The Cenozoic Urumieh-Dokhtar magmatic belt (UDMB) of Iran is a major host to porphyry Cu-Mo-Au deposits (PCDs). The UDMB extends for over 2 000 km in NW-SE direction, parallel to the Zagros Mountain Ranges in western Iran. The majority of the known PCDs occur in the southern section of the belt, also known as Dehaj-Sarduyeh magmatic belt, or Kerman belt (Fig. 1). Vein type, base and/or precious metals deposits are also common and some are spatially associated with the PCDs. Examples of such associations are observed in Miduk and Sarae in southern UDMB and Masjed-Daghi in northern UDMB (Movagyar, 2011; Alirezai et al., 2010). The Latala Deposit occurs about 8 km north of the Miduk porphyry system. The area is covered mainly by Paleocene-Eocene volcanic and pyroclastic rocks of basaltic, basaltic andesite and trachy-andesite compositions, and minor marls and limestones (Figs. 2, 3). The volcanic and pyroclastic rocks are intruded by Miocene shallow intrusions of quartz diorite, quartz monzonite and granodiorite compositions; the rocks are host to a set of ore-bearing quartz veins (Figs. 1a-1c). Mineralization in Latala Deposit is controlled by faults and fractures. The ring structures and faults have important role in the distribution of hydrothermal alteration zones and mineralization in the Latala Deposit because they facilitate the movement of magmatic fluid in more distal parts (Figs. 1-2).
Figure 1. Polymetallic veins such as Latala and Chahmessi (shown with yellow pattern) surrounding intrusions and the Miduk porphyry modified after Jafari Rad and Busch (2011), Movagyar (2011) and Dimitrijevic et al. (1971); (c) Landsat-ETM7 of Shahre-Babak area, the study area "Latala" is shown by yellow box; (d) 3D map of the digital elevation model (DEM) of the study area, ore-bearing quartz veins and cores (shown with red line).
Figure 2. Stratigraphic sections of volcanic, volcanic-sedimentary and subvolcanic intrusions sequence of Bahre-Aseman, Razak and Hezar complexes (modified from Dimithrijevic, 1973).
The veins consist of quartz, calcite, pyrite, chalcopyrite, galena, sphalerite, bornite and minor sulfosalts, particularly enargite and mckinstryite (Ag, Cu)2S. The sulfides are oxidized at the surface and shallow depths to goethite, hematite, jarosite, malachite, azurite, cerussite and hemimorphite. The oxidation was associated with development of supergene argillic alteration. Hydrothermal alteration in the Miduk Deposit is distinguished by a proximal potassic assemblage, dominated by biotite and K-feldspar, grading outward and upward into a phyllic assemblage. A propylitic halo, marked by chlorite especially clinochlore, epidote, and carbonates, is well developed in the enclosing volcanic rocks. Strong alteration in the wall rocks varies from a proximal silicic to distal argillic/advanced argillic assemblage. McInnes et al. (2005) reported a crystallization age of 12.5±0.1 Ma (zircon U-Pb) for the Miduk porphyritic intrusion. The timing of mineralization in Miduk has been indicated by 40Ar/39Ar technique on hydrothermal biotite from potassic alteration zone, to be 11.3±0.5 Ma (Hassanzadeh, 1993). Isotope ratio 87Sr/86Sr=0.704 (Hassanzadeh, 1993) and geochemical results studied by Shahabpour (2007) and Agard et al. (2011) suggested that the Miduk Deposit was formed in the transition between an island-arc and continental margin-arc setting. According to the results of petrographic, geochemical data and isotopic values of sulfides from the Miduk porphyry Cu deposit and quartz-sulfide veins in the late epithermal base and precious metal deposit of Latala (Padyar, 2017), it indicated a subduction-related magmatic arc setting. According to geochemical studies such as negative Nb anomalies and high Sr contents, the shoshonite and the high-K calc-alkaline rocks can be formed by the partial melting of SCLM (subcontinental lithospheric mantle). Results of geochemical studies show contamination with crustal material (metasomatism) dominated during evolution of the parent magmas. During the successive injection of magma, water-rock interaction has a significant role in alteration of host rocks and mineralization in Latala area (Padyar, 2017). Mineralization in Latala epithermal base and precious metal vein type formed in three stages: Stage 1, quartz-sulfide veins contain pyrite±chalcopyrite± enargite. Mineralization occurs as open space fillings and show high-sulfidation epithermal environment. Stage 2, veins contain pyrite, chalcopyrite and zoned sphalerite, with quartz and hematite. Stage 3, quartz veins contain galena+sphalerite+chalcopyrite and quartz with overgrowth of calcite. Mineralization in this stage occurs as replacement bodies and contains Fe-poor sphalerite without zoning at the outer parts of the deposit. In these veins, euhedral quartz with sulfide mineralization occurs as open space fillings, minor replacement bodies and hydrothermal breccia (Padyar et al., 2017a, b). These quartz veins and veinlets contain copper and zinc mineralization. The lithology of Stage 2 contains tuff and limestone tuff and veinlet calcite and the tuff fragments. Cement contains quartz, little calcite, pyrite, chalcopyrite and galena (Fig. 4a). Drill-core "BH13" reached a depth of 80 m below ground level. The main range of mineralization is at depths of 65.40 to 76.25 m. Secondary mineralization is at depth of 76.80 to 78.45 m (Movagyar et al., 2011). Drill-core "BH14" has a depth down to 90 m below ground level. These samples of sphalerite were collected at depths of 30 to 36 m. Galena is generally more abundant than sphalerite in these samples and associated with quartz and little calcite (Figs. 4b, 4c). Lithology of the stratigraphic Stage 3 includes periodic tuff and limestone tuff and andesite (Fig. 4b).
