فصلنامه زمین شناسی اقتصادی
سال پانزدهم شماره 2 (پیاپی 37، تابستان 1402)

Macroscopic, microscopic and geochemical studies carried out on albite-bearing metasomatites and metasomatic rhyolites hosting the magnetite-apatite deposit of Chogharat indicate the presence of three generations of albite with different concentrations of REE-Y-Ti-Th, in response to T-P reduction and chemical changes of the fluids and the ratio of fluid to rock. The geochemical analysis of the low Ca/Na fluids shows a deficiency in REE-Th mineralization in the white albites, while in the fluids with medium Ca/Na, the REE mineralization (REE>Th) has occurred in the pinkish albites. In contrast, fluids with high Ca/Na indicate Th mineralization (Th>REE) in the red albites. The stable isotopes of C-O on the paragenetic calcites show REE-Y-Ti-Th mineralization of albites due to High-T hydrothermal fluids. Otherwise, the stable O-C isotopes of the Ghoghart apatites and stable isotopes of S in the ore deposits of the BMD verify the role of evaporitic brines and fluid-rock interaction on the mineralization. The presence of calcite and titanite, associated with the calcic-amphiboles and clinopyroxenes, Ca-inclusions in the thorite structure and Ca-content of the thorites, indicate thorite mineralization from the Co32- and Ca2+ fluids due to low activity of the chlorine. According to this study, the source of metasomatism is mainly evaporitic brines with a minor amount of magmatic and related hydrothermal fluids. Mineralization is the result of interaction of the magmatic and hydrothermal fluids of the Late Ediacaran- Early Cambrian plutonic/ subvolcanic intrusions with the evaporitic brines, derived from the synchronous evaporitic sequence.

The Zanjan-Takab complex is a metamorphic belt with NW-SE trend that includes gneiss, amphibolite and gneissic amphibolite, old metagranites, pelitic schists with migmatites and metaophiolites. Takab mafic migmatites, based on field evidence and partial melting degree, are divided into two main groups of metatexites with patchy, ophthalmitic, diktyonitic, agmatic, stromatic structures and diatexites with schollen, ptygmatic, folded, stictolithic, phlebetic, schliren, nebulitic structures. These migmatites consist of mesosome part with textures of porphyroblastic, xinoblastic, granoblastic and nematoblastic and main minerals plagioclase, hornblende, biotite, melanosome part with nematoblastic, xinoblastic, granoblastic and oriented textures and main minerals hornblende and plagioclase. The leucosome part is composed of granular, sympletic and myrmekitic textures and the main minerals are plagioclase, quartz, k-feldspare, titanite, hornblende and biotite. Investigating the shape of the crystal size scatter diagrams (CSD) shows the physical conditions and petrological processes are effective in the studied rocks. In order to investigate these processes, plagioclase crystals in 4 leucosome samples were quantitatively analyzed with the help of Jmicro vision and CSD Corrections software, and then the results obtained from the analysis of different leucosome samples were compared. The crystal size scatter diagrams of plagioclase crystals show two stages of growth with different speeds in the studied samples, so that the larger crystals (the end part of the curved diagram on the right) belong to a melt that is at greater depths or it cooled in a calmer environment. Nevertheless, the initial part of the diagram on the left side crystallized in more superficial areas and at a higher speed.

Producing mineral potential model using GIS software has been increased over the past years. In this study, predictive map consisted of argillic alteration, philic alteration, iron oxide alteration, reduction to pole of aeromagnetic data, lineaments, cu geochemistry anomaly, and principal component analysis (component 3) were prepared from Shahre Babak area. For training model, 37 mineralized points were used. Point pattern analysis was used as well for making non-deposit points and for training model, percepteron artificial neural network with two layers was applied. The training model was used to prepare the final mineral potential model. Based on the mentioned model, the main promising areas were identified to be in the northwest and eastern part of the studied area. Moreover, two areas in the northern and southwestern parts of this area were identified for additional studies. For evaluating the model, ROC curve was used. ROC curve shows high precision of the produced model. For more evaluating, sensitivity, specificity, positive predict value, negative predict value, accuracy, and kappa were computed. The coefficients confirm the high accuracy of the mineral potential model.

Ruchun-Mazar region is located in southern Sanandaj-Sirjan Zone, southwest of Baft city in Kerman province, Iran. Seh Chah, Chah Sorbi, Chah Nar, Zardbazi Dar, and Chah Sorbi Arjmand Pb-Zn deposits located in this region were investigated. The most outcrops of the geological units in the area include the Paleozoic metamorphic complexes of Gol Ghohar (amphibolite, gneiss and micaschist), Ruchun (schist, marble, calcschist, black chert, slate and phyllite), and Khabar (marble, calcschist). Microdioritic, monzodioritic and diabasic dykes have intruded into the metamorphic units. