فهرست مطالب akram ostadhosseini

The study area is situated 21 km SW of Ardestan city and 80 km NE of Esfahan (Central Iran). and according to the sedimentary structural divisions (Fig. 1; Aghanabati, 1998) in the central part of Urumieh-Dokhtar Magmatic Belt (UDMB) The UDMB in the Alpine-Himalayan orogenic belt, the most productive metallic belt of Iran, composed of basic to acidic volcanic and plutonic rocks, tuff and agglomerate. The UDMB represents geochemical characteristics of subduction zones with features of calc-alkaline locally toward alkaline (Berberian and Berberian, 1981; Alavi, 1994; Shahabpour, 2007; Omrani et al., 2008; Ghorbani and Bezenjani, 2011; Yeganehfar, 2013; Rajabpour et al., 2017). The UDMB hosts several porphyry Cu±Mo±Au deposits including Sungun, Sarcheshmeh, Kahang, Darehzar, Nowchun and Meiduk (Atapour and Aftabi, 2007; Zarasvandi et al., 2015; Zamanian et al., 2016; Alirezaei et al., 2017; Jamali, 2017) and associated porphyry copper-gold, gold epithermal and manganese-iron deposits (Rajabpour et al., 2017; Ostadhosseini et al., 2018; Alaminia et al., 2020; Ostadhosseini et al., 2021). Different stages of Cenozoic magmatic activity in the middle segment of the UDMB around the study area consist of different successions of volcanic and intrusive rocks (Radfar, 1998). The Eocene to Miocene diorite- monzodiorite bodies were intruded the Eocene volcanic and subvolcanic rocks. In the middle of the area, these intrusive units are juxtaposed with a fault boundary (Marbin fault) adjacent to Eocene volcanic units. 
 
The Eocene volcanic stage is dominated by basalt, andesitic basalt, andesite, tuffs and ignimbrites rocks. Quaternary sediments are widespread in the northeastern and southern parts of the area. The oldest rock unit of this area is the Shotori dolomite formation trending NW-SW and belonging to Triassic age and located in the southwest of the study area. Cu mineralization occurs within the Eocene volcano-sedimentary sequence. The purpose of this study is to determine the type of Cu mineralization based on the mineralization characteristics, geometry, texture, structure and alteration studies, as well as the geochemistry and tectonic environment of the host volcanic rock.
For the purposes of this study, 60 thin sections of volcanic rocks and 30 polished thin sections of ore samples were studied by a standard petrographic microscope under reflected and transmitted lights. 10 surface and drill–holes samples from volcanic rocks were crushed and powdered in tungsten carbide swing mill for whole-rock analysis. The chemical analyses were performed for the major elements using X-ray fluorescence (XRF) and trace elements using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Electron microprobe analyses were performed, using a JXA-8100 electron microprobe. Operating conditions were 35 kV accelerating voltage, a beam current of 20 nA, and a beam diameter of 2-10 μm.
All the petrographic studies as well as chemical analyses including XRF, ICP-MS and EPMA were carried out at the Seoul National University Laboratories, Seoul, South Korean.
The dominant rocks of the area under study are basalt, basaltic andesite, andesite and a small volume of pyroclastic rocks which are metaluminous composition and calc-alkaline affinity. Geochemically, they are enriched in LREE relative to HREE, enrichment of LILE and negative anomalies of HFSE (i.e., Nb, Ti), pointing to characteristics of subduction-related magmatic possibly generated by partial melting of metasomatized lithospheric mantle source. As the discrimination diagrams of tectonic setting display, the volcanic rocks are also classified as a subduction-related magmatic arc. Alteration zones were developed in the rock types including silicic, propylitic, argillic, sericitic and zeolitic. The propylitic and silicic alterations were extended within the mineralized zones. The propylitic alteration is the dominant alteration consisting mainly epidote, chlorite, and calcite. The silicification zone consists of crystalline quartz-formation, which occurs as veins and veinlets including some copper minerals. The carbonate alteration is observed in basaltic andesite and andesite rocks. Copper mineralization is mainly strata-bound, and occurs partially as veins, veinlets and disseminated in the andesite, basaltic andesites, and basaltic rocks. Based on microscopic studies, three mineralization stages were recognized in the Rahimabad deposit including pre-mineralization, mineralization, and post-mineralization stages. In the pre-mineralization stage, pyrite is formed in decreasing conditions in the host rock. In the main mineralization stage, pyrite is replaced by primary Cu and Ag sulfide minerals such as chalcopyrite, bornite, chalcocite, digenite, jalpaite and acanthite. Finally, in the post mineralization stage, copper sulfide minerals are replaced by secondary copper sulfide minerals (chalcocite, covellite and digenite) and oxide minerals (malachite, azurite, goethite and hematite).
The Rahimabad Cu (Ag) deposit lies in the SW of the Ardestan city in the Urumieh-Dokhtar Magmatic Belts, Central Iran. In this area, Cu and Ag mineralization is observed in the volcano-sedimentary rocks. The copper (Ag) mineralization occurs in andesite, basaltic andesite and basaltic lavas. These rocks are meta-aluminous and have a calc-alkaline affinity and indicate a subduction-related magmatic arc. The main alterations zones are silicic, propylitic, argillic, sericitic and zeolitic. The geometry of mineralization is strata-bound and the texture and structure of mineralization is open space filling, disseminated, vein-veinlet and replacement. Based on microscopic as well as EPMA data, the most important Cu and Ag minerals include chalcopyrite, bornite, chalcocite- covellite group minerals, malachite, azurite, acanthite and jalpaite, which are accompanied by magnetite and hematite. Pyrite is mostly observed as a separate mineral in the host rock. The overall mineralization characteristics and tectonic setting, the type of host rock, geometry, texture and structure, mineralogy and the paragenetic of Cu minerals and finally the alteration zones with different types of copper deposits document that the Rahimabad copper deposit share many features with those of Manto type copper deposits.
Acknowledgment
The present study was financially supported by the Cu-Au company of Ardestan. The authors are grateful to Mr. Sharif for providing sampling facilities and let us access to drill cores and exploration data.

