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علوم زمین | سال:1388 | دوره:18 | شماره:71

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مرکز اطلاعات علمی SID1
مرکز اطلاعات علمی SID
مرکز اطلاعات علمی SID
مرکز اطلاعات علمی SID
مرکز اطلاعات علمی SID
مرکز اطلاعات علمی SID
مرکز اطلاعات علمی SID
Writer: 

ZOHDI A. | AADAABI M.H.

Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    105
  • End Page: 

    114
Measures: 
  • Citations: 

    0
  • Views: 

    198
  • Downloads: 

    97
Abstract: 

Carbonate sequences of the Taleh-Zang Formation mainly consist of large benthic foraminifera (e.g., Nummulites and Alveolina) along with other skeletal and non-skeletal components. In this formation, the water depth during deposition was determined based on the variation and different types of benthic foraminifera and other components in different facies. Microfacies analysis led to the recognition of 10 microfacies that are related to 4 facies belts such as: tidal flat, lagoon, shoal and open marine. The absence of turbidite deposits, reefal facies, gradual facies changes and widespread tidal flat deposits indicate that the Taleh-Zang Formation was deposited in a carbonate ramp environment. Due to the great diversity and abundance of larger benthic foraminifera, this carbonate ramp is referred to as "foram-dominated carbonate ramp system". Comparison between elemental and isotopic compositions of biotic (benthic foraminifera) and abiotic (micrite) components in Taleh-Zang Formation shows an equilibrium condition due to minor biological fractionation and kinetic effects such as growth rate or other unknown factors. Thus, palaeotemperature calculation of seawater based on heaviest oxygen isotope values of biotic and abiotic carbonates are similar. Petrographic and geochemical studies illustrate that these carbonates were affected by weak meteoric digenesis in a closed diagenetic system with a low water/rock interaction.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    115
  • End Page: 

    122
Measures: 
  • Citations: 

    0
  • Views: 

    147
  • Downloads: 

    127
Abstract: 

Joint study is one of the primary jobs in many geological, mining, geotechnical and petroleum exploration projects. Up to 10 features of joints are gathered during each field survey, while only two of them (dip and dip direction) are normally used to classify these complex features. This paper proposes a new method for joint set classification which can use more than two surveyed features. A synthetic set of 8 joint set, each joint defined with 4 features (dip, dip direction, type of infilling and amount of infilling), created in a way that with two features (dip and dip direction) sets could not be differentiated. Necessary program developed to use Bayesian classifier to sort 8 synthetic joint sets in 4D space. Present study showed that all 8 sets can be successfully differentiated by using Bayesian method.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    123
  • End Page: 

    128
Measures: 
  • Citations: 

    0
  • Views: 

    151
  • Downloads: 

    108
Abstract: 

Kamtal intrusion is located in East Azarbaijan province, NW of Iran, near the Armenia border. The Kamtal intrusion consist of an acidic part with monzogranitic composition and an intermediate- basic part which compositionally composed of monzonite, monzodiorite, quartz  monzonite, quartz monzodiorite and gabbro. Gabbroic rocks exist in the form of small lenses in the southeast of Kamtal intrusion within the intermediate part. The intermediate- basic part has been intruded by the acidic part. Both acidic and intermediate parts are high-K calc-alkaline, metaluminous in character and classified as I-type granitoids; while, the gabbros have tholeiitic nature. Both acidic and intermediate rocks show a LREE rich pattern and high LREE/HREE ratio. These two parts have differences in MREE enrichment. From similarity in REE patterns of acidic and intermediate rocks a genetic relation can be discerned. Negative anomalies of Nb and Ti can be seen in all rock phases of the Kamtal intrusion, representing the subduction zone setting. Comparison of trace element variations with those of granitoid rocks of different tectonic settings show similarities between Kamtal intrusion and Andean volcanic arc granitoids. Furthermore, Kamtal intrusion can be classified as VAG based upon tectonic setting discrimination diagrams. It is concluded that, Kamtal intrusion probably is the result of Neotethys oceanic crust subduction beneath the Caucasus continental plate.  

