Economic Geology
Maryam Emami Jafari; Saeed Alirezaei; Iraj Rasa; Jochen Kolb
Abstract
The Hired gold deposit in the Lut block, East Iran, is closely associated with an intermediate-mafic intrusive complex consisting of granodiorite to diorite, hornblende quartz-monzonite, and gabbro-diorite intruded into Eocene volcanic rocks. The intrusions are distinguished by high contents of CaO, ...
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The Hired gold deposit in the Lut block, East Iran, is closely associated with an intermediate-mafic intrusive complex consisting of granodiorite to diorite, hornblende quartz-monzonite, and gabbro-diorite intruded into Eocene volcanic rocks. The intrusions are distinguished by high contents of CaO, FeOt, and MgO, and rather low K2O+Na2O implying they crystallized from weakly differentiated magmas. This subject, and the relatively high Mg# (36.36 to 52.32) imply the involvement of a mantle source in the production of the parent magma. The intrusions are metaluminous, calc-alkaline to high-K calc-alkaline, and distinguished by the occurrence of ilmenite as an accessory mineral. Mineralization occurs in veins and veinlets disseminations in the granodiorite intrusion and the volcanic rocks, closely associated with tourmaline, silicic, and carbonate alterations, and is distinguished by abundant pyrrhotite, arsenopyrite, pyrite, and minor chalcopyrite, galena and sphalerite. Gold occurs mostly as submicroscopic grains in the pyrite and arsenopyrite. The mineralogical and geochemical attributes of the intrusive complex, and the ore mineralogy, allow the Hired to be classified as a gold deposit related to reduced I-type granitoids. The reducing nature of the parent magma can be explained by introduction of reduced crustal materials into the source area, and/or assimilation of carbonaceous metasedimentary rocks.
M. R. Bakhshi Mohebbi; A. A. Moridi farimani; R. Moezzi nasab
Abstract
Among the sedimentary units of the east flysch basin in the Nosrat-Abad area, where in the 105km northwest of Zahedan, there is a sandstone-conglomerate unit with an Oligo-Miocene age. The depositional environment of this deposit was fluvial which has been morphologically dissected in several portions; ...
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Among the sedimentary units of the east flysch basin in the Nosrat-Abad area, where in the 105km northwest of Zahedan, there is a sandstone-conglomerate unit with an Oligo-Miocene age. The depositional environment of this deposit was fluvial which has been morphologically dissected in several portions; this unit covers the Eocene sandstone-shale deposits by an angular unconformity about 30 degrees. The measured thickness is about 2650 meters. The composed particles and pebbles are in various grain size. On the other hand, sandstone, siltstone, and mudstone accompany the conglomerate unit. Field observations document the unit was formed in a fluvial depositional environment. Imbrication and cross, smooth, and lens-shaped bedding are the main recognizable sedimentary structures. Moreover, the caved and filled structure are seen. Note that there is difference between the lithology of the pebbles in the conglomerate and the rocks composing the flysch zone, the pebbles could be originated from the west side, where in the Lut block. The recognized fossils from limestone pebbles are belong to the families such as Orbitolina, Alveolina, Nummulite, and Miliolid, consequently, the age of conglomerate-sandstone unit must be younger than Eocene and cover by Conglomarate Quaternary probably could be Oilgo-Miocene.
M.A Alimi; M.M Khatib; KH Hessami Azar; M.R Hayhat
Abstract
An array of en-echelon strike-slip faults in eastern Iran results in the formation of releasing and restraining bends or stepovers, within which some faults are hidden in the extensional and contractional parts of the structures. This is investigated in the East Neh-Esmaeilabad left-stepping restraining ...
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An array of en-echelon strike-slip faults in eastern Iran results in the formation of releasing and restraining bends or stepovers, within which some faults are hidden in the extensional and contractional parts of the structures. This is investigated in the East Neh-Esmaeilabad left-stepping restraining stepover. Transpressional deformation in the transverse structure associated with the stepover is expressed as folding and uplifting in the Late Neogene, Quaternary and recent deposits, revealing the Shusf fault as a hidden and blind thrust. Processing of magnetic anomaly maps shows the existence of the Shusf magnetic lineament, which consistently well correlates with the Shusf fault and its hidden segments. Also the hidden part of the fault was investigated by the differential GPS profiles constructed perpendicular to the trend of the Shusf fault scarp. In this study, we used surface morphology surveys, fan median method and satellite images to calculate the cumulative horizontal and vertical offsets related to the Late Quaternary active tectonics along the Shusf fault, measuring mean values of 92 and 4.25 m, respectively. Analysis of the velocity vector recorded in the Nehbandan geodynamic station across the Shusf fault indicates the present-day evolution of the stepover expressed as uplift and left-lateral displacement.
E. Gholami; M. A. A. Nogole sadat; M. M. Khatib; A. Yassaghi
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 ...
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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.
