Pb-Zn-Ag vein and listwaenite types of mineralization in Crnac deposit,
Western Vardar zone, were deposited within several stages: (i) the
pre-ore stage comprises pyrite, arsenopyrite, pyrrhotite, quartz,
kaolinite and is followed by magnetite-pyrite; (ii) the syn-ore stage is
composed of galena, sphalerite, tetrahedrite and stefanite; and (iii)
the post-ore stage is composed of carbonates, pyrite, arsenopyrite and
minor galena. The vein type mineralization is hosted by Jurassic
amphibolites and veins terminate within overlying serpentinites.
Mineralized listwaenites are developed along the
serpentinite-amphibolite interface. The reserves are estimated to 1.7 Mt
of ore containing in average 7.6% lead, 2.9% zinc, and 102 g/t silver.
Sulfides from the pre- and syn-mineralization assemblage of the vein-
and listwaenite-types of mineralization from the Crnac Pb-Zn-Ag deposit
have been analyzed using microprobe, crush-leachates and sulfur
isotopes.
The pre-ore assemblage precipitated under high sulfur fugacities
(f(S(2)) = 10(-8)-10(-6) bar) from temperatures ranging between 350
degrees C and 380 degrees C. Most likely water-rock reactions, boiling
and/or increase of pH caused an increase of delta(34)S of pyrite toward
upper levels within the deposit. The decomposition of pre-ore pyrrhotite
to a pyrite-magnetite mixture occurred at a fugacity of sulfur from
f(S(2)) = 8.7 x 10(-10) to 9.6 x 10(-9) bar and fugacity of oxygen from
f(O(2)) = 2.4 x 10(-30) to 3.1 x 10(-28) bars, indicating a contribution
of an oxidizing fluid, i.e. meteoric water during pre-ore stages of
hydrothermal activity. The crystallization temperatures obtained by the
sphalerite-galena isotope geothermometer range from 230 to 310 degrees
C. The delta(34)S values of pre- and syn-ore sulfides (pyrite, galena,
sphalerite, delta(34)S = 0.3-5.9 parts per thousand) point to magmatic
sulfur. Values of delta(34)S of galena and sphalerite are decreasing
upwards due to precipitation of early formed sulfide minerals. Post-ore
assemblage precipitated at temperature below 190 degrees C.
Based on data presented above, we assume two fluid sources: (i) a
magmatic source, supported by sulfur isotopic compositions within pre-
and syn-ore minerals and a high mol% of fluorine found within pre- and
syn-ore leachates, and (ii) a meteoric source, deduced by coincident
pyrite-magnetite intergrowth, sulfur isotopic trends within syn-ore
minerals and decrease of crystallization temperatures from the pre-ore
stage (380-350 degrees C), towards the syn-ore (310-215 degrees C) and
post-ore stages (<190 degrees C). Post-ore fluids are Na-Ca-Mg-K-Li
chlorine rich and were modified via water-rock reactions. Simple mineral
assemblage and sphalerite composition range from 1.5 to 10.1 mol% of
FeS catalog Crnac to a group of intermediate sulfidation epithermal
deposit. (C) 2011 Elsevier B.V. All rights reserved.