نشریه علوم زمین خوارزمی
سال هفتم شماره 1 (بهار و تابستان 1400)

Takht coal mine located in the Gheshlagh coal-bearing large synclinorium in northern flank of the Alborz Mountains in East of Golestan province has been investigated for evaluation of concentration of trace elements such as gallium (Ga), germanium (Ge), vanadium (V), scandium (Sc), uranium (U), lanthanum (La) and cerium (Ce). Coal samples studied in this research were categorized into bituminous, sub-bituminous-lignite, lignite and peat types according to chemical analysis of major element (CHNS wt%) constructing the coals. ICP-MS analysis of coal samples show that most of trace elements in Takht coal mine have very low concentrations to those of hard and brown coals around the world, however they displayed slightly enrichment in V (up to 88 ppm), Zr (up to 96 ppm) and Sc (up to 16) compared to global average concentration in coals. Low concentration of trace elements in the Takht coal mine could be attributed to inherent poverty of the Shemshak sedimentary basin of such elements. It could be related to the absence of trace elements-bearing source rocks (e.g., granitoids, carbonatites, pegmatites and periodotites) as source rocks of Shemshak Group sediments in the study area. Therefore, it seems that formation and evolution of the Shemshak Group is occurred in a sedimentary basin with normal concentrations of the trace elements that led to formation of a trace element-poor coals.

In this study, the pollution of the Revenj River sediments with heavy elements has been studied. Revenj River catchment with an area of ​​131 Km2 is located 20 kilometers from the city of Torbat-e-Jam (northeast of Iran). To investigate the contamination of sediments with heavy elements, 15 samples of sediments were taken from the area and analyzed by ICP-MS. In order to monitor the contamination of Revenj River sediments with heavy elements, Enrichment Factor and Contamination Factor were used. Chromium with low eenrichment and iron and nickel with no enrichment have similar geochemical behavior and originate from weathering and erosion of ultramafic rock units and have caused low pollution. Arsenic and lead are low pollution and copper is moderately pollution in the area. Shemshak Formation has led to a focus on arsenic and lead pollution at the beginning of the Revenj River catchment. The passage of tributaries over the granite units and the confluence of these tributaries at the end of the catchment with the Revenj River has led to relatively severe enrichment and contamination of copper and lead in the sediments at the end of this catchment. The pollution load index shows the concentration of pollution at the beginning and end of the catchment area, which is in line with the previous indicators.

Talesh alkali basalts (TAB), accompanied by Upper Cretaceous sedimentary units, are exposed in the western Alborz (North of Iran). Clinopyroxene, plagioclase, ± alkali feldspar are the main minerals in these rocks. The geochemical characters such as high contents of TiO2 (1.68-2.96 wt.%), K2O+Na2O (3.09-9.06 wt.%), and high ratios of (La/Yb)N (9.3-23.4), and Nb/Y>1(1.51-3.9), are consistent with their alkaline composition. In the primitive mantle-normalized multi-elements diagram, these rocks show enrichment of all incompatible elements that are similar to intraplate basalts or oceanic island basalts (OIB). The trace element ratios such as Zr/Y (5.52-10.80), Ta/Yb (1.12-2.65), Th/Yb (1.80-5.81), and Ti/Y (418-753) plot within the range of the alkali within plate basalt. Therefore, the Talesh area in the western Alborz recorded an intra-continental volcanic activity during the Late Cretaceous. This magmatism was generated by lower partial melting (3-7%) of an EMII-enriched asthenospheric mantle source of garnet lherzolite facies. The presence of the high-Ti alkali basalts in Talesh and other parts of western and central Alborz (such as southern Lahijan and Marzanabad basalts) to Georgia could be interpreted by forming a rift system on the southern margin of Eurasia from the Lesser Caucasus to the central Alborz during the Late Cretaceous.

Gholeh- Sukhteh sub-volcanic intrusion as part of the Toroud – Chah-Shirin magmatic belt, is located in the northern part of Central Iranian structural zone. A volcano-pyroclastic sequence of Eocene including of red-purple tuffs, volcanic breccia, and agglomerate is the host rocks. In order to investigation of the emplacement mechanism of this sub-volcanic intrusion, anisotropy of magnetic susceptibility (AMS) is used. The pluton is dioritic porphyry and belongs to ferromagnetic and magnetite series granites. Presence of magnetite is confirmed by microscopic observations and mineral chemistry. The highest degree of anisotropy (P%) that is sign of strain, is observed at the northern east to west - southwest of the intrusion. Highest areas and around the roof of Gholeh-Sukhteh intrusion, shaped parameter (T) is oblate. Some stations at the south-western part of intrusion have high-plunge magnetic lineations and prolate shape parameters. This part can be considered as feeder zone. Furthermore, the circular to ellipsoid shape of the pluton, roughly concentric magnetic pattern through the sub-volcanic intrusion, intense crushing and deformation at the country rocks especially at western margins are the main evidences that the pluton emplaced as a balloon.

