فصلنامه زمین شناسی ایران
پیاپی 62 (تابستان 1401)

Understanding the geological phenomena created by dissolution can be a great help in understanding karst systems. Hence, geology is usually the first step in studying the karstification process. Abegarm is located in the Central Iran structural zone and includes the Formations of the Paleozoic, Mesozoic and Cenozoic eras. The most important carbonate formations in Abegarm are Soltanieh, Ruteh, Elika, Lar and Qom formations. In this study, karstification potential was investigated after field work and sampling of carbonate rock units and comparing them in terms of the development of karst landforms. Sampling of karst springs in both dry and wet periods, as well as measurement of EC, pH and temperature on the ground were performed. Remote sensing studies were performed by ILWIS software on Landsat satellite images for isolation and calculation of the area of ​​carbonate formations. AqQa software was used to review and interpret the findings of chemical analyses and Phree Qc ​​software was used to model water chemistry. The most important karst landforms in the region include karrens, vugs, caves, and karst springs. Based on the combination of field studies and remote sensing data, the intensity of karstification in the Abegarm area graded from high to low, include: Qom, Soltanieh, Lar and Cretaceous formations. Based on karst development classification, Abegarm karstification is merokarst (incomplete) and shallow; and based on the karst cycle classification it is classified as juvenile to young.

The Shemshak Group is well-exposed in Ramsar coal-bearing region and consists of four formations; Ekrasar, Laleband, Kalariz and Javaherdeh. The Laleband Formation lies conformably and gradationally on top of Ekrasar formation and its upper contact is conformable and sharp under Kalariz formation. It contains scattered plant macrofossils of Norian-Rhaetian age. The studied section contains well-preserved and scattered plant macrofossils belonging to three orders as Equisetales, Filicales and Pinales. Based on the occurrence of Neocalamites sp. cf. N. carcinoides, Dictyophyllum sp. cf. D. exile, Clathropteris meniscoides and Cycadocarpidium erdmani and stratigraphic position of fossil bearing layers, Late Norian – Early Rhaetian age is suggested for the studied beds.

The Madanjoo prospect is one of the eastern anomalies in the Sangan mining district. This area is located in the eastern part of the Cenozoic Alborz volcanic-plutonic arc. The geology of the area includes Jurassic shaly sandstone, lime mudstone, and sandstone, Upper Cretaceous limestone and dolomitic limestone, and Upper Eocene tuff and lava flow sequences, Middle Eocene skarn rocks, and Quaternary sediments. The most important occurrence in the Madanjoo area is the penetration of ferrous fluids into terrigenous and carbonate formations, skarnization, and iron mineralization, which is characterized by the presence of magnetite and calcsilicates minerals. based on type and frequency of calcsilicates, The skarn zones include olivine-pyroxene-garnet skarn, garnet-pyroxene skarn, garnet skarn, pyroxene-wollastonite-magnetite skarn, magnetite skarn, phlogopite skarn, tremolite-actinolite skarn, and epidote skarn. Iron mineralization occurred as massive, banded, vein-veinlets, breccia, and disseminated forms mostly in the Upper Cretaceous limestone and dolomite rocks and along NE-SW fault zone trend. Magnetite is the main ore mineral accompanied with pyrite, chalcopyrite, pyrrhotite, and secondary iron minerals. The composition of the Madanjoo garnet, pyroxene, and olivine are andradite-grossular (mostly andradite), diopside-hedenbergite (mostly diopside), and forsterite, respectively. Thermobarometry study based on pyroxene chemistry show that pyroxenes crystallized in temperature range of 458-689 °C, pressure of 2.21 kb, and depth range of 1-2.5 km. Three main paragenetic stages of skarn formation and ore deposition were recognized in the Madanjoo deposit: (1) a prograde stage developed with prograde garnet and pyroxene forming at 330° to 410 °C with a fluid salinity between 33 to 58 wt.% NaCl equivalent, (2) a retrograde garnet, tremolite- actinolite, and calcite which formed at 120° to 300 °C with fluid salinity of 16 to 49 wt.% NaCl equivalent, and (3) a post-ore stage with calcite and minor quartz veins that developed at 95° to 190 °C with salinity range of 2 to 15 wt.% NaCl equivalent. Possible iron ore formation mechanisms include: fluid mixing, boiling, and dilution with meteoric waters along with decreasing temperature. Finally, the Madanjoo iron mineralization is introduced as a magnesian exoskarn iron deposit.

