مقالات

Preparation of Mineral Prospectivity Models (MPM) is one of the most important stages for identification and exploration of a specific type of mineralization in study area. To this end, the use of all available exploratory data has been developed using the data and knowledge-based MPM modeling. In this research, the fuzzy-gamma knowledge-based method has been used to identify areas susceptible to Au hydrothermal mineralization in the Dehsalm area, east of Iran. The input data for the modeling including information obtained from the processing of geochemical stream sediment data using a robust compositional factor analysis method, hydrothermal alteration layers derived from satellite images processing and fault density maps of the region. The input layers are made in the form of a raster after the initial preprocessing, and by using the fuzzy coefficient of 0.95, the final exploratory model is prepared. The results of field survey in anomalous areas, indicate the proper functioning of this method in identifying the promising areas of gold mineralization in study area.

Nowadays, remote sensing studies are considered as one of the best methods in mineral prospecting. Considering that most of the important deposits of the world, such as porphyry copper and epithermal gold deposits are widely located in altered areas, identification of the alterations can be a very good exploratory guide for these types of deposits. The spectral 123 difference between altered and unaltered rocks is the most important way of detecting alteration areas and thus exploring ore deposits by means of remote sensing. In this research, Aster images were used to identify alteration areas. Geometric corrections were made on images in order to reduce the spatial errors caused by displacements and distortions related to sensors. Radiometric corrections were also applied to reduce the spectral errors caused by atmospheric effects. Subsequently, mineral prospectus areas were identified using false color composite, band ratio and principal components analysis. Due to the fact that the results of these methods are grayscale images, a concentration-area fractal method was used to distinguish the regions containing the alterations. Using the results of these methods, some areas with the highest probability of mineralization were introduced which were compatible with the ground control points.

A stream sediment geochemical exploration was carried out to determine the mineral potentials in Sepestan area, Shahrakht, Souther Khorasan. 190 samples were taken in an area of about 190 KM2. The samples were analyzed for 51 elements by ICP-MS. Upon data processing the Factor Analysis was applied. Four factors were selected which expressed 75.29 % of the total variance. Factor 1, 2,3,4, indicated as 33.96% ,22.24%. 11.52%, and 7.39% of the total variance respectively. The scores map of factor2 and factor3 were the potential areas for the element Ni, Cr, and Ba.

The Cheshmeh Noghreh area located in Taknar Inlier Zone (TIZ), bordered by Rivash fault in the north and Doruneh fault in the south. This area with six volcanic cycles is a part of Tertiary cover of narrow wedge shaped of Taknar uplift. The magmatic evolution based on lithostratigraphic successions and petrographic descriptions of rocks is realized by a trend of differentiations which originated the silica-rich residual solutions during the last stage of volcanic activity (EV6). The steeply faults of 75◦ to 80◦ in northern part of Cheshmeh Noghreh, played the role of pathways and feeder zones to migrate the residual solutions and finally to occur W-E to NW-SE trending of alteration zones and related anomalous blocks (A to E) of Au 11 and base metal assemblages. The block No. A just in the north of Cheshmeh Noghreh includes a plunged recumbent synclinal structure, composed of Eat and ESh-2 rock units of middle Eocene age, which have been strongly silicified and overprinted by alunite alteration and lastly produced ore parageneses of framboidal pyrite, gold, chalcopyrite, bornite, sphalerite, galena, tetrahedrite, jamesonite, barite and stack piles of vuggy quartz gangues. Physicochemical parameters of residual ore-forming solutions determined by fluid inclusions studies in quartz gangues indicate the following data: TH= 190◦ to 240◦, total density= 0.6 to 0.9 gr/cm3, depth of formation 60 to 1500m, salinity= 4.5 to 6.5 Wt% NaCl eq and pressure (P) = 15-300 bar which approved an epithermal type of ore-mineralization. From the geological-structural observations, different type of alterations and related ore-assemblages as well as micro-thermometric data, it is concluded that exploration approach in the Cheshmeh Noghreh area confirmed gold-bearing high sulfidation epithermal type of ore-mineralization.

Structural systems related to iron mineralization in the Sangan- Khaf iron ore deposits, in accordance with the compressive-shear structures of structural zones of central Iran and Lut blocks, have a direct relationship with the deformation, fractures, and faults, others linear structures and the influence of igneous bodies as the source of the fluid transport have the final effect in mineralization. The purpose of this study was to investigate and identify tectonic structures at C-North ore deposit, Sangan and their analysis with suitable methods in order to achieve a tectonic model (unstable zones) so that the results can be used to design the slope stability with attention to safety and economics factors. In the first stage, structural survey (faults and fractures) in different walls were separated by lithology at C-North ore deposit and then performed statistical analysis using Dips.5.1 software for each of the wall, including the pole plot, contour plot, rose diagram, and the major plane plots of the fractures and faults. In the second stage, Ground Penetration Radar (GPR) study was carried out to investigate the structural and water content zones at C-North ore deposit. In this study, the fault density was calculated using three parameters: length, intersection and fault congestion. Structural studies showed that part of the low electrical resistivity zones is in coincident with the fault lineaments, while other parts are associated with alteration zones due to the performance of the late processes of crystallization of the magma of the intrusive bodies of the region. The fault zones have N, NW-S, SE trend. There are a number of W-E trend. These zones have a relatively low electrical resistivity which, in high rainfall season, are considered as saturated zones of underground water and are considered as pathways that transfer underground water to pit. The results of integration geological and GPR surveys with the fault density map are in the perfect match. The methods mentioned in this study can be used to study the stability of mines and to identify unstable zones in other ore bodies.