The Arghun intrusion is located in the southwest of Mahneshan and has penetrated in the Precambrian metamorphic rocks. The study area is part of the Central Iran zone. Lithologically, the main composition of this intrusion is gabbro and it has the mineralogical composition of plagioclase, pyroxene, hornblende and opaque minerals. Based on the geochemical composition, the magmatic nature of the study rocks is calc-alkaline. Their normalized REE pattern to the chondrite shows the enrichment of LREEs relative to HREEs. The negative anomalies of the Nb and Ti elements are observed in the spider diagrams normalized to the chondrite, which is characteristic of the subduction zone magmatism (active continental margin arc and island arc magmas). Also, LILEs enrichment and depletion of HFSEs elements indicate subduction arc magmas. The tectonic setting discriminant diagrams also show the characteristics of the island arcs and the active continental margin. Also, the study of the spider diagrams shows the involvement of subduction fluids in the formation of the study rocks. Comparison of the study gabbro intrusion with the north of the Takht-e-Soleiman intrusion and Aghdareh granite indicates that the magmatic series are the same and their spider diagram pattern are similar.

Anomaly XVI-B located in Central Iran Structural Zone. The oldest rock formations in this study area are related to metamorphic rocks which are included gneiss, micaschist, amphibolite and megmatite. Mineralized intruded mass distinguished by alkaline diorite-syenite that cut Bonoshorow metamorphic complex and limestone units. Metallic mineralization is occurred in syenite, gabbro and skarn rocks. Magnetite is the most abundant mineral in anomaly XVI-B and also it has been seen as stripe, mass, disseminated and filling empty space textures. The magnetite grains are shaped to shapeless. Magnetite is oxidized near the surface and converts to hematite, goethite and other iron oxides. Another metallic mineral which are associated with magnetite are pyrite, and chalcopyrite, which have been found in quartz, actinolite, calcite, and epidotite that come with various forms within host rocks, syenite, gabbro, and skarn. According to the graphs of rare earth elements in iron mineralization and intruded units indicates the possible similarity of the source of iron mineralization with intruded mass. The grade of iron oxide in ore deposit varies between 25 and 75 percent. The iron element has a negative correlation with oxide of titanium oxides, magnesium, manganese, phosphorus, potassium and sodium. Based on cobalt relationship with nickel, chromium - nickel, and chromium - vanadium, so anomaly XVI-B iron deposit is related to the hydrothermal deposits. Due to the ratio of Al / Co and Sn / Ga, anomaly XVI-B is recognized as a skarn type deposit. Based on the scattering patterns of the rare elements, anomaly XVI-B is more similar to the skarn type deposit. Geological and mineralogical evidence, as well as the geochemical properties of the magnetite, indicate that skarn deposit is source of iron mineralization. Iron is transported by the hot fluids that come from intruded units that accumulates between boundary of metamorphic and marble units. δ34S value is between 21.24% - 22.27%. The source of Sulphur isotope is meteoric and ancient marine water. As a result, the accompaniment of magnetite with pyrite can be found that the source of magnetite is identical with pyrite.

The Kamyaran ophiolites, with the age of Late Cretaceous, are a part of the Iranian Mesozoic ophiolites, which are exposed in the SW of Zagros Main Thrust. This massif is bordered at the NE by the Sanandaj-Sirjan metamorphic rocks and at the SW by the Bisotun limestones and Kermanshah radiolarites and then by the Zagros Fold-Thrust Belt. The Kamyaran ophiolite is made of the mantle and crustal sequences. The crustal sequence is distinguished by pillow lavas, sheeted dike complex, and lava flows. The positive LILE anomalies with the HFSE depleted confirm their arc-related affinity. The geochemistry signatures of sheeted dikes show that these rocks have two different patterns. The REE pattern in some of the sheeted dikes samples with the pillow and flow lavas sample is similar to E-MORB; their element ratios support this likeness too. The positive LREE and LILE anomalies with the depletions of the HFSE suggest the calc-alkalic tendency and subduction-related affinity for these rocks; however, dacitic dikes with the flat REE pattern, LILE enrichment, and HFSE depletions have the Island-arc tholeiites affinity. The similarity of element ratios in all the samples may suggest that these rocks have the same magma source, and the tectonic environment of the ophiolitic rocks can be correlated with the oceanic subduction environment.