Chahpalang iron index is located in 90 km northeast of Ardakan city in Yazd province and Central Iran structural Zone. Rock units in the study area consist of meta-volcanics, recrystallized carbonates and schists. Ore body is hosted by meta-volcanics and carbonate rocks. Magnetite (two types), hematite (three types) associated with a few pyrite and secondary minerals of goethite, limonite are as ore minerals. Outcrops of orebody are disseminated, lenses and veins in the host rock. Disseminated, massive, corrosion, brecciated, replacement, network are textures of mineralization and alteration halos are chloritization, epidotization and sillicification. Total iron values vary between 28 and 91% in the samples. Low values of Cr, V and Ni-Co diagram confirm hydrothermal origin of Chahpalang iron index. REE values are between 10 and 110 ppm and distribution pattern diagram of these elements indicate the decreasing trend from LREEs to HREEs, resulting the fractionation of these elements in the hydrothermal process. Negative Ce and positive Eu anomalies and REE calculated ratios show the similarity of Chahpalang iron index with hydrothermal deposits.

The purpose of this study is to determine geochemical anomalies on lithogeochemical data from Ardestan area, Central Iran, using concentration-number (C-N) fractal modeling and staged factor analysis. Staged factor analysis is used to the recognition of genetic correlation and elimination of non-indicator elements in three steps. Factor scores of elements were calculated and geochemical data classified by the C-N fractal model. According to the anomaly values, the distribution of elemental concentration for Mn and F1-3 were divided in four classes and five geochemical groups of Cu, Ag, Fe, F2-3 and F3-3 have been identified. Main geochemical anomalies are located in the NW, NE and SE of the study area. Obtained results from fractal and factor analyses is confirmed by field observations, petrographic and mineralographic studies, indicating pyrite, chalcopyrite, chalcocite, covellite, argentite, malachite, azurite, magnetite, hematite and pyrolusite are main ore minerals hosted by andesites and basaltic andesites.