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    129
  • End Page: 

    136
Measures: 
  • Citations: 

    0
  • Views: 

    292
  • Downloads: 

    100
Abstract: 

Arghash gold district is located in the eastern Sabzevar zone. The basement of this zone consists of Precambrian metamorphosed rocks and Paleozoic-Mesozoic epicontinental sediments. The basement is covered by Upper Cretaceous ophiolitic mélange and Tertiary magmatic and sedimentary rocks. Arghash district includes five gold-bearing vein systems, Au-I–Au-V, and one Sb vein, occurring in Tertiary intermediate to silicic volcanic rocks, tuffs, granite, and diorite. Intensive alteration, dominated by clay minerals, is confined to 1 to 5 m from the veins. The intensive argillic alteration is bordered by irregular zones of moderate to weak argillic and propylitic alterations.Mineralization is mostly confined to veins. Pyrite is the main sulfide mineral and includes four generations: 1) disseminated euhedral to anhedral, fine- to coarse-grained pyrite (Py-I), locally associated with minor chalcopyrite, marcasite, tetrahedrite-tennantite, and arsenopyrite; native gold grains occur in quartz associated with the pyrite; 2) framboidal pyrite (Py-II) which contains up to 960 ppm Au; 3) arsenian pyrite overgrowths (Py-III) which contain up to 1980 ppm Au; and 4) fracture-filling, anhedral, barren, late stage pyrite (Py-IV). Gold occurs as nanoparticles as well as unstable solid solutions in the framboidal and arsenian pyrite.Homogenization temperature (Th) and salinity were measured on fluid inclusions in several quartz and calcite samples. Th varies from 186o to 357oC, and 169o to 313oC, and salinity from 0.2 to 5.3 and 0.7 to 1.9 wt. percent NaCl equiv. for quartz and calcite, respectively. The low salinity character of the ore forming fluid is consistent with the ore mineralogy and metal contents. The variation in salinity and Th could be explained by a combination of boiling and mixing (dilution) of a hotter and more saline fluid with a cooler and less saline fluid. These processes led to the deposition of gold in the veins. The ore mineralogy, textures, alteration, homogenization temperatures, and salinities, are typical of low-sulfidation epithermal precious metal deposits.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    13
  • End Page: 

    18
Measures: 
  • Citations: 

    0
  • Views: 

    172
  • Downloads: 

    89
Abstract: 

Right lateral shear between Central Iran and Afghanestan caused activity of N-S and NW-SE fault zones in eastern Iran. Faults interaction effect on creation of restraining zones and out-crop of ophiolitic rocks along fault zones. Study of geometric and kinematic of structures approache to recognition of structural evolution in fault zones of North-North East Lut plain (north part of Sistan structural zone).The activation of different structural trends in eastern Iran, Sistan zone, causes a deformation style which is significant different from nearby structural zones. This is referred to the interaction of faults with dominant strike slip mechanism and different N-S and NW-SE trends. This interaction with the greater effect of N-S trends causes development of restraining zones and curved fold axial trends in area between the en-echelon areas of the N-S tending faults.From point of view of structural geology the study area could be divided in two main parts: A) Activity of N-S strike slip right-lateral fault zones construct wall damage zones and tip damage zones. En-echelon N-S faults construct link damage zones with ophiolitic out-crops in the overlap area (such as Kasrab and Torshab).B) Fault zones with NW-SE trend, have right-lateral shear with compressional component mechanism (such as SE Birjand and SE Qaen) that has resulted to a broad and continuous out-crops of ophiolitic rocks. Shortening of folded sedimentary rocks (Tertiary) increased in eastern Sahlabad (Hosseinabad, Pureng, Chakhoo, Shourak, Marghzar, Zahab) from north to south. As an accepted theory displacement increase toward the center part of faults, that could be seen Shooshk-Cheshmehzangi fault zone. This suggests that shortening is related to the fault movement. Unconformity between Tertiary and Cretaceous rocks, out-crop of ophiolitic rocks in the compression area, existence of NE-SW compressional axes along two major trends and growing of fault damage zones in the crossing of two major trends in the NNE Lut plain, demonstrate that major mentioned trends had contemporaneous activity. In the restraining zones, thrust faults causes surface emplacement of older ophiolitic rocks. The more exposure of these older rocks and presence of thrust faults in northern portion of the study area where NW-SE trending faults are abundant, imply the greater effect of the N-S trending faults. Since the major shortening axes in the Sistan zone are considered to be constant, increase in deformation through shortening measurements of the folds also constrain the greater effect of the N-S trending faults.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    137
  • End Page: 

    142
Measures: 
  • Citations: 

    1
  • Views: 

