Iranian Journal of Crystallography and Mineralogy
Year:2008 | Volume:16 | Issue:3|Papers Count:13

Kuh–e-Zar gold deposit located in central part of Khaf–Bardaskan volcano-platonic belt and about 40 km west of Torbat-e-Heydariyeh area in Khorassan-e-Razavi province. The extensive exploration of the last decade done in the above belt has been caused the exploration of several Iron oxide copper–gold deposits, such as Kuh-e-Zar deposit. Several types of Tuff and Acide to intermediate lavas (lover tertiary) are widespread all over in the area. Mineralization appeared in different type such as vein, stockwork and Hydrothermal breccia in strike sleep fault zone which are hidden inside volcano plutonic rocks.The average gold grade is between 3.02 ppm and ore reserve is estimated more than 3 million tons (cut off grade = 0.7 ppm). The copper grade in mineralized zone located in intrusive bodies between 0.3 to 1.1%. The main mineralized zones are Quartz and specularite (more than 30%). However, the various types of sulfides are very rare on surface. Pure gold can be observed together with Quartz and Specularits. Based on consideration of oxygen stable isotope (d18O) in Quartz and siderite as well as sulfur (d34S) in chalcopyrite, geochemical investigation and micro thermometric study has caused the gold mineralization through magmatic fluid with low sulfide content and high oxidation state. It is clear that the kuh-e-zar mineralization in case of paragenesis, alteration and dimension has been the only case all over the world. Regarding the lack of recognized and similar sample in the world, this deposit is a new and different variety of Iron Oxide Cu-Au (IOCG) deposit. It is introduced and named as Iron Oxide Gold deposit (IOG) or Specularite rich Gold deposits. This deposit has unusual richness in gold and LREE and is poor in copper.

Several igneous-evaporitic rocks complexes, belonging to Lower Cambrian, are exposed in High Zagros. These rocks exposed parallel to the Zagros main thrust as diapir-shaped bodies. Basaltic rocks are the most common rocks but microgabbro, microdiorite, andesite and trachyte are the rocks of this complex. The studied clinopyroxenes are usually fresh mafic mineral in these rocks and display sector zoning features. On the base of mineralogy and mineral chemistry, the pyroxenes are in the range of titan-augite to diopside composition. The geochemical study of the clinopyroxene as well as the discrimination diagrams were used in this study, point to the transitional to alkaline nature of magmatism which occurredv in a within continental plate rift environment.

Mehdiabad Zn-Pb-Ba deposit is located 110km south-east of Yazd, in the Central Iran structural zone. The stratigraphic succession consists of three sedimentary formations of lower Creataceous age. The Sangestan formation,i.e, the lowest unit of shale and siltstone with calcarenitic interbeded layers. This unit is overlain by ankeritic massive dolomite and dolomitic limestone of Taft formation. The Abkouh formation at the top is composed of cherty or clayey limestone with conglomeretic intercalation, lenses of massive reef limestone and calcareous shale. The structure of orebody shows a half-graben with a vast N-S synform being complicated by the presence of polyphase faults. The main normal fault is Tappeh Siah fault, suggested to have been active during and after the period of sedimentation. Major economic minerals are sphalerite, galena and barite with minor pyrite, chalchopyrite in sulfide zone. Oxide ores contain smithzonite, hydrozincite, hemimorphite and cerussite. Mineralization occurs in stratiform-lenticular orebodies and concordant with host rocks. Also orebodies showing laminated, disseminated, open space filling, karst filling, colloform and botryoidal textures.

Cutting samples from evaporite deposits of Member Two of Gachsaran Formation in well #1 at Ab-Teymure Oil Field have been studied by petrographic microscope, SEM with EDX attachment and XRD to identify the halite crystal shapes. This study led to recognition of three stages, including flooding, concentration and desiccation, for the formation of halite in salt pan. In the flooding stage, the flooding water dissolves the saline crust in the floor of salt pan, which are flat and vuggy. At the second stage, dissolution of halite and evaporation continued. As the concentration of brine increased, rafts, plates and hopper shapes of halite crystals form at the air-brine interface. Finally, these crystals precipitated to the bottom of the salt pan as the weight of crystals increased. At the last stage, salt pan was dried and hyper saline condition was dominated below the surface during lowstand. During this stage, halite crust formed on the surface of salt pan and clear crystals of halite in cubic and cumulative form may have been precipitated in vuggy pores that formed during dissolution of salt.

