فصلنامه زمین شناسی ایران
پیاپی 67 (پاییز 1402)

Jeirud Phosphorite Mine is located in the phosphate-rich horizon of the Jeirud Formation of the Lower Devonian sediments in central parts of Alborz geotectonic zone, North of Iran. The sediments of this formation are mostly composed of detrital rocks such as sandstone, sandy shales and sandy limestones. Phosphorite mineralization is mainly concentrated in the shales of middle parts of the Jeirud Formation. In this research, we have studied the concentration and the possibility of exploitation of rare earth and radioactive elements in these phosphorites. Lithogeochemical samples were randomly collected from phosphorite horizons. The samples were analysed by ICP-MS and ICP-OES not only for REE but also for major oxides and radioactive elements. The geochemical data show that the average of P2O5 is 29.60 %. The average of U and Th is 4.97 and 8.64 ppm respectively. Also, this data show that concentration of REEs in these samples are , 3times more than rare earth elements in North American shales (NASC) and 2.6 times more than Past Archaen shales (PAAS). REE concentration of these phosphorites were normalised to North American shales (NASC) and Past Archaen shales (PAAS). The spider diagram shows positive patterns to REE, especially in Ce and Eu. Also, this spider diagram represents the diffrentiation of LREE with respect to HREE. This diffrentiation occurred due to preferential absorption mechanism and during late diagenesis in these sediments. The average concentration of P and REE is realtively high and it seems to be economic for next minning activites. But the average concentration of U and Th is too low and not economic for exploration.

In this paper it is attempted to reconstruct the depositional environment of the Jeirud Formation in Aro section. The Jeirud Formation (Late Devonian) is composed of about 45 meters of clastic sedimentary units in the southwest of Firoozkuh city, southern Alborz area. To carry out this research a field work was done during which a precise and detailed sedimentary log of the section was prepared and 52 samples from different lithologies of the formation were collected. Thin sections were prepared from all conglomeratic and sandstone samples, besides some thin sections were prepared from mudrocks and just 1 sample of paleosoil and then all were petrographically studied. In the study area, both basal and top boundary of the Jeirud Formation is disconformable with Mila and Mobarak formations respectively. All facies in the section include clastics (conglomerates, sandstones, mudstones and a paleosoil horizon). The facies were classified based on Miall classification so that conglomeratic facies comprise Gcm and Gmm; sandstone facies comprise Sh, Sp and Sm and mudrocks include Fl and Fm facies. Combined field and lab studies resulted in identification of two sedimentary facies associations including channel fill and flood plain facies associations. The reconstructed sedimentary environment of the Jeirud Formation in the Aro area represents a braided river depositional environment. The lower parts of this formation represent a finning-upward sequence which indicates deposition within a braided river channel subenvironment (conglomerates and sandstones) and the upper part is dominated with mudrocks with a paleosoil horizon representing deposition in a flood plain subenvironment.

Calculating the amount of shortening, the angle between ridges, the slope of the main thrust and the percentage of thinning of the front ridge compared to the back ridge in the middle and northwestern parts of Sulabder anticline shows the folding style related to fault propagation in these parts. The calculation of these geometrical parameters in the south-eastern part of the Sulabder anticline also shows the faulted detachment folding style. The change of folding class from 1c to 2 and 3, as well as the change of fold style from detachment folds to fault propagation style, are a sign of increased shortening, deformation progress and evolution of folding from the south-eastern part. This represents that in the initial stage the thrust fault system belongs to the middle and north-western parts, which are in the developed stages of the thrust fault system. The interpretation of seismic sections perpendicular to the Sulabder anticline in different sections shows that the Sulabder anticline in a raised wedge form is higher than the adjacent structures due to the action of the thrust faults on the northern and southern edges. In the Solabdar anticline, the performance and mobile behavior of marl-shale units of Pabdeh and Gurpi formations, due to its high thickness and formable rheology as an intermediate separation horizon, create different folding styles at the top and bottom of this unit. It also caused displacement in the axis of the upper and deeper parts of anticlines.