    157
  • Downloads: 

    91
Abstract: 

The shear wave velocity structure in Bam city is estimated in this paper. A double circle array observation of microtremors was conducted in south-east of Bam. Spatial Auto-correlation Coefficient (SPAC) method was utilized to determine phase velocity dispersion curve of Rayleigh wave in frequency range from 1.6 to 2.3 Hz. An inversion scheme based on Genetic Algorithm was employed to estimate the VS profile up to 400 m at the site under study. The inverted shear wave velocities are compared with the available down-hole data, and are found to be in good agreement. It verified the reliability of the estimated shear wave velocity profile and confirmed the use of SPAC method as a good alternative to the conventional approaches due to relatively low costs, ease of operation and analysis, accuracy, and ability to explore soil profile up to large depth.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    143
  • End Page: 

    148
Measures: 
  • Citations: 

    0
  • Views: 

    240
  • Downloads: 

    114
Abstract: 

Stabilization of potentially sliding terraces and natural slopes are of great importance from view point of resident security, environment protection, river engineering and water and soil conversation. Soil reinforcement using tree toots is one of methods being studied by many researchers. Most of them have worked on the effect of root density and few of them on the root diameter leading to contradicting results. In this paper the combined effect of root diameter and density on the shear resistance of soil is investigated by series of in-situ direct shear tests. Eighteen tests were carried out on soil having Willow roots and the results were compared with those of non rooted soil as reference. To explain the observations, a new parameter referred to as root diameter-density index (RDDI) was defined. The results reveal that an increase in RDDI causes a significant increase in the apparent cohesion of rooted soil, but a little decrease in the internal friction angle. In both cases the rate of variation decreases with increasing RDDI and tends to a little value; however the extreme values of 212% and -15% were observed respectively. As general conclusion for rooted soils, the dominance of variation of apparent cohesion with respect to that of internal friction angle results the shear resistance ameliorates within a range of RDDI, and for further values it tends to a stabilized value. Also, for practical purposes, a relation was developed to be used by designer engineers.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    149
  • End Page: 

    154
Measures: 
  • Citations: 

    0
  • Views: 

    240
  • Downloads: 

    125
Abstract: 

The Sharafabad auriferous epithermal vein system is located in the Alborz-Azarbaijan magmatic assemblage in northwestern Iran. The veins are hosted by Eocene andesitic volcanic and pyroclastic rocks and tuffs. Wall rock alteration includes an inner silicic zone often bordered by argillic and propylitic zones. Mineralization is mainly restricted to silica and silica-carbonate veins and veinlets in faults and fault zones. A total of 18 ore-bearing veins have been identified. The veins vary from 10 -1000 meters in length and 0.5-10 meters in width, respectively. Pyrite is the main sulfide, commonly associated with subordinate chalcopyrite, sphalerite, and galena. Gold occurs as scattered microscopic grains in quartz and pyrite, and along the grain boundaries of the sphalerite, galena and chalcopyrite. Silica occurs as gray quartz, white quartz, clear quartz, opal, chalcedony, and minor amethyst. On the basis of crosscutting relationships and mineral paragenesis, four stages can be distinguished: (I) pre-mineralization, (II) mineralization, (III) post-mineralization and (IV) supergene. The gold and the base metals sulfides occurred in the mineralization stage. Fluid inclusion data have been obtained from the ore-stage gray quartz and sphalerite, carbonates, and the late clear quartz and amethyst. The fluid inclusions from the gray quartz indicate homogenization temperatures of 170-270oC and salinities of 1 to 8.7 wt% NaCl equiv. The fluid inclusions in the sphalerite indicated homogenization temperatures of 215-265 ºC, and salinities of 10.8-15.3 wt% NaCl equiv. The carbonates formed at lower temperatures, between 160-250oC, from fluids of low salinities, at 1.5-3.8 wt% NaCl equiv. Amethyst from final stages of vein formation, not associated with sulfides and gold was deposited at 173-203oC from fluids containing 3.5 to 9.5 wt% NaCl equiv. The coexistence of vapor-dominant and liquid-dominant inclusions in quartz and sphalerite suggests that boiling occurred during the evolution of the ore fluids. The occurrence of boiling is supported by hydrothermal breccias, bladed calcite, and adularia. Fluid inclusion data suggest that ore was deposited at an average depth of about 400 m below the paleosurface. Considering the intermediate argillic alteration, association of gold with base metal sulfides, and the moderate salinities, the Sharafabad district can be classified as an intermediate-sulfidation epithermal system.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    155
  • End Page: 

