فصلنامه زمین شناسی ایران
پیاپی 65 (بهار 1402)

The study rocks outcropped in the northeast Semnan area. These rocks, composed of monzogabbro-monzodiorite, was intruded in the Eocene sedimentary and volcanic rocks. Plagioclase and clinopyroxene are the main constituent minerals of these rocks. The study rocks represent granular and poiiklitic textures. Based on EMPA data, clinopyroxenes, and plagioclases are diopside and augite and andesine, labradorite and bitonite in compositions and formed in temperatures ranged from 1104 to 1168 and less than 700 °C respectively. On the basis of tectonic discrimination diagrams, the investigated samples fall into volcanic arc domain resulted in subduction of Neothetian oceanic lithosphere beneath Central Iran block.

Bar dam has been constructed in northwest Neyshabur city, off-stream Bar river to provide the urban drinking water and Neyshabur steel factory water demand, respectively. The water balance of the Bar dam has indicated 35-70% water seepage from the dam reservoir during six trial water intakes. The significant seepage, high concentration of solutes in the leaked water, impact on water resources planning and projected allocations threaten the stability of the Bar dam. Analysis of the observation wells hydrograph indicated major water seepage from the central part of the foundation of the main dam site and minor seepage from other areas. water seepage modeling using MODFLOW software showed that 75% of the volume of the leaked water passed through the foundation of the main dam site. Furthermore, the chemical analysis of the leaked water samples indicated an increase in total dissolve solids to more than 5 to 10 times, especially in the central and left areas of the dam reservoir. The amount of the dissolved material due to water seepage from the main dam site was calculated based on the data collected from the modeling of water seepage from the dam reservoir, results of hydrochemical sampling, time series analysis of the seepage rate, and mass balance of the dam reservoir water. Finally, the effect of dissolution on the increase of porosity was investigated and based on the results,the maximum annual development of porosity in the middle part of the main dam axis was about 0.06%.

The study area is located in the south of Qushadagh mountain range, in the north of Asbkhan village, Heris township and in East Azarbaijan province. In terms of structural geology of Iran, this area is located in the main zone of Central Iran and Alborz-Azerbaijan sub-zone. The geological units of the region are including Eocene igneous and pyroclastic rocks with combination of andesitic, Trachyandesitic, basaltic, tuffic and ignembritic. The semi-deep intrusive mass with Oligocene age, with the combination of quartz diorite, diorite and quartz monzonite in the form of stock and dyke is exposed in the area. Structural studies, including fault plates, slickenside on them, and the joints system in various lithologies, indicate at least two general stress directions in the range, Which can be created following one tectonic regime or two tectonic regimes. If we consider the tectonic regime as a phase and consider the tensors with different directions as the result of rotation in the fault plates, We can introduce a general strike-slip regime with a general north-south trend that controls the existing structures of the region. At the same time, the infiltration of intrusive masses has caused the disintegration of these structures and made the issue more complicated. In general, faults with a northwest-southeast trend and a right on strike-slip mechanism, form the main structures of the area.Other faults are controlled by the main structures following the Riddle fractures system. Based on the system of joints in four different lithologies, lithological units from old to new include: basaltic andesite, quartz diorite, quartz monzonite (porphyry mass) and diorite, which from old to new reduces the diversity of the joints system. The northwest-southeast tectonic system has been involved in the development of argillic alteration and the northeast-southwest system has been important in the development of siliceous and mineralized veins.

Ghezeljeh deposit is located in the Central Iranian zone, in the Zanjan province and northeast of the Mahneshan city. The rock units in this area belongs to the Oligo-Miocene, which contain Lower Red, Qom and Upper Red formations. The Upper Red Formation in Ghezeljeh region has about 750 m thickness and mainly consists of brown to green marl intercalations with sandstones. In this area, the alternation of marl and sandstone sequences contain sandstone layers with thickness about 2 to 8 meters, which in two horizons, the copper-lead and zinc mineralization has occurred. Copper mineralization, in addition to being observed inside the sandstone unit. In the Ghezeljeh deposit, the host rocks of the copper ores, are gray sandstones and conglomerates which are intercalated with red and gray marl units. According to field and microscopic studies, the main ore mineral consist of pyrite, chalcocite, chalcopyrite, bornite, galena and sphalerite which associated with the secondary minerals such as serosite, malachite, azurite, covellite, smithzonite and goethite. The ore mineral textures consist of disseminate, framboidal pyrite, solution seams, interparticle cement, replacement and relict. Preliminary fieldwork studies in the Ghezeljeh region also show that organic matter including plant remains and diagenetic pyrite are the effective factors to concentrate and mineralization. It is considerable that the grade of lead, zinc and copper, in Ghezeljeh deposit are 6%, 3% and 1%, respectively. Generally, host rock, tectonic setting, sedimentary environment, mineralogy, texture, mineralization control factors all confirm that the studied mineralization has more similarities with Redbed type copper deposits.