Dehzaman Iron ore deposit located in southwest of Bardaskan, Khorasan Razavi province. Geology of the study area consists of late Precambrian metamorphsed volcano-sedimentary units. Magnetite ± Specularite mineralization which trend East-West and dipping to the North, is hosted by metarhyolite- metarhyodacite with lower magnetic susceptibility (0 to 70×10-5 SI). Ground magnetic survey was carried out in central part of the area to delineate lateral and vertical distribution of Magnetite mineralization. Changes of total magnetic field intensity in central part were 15592 Gamma. The trend of magnetic anomaly in central part is East-West and coincides with Magnetite ± Specularite mineralization zone. According to first order derivative of magnetic data, the width of mineralization zone is estimated by 2-5 meters. Analytical signal map indicating edges of magnetic anomalies which coincide with mineralization and are collinear with faults and showing better picture for both of them. Depth of magnetic anomaly sources, magnetite, extends to more than 50 meters only in Eastern part of the study area.

Geochemical and geophysical exploration methods are more efficient and applicable due to the extent of the study area at the regional scale. Geochemical explorations include several categories such as stream sediment geochemistry, lithogeochemistry, hydrogeochemistry and geobotany. The stream sediments method is more applied for regional prospecting and preliminary exploration in order to recognize the mineral potential area. Using multivariate statistic methods, 635 stream samples have been studied for identifying the potential areas in Dehsalm 1:100000 geological sheet. Applying the R-mode factor analysis, resulted in extraction of six factors with the same number of score maps suggesting the possibility of mineral potential for some elements including gold, tungsten, copper, chromium, nickel, vanadium and lead in some areas. The identified promising areas can be used as appropriate exploratory targets for planning detailed and semi-detailed exploration steps.

Zaveh copper deposit is located in Khorasan Razavi province, SE of Torbat-e-Hydarieh, and in mid-section of Khaf-Kashmar-Bardaskan belt. Lithology of the area includes Jurassic and Cretaceous sedimentary rocks and Eocene volcanic rocks. Mineralization is structurally controled and occurred as vein-veinlet form with east-west trending and hosted by Jurassic rich quartz conglomerate. Primary minerals are chalcopyrite, pyrite, and arsenopyrite and secondary minerals are malachite, azurite, chalcocite, covellite, bornite, copper sulfates, wad (hydroxide manganese), hematite, goethite, jarosite, limonite, and minor chrysocolla. Silicification is the dominant alteration associated with vein mineralization. Propylitic, serisitic, carbonate and silicification alterations were observed in area’s volcanic rocks. Mineralization has anomaly of Cu (max 2.1%), As (up to 1%), Sb (105 ppm), Pb (4371 ppm), and Zn (max 1.1%). The two elements of copper and arsenic have the highest correlation in the region. Host rock, alteration, formation and development of mineralization of Zaveh mineralization is similar to hydrothermal vein-type deposits.

In regional scales, due to the extent of the study area, geochemical and geophysical exploration methods are more applicable, each of which is used in different ways. Among geochemical methods, the study of stream sediments is widely applied for regional prospecting and preliminary identification of the areas containing and extensive water basin. In this research, 635 samples were gathered from stream sediments for identification of mineral prospective areas in Dehsalm 1: 100000 geological sheet by combining factor analysis and concentration-area fractal methods. After pre-processing of the obtaining data and applying factor analysis, six factors were extracted. Then, in order to prioritize the potential areas, the concentration-area fractal method was applied to the samples factor scores. After extraction of the thresholds values, fractal classification maps of the factor scores were obtained and probable anomalous regions were determined.

The study area is located in northeastern of Iran and south of Mashhad city. Granitoid rocks consist of Alkali feldespar granite, granite, granodiorite, quartz diorite and diorite. The dominant textures in these rocks are hypidiomorph granular, poikilitic, graphic and myrmekitic. The main minerals are quartz, plagioclase, alkali feldspar, biotite and hornblende and minor minerals include tourmaline, apatite, zircon, esphene and opaque. Field, petrographic and geochemical studies indicate that the studied rocks are of S-type granitoids (of crustal origin) and are in tectonic position in the same range as collisions and volcanic arcs .