    160
Measures: 
  • Citations: 

    0
  • Views: 

    187
  • Downloads: 

    80
Abstract: 

In this study work the idea of the optimal design of GPS monitoring network is extended in order to estimate the parameters of a single strike slip fault: i.e. slip rate and locking depth. By using some numerical examples, the influence of the GPS station distances from the fault trace has been investigated. The results show that far GPS stations have more advantages for estimating of slip rate. In contrast, the near stations are important for locking depth.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    161
  • End Page: 

    166
Measures: 
  • Citations: 

    0
  • Views: 

    200
  • Downloads: 

    107
Abstract: 

Occurrence of acid rains in the region adjacent to Sar Cheshmeh Copper Smelter, 155 km southwest of Kerman, was established by the measurement of pH of precipitations during 2005 and 2006. This paper deals with the geochemical behavior of Na, K and Zn in the entisols and inceptisols of Sar Cheshmeh region which was subjected to acid rains. Laboratory experiments were performed on 12 undisturbed soil core samples (50 cm long, 6 cm in diameter) with acid solutions of pH=3.1, pH=4.1 and pH=5.6. The sprinkling lasted 31 days, simulating a rainfall of 370 mm and the drainages were analyzed. Soil properties and forms of Na, K and Zn in 0-15cm, 15-50cm and 30-50cm depths determined before and after the simulation. Results show that some elements can be mobilized and leached out of the soils of the study area by the action of acid rain. Acid rain causes a decrease in the exchangeable form of sodium and potassium while soluble form of these elements increases. Furthermore, acid rain causes an increase in the available and soluble form of Zn.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    167
  • End Page: 

    172
Measures: 
  • Citations: 

    1
  • Views: 

    268
  • Downloads: 

    149
Abstract: 

Considering glaciers as a main source of potable water in Iran, their investigations and protection are necessary. It means their parameters such as maximum and minimum altitude, area and perimeter, position of snow line and etc, should be estimated. In a time and expenses point of view, regarding research difficulties in these areas when using direct measurements approach and field working, remote sensing technology seems to be useful and efficient. IRS and ASTER satellite images, Arial photographs and DEM, have been used to identify and estimate different glacier parameters of Khersan glacier in the Zardkuh Mountain. Using various unsupervised classification algorithms on Aster images, different parts of glaciers are classified. Feature space and spectral wave of snow and ice have been used to recognize various parts of glacier, such as ice, last years frozen snow as well as frost snow. Ultimately DEM, fused images, information extracted from classification methods, and vision interpretation, have been applied to up to date the old map of the region and extract the boundary of glacier.

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Writer: 

NAZARI HAMID | RITZ J.F.

Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    173
  • End Page: 

    176
Measures: 
  • Citations: 

    0
  • Views: 

    249
  • Downloads: 

    167
Keywords: 
Abstract: 

The Taleghan Fault is located at the southern side of Taleghan valley in Central Alborz, 50 km north west of the Tehran mega city. Usually described as a south-dipping reverse fault, it could be the source of some of the strongest historical earthquakes recorded in the Tehran region, notably the 958 AD (estimated magnitude M 7.7). The fault stands out as one of the major active structure menacing the cities of Tehran and Karadj, representing together 12 millions inhabitants. In order to analyze the recent activity of the fault, a morphological study was carried out along the fault combining satellite imagery, aerial photographs and Digital Elevation Model. We found out an active branch that had never been described whereas the fault classically mapped appears inactive. Detailed field work along the branch allows us to show that the fault had its vertical component recently reverted from reverse movement to normal movement. One of the measured ratios of accumulated horizontal / vertical displacements associated to the left lateral and normal movement is 2.5-5. The strike, estimated dip and rake in the eastern part are 105o, 60o and 40o respectinely making it a left lateral- normal strike slip fault in this part of the Central Alborz.

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Writer: 

KEBRIAEI ZADEH M.R.

Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    19
  • End Page: 

    30
Measures: 
  • Citations: 

    0
  • Views: 

    135
  • Downloads: 

    119
Abstract: 

Geirud Formation has a wide distribution in the Damghan region. The Formation Lithology is mostly composed of limestone, marly limestone, shale and quartizic sandstone and its thickness ranges from 10 - 200 meters. Brachiopoda of Geirud Formation in the southwest, north and northeast of Damghan region (Darvar, Simeh- Kuh and Deh- Molla sections) were studied and resulted in recognizing some species that are as follows:Schellwienella sp., Mesoplica sp., Sentosia sp., Schizophoria impressa, Leptagonia sp., Aulacella interlineata, Zaigunrostrum iranicum, Leptocaryorhynchus jamensis, Araratella dichotomians assimulata, Araratella sp., Centrorhynchus charakensis, Megalopterorhynchus chanakchiensis, Paurogastroderhynchus nalivkini, Paurogastroderhynchus bikniensis, Cleiothyridina coloradensis, Cleiothyridina sp., Athyris tau, Composita cf. globosa, Lamellosathyris sp., Cyrtospirifer sergunkovae, Cyrtospirifer sp., Cyrtiopsis graciosa chakhaensis, Cyrtiopsis lapparenti, Prospira struniana, Prospira lapparenti, Rigauxia cyrtinaeformis, Rigauxia crassiplicatus, Dichospirifer thylakistoides, Eobrachythyris sp., Toryniferella echinulata, Cryptonella sp.Based on the above mentioned Brachiopoda an age of Early Famennian-Late Famennian can be considered for carbonate part of Geirud Formation in the these sections.Also, Geirud Formation in the sections is equivalent with middle and upper parts (with the exception of Rossirhynchus biozone) of Geirud Formation in the type section (Central Alborz).

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Writer: 

GHANBARI ALI

Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    3
  • End Page: 

    8
Measures: 
  • Citations: 

    1
  • Views: 

    374
  • Downloads: 

    503
Abstract: 

The results of over 100 geotechnical site investigations in different zones of Tehran alluvium in the south part of Tehran city were analyzed to determine the correlation of modulus between elasticity and SPT number of soil in southern Tehran alluvium. The alluvial deposits in southern Tehran are composed mostly of fine-grained materials or coarse-grained soils with silt and clay particles. Based on the soil material properties, the study area is divided into three sections. In each section, the results of a large number of in situ and laboratory tests are classified and analyzed to determine the elastic modulus of soil. The study shows that, for the first part of the area the modulus of elasticity from plate load test correlates well with SPT number and for the second and third parts, the direct shear and triaxial tests have an acceptable correlation with SPT number. Formulas relating elastic modulus to standard penetration test number are given and compared to those reported in the literature. Also, from the analysis of data it was seen that the elastic modulus of soil is increased with increase of maximum soil particles. Finally average results for unconfined strengths of fine grained soil in alluvium of the south of Tehran are presented.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    31
  • End Page: 

    44
Measures: 
  • Citations: 

    0
  • Views: 

    165
  • Downloads: 

    98
Abstract: 

Peridotites (Cpx-bearing harzburgites, lherzolites, wherlites and dunites) associated with pegmatite gabbros, gabbro impregnations, gabbroic-diabasic dikes, pyroxenites and websterites are the main constituents of the mantle sequence in the Nain ophioliote assemblage. Petrographic and geochemical studies indicate that peridotites in the Nain ophiolites are Cpx-bearing harzburgites with Al-rich spinels (Cr#=16.12-41.55) equilibrated at about 1000oC. Pegmatite gabbros are found as small pockets within peridotites showing deformed clinopyroxenes and plagioclases. Gabbro-diabase dikes, mostly rodingitized, injected into the peridotites without chilled margins. These dikes are geochemically co-genetic with pillow lavas and micro-gabbros of the crustal sequence, but display variable degrees of partial melting. Based on the geochemistry of the mafic rocks and the peridotites, we suggest that Nain ophiolites were developed in a back arc spreading basin.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    45
  • End Page: 

    52
Measures: 
  • Citations: 

    0
  • Views: 

    502
  • Downloads: 