Figure 4. Photographs showing (a) drill-core "BH13-77" with a vein in tuff fragments containing pyrite, chalcopyrite and zoned sphalerite; (b) drill-core "BH14-30" with a vein containing galena, sphalerite, pyrite and chalcopyrite; (c) drill-core "BH14-36" where galena is generally more abundant than sphalerite and associated with quartz and little calcite; (d) sphalerite minerals extracted by heavy-liquid separation from 10 samples of the deep drill core.
The chemical compositions of the samples bearing mineralization are presented in Table 1 and their average compositions are plotted in the (Cu+Pb+Zn)-Au-Ag diagram of Fig. 5. The Ag/Au ratio in samples of Latala boreholes is higher than 20. The concentration of Ag is directly related to boiling process (Pirajno, 2009). Maps of the distribution of metals and the triangular diagram show distinct metal zoning patterns for base metals and priecious metals (Figs. 5a-5c). The high ratio of Zn/Pb is visible in the triangular diagrams. The triangular diagrams (Figs. 5a-5c) show the distribution of base metals and the ratio of these elements, in the 3 stages of mineralization in Latala epithermal base and precious metal vein type and the two stages of sphalerite mineralization. The ternary Cu-Pb-Zn metal ratios diagram of Latala Deposit is shown in Fig. 5a. Latala Deposit is characterized by Cu-Au, Zn-Pb-Cu and Zn-Pb groups according to relative proportions. The ternary Cu-Pb-Zn metal ratios diagram of sphalerite-quartz veins (Fig. 5b) shows the distribution of metal zoning and two stages 2-3. The ternary diagram of the Aggeneys-Gamsberg of SEDEX type (Pirajno, 2009) (Fig. 5c) compared with metal zoning from quartz veins in Latala Deposit shows two different directions of metal zoning for the two types of ores such as SEDEX deposit and the vein type, base metal deposit associated with porphyry systems.
Drillcore Depth (m) Sample number Au Ag Cu Pb Zn BH13-B14-2 77.0-77.8 18 0.19 10.24 291.8 6 060 24 730 BH13-B14-3 77.8-78.6 19 0.31 16.8 755.9 1 396.5 31 790 BH14-B6-5 29.8-30.8 11 0.4 112 16 000 5 010 2 260 BH14-B7-1 30.8-31.8 12 0.4 110 12 000 23 000 15 000 BH14-B7-6 35.8-36.8 17 0.038 66 13 000 52 000 54 000 BH14-B8-1 36.8-38.0 18 0.078 23 1 595 1 600 2 600
Table 1. Chemical compositions (Au, Ag, Cu, Pb and Zn in ppm) of quartz+galena+sphalerite veins collected at various depths
Figure 5. (a) Ternary diagram showing Cu-Pb-Zn metal ratios from quartz veins. Latala Deposit is divided into Cu-Au, Zn-Pb-Cu and Zn-Pb groups. (b) Ternary diagram showing Cu-Pb-Zn metal ratios from sphalerite-quartz veins. (c) Ternary diagram of metal zoning of the Aggeneys-Gamsberg SEDEX ore field as being related to the distance from the source of the mineralizing fluids (Pirajno, 2009) compared with distribution metal zoning from quartz veins in Latala Deposit.
Cathodoluminescence (CL) imaging indicates multiple quartz generations in single grains. In general, euhedral sphalerite grains are associated with quartz and galena in the core of the veins implying several events of circulating fluids (Figs. 7a-7c).
