GEOSCIENCES
Year:2008 | Volume:18 | Issue:69|Papers Count:19

The Hired gold mineralization is located 140 km South of Birjand, Southern Khorasan, and north of Lut Block. In the area, the Jurassic and Cretaceous units are covered by Tertiary volcano-sedimentary sequences. Granite, granodiorite-quartzdiorite and gabbronorite bodies have intruded Tertiary sequences, and mineralization occurs within or at periphery of a subvolcanic granodiorite-quartzdiorite stock with porphyry texture. The existence of ilmenite within subvolcanic granodiorite-quartzdiorite bodies which the lack of magnetite and low magnetic susceptibility (1.5*10-4 SI Units) as well as low ratio of Fe2O3/FeO (<0.5), they are classified as ilmenite or reduced (low fO2) granitoid rocks.Mineralization in Hired area is divided into three main zones based on the distance from the stock. The mineralized zones are as follow: intrusion-hosted mineralization, proximal mineralization and distal mineralization. These three zones are different in host rock, mineralogy, alteration, structure, texture and metal assemblage.In the intrusion-hosted mineralization, the ore-bearing unit is subvolcanic granodiorite-quartzdiorite stock. Three types of major vein-veinlets observed within the stock, including vein-veinlets of tourmaline-quartz-sericite and sulfide (TQSS), quartz-calcite and sulfides (QCS) and quartz-calcite with rare sulfide (QC). The vein-veinlets include sheeted and stockwork arrays. The proximal mineralization occurs in volcano-sedimentary sequences. These sequences include tuff, andesite and conglomerate components. The sulfides occur as disseminated, vein-veinlet and massive textures. Stockwork and rarely sheeted vein-veinlets in this type of mineralization contain quartz, calcite and sulfides. Sericitization, silicification and carbonatization are the principal alterations associated with mineralization zone. The distal mineralization occurs in faults with low angle dips, trending NE-SW and NW-SE. These faults are filled with silica and carbonates, with iron oxides and hydroxides at the surface.The comparison of the most important characteristics of Hired mineralization (including tectonic setting, host rock, mineralogy, mineral paragenesis, ore content, structure, texture and alteration) with the characteristics of different types of gold mineralization suggests that the Hired gold mineralization shows most similarity with the gold mineralization related to reduced granitoid intrusion. This type of mineralization is reported for the first time from Iran.

Carbonate sediments of Permian age crops out in different parts of Iran. based On the foraminiferal content, they are attributed to Bolorian (?), Kubergandian to Dorashamian stages. These biogenetic limestones have plenty of Fusulinaceaa, non-fusulinid smaller foraminifers and algae, and they are a basis for determination of age, establishment of biozonation and paleogeography of Permian based on fusulind content. In some localities, chiefly in the north and northwest of Iran because of the distribution of Fusulinid are very rare paleoecological and paleo environmental factors. Despite this situation, smaller foraminifers, especially uniserial ones have a very important role in carbonate sediment make up, determination of age and reconstruction of pale environment. In this paper, this important and crucial role of uniserial foraminifers is discussed.

Meyamey fault, one of the major faults in the northeast of Iran, has played an important role in the regional depositional basin development and created many geomorphologic features. This fault has proved to be an important subject for study in terms of structural geology, fault mechanisms, fault interactions and the relation between faults and folds. Field measurements in the eastern part of the Meyamey fault zone depict that faults are mainly striking towards NE with dips of up to 50° and gentle lineation. Folds also follow the same trend. Calculated maximum stress axis in Armain fault is in NE direction, whereas in Meyamey and Ghods faults are in SE direction and are horizontal. Moreover, in the eastern Meyamey fault area, this fault shear zone Chah Seidabad fault, in which X and R, R fractures are evident.

Erosion and sedimentation are among the natural processes continuously changing the land surface. This deformation may affect the development activities of the coastal areas such as Bandar Anzali region. In order to evaluate the potential of erosion in the region, various methods of zonation mapping were reviewed. The region was divided into a number of grid lines and the weight of each grid was measured. The computer program Arc-GIS was used to calculate the weighing factors of each cell and finally to draw the zonation map. In this regard, five factors including lithology, slope angle, fault types, drainage pattern, and land-use (vegetation) were considered as major affecting factors on the erosion phenomena. The results showed that the effect of lithology and land-use are higher as accompanied by the effect of fault type and slope angle, and the effect of drainage pattern is most noticeable in mountainous areas. The geochemical characteristics of the sediments in Anzali wetland indicate that the percentage of SiO2, Al2O3, and CaO2 is higher than that of other elements such as FeO, MgO and MnO. These sediments represent the lithological setting of the provenance region of the originated sediments.