Using stream sediment geochemical exploration has been considered as a useful approach to explore the good potentials for many years. Problems might come up in the course of implementing resolving which may requires the use of more recent findings or auxiliary methods.
One of the areas which has faced special problems during the conducting geochemical exploration is the Orzooiyeh region on the border of Kerman and Hormozgan provinces. Stream sediment exploration was carried out in the area in the scale of 1: 100,000. This region includes two different geological zones that are the Sanandaj-Sirjan in the northern part and the Zagros in the southern part. During the statistical analysis and method of eliminating the effects of the upstream rock it was determined that most of the element of chromium’s anomalies are in compliance with the Bakhtiari and Aghajari units which are lacking in the economic importance in the chromium ore. Current geochemical exploration methods often extract the anomalies based on classical statistical methods (Yazdi, 2002). In these methods, the range of the anomaly is just determined based on simple numerical calculations and except for grade, any of the other parameters do not have a significant role in determining the anomaly areas. However, procedures such as fuzzy logic, neural system, regression and hierarchical analysis process enable the users to involve more parameters in data processing (Oh and Lee, 2010; Kumar and Hassan, 2013; Carranza, 2008).
For instance, using special algorithms has made parameters such as lithology and tectonic, geophysics and geochemistry effective in processing and determining the anomaly zones, and ranking each of the affective parameters in the anomaly based on their importance, and eventually achieving the maps and valuable anomaly areas possible (Bonham-carter, 1994; Carranza, 2008).
This study was conducted to identify the significant anomalies zones using AHP and GIS techniques.

AHP (Analytical Hierarchy Process) is the most comprehensive system designed for multi-criteria decision-making. This method was offered firstly by Sati in 1980, and has carried out numerous applications in different sciences until now. This technique also shows the consistency and inconsistency of the decision that is the outstanding benefit of this technique in multi-criteria decision-making and has been proposed for complex and fuzzy problems based on human brain analysis, and consists of three stages: basic, involving the creation of a hierarchy, determining priorities and logical consistency (Macharis et al., 2004).
In AHP, the factors are compared with each other in pairs and the highest weight is given to the layer that makes the maximum impact on determining the goal (Carranza, 2008). So in this research, after the detection of the effective factors in determining the anomaly areas in the study area, the factors have been weighed for prioritizing the criteria in their order of importance and the paired comparison matrix is formed based on the characteristics of the area and comparative studies for criteria and sub-criteria. After the formation of paired comparison matrices using approximate arithmetic average, the relative weight of parameters was calculated. Then, the researcher carried out the various stages of preparing and the extracting data layer deals with each of these factors in the GIS environment and finally the layers were integrated with each other and the entire range of the anomaly was ranked based on appropriate models.

The results of calculating the final weight criteria show that among the study groups, groups Geochemistry .0.45, lithology 0.45 and tectonic 0.1, respectively, are more significant. The ratio of consistency between these groups is 0.02 and is acceptable and the map prepared by the integration of these groups in the GIS environment according to calculated weights shows that a significant proportion of the false anomalies in the region have been eliminated, and the chromium anomalies associated with ophiolites and peridotites of the region show their best. Therefore, this method can be used for providing the mineral prospecting map that the abandoned mines located in the upstream of anomaly areas confirmed the efficiency of this method in the determination of the anomaly areas.

In the present study, the hierarchical process analysis method was utilized to eliminate the false anomalies caused by small and non-significant placer deposits related to the detrital formations in the region. The effective factors in determining the anomaly zones were determined and the final map was constructed by integrating groups, lithology, elemental geochemistry and tectonics that is, the anomaly zones map was drawn in the GIS environment. The results show that the region anomalies are related to ophiolite and ultrabasic and a little bit the region detrital. Therefore, a significant percentage of false anomalies associated with the regional detrital of the area was eliminated by this method and the real anomalies showed their best. This discussion indicates the efficacy of the method of AHP and GIS technique, and they can be considered to be effective methods to reduce the impact of Singenetic factors and naturally to eliminate false anomalies.