Fluid inclusion studies have been performed on quartz samples from different veins at different depths in association with sphalerite minerals and chalcopyrite, pyrite and galena. Petrographic analyses of fluid inclusions from sphalerite and quartz have shown that the ore-related fluid inclusions are two phase liquid+gas inclusions (Figs. 7e-7h). The gas phase occupies 16%-24% of the total inclusion volume when observed at room temperature. Microthermometric results from sphalerite- hosted fluid inclusions are illustrated in Table 2. The final melting temperature of ice (Tm ice) in primary inclusions range between -0.1 and -4.9 ℃. All inclusions were homogenized to the liquid phase on heating. Halite-saturated brine inclusions were never found in quartz associated with the sphalerite minerals and chalcopyrite, pyrite and galena. Fluid inclusions in sphalerite consist of common aqueous-carbonic inclusions two (liquid H2O+CO2-rich supercritical fluid) or three (liquid H2O+liquid CO2+vapor CO2) phases. Dissociation of clathrate (Tm clathrate) occurs at temperatures 5.2 ℃. The number of primary two-phase inclusions suitable for measurement is significant in such samples. Homogenization temperatures exhibit a range from 232 to 250 ℃, for Fe-bearing sphalerite (quartz+ sphalerite+pyrite+chalcopyrite) and homogenization temperatures exhibit a range from 198 to 284 ℃ for Fe-poor sphalerite (quartz+galena+sphalerite+chalcopyrite veins) (Table 2). Homogenization temperatures for quartz associated in the paragenesis with sphalerite (vein BH13 with sphalerite+pyrite+ chalcopyrite) exhibit a range from 144 to 285 ℃. For quartz associated with (galena+sphalerite+chalcopyrite vein BH14). The homogenization temperatures are in the range of 157-247 ℃. Overall, the salinity of the inclusions observed in quartz range from 0.5 wt.% to 7.2 wt.% NaCl eq. (Table 2).
Sample No. Number analyses Stage Composition Host mineral Th (℃) Tm CO2 Tm clathrate Tm ice Salinity (NaCl%, wt.% eq.) Density (g/cm3) BH13-77 20 2 L+V Sp 144-285 (Ø214) (-0.1 to -4.9) 0.2-7.7 (Ø5.3) 0.8-1.0 BH14-30-36 15 3 L+V Sp 157-247 (Ø219) 5 (-0.3 to -4.6) 0.5-7.2 (Ø4.0) 0.8-1.0 BH13-77 5 2 L+V Qtz 232-250 (Ø237) (-1.7 to -3.8) 2.8-6.1 (Ø4.5) 0.8-0.9 BH14-30-36 25 3 L+V, L+V+CO2 Qtz 198-284 (Ø235) -56.6 (-0.8 to -3.9) 1.3-6.2 (Ø3.7) 0.8-0.9
Table 2. Summary of fluid inclusion data for sphalerite bearing veins in the Latala vein-type deposit. Ø. Average; Qtz. quartz; Sp. sphalerite
Sulphur isotope composition (δ34S) of sulfide minerals in sphalerite bearing veins of Latala Deposit is shown in Table 3. In this paper we used the method of Li and Liu (2006) for the calculation of sulfur isotope fractionation in sulfides. The δ34S ranged between -9.6‰ and -2.1‰ (n=4) for galena and sphalerite. These δ34S of H2S ranges after calculation of sulfur isotope fractionation in sulfide range from -7.1‰ to +0.6‰ (n=4). The δ34S of H2S has been calculated based on the homogenization temperatures obtained from fluid inclusions. This practice is important to understand source sulfur and formation condition of sulfide minerals as reviewed by Seal (2006), Rye(2005, 1993), Filed et al. (2005), Ohmoto (1972), and Sakai (1968). The various sulfur isotopic compositions suggest an igneous source with contamination of wall rock in the hydrothermal system of Latala.
Sample No. Weight (mg) δ34S (x, CDT) mineral δ34S (x, CDT) H2S %S Comment BH5-36 0.940 -5.70 -3.30 22.20 Galena; ~30% sphalerite BH13-77 0.916 -2.13 +0.57 32.64 Galena; < 20% quartz BH14-30 0.925 -9.55 -7.05 19.33 Galena; < 20% quartz BH14-36 0.935 -6.12 -3.82 28.64 Galena; < 20% quartz
Table 3. Sulphur isotope composition (δ34S) of galena from Latala area. Calculation of sulfur isotope fractionation between galena and H2S (the method suggested by Li and Liu, 2006).