Tectono-geomorphologic features such as pressure ridges along strike-slip faults provide a reliable way to determine the fault displacement. The E-W trending active and strike-slip northern Mishow Fault is continuation of great Tabriz fault, that its activity has created numerous geomorphologic traces. We document pressure ridges about Baghlar basin as a geomorphic effect of northern Mishow fault, based on tectono-geomorphic interpretation of field geologic and geomorphic observations. our results show that Pressure ridges of study area by the names of Sisdah and Tapah-Bashy, are developed along northern Mishow fault, which resulted from long-term tectono-geomorphic growth in Quaternary, specially. Present pressure ridges development indicate neotectonic movements in the study area. Occurrence of three phenomena of river diversion, river capture and continous go back of elbow of capture in a small segment of Baghlar basin, are the most important effects of high dynamics and durability of slope instabilities in pressure ridges. This case study, thus, provides a good example for understanding the long-term tectono-geomorphological evolution of a major intracontinental strike-slip fault.

In this research, separation of paleostress phases in the central part of Dehshir fault is investigated based on the study heterogeneous fault-slip data and their related slickenside lineation’s. These data are measured from the Certaceous (Taft limestone), early Eocene (Kerman conglomerate) and Eocene (Volcanics) formations. The main criteria used here to identify sense of fault-slip are stratiographic separation, accretionary mineral steps, Riedel shears and tension gash. The existing faults iberegion of investigated often show two NE and NW trend in which the latter is usually dominant. Based on the study of heterogeneous fault-slip data and their related slickenside lineation’s and using the multiple inverse methods, at least two phases expected. These phases show that the axis of maximum principal stress, s1, is at NE trend and that of minimum principal s3 is, at NW trend. The location of s3  usually indicates that the strike-slip and reverse strike-slip faults mostly occur in the on lnaddition, the shape of the stress ellipsoid is prelate in the region. 

Damavand volcano is one of the most important geological features in Iran. Although a variety of studies are available about this volcano, there are different problems associated with existing data from Damavand including: they are not stored in a consistent and organized way, they are not directly applicable in users’ information systems (such as GIS), and they are not easily accessible and sometimes not accessible to users. In addition, clear and accurate studies about geomorphological-environmental specifications of Damavand are not still available. Considering these facts, this paper aims to describe design and implementation of Damavand geomorphological-environmental database and then disseminating it using WebGIS. In this research project, firstly, required spatial and attribute data were identified. Then, using available maps, satellite imageries, aerial imageries, and field works, required data were produced, completed and complemented. After that, the proposed database was designed and implemented and finally the mentioned data were stored in the database. By conducting these stages, the Damavand geomorphological-environmental database was established. At the next stage, an interactive WebGIS was designed and implemented in Geological Survey of Iran (GSI). At the last stage, the database was linked to the WebGIS and disseminated via that. At the time of writing this paper, the Damavand WebGIS and hence the geomorphological-environmental database is accessible via GSI intranet. The WebGIS can also be connected to internet in order to make the database accessible for public. Establishing such database for other geological-related datasets and its dissemination using WebGIS can significantly resolve current problems associated with these datasets from storage, accessibility and applicability perspectives.

The Thalassinoides bearing calcareous sandstone and sandy limestones of Oligocene age unconformably overlay the Eocene volcaniclastic rocks and gradually pass into the lacustrine sediments (Miocene? in age) in the study area. These layers are dominated by Thalassinoides suevicus (Rieth 1932) in the Y shaped boxwork cylindrical and bifurcating burrows, which are mainly filled actively by trace maker(s). The bioturbations in the layers are categorized into five ichnofabric classes, which are equal to standard ichnofabric indexes of 1 to 5. Frequency of the ichnofabric classes are 40.37, 15.9, 8.85, 4.97 and 29.9 percents, respectively. Ichnofabric variations of the studied layers are arranged in seven bioturbated upward cycles, which are divided into two groups. The first group shows low ichnofabric fluctuations and a constancy in the bioturbation, where the second group shows high ichnofabrics fluctuations and variability in the bioturbation. Results from the study show that the Thalassinoides in the studied section formed in conditions similar to those of Cruziana and Glossifungites ichnofacies.

