FLUID INCLUSION THERMOMETRY, STABLE ISOTOPE GEOCHEMISTRY AND GENESIS OF A SPECULARITE-RICH CU-AU-AG DEPOSIT, QALEH-ZARI MINE, IRAN

The Qaleh-Zari specularite- rich Cu-Au-Ag deposit is located 180 Km south of Birjand, in eastern Iran. Host rocks are mainly Tertiary andesite and andesitic basalts and some Jurassic shale and sandstone.

Three major sub-parallel steep quartz veins are identified. No.1 vein is about 650 m long and No.3 vein is less than 500 m long. No.2 vein is traced for more than 3.5 km horizontally along strike (N40° W) and more than 350 m down dip.

Paragenesis: Stage I: specularite, quartz, Fe-chlorite, chalcopyrite and sulfosalts. Specularite deposited first and forms 10 to 25 percent of the vein. Stage II: quartz, chalcopyrite, pyrite, chlorite ± hematite ± sulfosalt minerals. Stage III: quartz ± pyrite ± chalcopyrite. Stage IV: hematite, quartz, and ± calcite. Ore grade is 2 to 9% Cu, Ag 100 to 650 ppm, and Au 0.5 to 35 ppm. Propylitic alteration is dominant and epidote is very abundant. Argillic alteration is locally present. Silicification is mainly found within the vein zone. Temperature of homogenization of primary fluid inclusions in quartz associated with specularite and Cu, Ag, and Au mineralization was between 240°C and 360°C. The salinity of ore fluid was between 1.0 and 6.0 wt% equiv. NaCl and the CO₂ was < 0.1 mole%. The fluid was very oxidizing, Log fO₂ was between -13 and -28 (T 300°C). The d³⁴S ‰ (CDT) values of pyrite and chalcopyrite are between 0.4 and 2.2‰. The origin of the sulfur may be: 1) direct input from a buried pluton, or 2) leached from the host volcanic rocks.

The d¹³C‰(PDB) values of calcite are between 16.9 and 17.4‰ and the calculated carbon isotopic composition of the fluid is between 7.4 and 9.8‰. The oxygen isotopic values d¹⁸O‰SMOW are between 7.4 and 9.8‰, overlapping the range of magmatic water. Some important differences between Qaleh-Zari and other Fe-Oxide Cu-Au deposits are: (Jensen and Barton, 2000, Barton and Johnson 2000 and Hitzman, et al., 1992): 1) The salinity is very low (< 6 wt% NaCl equiv.), 2) absence of magnetite and apatite, and 3) low REE and P.