Lower Cretaceous carbonate units of the Kuhzation, karstification and dolomitization, studies of 40 samples of these carbonate units indicated aragonite as original mineralogy in closed to semi-closed diagenetic system.

The Estand granitoid pluton is located in the southwest of Birjand, in the eastern edge of the Lut block, It is located near the Neh Western fault, and branches of this fault have cut off this pluton and the surrounding rocks. Its lithological composition includes: tonalite, granodiorite and granite (monzo-syenogranite) and its minerals are quartz, plagioclase, microcline, orthose, biotite, muscovite and garnet. The Estand granitoid is high-potassium calc-alkaline, peraluminus and S- type, which is derived from a poor of clay metagreywacke origin. The uniform and coordinated trend of the samples in the rare earth elements and spider diagrams normalized to the primary mantle and chondrite shows the genetic relationship and they are co-genetic with each other and the enrichment in LREE, Th, U, K, La and Pb elements and the depletion in HREE, Nb, Ti, Sr and P reflect the role of continental crust and crust-derived melt. The rocks of this pluton have formed in a post collisional setting, in a normal continental collision arc, due to the melting process in the upper crust. The geochemical evidence shows that this pluton is obtained only from crustal component without intervention of the mantle, by biotite dehydration. In addition, heat from shear zone and collision areas could play a role in melting the sediments of its source. The pressure and temperature diagrams show water pressure of ≥5 kbar and temperature of 750 to 800 °C for granitoid pluton and temperature of 830 to 850 °C for its enclave.

Abgarm ultramafic complex in termination of the southeast of Sanandaj- Sirjan is a part of the Haji Abad- Esfandagheh ophiolitic belt. This body consist of three different types of rocks includes of ultramafic rocks, mafic and metamorphic. Most ultramafic rocks are harzburgite, dunite, and lherzolite that harzburgites are more than 85 volume percent of this complex. Microscopic evidence suggests that there are several generations of minerals in these rocks. In addition, mineral chemistry data indicate that the Abgarm harzburgites have been formed in an environment similar to those considered for MORB peridotites and they passed about 15% partial melting. Pyroxene porphyroblasts and Olivin- Spinel thermometry in these harzburgites shows 816- 992 and 708- to 840 0C. Moreover, fO2 calculation gives a redox state that lies within a range of 1.6 log bar units around the Fayalite–Magnetite- Quartz buffer FMQ (log = -0.8 - 0.9 log-bar units) in the range of pressure of 1.2 and 2 GPa. For them and suggest that they have been equilibrated in spinel peridotite field for Abgarm peridotites. Chemical evidence shows that these rocks are similar to abyssal peridotites and probably formed in a back-arc basin environment.

Boroujerd-Nezam Abad zone widespread along NW-SE trend in part of Sanandaj-Sirjan zone. Borujerd-Nezam zone consists of hornfels, schist, phyllite, migmatite, granite and granodiorite rock types. Metamorphic (hornfels and schist) and igneous (granitoids) rocks are known as host pegmatitic dykes. Quartz, feldspar, muscovite and tourmaline are the most common pegmatite, and mica are as muscovite type with tendency to Li-bearing muscovite. Rb, Sr, Ba and Al are relatively enrichment, but REE, U, Sn and Ga and also Li, Ta and Cs show depleted. Enrichment index such as Mg/Li vs Li, Rb vs K/Rb and Ta vs Ga diagrams show that studied pegmatites are barren in REE and trace elements. Comparing to REE rich pegmatites, they show slight enrichment in LREE relative to HREE.

