Journal of Economic Geology

97-110

Authors: Farid Moore; Saleh Deymar; Batoul Taghipour

Most skarn deposits are directly related to magmatic activity, and there is a systematic correlation between composition of causative plutons and the metal contents of the related skarns. Darreh Zerreshk deposit is located in southwest of Yazd. Petrological and geochemical studies show that Darreh Zerreshk granitoid ranges in composition from granite through quartz monzodiorite and has subalkaline, calc-alkaline and metaluminous to prealuminous characteristics like most worldwide skarn granitoids. This study shows that geochemical characteristics of the Darreh Zerreshk granotoid rocks are similar to granitoids of Millstream Cu-Fe skarn deposit in Canada, Fe skarns in British Columbia and Au-Cu skarns in the RioNarcea gold belt in Spain. The similarity between REE patterns in Darreh Zerreshk intrusion and skarns also confirms the strong petrogenetic relationship between magmatic and skarnization processes.

127-145

Authors: Mehrab Moradi; Mohammad Hasan Karimpour; J Eleng Farmer; Charlz Stern

The study area is located south of Ghonabad in Eastern Iran. This area is situated between two major faults, Darouneh to the north and Dashtbyaz to the south. The movements of these faults cased major dislocation of this block. Najmabad granodiorite to granite batholith is elongated trending east-west 2×8 Km2. Mineralization is associated with granite and monzonite. Alteration zones are: propylitic, sericitic, argillic and silicification. Chemically, granite-granodiorite is met-aluminous,, spider diagram normalized to lower continental crust show enrichment of LILE such as Rb, Cs, K and LREE (La, Ce) , depletion of Ti, Sr, Ta, Nb, Ba, Cs. Based on low values of magnetic susceptibility [(5 to 11) × 10-5 SI], therefore it is classified as belonging to the ilmenite-series (reduced type).The result of U-Pb zircon age dating of granodiorite is 161.85 Ma (Middle Jurassic, Callovian time). Based on Initial εNd isotope values for granodiorite is -6.51, initial 87Sr/86Sr and 143Nd/144Nd ratios for granodiorite is (0.70913 and 0.512095), the magma for granite and granodiorite originated from the continental crust. During Middle Jurassic (Callovian) due to continental collision, Upper Triassic to Lower Jurassic rocks is regionally metamorphosed. During the continental collision, Middle Jurassic (164-162Ma) reduced type granitoid magma (Ilmenite series, continental crust melting) formed and intruded these regional metamorphosed rock in Najmabad, Shah Kuh and Sorkh Kuh area.

165-181

Authors: Ali Abedini; Rahim Masumi; Ali Asghar Calagari

Kajal kaolin deposit is located ~20 km northwest of Hashtjin, Ardebil province. Field evidence and laboratory investigations show that the deposit is an alteration product of ignimbrites, tuffs, and trachy-andesites of Eocene age. According to mineralogical data, the major rock-forming minerals include kaolinite, montmorillonite, polygorskite, orthoclase, zeolite (stilbite), quartz, and chalcedony. Mass change calculations of elements, with assumption of Ti as immobile monitor element, indicate that leaching and fixation are two prominent regulators for concentration of major, minor, trace, and rare earth elements in the deposit. The distribution pattern of REEs, normalized to ignimbrite, in kaolin samples illustrates a weak fractionation of LREEs from HREEs coupled with strong negative Eu anomaly during the evolution of the deposit. Calculations of correlation coefficients among elements show that there is a high intrinsic correlation between HREEs in the studied samples. According to geochemical indices, it can be inferred that the hypogene alterations are superimposed by supergene ones in the course of evolution of the deposit. In accordance with the mode of distribution of elements in the deposit, it appears that the behavior of elements during kaolinization of ignimbrites was affected by the function of factors such as pH, redox potential, temperature variations, high fluid to rock ratio, preferential adsorption by clays and iron oxides, discrepancies in the stability rate of minerals, abundance of complex-forming ions (CO32-, F־, Cl־, PO43-, and SO42-), and isomorphic substitution. The obtained results indicate that epithermal acid-sulfate solutions along with acidic supergene solutions originated from oxidation of hypogene pyrites played an important role in development of the deposit. Further geochemical considerations show that clay minerals along with secondary phosphates like monazite, rabdophane, and xenotime are the potential hosts for REEs in the deposit.

