalerite and g alena (100-1600 ppm Ag); hocartite (similar to [Ag, Cu], [Fe, Zn] SnS4 ) is intergrown with pyrargyrite and occurs as inclusions in pyritic o res at Niedermulleralm. Pyrite, arsenopyrite, and chalcopyrite are pre sent in minor amounts. Au-Ag alloys with Ag contents ranging between 4 0.4-49.5 wt.% (electrum) and 73.5-74.2 wt.% (aurian silver) have grain sizes between 2 and 60 mu m and are frequently associated with freibe rgite, pyrite and quartz. Drassnitz is a silver bearing base metal dep osit with a possible but not proved silver enrichment in the uppermost similar to 100 m of the vein system. Arsenopyrite, pyrrhotite, chalco pyrite, sphalerite, bournonite, Ag-tetrahedrite, and galena are the do minant ore minerals, locally accompanied by substantial amounts of zin cian stannite (similar to 25 mol.% kesterite), ferberite, scheelite, a nd minor amounts of molybdenite, native bismuth, ullmannite and a silv er sulfosalt. The most common types of hydrothermal wall-rock alterati on are phyllic alteration (sericitization), silicification, carbonatiz ation, and sulfidization. The alteration zone does not exceed a few de cimeters on both sides of the veins. Fluid inclusion studies of quartz reveal formation temperatures of 165-250 degrees C (Plattach) and 165 -220 degrees C (Niedermulleralm). The corresponding data for the Grako fel and Drassnitz ores are 180-330 degrees C and 210-365 degrees C, re spectively. The salinities vary between 3-7 equiv. wt.-% NaCl (Niederm ulleralm, Plattach, Drassnitz) and 4-13.3 equiv. wt.-% NaCl (Grakofel) . A shallow-seated plutonic or subvolcanic magma (quartz porphyrite?) could be the reason for telescoping, different temperatures and heat g radient within the mineralized zone. The isotope compositions of the f luids give evidence for their metamorphic origin, probably contaminate d by a minor meteoric component.