    298
Abstract: 

Organizational structure, along with goals, human resources and technology, is among the major elements of an organization. Hence, its study and analysis lead to more fundamental transformations and finally increase of organizational capabilities. In current research, organizational structure of Geological Survey of Iran (GSI) is studied and analyzed, aiming to identify the GSI status quo and provide it with an ideal structural model. To achieve desirable goals, an extensive literature review has been carried out. Then, a qualitative research methodology has been adopted and relevant data have been collected. All data have been triangulated using three different procedures: library research, conducting interviews with GSI skilled experts and studying on the organizational structures of 45 geological surveys. The comparative study on the structures of geological surveys has shown that the average number of levels in organizational hierarchy is 3.08 and the average number of major departments at the top organizational level is 6.4. These numbers for GSI are respectively 3 and 11. Furthermore, about 78% of geological surveys in the world use functional departmentation.With the help of the findings of this study, an adhocratic organizational structure has been suggested for GSI. Furthermore, some changes have been proposed to the current structure of GSI, such as separation of institutional and technical sections and use of matrix departmentation for project-based departments. To practically enjoy new structure, some changes to the nature of financial processes and establishment of a project management center for coordination of activities in project-based and functional departments have been suggested too.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    53
  • End Page: 

    62
Measures: 
  • Citations: 

    0
  • Views: 

    335
  • Downloads: 

    188
Abstract: 

Miveh–Rud area is located 50 km north of Tabriz and 65 km west of Ahar at 36o 33′ 02″to 38 o, 34′ 52″ N and 46o 12’ 20” to 46 o 14’ 35” E. The oldest rock unit in the area includes a thick sequence of Paleocene sedimentary rocks comprising of sandstone, shale, siltstone, marl and marly limestone that have been intruded by a porphyritic intrusive body and dykes of granodioritic to diabasic composition (probably Oligocene in age). The intrusive rocks resulted in the formation of hornfels, skarn and alteration in Paleocene rocks. All of the mentioned rock units are unconformably covered by Pliocene age trachyte, trachyandesite. Alteration of potassic, sericitic, argillic, propylithic and silicification types occurred in the subvolcanic and sedimentary rocks, while there is no observed alteration in the volcanic cover. Anomalies of Au, Ag, Sb, Cu, Bi, W and Mo detected by geochemical investigations are confirmed by field evidences.The anomalies of Sb, Ag, Au and As are located in the northern part, while the Cu, Co, W and Mo anomalies are in the southern part of the area. The degree of the contact metamorphism decreases toward the north and the potassic alteration can be shown mostly in the southern part of the area. This may suggest uplift and erosion of the southern part compared to northern part of the studied area. Composite halos of As, Pb, Ag / Cu, W and Co confirm the results. The mineralization includes formation of skarn, epithermal and sheeted veins. The epithermal veins cut the skarn and other contact metamorphic rocks.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    63
  • End Page: 

    68
Measures: 
  • Citations: 

    0
  • Views: 

    212
  • Downloads: 

    244
Abstract: 

There are a few iron deposits in the north and northeastern part of Semnan city that none of them has a systematic exploration background. Ojat_Abad deposit is one of them located in 63 km of north-east of Semnan at the southern side of Semnan-Damghan main road. A magnetic survey including 1200 measuring points has been recently performed to explore the deposit within an area of 89 acres. The prepared total and residual magnetic field maps clearly demonstrate the existence of iron anomaly at seven locations in a zone with northeast - southwest trend. In this paper, attempt has been made to obtain more qualitative and quantitative information for the recognized anomalies by performing two and three dimensional (2D, 3D) numerical modeling. To achieve the goal, the residual anomaly map, obtained by professional software called Modelvison Pro is used. It was found that the results of 2D and 3D modeling confirm each other in the most cases and in addition are in quite good agreement with the results of existing mining excavations. The obtained results also demonstrate the explored anomalies locate separately, and except one of them, all are located at a depth less than 35 meters.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    69
  • End Page: 

    80
Measures: 
  • Citations: 

    1
  • Views: 

    221
  • Downloads: 