Sarbisheh area is located in the west of Sarbisheh and southeast of Birjand, South Khorasan province. This area is located in the Birjand ophiolite melange zone and is a part of the northern part of the Iranshahr-Birjand metallogenic belt. The lithological units in this area include ophiolite melange, flysch facies sediments, pyroclastic rocks and Quaternary sediments. Geochemical studies of stream sediments and identification of geochemical indicators of mineral resources in the region were performed using the results of geochemical analysis and principal component analysis. Remote sensing studies were performed on the ASTER and Landsat satellite images using color composite, selective principal component analysis (crusta) on the Landsat 8 satellite imagery to identify the alteration zones. The lineaments of the region were drawn using the high-pass filter method of the ASTER satellite image and the Google image. Finally, by creating layers of geological units, geochemical data, alteration and lineament and integrating them with fuzzy method, areas with potential mineralization of nickel, chromium, cobalt, copper, lead, zinc and magnesite were identified.

Calcareous springs of Ab-e Ask are located 85 km northeast of Tehran, in the southern range of the Damavand volcano. Microscopic studies represent the existence of four abiotic and two microbialite facies in the Ab-e Ask travertines. The travertines are the main deposit types of these springs. Based on sedimentation sequence and lithofacies these travertines are categorized as first type (vent and channel), second type (pound, dam, and cascade), and third type (laminated) travertines. On a δ18O versus δ13C plot (VPDB), these travertines are plotted in the oncoid and crystalline crust lithofacies fields. These facies show the character of hydrothermal spring and set the spring in the thermogenic group. Positive values of the Langelier Saturation Index (LSI) for Pashnak, Nadaali, and Zagh springs indicate that these water samples are supersaturated with respect to calcium carbonate, which leads to considerable sedimentation around the springs. In contrast, a negative LSI value at the Sare Pole spring indicates the water is undersaturated with respect to calcium carbonate. Therefore, this spring has a lesser role in travertine deposition compared to the other springs. Also, the position of the samples on the modified Gibbs and Van Wirdum diagrams, suggests that the interaction of water with carbonate and to some extent silicate rocks is considered as the most important source of Ca and Na.

The use of different geospatial layers In the exploration and determination of the mineralization zones, will lead to more reliable results. In this study, the investigation of iron mineralization zones was done using airborne magnetic data and three types of satellite images (i.e. ASTER, Landast-8 and Sentinel-2) in the Esfordi area. The reduced-to-pole filter, the upward continuation at altitudes of 200, 500 and 1000 meters, the analytic signal, the horizontal tilt angle, and the first vertical derivative were then employed on airborne magnetometry data. Argillic, phyllic and propylitic alterations, iron oxide and gossan zones and structural lineaments were extracted through satellite imagery data processing. The analytical signal and horizontal tilt angle indicators were used as the main geophysics footprints to identify the magmatic intrusions and geological lineaments, respectively. In addition, three satellite imagery indicators were used in final identification of iron-bearing zones. The weight of each layer was calculated by simultaneous analyses of the concentration-area fractal curve, the prediction-area plot, and the use of 22 Fe-bearing occurrences in the studied region. Note that the analytical signal layer with the prediction rate of 76 % has the highest weight among all layers. In other words, this layer has occupied 24% of the study area as favorable zones by which 76% of the known Fe occurrences are delineated. Iron ore potential map was prepared from integration of all geospatial indicators through the weighted multi-class index overlay method. The generated map has an intersection point with a prediction rate of 78% which has higher weight than the other individual indicators. According to this map, new iron mineralization potentials are observed in the east and southeast of the Esfordi area.