The study area is located in 25 km SE of Ahar and 40 km NW of Meshkin-Shahr around Naqadouz village. Hydrothermal alteration has resulted in the developing of Argillic, Argillic - Silicic, Silicic and propilitic zones in this area. Based on petrographic studies, the altered rocks are basaltic andesite, andesite, dacite, rhyolite and lithic tuff in composition, with porphyry, glomeroporphyry, hyalomicrolithic and microlithic porphyric textures. The XRD analysis of altered samples show cristobalite, natrilite, kaolinite, quartz, albite, sanidine and orthoclase as the main minerals. Geochemical studies indicate that the alteration fluid has hydrothermal source and supergene processes are more important than hypogene processes. In this study, we use the immobile element method to calculate mass-changes and trace elements transmission amount during hydrothermal alteration. The Eu/Eu* ratio is higher in altered samples than relatively unaltered samples and the ratio of Ce/Ce* is more than 1for the relatively unaltered and most altered samples. The ratio of (La/Yb) n indicated that the depletion of HREE in altered samples is more than LREE, and LREE enrichment can increase this ratio. The lower ratio of (Tb/Yb) n in altered than unaltered samples indicate less depletion of HREE relative to MREE. Considering the distribution pattern of REE’s in alteration zones, it seems that the behavior of elements are controlled by pH, T & P changes, Eh, preferred absorption by clayey and iron oxide minerals and ligands frequency including SO2-4 , PO4+3 , CI-, F-, CO2-3 .

Palynological data are used for palynostratigraphy and reconstruction of some environmental parameters of the Middle Jurassic (Bajocian - Callovian) deposits at the Tapal stratigraphic section, west of Shahrood, eastern Alborz. The studied strata (Dalichai Formation) contain diverse, relatively well-preserved palynofloras, including miospores (spores and pollens), dinoflagellates cysts, fungal spores, foraminiferal test linings, acritarchs and Tasmanites. The palynofloras include 22 species of spores (belonging to 18 genera), 15 species of pollen (attributed to 9 genera) and 28 species of dinoflagellate cysts (assigned to 15 genera). Based on the stratigraphic distribution of miospores, the Klukisporites variegatus-Araucariacites australis-Cerebropollenites macroverrucosus Assemblage Zone is recognized in the sequence examined, Presence of some index dinoflagellate species led to the identification of three successive biozones including, in an ascending order, Cribroperidinium crispum Total Range Zone (late Bajocian), Dichadogonyaulax sellwoodii Interval Zone (Bathonian – early Callovian) and Ctenidodinum continuum Interval Biozone (early - middle Callovian). To reconstruct some parameters of the sedimentary environments of the studied strata, evidences such as frequency and diversity of spores attributable to ferns, relative abundance of drier/wetter and warmer/cooler elements in different plant communities, ratio of palynological elements and palynofacies, presence of index shallow water dinoflagellate cysts for instance Dichadogonyaulax sellwoodii, Ctenidodinium spp., Valensiella ovulum, Pareodinia spp., Nannoceratopsis gracilis, abundance of proximate dinocysts forms, presence of fungal spores and warm - temperate water dinoflagellate (Gonyaulacysta centriconnata, Nannoceratopsis pellucida, Gonyaulacysta jurassica, Pareodinia ceratophora) are utilized. Based on the above criteria, the material examined seems to have been deposited in a marine margin, low oxygen environment, with low rate sedimentation, under hot and humid climate conditions, where the surrounding terrestrial vegetation was dominated by ferns.