فصلنامه زمین شناسی ایران
پیاپی 54 (تابستان 1399)

A metamorphic rock complex consists of slate, phyllite, micaschist and marble with NE – SW shistosity has cropped out in Neybaghi area in the NE of Myaneh.  Impure marbles occur as thick and thin layers or massive bodies within the centeral area of this complex. Textural and mineralogical evidences, revealed two metamorphic stages.  The early stage is testified by the minerals such as pyroxene (diopside), epidote (clinozoisite), amphibole 1 (edenite-pargasite) and plagioclase 1.  The main stage have chlorite (clinochlore), phlogopite, amphibole 2 (tremolite) and plagioclase 2.  P-T-XCO2 have been estimated for the early and main stage of metamorphism by computing nonideal and asymmetrical fugacity and activity and programing in THERMOCALC software for fluid and solid phases.  The estimations give pressure, temperature and XCO2 of 9.5Kbar, 660°C and 0.35, whereas the main stage has been constrained at P=4.2Kbar, T=510°C, XCO2=0.4. The obtained P-T path shows that the Neybaghi marbles were formed under medium pressure condition and overprinted by a low pressure metamorphism.  This type of P-T trend can be formed in collisional tectonic regime.

Late Triassic deposits of Shemshak Group in Emarat section at about 30 km south of Amol and Emamzadeh Hashem section and about 50km north east of Tehran in Central Alborz have been studied for some paleoclimatic and paleogeographic indicators. The data used in this study include: 10 point counting of sandstones, 13 main oxide analyses, 8 species of plant fossils and 4 genuses of palinomorphs. Lithological and geochemical data were restricted to the Late Triassic deposits. Important events of the Late Triassic such as: Late Norian and Middle Rhaetian droughts were revealed by the presence of gypsum beds. This study indicates that lithological signatures are clearly consistent with the mentioned global event and this tracer can be a good basis for controlling other age-related paleontological data. Comparison of the Alborz and Siberian plant fossils indicated that the study area did not have significant differences compared to more northern regions such as Siberia. The investigated palinomorphs indicated that most of them are hygrophytic and mesophytic and some of them had more well-known origin which belonged to some ferns. The point counting data revealed that the source area of the sediments experienced dry to semi-humid climates. This study also confirms that the Alborz region was part of Eurasia, due to the Eo-Cimmerian orogenic event based on recognized plant fossils.

Baghalbid iron mineralization is one of the eastern anomalies of Sangan iron mines. This area is geologically located in the north-eastern part of Lut block. In this area, Paleozoic and Mesozoic units such as schist, phyllite and sandstone are in contact with Tertiary igneous units and Neogene sedimentary rocks. The iron mineralization occurs as hematite in the upper part of a brecciated volcanic layer with a length of more than 1 km. The footwall rocks contain breccia, tuff and sandstone and hanging wall rocks contain subvolcanic granodioritic dikes. The hematite occurs as open space filling in breccia, indicating that the iron mineralization is classified as epigenetic type. Barite, calcite, and quartz were also formed in fractures and open spaces of iron-bearing horizon. In addition to the iron, copper mineralization occurs as quartz veins containing chalcopyrite and malachite in footwall rocks. The iron oxide contents vary from 8 to 55 wt. % in the iron-bearing horizon. In mineralized rocks, the amount of chromium, vanadium and phosphorus is relatively low, while those of barium, arsenic, silver and antimony are relatively high, and LREE and LILE show enrichment relative to HREE and HFSE, respectively. According to geological, mineralogical and geochemical characteristics, ore texture and structure, REE pattern, the Baghalbid iron mineralization is classified as hydrothermal type. The iron was probably leached from pyroclastic rocks by hydrothermal fluids and was re-concentrated in the upper permeable breccia and conglomerates.

Rivers are the key resources for drinking and agricultural purposes and the assessment of water quality is very important. In this study, a detailed investigation has been made for identifying the natural and anthropogenic processes that offected the quality of Gorganrood and its tributaries water in the Gonbad-e-Kavoos district. The Gorganrood is the longest river in the Golestan province (NE of Iran).  During previous years, various wastewaters (i.e. domestic, agricultural and industrial) produced in Gonbad-e-Kavoos district have been discharged into the Gorganrood. To evaluate the chemical quality of water in the study area, 37 water and 6 wastewater samples were collected. The physicochemical parameters including pH and EC were determined in situ by an EC/pH meters. The concentration of major ions was measured using the standard methods. The piper and Wilcox diagrams were used to assess the water type and water quality for irrigation, respectively. Scatter diagrams were used to assess the hydrochemical processes influencing the chemistry of the water samples. Results of this study indicate that the pH and EC values of the water samples decrease in the city district. This is due to the discharge of urban wastewaters with lower EC and pH values which leads to the dilution of the river water. The lower concentration of nitrate in water samples collected in the city district is probably due to the denitrification process. Results show that the prevailing water types of Gorganrood and its tributaries are Na-SO42- and Na-HCO3-, respectively. The entrance of tributaries enhances the Gorganrood water quality for drinking and agricultural puposes. Along the river course, the natural processes of halite- gypsum- anhydrite dissolution and ion exchange, as well as anthropogenic factors (discharge of agricultural and urban wastewaters) deteriorate the water quality.