193-216

Authors: Mohammad Hasan Karimpour; Azade Malekzadeh Shafaroudi; Akbar Esfandiarpour; Hasan Mohammad Nejad

Neyshabour turquoise mine is located in northwest of Neyshabour, southern Quchan volcanic belt. Eocene andesite and dacite forming as lava and pyroclastic rocks cover most of the area. Subvolcanic diorite to syenite porphyry (granitoids of magnetite series) intruded the volcanic rocks. Both volcanic and subvolcanic rocks are highly altered. Four types of alteration are recognized including: silicification, argillic, calcification and propylitic. Silicification is dominant followed by argillic alteration. Mineralization is present as stockwork, disseminated and hydrothermal breccia. Hypogene minerals are pyrite, magnetite, specularite, chalcopyrite, and bornite. Secondary minerals are turquoise, chalcocite, covellite, and iron oxides. A broad zone of gossan has developed in the area. Oxidized zone has a thickness of about 80 m. Mineralized samples show high anomalies of Cu, Au, Zn, As, Mo, Co, U, LREE, Nb, and Th. Both aeromagnetic and radiometric (U and Th) maps show very strong anomalies (10 × 5km) within the mineralized area. Based on geology, alteration, mineralization, geochemistry, and geophysics, Neyshabour turquoise mine is a large Iron oxide Cu-Au-U-LREE (IOCG) mineralized system. In comparison with other IOCG deposits, it has some similarities with Olympic Dam (Australia) and Candelaria (Chile). In comparison with Qaleh Zari and Kuh Zar mines, Neyshabour turquoise mine is the first Iron oxide Cu-Au-U-LREE (IOCG) mineralized system discovered in Iran.

231-249

Authors: Vahideh Alipour; Ali Abedini

The Zonouz kaolin deposit is located ~15 km northeast of Marand, East-Azarbaidjan province. Based on physical features in field investigations, such as color, five distinct kaolin types including (1) white, (2) lemon, (3) gray, (4) brown, and (5) yellow are distinguished in the deposit. Field evidence and petrographic studies indicate that the deposit is genetically close to trachy-andesite rocks. According to mineralogical data, the deposit contains quartz, kaolinite, montmorillonite, calcite, pyrophyllite, chlorite, muscovite-illite, dolomite, hematite, and anatase minerals. Geochemical data indicate that function of alteration processes on trachy-andesite rocks during development of Zonouz ore deposit was accompanied by leaching of elements such as Al, Na, K, Rb, Ba, V, Hf, Cu, Zr, Tm, Yb, and Lu, enrichment of elements such as U, Nb, and Ta, and leaching-fixation of elements such as Si, Fe, Ca, Mg, Ti, Mn, P, Cs, Sr, Th, Co, Cr, Ni, Y, Ga, LREE, Tb, Dy, Ho, and Er. Incorporation of obtained results from mineralogical and geochemical studies show that physico-chemical conditions of alteration environment, the relative stability of primary minerals, surface adsorption, preferential sorption by metallic oxides, existing of organic matters, scavenging and concentration processes, and fixation in neomorphic mineralogical phases played important role in distribution of elements in the deposit. Geochemical studies show that development of the deposit is relative to two types of processes, (1) hypogene and (2) supergene. The distribution pattern of REEs indicates that differentiation degree of LREEs from HREEs in supergene kaolins is more than hypogene kaolins. Geochemical studies indicate that minerals such as Mn-oxides, zircon, anatase, hematite, cerianite, and secondary phosphates (monazite, rhabdophane, churchite, and zenotime) are the potential hosts for rare earth elements in this deposit.

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.