Reserve evaluation is one of the most important parameters for mine designing and several methods have been developed in this regards. Among these methods, in addition to geostatistical methods, artificial methods such as Artificial Neural Networks (ANN) are suitable for reserve evaluation. In this research, geometrical and block model of ٍEsfordi phosphate mine are prepared and the reserve is estimated. The block model contains 100 thousand blocks with dimensions of 25×25×5 m. To estimate the grade of each block,both methods of geostatistical and ANN methods are used. For geostatistical estimation, normal kriging is applied. In ANN a perceptron multilayer network is used and for training of network LM method is considered. Based on geostatistical and ANN methods, the amount of estimated reserve is 16.5 Mt with an average grade of 11.44% and 17.5 Mt with an average grade of 11.83%, respectively, considering a cut-off grade of 6%. The results obtained from these two methods are identical to each other and difference is less than 6%. This estimation is a requisite for improving present design of the mine with an objective of selective mining up to sea level of +172.

Carbonate and siliciclastic sedimentary sequences of Sorkh Shale and Shotori Formations ( Lower and Middle Triassic) with a total thickness of 870 m , have a gradational and conformable contacts, at Behabad region of Bafgh in Central Iran. At the beginning of this sequence, shale, siltstone and sandstone gradually change into dolomitic carbonates of tidal flat sub-environment. Thick layered or massive sequence of mainly dolomitic rocks of Shotori Formation, are transitionally overlain by a limestone member namely Espahak limestone. Based on petrographic studies, four different types of dolomites (based on shape, crystal size and crystal boundaries), have been recognized. Dolomite type 1 (dolomicrite) formed during the first stage of sedimentation and under surface temperature, this is very early diagenetic dolomite. The other types, having coarse crystal size, formed during shallow to deep burial environments. Change of composition and temperature of dolomitizing fluids at several stages of diagenesis (early to late) led to formation of different types of Shotori dolomites. On the basis of geochemical studies (elemental analysis such as Ca, Mg, Sr, Na and stable isotopes such as d18C , d13O), formation of these dolomites occurred in a reducing environment and increasing temperature. The source of Mg is sea water for dolomite type 1, but for the other types of dolomites, Mg provided was by clay minerals diagenesis and basinal brine. The results of XRD and XRF on chlorite and montmorillonite clay minerals of Sorhk Shale Formation show a decrease in MgO content from 36% and 84% respectively compared to standard clay minerals. This reduction is due to diagenesis of clay minerals that exist in shales and Mg was originated from overlain layers. Measurement of organic carbon contents of dolomites and limestones showed that dolomites have several times more organic carbon than limestones. This information confirm that limestones rich in organic matter, are more susceptible to dolomitization. Microbial structures such as stromatolites, in the Shotori Formation have major role in trapping of organic matters. The calculated paleotemperature for the formation of early dolomites is about 39°C and for late diagenetic dolomite is 179°C .

The present study covers the area between 500E to 510, 30¢E of the Zagros Fold-and-Thrust Belt. The deformation pattern of west High Zagros Belt (HZB) has been considered to reflect a complete strain partitioning due to the Arabian oblique plate convergence and Central Iran. In this context the NW-SE trending Main Recent Fault (MRF) acts as rear boundary of the belt, kinematically taking up the strike-parallel component of oblique plate motion of Arabia, whereas the High Zagros Fault (HZF) with the same fault trend as MRF accommodates the orogen-normal shortening due to this movement. Using fault-slip inversion on fault planes mostly affecting the Bakhtiary conglomerate (Plio-Pleistocene in age) along the HZB, the deviatoric stress tensor and its shape factor (R) calculated at 29 stations. The geomorphic evidences and the fault kinematics show that the major parts of the HZF are consistent with strike-slip kinematics. This implies that the HZF also accommodates some part of strike-parallel component of oblique convergence collision.