Ahmadabad calamine deposit is located in Posht-e Badam block, 80 km of northeast of Bafgh. The dolomitic unit of Shotori Formation is Middle Triassic age and is ore deposit host rock. Primary non-sulfide mineralization belongs to the Upper Triassic to Jurassic and includes galena, sphalerite and pyrite since being affected by subsequent tectonic phases- are crushed, uplifted, weathered and oxidized and produced non-sulfide minerals. Calamine, Cerussite, wulfenite, iron oxide and hydroxide are the most abundant non-sulfide minerals in the region. Mineralogical and field observations revealed that calamine is formed in two ways, i.e. direct replacement and wall- rock replacement. Direct replacement calamine is formed at the site of primary sulfide mineralization and has more mineralogical variability compared with the wall-rock replacement type. Mineralogical characteristics of the minerals revealed, metal-rich solutions perform non-sulfur mineralization in the unsaturated zone, within the porous host rock and the type of mineral is affected by changes in carbon dioxide pressure and ambient pH. The average values of the oxygen stable isotope data of hydrozincite is 25.5‰; therefore, the average temperature for the formation of this mineral is 29 ºC. Chemical analysis showed that the direct replacement calamine has more lead and the other type has more zinc, and due to the high concentration of arsenic and cadmium in the mineral composition of the area, more attention should be paid to the environmental issues.

Torud - Chah Shirin volcanic-plutonic complex, related to Eocene series, is located about 130 kilometers south of Shahrood, in the south and north of Torud village. This zone is located in 54˚20' to 55˚20' east longitude and 35˚10' to 35˚40' north latitude. The presence of several mineral occurrences, especially base metal veins of epithermal origin and the intrusion of igneous acidic to intermediate bodies in volcanic rocks of the area caused different alternation and mineralization in some parts of the area and increased the economic importance of the magmatic complex for geological studies. False color composites (FCC), band ratios (BR) and spectral angle mapping (SAM) which were performed on ASTER dataset for discrimination of alteration of argillic, advanced argillic, phyllic and prophyllitic zones and evaluation of results by XRD analysis, are the fundamental information for this research. The field studies and XRD analyses of different zones resulted in adaptation with logical operator algorithms and revealed unremarkable volcanic alteration zone in the south of Torud, in comparison with volcanic zone in the north of Torud. In addition, altering in threshold of algorithm band ratio can be used to find better results in discrimination of argillic and phyllic alterations. Then based on the presence of indicator minerals of advanced argillic alteration in the north of Torud, like alonite and prophillite, the optimal threshold for discrimination of this zone from argillic zone by logical band ratio algorithm was determined. The results were evaluated as acceptable, compared to field study. On the other hand, spectral character of remarkable minerals of this zone, like chlorite and epidotite, in band ratio of Aster 8(9+7) with threshold of 2.3, is reported appropriate for land surveying of proplitic zone in the north and south of Torud village.

Extensive outcrops of Eocene flysch deposits are available in the Khash area, south-east Iran. These flysches comprise sedimentary cycles of marl, shale, siltstone, and sandstone with erosional structures such as groove and flute casts. The studied sediments are deposited as a result of event-sedimentation. Diverse graphoglytids have been collected from an outcrop of these sediments, located 15 Km west of Khash. Seventeen ichnogenera have been determined among the studied deposits. Most of these trace fossils were formed in the pre-event sedimentation phase on the muddy substrates, and they include Desmograpton, Helminthorhaphe, Paleodytion, Protopaleodictyon, Scolicia, Spirophycus, Spirorhaphe, Squamodictyon, Urohelminthoida. Post-event trace fossils are low in ichnodiversity and form in the sandy or silty substrates, they consists of Halopoa, Helicodromites, Helminthopsis, Nereites, Paleomeandron, Phycosiphon, and Planolites. Some of the trace fossils such as Paleodictyon are aligned with respect to the paleocurrent directions, and were affected by the currents. It seems that fine-grained pre-event sediment surfaces was favorite for K-strategist, while post-event sediments were occupied by R-strategist trace-makers.