Journal of Economic Geology

1-13

Authors: Alireza Zarasvandi; Hoshang Pourkaseb; Adel Saki; Somaye Salamab-Allahi

The Mandan and Deh-Now bauxite deposits are located 40 km northeast of Dehdasht in Kohgiloye and Boyer-Ahmad province in the Zagros simply folded belt. The deposits were formed in the oldest rocks of the area of late Cretaceous age. The bauxite horizon is situated between Sarvak and Ilam formations. The aim of this study is to determine the mineralogy and texture relations of the deposits in order to determine the environment and status of bauxite mineralization. In this way, samples were selected from these bauxite deposits for mineralogical studies based on microscopic and XRD techniques. The bauxite horizon in the Mandan deposit consists of white, gray, black, pisolitic, red and yellow bauxites. The sequence was repeated in the Deh-Now without black and gray bauxites. Mineralogy is similar in all bauxitic layers and the main textures are pisolitic-ooide, ooide-spheroid, pisolitic, pelitomorphic and pseoudomorphic. Bohmite, diaspore, kaolinite and calcite are the most important minerals in both bauxitic layers of the Mandan and Deh-Now deposits. Due to bohmite mineralization in the study area, erosional and intense weathering environment in the Touronian-Cenomanian could be suggested for the deposition of bauxite in these deposits. Existence of interclasts in the pisolites and ooides indicate that these bauxites were transformed from the primary in situ environment to karstic sedimentary basin as authigenic origin. These studies indicate that there are two mineralized facies with different environmental status: (1) oxidation facies with bohmite, diaspore, kaolinite and hematite minerals and (2) reduced facies with pyrite, diaspore and chlorite mineralization. The lack of reduced condition at the Deh-Now deposit shows that the deposit formed only in oxidation status.

29-40

Authors: Mohammad Reza Shayestehfar; Mohammad Mohammadi; Ali Rezaei

The study area is located in the south of Kerman province and in the Esphandoghe- Dolatabad zone. Numerous chromite ores were found in the area that has been explored by surface outcrops. With respect to the previous exploration- exploitation works and the absence of the pilot layer, the best option was the boreholes’ drilling was the best choice in order to complete the detailed information. For the detail- exploration and ore evaluation, the exploratory boreholes and profiles designed after the exploration surveying, geology and the primary sampling. Exploratory boreholes are based on surface information and the present trenches on the hanging wall of the chromite veins are also designed in such a way that each borehole cut across the chromite vein in the depth of 15 meters. Based on previous results from the drilled holes, drilling results and with respect to the geological characteristic of the area, the exploration method of the mine for the first year has been selected on the open pit method and for the next years, cut and fill underground method. This deposit is having high economic values based on concluded results.

61-77

Authors: Behzad Mehrabi; Ebrahim Tale Fazel; Ali Nokhbatolfoghahai

The Iranian East Magmatic Assemblage (IEMA) in the Central Lut region, hosted porphyry and vein-type polymetallic mineralization. The GaleChah-Shurab mining district is located in NW of the IEMA. Volcanic and subvolcanic bodies in the area are composed of calc-alkaline porphyry quartz-latite, porphyry dacite and rhyodacite and hornblende-biotite andesite, equivalent to I-type granite. They emplaced in Tertiary and intruded the Jurassic shale, siltstone and limestone basement (Shemshak Fm). The faults, joints and fractures, are the main controls on the mineralization, in forms of disseminated, vein, veinlet and minor stockwork and brecciation type mineralization of Pb, Zn, Cu, Sb and trace elements. Vein and veinlet of Pb+Zn±Cu±Sb in the Gale-Chah abandoned mine accompanied by carbonate and silicic alterations in association with galena, sphalerite, pyrite, chalcopyrite, bournonite and tetrahedrite as the hypogene ore minerals and their supergene products including cerussite, covellite, digenite and second-generation colloidal pyrite. The Pb+Zn+Cu+Sb mineralization associated with sericitic and silicic alterations in the Shurab abandoned mine, is composed of two types of mineralization, veinlet and brecciation vein in the porphyry dacite boundaries with Jurassic shale and sandstones, and the disseminated and disseminated-veinlet mineralization which is hosted by the altered porphyry dacite and rhyodacite intrusive rocks. The mineral assemblages are galena, sphalerite, stibnite, As-bearing pyrite, chalcopyrite and tetrahedrite-tennantite complex hypogene-sulfide ore as a hypogene ore, and malachite, covellite, cerussite and melancoitic pyrite as a sulfide-oxide supergene ore. The Pb+Zn+Sb±As±Ag polymetallic occurrence is associated with sericitic, carbonate and chloritic alteration assemblage in the Chupan occurrence, in two forms, I) vein, veinlet-stockwork (30m depth) confined to fault structures and II) disseminated-replacement (below 70m) mainly hosted in rhyodacite and porphyry dacite rocks. The hypogene minerals are galena, sphalerite, stibnite, pyrite, realgar-orpiment, arsenopyrite, and chalcopyrite with extensive occurrence of oxide-sulfide supergene products, such as Mn-oxide, hematite, malachite and colloidal pyrite. Fluid inclusion study show that disseminated veinlet Cu and disseminated-replacement polymetallic mineralization at the Shurab and Chupan deposits, respectively occurred in the high temperature, salinity and depth compared to vein-veinlet Pb and Zn mineralization of Gale-chah deposit. It seems that the mineralization is related to hydrothermal fluid evolution affected by mixing with cold and low salinity meteoric water.

94

Authors: Reza Arjmandzadeh; Mohammad Hasan Karimpour; Sayed Ahmad Mazaheri; Joze Fransisco Santos; Jorj Medina; Sayed Masod Homam

West directed subduction zones show common characteristics, such as low structural elevation, deep trench, steep slab and a conjugate back-arc basin that are opposite to those of the east directed subduction zones. The tectonomagmatic and metallogenic setting of the Lut Block is still a matter of debate and several hypotheses have been put forward. Despite some authors denying the influence of the operation of Benioff planes, the majority propose that it occurred beneath the Afghan Block, while others consider that oceanic lithosphere was dragged under the Lut Block. Cu-Au porphyry deposits seem to occur in an island arc geotectonic setting during the middle Eocene while Mo-bearing deposits are coincident with the crustal thickening during Oligocene. We introduce new trace element and isotope geochemical data for granitoids and structural evidences testifying the two-sided asymmetric subduction beneath both Afghan and Lut Blocks, with different rates of consumption of oceanic lithosphere.