    200
Abstract: 

Ahmad-Abad Zn, Pb (Mo) deposit is located in Central Iran and Posht-e-Badam Block. This deposit is limited in dolomitic units of Shotori Formation (Middle Triassic) with lens type geometry parallel to layering Ahmad-Abad Zn, Pb (Mo) mineralization which is a stratabound ore deposit and sometimes vein type. The result shows that the ranges of Zn are 5-20% (average 9%), Pb 5-9% (average 5%) and Mo 83 ppm to 3.09% (average 0.7%). The study of lithogeochemical sections indicates that mineralization has occurred in a specific stratigraphic position related to special sedimentary facies including dolomitic Oosparite Ooide grainstone dolosparite facies. Faloric and texture of ores include laminated, disseminated, open-space filling, massive, brecciated, vein and veinlet, stylolite fishing and replacement. The presence of textures such as laminated, disseminated and stylolite type which is related to Ooide grainstone reveals that ore formation has occurred during diagenetic stage in a bar environment.As a result of faults activing, formation of horst-graben structure and supergene processes in the region, ore minerals occur as non-sulfide (hemimorphite, cerussite, and wulfenite) and small amount of sulfides such as galena, sphalerite, wurtzite and pyrite. Fluorite, celestite and gypsum are also present in a minor amount. The lack of copper and silver is a significant characteristic of this deposit.Characteristics features of Ahmad-Abad ore deposit, including carbonate host rock, disseminated and laminated texture, lens-type geometry parallel to bedding, predominance of Zn over Pb, lack of igneous bodies, lack of Cu-Ag mineralization, indicate that the deposit formed in a situation and condition similar to Bleiberg Zn-Pb (-Mo) deposit in Austria.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    81
  • End Page: 

    84
Measures: 
  • Citations: 

    0
  • Views: 

    377
  • Downloads: 

    130
Abstract: 

A moderate earthquake (MW= 6.0) struck the Qeshm Island in the Hormozgan province on November 27, 2005 (17:22 GMT) and resulted in a severe damage and about 10 casualties. The main-shock was followed by an aftershock with magnitude MW=5.5 with different focal mechanisms from main-shock. A dense local network including 17 stations was installed in the region for aftershock study. Analysis of aftershock data shows diffuse distribution of the aftershocks; however, an alignment trending NW consistent with main shock focal mechanism is clear at depth. Two types of focal mechanisms can be observed: strike-slip and reverse. Diffused pattern of aftershock seismicity and focal mechanisms do not allow us to make a distinction between two possible explanations: occurrence of the second event in NW oriented strike-slip fault or partitioning of the deformation in the western border of the Hormoz Straight by reverse and left-lateral strike-slip faults.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    85
  • End Page: 

    90
Measures: 
  • Citations: 

    0
  • Views: 

    367
  • Downloads: 

    110
Abstract: 

The study area is located about 20 km to the east of the Heris town in northwest Iran, and lies in the Alborz-Azarbaijan geological zone. The occurrence of lava domes associated with thick lava flows, volcanic breccias, and ignimbrite layers indicate an important eruptive center in the study area. The investigated volcanic rocks are of lower-middle Eocene time and associated with upper Eocene I-type granitoid intrusions. Hydrothermal fluids derived from the granitoid rocks, considered to be cogenetic with the volcanic rocks, led to local alteration and mineralization in the volcanic rocks. According to chemical classification, the volcanic rocks are andesite, andesitic-basalt and trachy-andesite. The textures vary from porphyry to microlitic porphyry and hyalomicrolitic and the phenocrysts are mostly plagioclase, alkali-feldspar, augite, hornblende and biotite. Sieve texture and selective alteration in some plagioclases, occurrence of biotite and hornblende with opacitic rims, associated with other disequilibrium textures are characteristic features of the rocks. Plots of the samples on the SiO2 vs. Na2O+K2O, AFM, and SiO2 vs. K2O diagrams show that, similar to the associated granitoids, the volcanic rocks are high- to medium- potassium calc-alkaline in nature. Chemical characteristics of the rocks suggest enrichments in a subduction zone or crustal contamination, rather than a within-plate enrichment trend. Plots of Rb/Ba vs. Ti/Y, and Nb/Zr vs. Nb show that the chemical composition of these rocks were controlled typically by fractional crystallization and the role of magma mixing was not significant in the evolution of the rocks. Plots of the samples on tectonic setting discrimination diagrams of basalts and andesites, based on Th, Ti, Zr, Nb, and Sr contents, indicate that the studied rocks belong to calc-alkaline volcanic arcs. Compared to andesitic rocks from typical tectonic environments, the compatible and incompatible elements patterns for the andesitic rocks from the study area are more consistent with a post-collision volcanic arc setting.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    9
  • End Page: 

    12
Measures: 
  • Citations: 

    0
  • Views: 

    326
  • Downloads: 

