Economic Geology
Mahin Zolfaghari; Ghasem Nabatian; Amir Morteza AzimZadeh; Maryam Honarmand; P. Azizi
Abstract
Pirgheshlagh Cu-Zn-Pb deposit is located in the Central Iranian zone, north-east of the Mahneshan in the Zanjan province. The Kahar Formation with Precambrian age is the oldest Formation in the area which cutted by the granitic dykes. The Pirgheshlagh Cu-Zn-Pb mineralization occurred mainly as tabular-shape ...
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Pirgheshlagh Cu-Zn-Pb deposit is located in the Central Iranian zone, north-east of the Mahneshan in the Zanjan province. The Kahar Formation with Precambrian age is the oldest Formation in the area which cutted by the granitic dykes. The Pirgheshlagh Cu-Zn-Pb mineralization occurred mainly as tabular-shape within the metamorphosed sandstones, meta-andesitic tuff, meta-crystal lithic tuff and meta-andesite rocks. Based on the field and microscopic studies, the main minerals consist of chalcopyrite, sphalerite, galena, pyrite, arsenopyrite and minor magnetite. The ore textures consist of disseminated, laminated, massive and veinlet which the veinlet texture is occurred mainly in the lower part of deposit. Secondary minerals such as smithsonite, cerrusite, chalcocite, covellite, malachite, azurite, goethite and lepidochrosite have formed during supergene processes. The main alterations in the Pirgheshlagh deposit include silicic, sericitic, chlorite and carbonate. The results of this study suggest that the Cu-Zn-Pb mineralization in the Pirgheshlagh deposit is a Besshi-type valcogenic massive sulfide (VMS) mineralization.
A Ahmadi-Torkmani; M.R Ghassemi
Abstract
The present research uses precise field data to provide a balanced cross-section of the Mahneshan area, and investigate nature of depth distribution of its major structures. Our structural studies indicate that the Mahneshan and Anguran faults are two major faults, which penetrate deep into the crust ...
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The present research uses precise field data to provide a balanced cross-section of the Mahneshan area, and investigate nature of depth distribution of its major structures. Our structural studies indicate that the Mahneshan and Anguran faults are two major faults, which penetrate deep into the crust and cause a considerable amount of horizontal shortening in the area. In a more specific way, the Anguran fault roots deep into the middle crustal levels of about 21 km, and thrusts the whole Phanerozoic sequence and even parts of the Precambrian basement rocks over the younger strata. We believe that the abovementioned thrust originates not from a low-competency decollement plane, but from a ductile shear zone in deep crust. Evidences for development and conditions of such shear zone are present in the Precambrian basement rocks of the Anguran fault’s hanging-wall. We suggest that the decollement surface for the Mahneshan thrust, which is located in the shallower depths (13 km), is related to probable occurrence of evaporitic materials equivalent to the Hormoz Series beneath the Kahar Formation. Syn-sedimentary deformation within the Qom Formation in the hanging-wall of the Anguran thrust, as well as other evidences present in Neogene deposits of the area suggest that the thrust fault has been active since Oligocene. Restoration of displacements across the Anguran fault, and comparing the results with inception age for the fault suggests that the Anguran fault has been active with a slip rate of about 1 mm/yr. The structural features in the Mahneshan area indicate that thick-skinned faulting along with thin-skinned tectonics have resulted in a considerable amount of thickening of the crust in the region; this observation is in accordance with abovementioned characteristic of the crust in the Sanandaj-Sirjan zone.
J. Daneshian; M. Shahrabi; M. Akhlaghi
Abstract
75 samples of the Qom Formation in Andabad, northeast Mahneshan, were investigated. The Qom Formation in the examined section with a thickness of 301m, mainly consists of limestone and marl, and disconformably overlies the Lower Red Formation and lies under the sediments of the Upper Red Formation. A ...
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75 samples of the Qom Formation in Andabad, northeast Mahneshan, were investigated. The Qom Formation in the examined section with a thickness of 301m, mainly consists of limestone and marl, and disconformably overlies the Lower Red Formation and lies under the sediments of the Upper Red Formation. A study of foraminifera was led to identifying 42 genera and 70 species of the benthonic and plankthonic foraminifera, which 37 genera and 57 species is reported from this area for the first time. Among them, benthonic foraminifera have more varieties and abundances, and used for biostratigraghy. Based on the identified foraminifera, the Andabad section is comparable to Assemblages Zone 1 and 2 introduced by Adams and Bourgeois. On the basis of occurrence of the index foraminiferal species and their stratigraphic distribution, the age of the Qom Formation in the studied section is Early Miocene (Late Aquitanian to Burdigalian).The assemblage, abundance, and species diversity of foraminifera in the examined samples shows noticeable changes in the paleoenvironmental conditions. The maximum diversity of foraminifera is sixteen species. Based on species diversity, the strata classified to nine assemblages A to I. The abundance of foraminifera in each assemblage indicates that the sediments of the Qom Formation belong to inner shelf environments.