Pollution sources are basically divided into two groups: geogenic and anthropogenic. Geogenic sources include pollution from geological formations, mineral indices, mineral springs, brackish and saline water sources, and industrial activities, transportation, using agricultural fertilizers, mining activities, and wastes and effluents can be mentioned as anthropogenic pollution sources. Essential nutrients and other metals may enter the food web through the soil. The natural concentration of potentially toxic elements in the soil is usually low, except in the case of soils composed of ore minerals. The amount of trace elements in soils can also increase sharply due to human activities. In recent years, industrial and agricultural development in Iran has grown exponentially and various researches have been focused on assessment of environmental pollution. Therefore, it is necessary to use a set of different quantitative and qualitative methods of soil pollution assessment to gain a better understanding of the extent of pollution. Regarding the pollution of Khiavachay River in Sabalan geothermal region by natural springs and Meshginshahr iron mine, and due to irrigation of arable lands by this river, the aim of this study was to evaluate the pollution of arsenic, cobalt, lead, zinc, copper, iron, manganese and chromium using geochemical indices and statistical methods in the surface soil of Meshginshahr city.

A total of 14 soil samples (0-20 cm) were collected using composite sampling method from agricultural lands irrigated by the water of Khiavachay River. The samples were dried at room temperature, then a part of them passed through a 230 mesh sieve for digestion by four acids and elemental analysis by induction coupled plasma mass spectrometer (ICP-MS) in Zarazma laboratory. In this study, Geo-accumulation index (Igeo), contamination factor (CF) and enrichment factor (EF) were used to determine the severity of soil contamination with heavy metals. Also, in order to investigate how the elements relate to each other and also to determine their origin, the results were analyzed using statistical analysis. Descriptive statistics, correlation coefficient and principal component analysis were performed using SPSS 20 software.
 

Comparison of the concentration of elements in the region with their world average in soils and Earth crust shows that the average concentrations of arsenic, zinc and phosphorus in the agricultural soil of Meshginshahr are higher than their values in the world soil and Earth crust. Among the studied elements, As, P and Fe with values of 68.61, 34.27 and 30.76% respectively show the highest coefficients of variation in the region. The high variation coefficient, especially for As, indicates high concentration differences in different parts of the study area and possibly differences in the source of the contaminant. The results show that the amount of arsenic in the soil of station S1 (Moil village, adjacent to the iron mine) is in the range of severe to extremely polluted (Igeo level is 4.62). It is also present in 78% of the collected samples (11 samples) in the range of moderate to severe contamination (Igeo level between 2.37 to 2.95) and in two stations in the range of moderate contamination (Igeo level between 1.79 to 1.87). Zinc is in the moderate contamination range at all sampling points (CF between 1.04 and 2.27). Iron, lead and copper are in both the medium and low pollution ranges, and cobalt, chromium and manganese are only in the low pollution range. Therefore, the region shows significant enrichment to arsenic. These results are in good agreement with the previous study on the Khiavachay River and are reasonable considering the type of formations and irrigation of agricultural lands with arsenic-contaminated water. The results obtained from the pollution indices indicate that the maximum arsenic pollution is present in station number one and close to the iron mine of Moil village. High correlation of arsenic with iron (r = 0.911) and lead (r = 0.637) and its negative correlation with phosphorus (r = -0.65) was observed. The negative correlation of arsenic with phosphorus can be due to the competition of these two elements in the form of anions (arsenate and phosphate) in adsorption by soil colloids. Among the iron ores of the region, the highest concentration of arsenic has been measured in limonite. In the process of limonite formation, insoluble free hydride is formed by the oxidation of divalent iron, and during this reaction, arsenic, which originates from hot springs and hydrothermal waters of the region, is co-precipitated with iron. Therefore, As in the Moil iron mine has secondarily deposited in limonite under the influence of geothermal resources and hot springs. The results of correlation coefficient have been confirmed by principal component analysis.

Existence of hydrothermal springs with high concentration of arsenic, which are considered as causes of water pollution in Khiavachay River, and irrigation of agricultural lands with river water are important factors of arsenic enrichment in the soil of the region. Considering the amount of geo-accumulation index, the soil of the study area has moderate to severe As contamination. The results of the enrichment factor indicate significant enrichment for As and moderate enrichment for P, which is influenced by geological formations and natural factors for arsenic and anthropogenic factors for phosphorus. The results of statistical analyzes showed the important role of Moil iron mine and hydrothermal springs in the region in increasing the concentration of As, iron and lead in the soil of the region. Considering the negative effects of soil pollutants on the environment and due to the high concentration of arsenic in the study area, it seems necessary to study the concentration of this element in crops in the region and assess the health risk. For this purpose, evaluation of mobility and bioavailability of elements by sequential extraction methods, study of the role of soil physicochemical parameters in elemental mobility and investigation of the role of plant species in the uptake of pollutants from soil can be of great help in better analysis of the results.