    139
Abstract: 

Sabzevar ophiolitic belt is located in the northwest of Iran, north of Sabzevar. The current study is carried out for the first time in Iran with an exploration approach in the western part of the belt. Study of Platinum Group Elements (PGE) is of high importance for determining the genesis and economic evaluation of chromite deposits specifically in ophiolitic complexes. Chondrite-normalized PGE patterns of the chromitites related to ophiolites have a negative slope suggesting that during initial stages of magma crystallization, chromite preferentially removed compatible PGE from the magma. These patterns in the Sabzevar chromitites imply that these rocks are related to ophiolitic complexes (Alpine type). Chromite ore bodies which exhibit a relatively high incompatible/compatible element (Pd/Ir, Cu/Ni) ratios are derived from a more evolved magma with a lower fractional melting degree and do not seem to be of economic importance; this ratio in Al-rich chromites is higher than that of Cr-rich type. Pd/Ir ratio in Sabzevar chromitites on the average is less than 1, similar to many important chromite ore bodies related to ophiolitic complexes throughout the world. This ratio being low, as well as high chromium number (Cr/Cr+Al>0.60) suggests that this complex can be considered to contain a significant potential for economic and metallurgical chromite. Furthermore, the complex does not contain chromitites of uniform composition in chalcophile elements. PGE patterns of peridotites in the study area also show that these units in upper parts of the Gaft area are similar to ultramafic cumulates of oceanic crust, while in lower parts of Faroumad area related to mantle sequences.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    91
  • End Page: 

    96
Measures: 
  • Citations: 

    0
  • Views: 

    199
  • Downloads: 

    126
Abstract: 

Fars region in southwest Iran lies at the Zagros foreland and is bounded to the north and east by the Zagros thrust, to the west by the Kazerun fault, and to the south by the Hormoz Strait and the Persian Gulf. Thrust faults and associated folds are the main structures in the Fars region. The structures are trending NW to SE, the same trends as in the Zagros fold- thrust belt. The structural analysis of four anticlines in the interior Fars region based on the interpretation of seismic reflection lines and construction of structural sections on the basis of well data and field measurements indicates that fault propagation folds and fault detachment folds can be distinguished taking into consideration the geometry of the folds and the fault-fold relations. Based on measured parameters, the Ghareh Bulagh anticline is consistent with a fault propagation structure, while the Derz and Shirkhan anticlines with fault detachment structures. According to seismic reflection profiles and structural cross sections, the Chahkileh antiform is converted to a syncline at depth. The extent of shortening, based on the balanced structural cross sections, has been calculated to be around 14 percent.

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Journal: 

GEOSCIENCES

Issue Info: 
  • Year: 

    2009
  • Volume: 

    18
  • Issue: 

    71
  • Start Page: 

    97
  • End Page: 

    104
Measures: 
  • Citations: 

    0
  • Views: 

    182
  • Downloads: 

    84
Abstract: 

The Astaneh granitoid massif in the Sanandaj-Sirjan zone, covering an area of about 30 km2, located in 40 km to Arak city, is mainly composed of granodioritic rocks. They are widely affected by hydrothermal alteration and six alteration zones including phyllic (sericitic), chloritic, propylitic, argillic, albitic and tourmalinization zones are identified in this area. Calculations of chemical index of alteration (CIA) indicates that phyllic (sericitic), chloritic, propylitic, argillic, albitic and tourmalinization alteration zones underwent the hydrothermal alteration about 63.47%, 59.73%, 61.54%, 63.69%, 60.61%, 65.43% respectively. The mass changes of elements, based on Al (as a monitor immobile element), indicate that considerable amounts of oxides such as Fe2O3, MgO, CaO and TiO2 and also LFSEs such as K, Rb, Sr, Cs and Ba in all of the alteration zones were depleted. The results show that SiO2 was added to the phyllic (sericitic), argillic and tourmalinization alteration zones by metasomatizing fluids. Al2O3 was immobile and its mass was essentially unchanged during alteration. Other oxides such as MnO, Na2O, K2O and P2O5 and also LOI show dissimilar behaviors in the different zones. In all of the zones there is depletion in Sc and Y (HFSE). Also the Ga (except in chloritic zone) and U (except in phyllic zone) were depleted. In the phyllic zone, La, Ce, Pr, Nd (LREE), Sm, Eu, Gd (MREE) and Yb (HREE) were added; however, Dy, Er and Ho were depleted, whereas Tb and Lu were unchanged. In all zones the REEs were depleted except in the chloritic zone where Eu and Yb were added and Lu was essentially unchanged during alteration.

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