The Barfakeh lead and zinc ore deposit is located 40km NW of Shahrood in the East Alborz techtonic zone. The rocks adjacent to this ore deposit include the Shemshak formation, which consists of shale and sandstone with the age in the upper Terias to Lias range, tuffs of the Karaj formation, and Conglomerates of the Fajan formation. The host rock of the ore deposit is the massive limestone of Lar formation with the age of upper Jurassic. The ore deposit, as epigenetic and stratabound and open-space filling, has formed lens and veins with general trend of NW-SE and general dip direction of SW. The Barfakeh ore deposit belongs to the Mississipi-Valley type deposit from the zn rich type. Mineralography and X-Ray diffraction studies reveal that Galena and Cerusite are the major minerals for lead, and Smithsonite and hemimorphite are the major zinc minerals. Sphalerite was not detected in microscopic and even X-Ray diffraction studies. The amount of Galena is also low and in its margins it has been replaced by carbonate minerals. It may be argued that the primary minerals of the Barfakeh ore deposit were presumably sulfide minerals, i.e. Sphalerite and Galena, which have been altered by secondary minerals. Furthermore, based on X-Ray diffraction studies, rare minerals including Magnesite ferroan, Magnesite nickeloan, and Calcite manganoan were recognized. 

Chah Torsh intrusive body in S-W of Nadushan is a small part of extensive magmatism of Oligo-Miocene age in Urumieh-Dokhtar magmatic belt. This is the largest intrusive mass of SW of Nadushan complex which are all outcropped as masses cut through Eocene volcanics. The Chah Torsh intrusion consists of two phases with porphyry and granular textures. Geochemical properties of two phases on the basis of trace elements contents and variations on Harker and spider diagrams indicate that they can be comagmatic. Lower ratio of Rb/K and silicate amount in granular phase in comparison to porphyry phase with higher amounts of HFSE such as Y, Zr, Th, Ta and Ti showing that the granular phase is a poor silica residual resulted from fractional crystallization of monzogranitic porphyric phase. High amounts of REE in Chah Torsh parent magma from one hand and high K content on the other hand resulted in decreasing P solubility in granodioritic melt causing apatite fractionation.

Barika gold mineralization occurred in a Cretaceous metavolcano-sedimentary sequence at northwestern Sanandaj-Sirjan zone. Gold-rich volcanogenic massive sulfide mineralization occurred in a rhyolite to rhyolitic tuff unit which is completely in Barika shear zone. Based on electron microprobe studies, gold is observed to form electrum mostly, and in lattice of other minerals, such as pyrite, galena, tetrahedrite- tenantite, bournonite- boulangerite, twinte- vinnite. The main effect of deformation on the gold mineralization is migration of submicroscopic gold to cracks and crystal defects in minerals to form electrum under low to moderate strain and release of electrum from fractured mineral under higher strain. This behavior of gold can increase recovery of gold in Au-bearing ore deposits (Huston et al., 1992).    

The submarine volcanic rocks of Totmaj volcano-sedimentary sequence, located at 25 Km southeast of Kashan city, have suffered extensive non-uniform propylitization. Based on field and petrographical studies, the volcanic rocks can be classified into three alteration zones: chlorite-epidote zone, epidote zone and hematite zone. The secondary hydrothermal minerals formed in the volcanic rocks include epidote-chlorite, calcite and hematite. These minerals have pseudomorphly replaced the primary phenocrysts (e.g. plagioclase, amphibole, and pyroxene) or have filled veins and vesicles. Stable carbon and oxygen isotope analysis of the hydrothermal calcite indicate that the d18O and d13C values range from -9.2 to -11.3 and -2.02 to -6.02 per mil respectively. Thus, seawater has been a source for hydrothermal fluid which by circulation into the hot submarine lavas, caused to leaching of some elements such as Fe and Mg from the altered rocks with the exception of epidote-chlorite zone. Also, the seawater circulation leads to an increase in Na ratio in the rocks. Geothermometrical studies on hydrothermal chlorite showed that these minerals have formed at a temperature between 240 to 300oC. Furthermore, the ranges of temperature stability of coexisting secondary minerals in the volcanic rocks are compatible with those of the green schist facies.

Bauxite deposit of Permo-Triassic age in northeast of Bukan was developed stratiformly along the boundary between Ruteh and Elika formations, and includes four distinct rock units. This deposit was affected by tectonic and morphological processes. Mineralogical and geochemical investigations showed that during weathering processes, two mechanisms of ferrugenization and deferrugenization played crucial role in formation of minerals such as diaspore, boehmite, hematite, goethite, kaolinite, pyrophyllite, clinochlore, illite, montmorillonite, anatase, rutile, albite, sanidine, quartz, and calcite in this deposit. By taking notice of field evidence and of mineralogical and geochemical data, the basalts (whose remnants are still present along the contact of this deposit with carbonate bedrock) are the potential parent rock of this deposit. The distribution pattern of REEs (normalized to chondrite and basaltic parent rock) along with anomaly variations of Eu, Ce, and (La/Yb)N indicates differentiation of LREEs from HREEs during bauxitization processes. Further geochemical considerations indicate that the concentrations of LREEs were occurred by hematite, goethite, manganese oxides, cerianite, and secondary phosphates (rhabdophane, vitusite, gorceixite, monazite) and of HREEs by clay minerals, rutile, anatase, zircon, euxenite, and fergusonite. Incorporation of the results obtained from mineralogical and geochemical investigations suggests that in addition to factors such as pH of weathering solutions, ionic potential, composition of the parent rock, and fixation by residual minerals, adsorption processes also played crucial role in enrichment of REEs during moderate to intense lateritization in the study area.