The Oligo-Miocene Asmari Formation forms the main reservoir rock of many Dezful Embayment fields. Microfacies analysis, diagenetic features, and sequence stratigraphic evaluation of the Asmari Formation were carried out based on the petrographic investigation, petrophysical logs, and core measurement porosity and permeability data. Petrographic analyses led to the identification of twelve microfacies indicating five subenvironments including tidal flat, lagoon, barrier (belonging to inner ramp), middle ramp, and outer ramp, all of which are representing a homoclinal ramp. Tidal flat, lagoonal, and barrier microfacies are mostly present in the upper parts of the Asmari Formation, while middle and outer ramp microfacies were largely developed in the middle part. Cementation, compaction, dolomitization, dissolution, and fracturing are the main diagenetic processes in this formation. Compaction and cementation have negatively affected reservoir quality while fracturing, dolomitization, and dissolution contributed to reservoir quality enhancement. The sequence stratigraphic studies represent three 3rd order sequences of early Aquitanian, late Aquitanian, and early Burdigalian age based on the main features of microfaces, their depositional environments, and shallowing and deepening-upward trends. Microfacies of the Transgressive System Tract (TST) have been affected by compaction, dissolution (moldic), cementation, and slightly dolomitization in the middle to outer ramp parts. The Highstand System Tract in the inner ramp part has been affected by dolomitization, dissolution, and fracturing close to the sequence boundaries, and has a better reservoir quality than the Transgressive System Tract.

Arsenic is one of the heavy metals having harmful effects on human health if enters into the environment and water resources, so the major challenge of arsenic exposure is related to drinking water. The study area is Takab watershed in West Azarbaijan, which includes two large Zarshouran and Agh Dareh gold mines in Carlin type. Carlin gold mines are sulphidic that are able to pollute the downstream environmental resources such as arsenic. In this work, the carcinogenic and non-carcinogenic health risks associated with arsenic was evaluated for the human community, who are living in Takab watershed and are exposed to arsenic through oral and dermal pathways with contaminated water sources . 45 water samples were randomly collected from surface and groundwater resources in the study area with regard to expert judgment and the distribution points, analyzed by ICP-MS method. Then, the health risk was assessed using by target cancer risk (TR), risk coefficient (HQ) and index hazard (HI). The total results showed that arsenic contamination is derived from volcanic activities and Quaternary alteration and gold mining activities in the east and north of the region. Most of the samples were revealed a range of 9-10 and -100 to -250 mV as pH and oxidation-reduction potential, respectively, which indicates the predominance of arsenate species (As5+) in the form of H2AsO4-. HQ and HI values are more than 10 in 52% of the samples, which indicate the high health risk in people living in the study area. Carcinogenic risk level varies from 0 to 2×10-7, which shows no carcinogenic risk to very high risk by arsenic contamination in water resources. Overall, there are both risks of carcinogenesis and non-cancerous impact in the east and north of the region for intake by ingestion, drinking and skin contact due to water contamination from the natural and anthropogenic sources. Therefore, it is recommended to pay special attention to continuous monitoring for potential contaminant, different methods for preventing exposure to polluted water resources and treatment methods in order to minimize the health risk of the population.

The northwest zone of Saveh city is located in the Indes, Kooshk e Nosrat, Avaj, and Aipak fault zones. Indes, Kooshk e Nosrat, Avaj, and Aipak faults are considered the major faults in central Iran, which are also active in the Quaternary, and their last movements are attributed to the present time. Therefore, the estimation of morphometry to identify the effect of active tectonics on the tectonic evolution of drainage basins seems necessary. In this study, six important morphotectonic indices were analyzed including the longitudinal gradient of the river, asymmetry of the drainage basin, hypsometric integral, drainage basin shape, the ratio of the floor width to the valley height, and mountain front. To model the formation of basins in the studied area, Arc Hydro software (Arc GIS add-ins) was used based on data derived from a digital elevation model. Then, 6 morphotectonic indices were compiled and classified on each of the basins. Finally, the Active Tectonic Index (IAT) was calculated, according to which the study area was classified into 4 categories including very high, high, intermediate, and low tectonic activity. According to the IAT index, 5% of the study area shows very high tectonic activity, 25% of the studied area has high tectonic activity, 65% of it has average tectonic activity and about 5% of the tectonic activity is low. Moreover, seismic acceleration was prepared to confirm the result of morphological indices in the estimation and analysis of active tectonics in the region. In this study, the highest level of tectonic activity can be seen in the north-eastern part of the area. In most sectors, the level of activity is high and intermediate, which is related to the activity of Kooshk-e-Nosrat, Aipak, and Avaj faults.