The masjeddaghi area with 8.5 km2 extent is located in 35 km for east of jolfa. The geological exploration started in this area in 2003 and soil sample method was chosen due to the geological situation topography and weathering , The sampling network was 100m*100m and 100m*200m and all samples were analyzed for 13 elements .including Au, Cr, Co, Ba, Cu, Pb, Zn, Ag, Be, Mo, Sn, Mn. The geological studies shows that the oldest rock unit outcropped is Eocene flysh widely distributed in southern and north eastern part of the area .Another outcrops are mainly volcanic ,subvolcanic complex of andesite and trachyandesite, quartz monzonite and agglomerate (oligomiocene). In this area brecciated veins of barite – silicious and Cu, Pb, Zn sulfids and various pyrite type of mineralization have been identified. data processing have been carried out for analytical results(comparing main and duplicated samples data),and indicate normal  distribution for Ni, Be ,Mn log distribution  for other elements.  That  these  two analysis methods,  factor  analysis  and  correlation matrix analysis  (using  standardizing  the  datas  (x- x`/s)) have been consictent. Regarding The composite haloes, the result of studies indicate Au ,Ag, Be anomalies in eastern part of the area and Cu, Mo anomalies in western part of ARPACHAI valley. Considering the lithology and its relation to geochemical anomalies of the area, probable presence of porphyric Cu mineralization in eastern part and epithermal high sulfide Au mineralization in quartz-barite veins are identify.

This paper describes a multidisciplinary approach for evaluation of statically triggered landslide that occurred in Germi, Ardebil province on 1382. With respect to the evidence, no other mass movement was recorded in the adjacent areas despite the geological and geomorphological homogeneity. Field observations indicate that subsurface water level changes are the most important parameter in triggering the landslide. Hence, the study was focused on an analysis of the role of subsurface water level changes in triggering the landslide. The slope inclines steeply at crown and very gentle towards the toe of landslide. Field data dealing with geomorphology, geophysics (vertical electrical sounding or VES) and geotechnics were acquired and analyzed with the service of Rock Work 2004 and Arc GIS softwares in order to investigate the cause effect relationships between water level changes and mass movement. The geophysical survey detected two buried paths on the flanks of landslide and a three layer internal structures composed of surface deposit, natural bed rock and saturated zones. Based on the results, 21 test pits were located and excavated to the depth of hard layer. Representative material of the study area was selected and tested. Based on the lab tests, the slope was analyzed using Slide Software and remedial measures were recommended.

All the earthquakes are transient and nonstationary. For lack of alternatives, in seismology as well as earthquake engineering, most data are still processed by using the Fourier analysis. The most difficulties in the Fourier spectral analysis are associated with nonlinearity and non-stationary nature of the data. Such methods cannot reveal the detailed information in the dispersion properties, the wave form deformation, and the energy-frequency distribution. In this study, a new technique based on the time-domain empirical mode decomposition has been explained, which enables us to analyze both short-term information and long-term structures in seismic waves. It provides insight into long term memory and local time behavior of seismic signals. Oscillation modes of Earthquakes and Explosions are compared to each others, relationships between each group of the same data and differences between different data are obtained based on the produced IMFs. With respect to the advanced methods such as discrete stochastic non-Markov process it has been shown that this technique gives better identification. Plotting the maximum frequency of different IMFs via position of them, gives an effective identification tool. In this study first the technique is explained and then the obtained results are illustrated and discussed.

Qareaghaj mafic-ultramafic intrusion (QMUI) is located in northwest Iran, 36 km NW from Urmia city. The QUMI is composed mainly of non-mineralized mafic and Fe-Ti-P-rich ultramafic rocks (FTP). The mafic rocks, mainly coarse-grained gabbro, microgabbro, metagabbro and ortho-amphibolite, have simple mineral assemblage (plg + cpx + ilm). Based on field observations, petrography and geochemistry, they are directly related to each other (comagmatic). The FTP forms numerous layers and sill-like bodies, ranging in thickness from ~5cm to several meters. These rocks with high proportions of olivine, apatite, ilmenite and magnetite, show unusual bulk composition (e.g., SiO2~21-30 wt%, Fe2O3t ~ 26-42 wt%, TiO2~5-11 wt%, MgO~9-20 wt%, P2O5 up to 5.1 wt%, Cr~40-160 ppm, Ni~7-73ppm, SREE~10-340ppm). The FTP totally included by mafic rocks with sharp and concordant contact shows magmatic lamination and follows general NW-SE trend of the QMUI. Field relationship, petrography and geochemical data suggest that the FTP is not related to mafic host rocks and indeed intruded later into gabbros during plastic, high temperature deformation in local shear zone.