Investigation of petrography, mineralogy and alteration of northern part of the Chahfiruzeh porphyry copper deposit, northwest of Shar-e-Babak, Kerman

The Chahfiruzeh porphyry copper deposit is located at 35 Km northwest of Shar-e-Babak in Dehaj–Sarduieh part of the Urumieh- Dokhtar magmatic arc (UDMA). The world class porphyry Cu deposits, such as Sarcheshmeh, Meiduk, Sungun and several other Cu-porphyry in the UDMA have been numerously studied, for example: Boomeri, et al., (2009, 2010), and Asadi et al., (2014). The Chahfiruzeh Cu porphyry is divided into two parts of the southern and northern deposits. The southern deposit was studied by Hezarkhani (2006), and Sheikhzadeh et al., (2011). This paper studies the northern part to distinguish mineralized rock units, alteration types, mineralization style, ore mineralogy and geochemical characteristics. Geology of the northern part of the Chahfiruzeh area consists of upper Cretaceous-Eocene andesitic lava, pyroclastic and volcanoclastic rocks that have been intruded by Oligo-Miocene intermediate stocks and dikes (Dimitrijevic, 1973). Neogene rocks in the area are mainly alkali basalt to dacitic domes and Quaternary alluvium deposits. During the field studies more than 100 samples were taken from the boreholes and outcrops. Among them 25 thin sections and 39 polished sections were studied by microscopic methods, 6 samples from the alteration zones, 8 samples from the less altered rocks and 25 samples from the mineralized rocks were examined and analyzed by XRD, XRF and ICP-OES, respectively. The analyses and XRD data are presented in Tables 1, 2 and 4. The igneous rocks in the northern part occur as extrusive and intrusive. The extrusive rocks are dacite and andesite and intrusive rocks are diorite, granodiorite and quartzdiorite. They are porphyry in texture and high-K calc-alkaline in magmatic series. The main mineral in all rocks is plagioclase that has variable size, shape and texture. K-feldespar, amphibole, biotite and quartz are other primary minerals in the study rocks. Biotite, quartz, and K-feldspar occur also as secondary minerals that are associated with chlorite, sericite, clays minerals and sulfide and oxide minerals. Mineralization can be usually divided into the two hypogene and supergen types. The hypogene mineralization occurs mainly as silicic veinlets and disseminated in the intrusive porphyries and volcanic rocks. The silicic veins are in eleven types as follows: 1) quartz + chlorite + pyrite, 2) quartz + chlorite , 3) quartz + pyrite , 4) quartz , 5) chlorite , 6) pyrite + chalcopyrite + quartz , 7) quartz + magnetite , 8) pyrite , 9), chalcopyrite , 10) quartz + chalcopyrite + bornite, 11) molybdenite. The hypogene sulfides are pyrite, chalcopyrite, bornite and molybdenite that are associated with magnetite, hematite and ilmenite. The pyrites and chalcopyrites occur in all parts of the mineralized area from the surface to the depth while molybdenites and bornites occur only in the deep depths. The supergene mineralization occurs as small outcrops of iron oxide and hydroxide, copper carbonate and clay minerals. The alteration zones in the mineralized area are potassic, propylitic, phyllic and argillic. The main alteration is potassic that is characterized by biotite, sericite and chlorite and numerous sulfide-bearing silicic veinlets with or without orthoclase and magnetite. The orthoclase is probably present as anhedral in some parts and around the plagioclase. The hydrothermal biotites are fine and thin in shape and occur in groundmass. Magmatic biotites are also present as euhedral to subhedral grains. The propylitic alteration observes only in the surface as an outer zone and characterized mainly by chlorite and epidote. Calcite and clay minerals are other minerals of this zone while sulfides are rare. The phyllic alteration zone is characterized by a higher proportion of sericite, quartz veins and pyrite than the potassic alteration in the marginal parts of the mineralized area. The argillic alteration zone occurs locally in shallow depths. Based on XRD analyses, each one of the clay minerals such as kaolinite, montmorillonite, illite and dickite, are dominant in some samples.
The alteration map of the northern part is presented in Fig.15 for two depths of 10 and 400 meters. The potassic alteration is the main alteration type in both levels. In level 10, the inner potassic alteration is surrounded by phyllic and outer propylitic alteration, while in level 400, the inner potassic alteration is only associated with the local phyllic alteration. Distribution of copper and molybdenum in different boreholes indicate that mineralization has occurred mainly in the potassic and phyllic alteration zones (Fig. 16). The copper shows similar contents from shallow to deeper depths while Mo contents are higher in the depths of more than 500 meters (Fig. 16).
The following features show that the northern part of Chahfiruzeh ore deposit is a porphyry Cu-type ore deposit: style, grade, size and shape of the mineralization, alteration types, associated calc-alkaline intrusive porphyries and the tectonic setting.