Prediction of the transformation relations for minerals such as Iron and manganese bearing oxides are based on the percentage of other minerals were deposited in the iron bearing anomalies constitute one of the main aspects of geochemistry. In this article, the iron and manganese anomalies of Choghart and Narigan districts are considered. Transformation relations are obtained based on computation of the amount of an oxide with respect to another unknown oxide. The variation trends of Fe2O3 and MnO in different samples are considered too. Several diagrams are drawn and based on them, the transformation relations are obtained by chemical analysis of minerals occur in the deposit. The genesis (based on formation environment), the way of formation of rocks and the economical percentage of the mineral deposits with respect to the depth of sampling can also be determined. In Narigan mine, one of the best mineral that can be used for the study of fluid inclusion is quartz (because of its transparency, abundance and co-genetic with the ore minerals). For this region, the relation between the equivalent salinity of salt and temperature are studied. Fluid inclusion generally appears in the two gas and liquid phases (and sometimes solid inclusions). As the pressure on the fluid inclusion is increased the temperature difference between homogenization temperature and its trapping temperature increases.

The studied area is located in the north-east of Ardestan in Isfahan province. In Iran’s geological classification it lies in the central Iran zone. The volcanic rocks of the Kuh-e Dom area are predominantly rhyolite, rhyodacite, dacite, tuff, ignimbrite, andesite, banakite and basaltic-andesite. The major rock–forming minerals are quartz, plagioclase, alkali feldspar (orthoclase, albite), amphibole, biotite, clinopyroxene and olivine. Apatite, zircon and opaque minerals are common accessory minerals. Biotite, clinopyroxene, plagioclase, alkali feldspar and chlorite in various rock samples were chosen for electron microprobe analysis. The results suggest that feldspar phenocrysts show a large compositional range from andesine-labradorite to labradorite-bytonite in banakite and basaltic-andesite and oligoclase-andesine and sanidine in rhyolite and dacite. Clinopyroxene phenocrysts show a compositional range diopside to augite in banakite and basaltic andesite. Phenocryst of biotite in the studied rocks is essentially of similar composition, and they are phlogopite (Mg-rich). This observation suggests that clinopyroxene and phlogopite formed from a Mg-rich magma. Also mineral chemistry of volcanic rocks of Kuh-e Dom indicates that these rocks were generated from calc-alkaline to shoshonitic magma and are related to continental arc orogenic magmatism. Barometery of pyroxene indicates that this mineral formed from a water rich magma in pressure of 5 kbar. On the basis of geothermometery studies, crystallization temperature has estimated to be 720-800oC for acidic rocks and 1170oC for basic rocks. The geochemical investigations show two stages in Kuh-e Dom magma evolution: Stage I is represented by clinopyroxene and phlogopite formation in a magma chamber. Stage II of magma evolution is represented by crystallization of matrix during and after magma eruption. Probably sanidine with small amounts of apatite and magnetite crystallized from the quenched magma at this stage.

The study area is located 92 Km south-east of Torbat-e-Heydariyeh and 12 Km to the north of Shahrak village in Khaf-Dorouneh volcanic-plutonic belt. Mineralization was formed in fault zones where they cross the intermediate plutonic rocks. Propylitic alteration is widespread and is the dominant type in the area. Magnetite and Specularite with variation in the amount form major portion of mineralization zones. Other primary minerals are Quartz, Calcite, Pyrite, Chalcopyrite and Chlorite. Analysis of a few samples of mineralization for Au, Cu, Pb and Zn elements using the A.A.S method. The amount of copper is 0.2 percent and gold 44 ppb. Microthermometry study of fluid inclusions in Quartz indicated temperature ranges from 160oC to more than 430oC and relatively high salinity for mineralization zones. Thermometry study of fluid inclusions in Quartz-Chalcopyrite veins showed Temperatures between 160oC-203oC and relatively high salinity for the solution. Minimum and maximum salinity that obtained were equal to 19 and 31 percent respectively in terms of NaCl. The closest compound system for fluid inclusions was determined H2O-NaCl-CaCl2 triple system. Considering high amount of magnetite and high value of magnetic susceptibility in mineralization, ground magnetic survey was carried out which resulted to the delineation of areas of covered mineralization. Interpretation of magnetic anomalies in profiles, was indicative of the continuation of surface mineralization and increase of magnetite with depth.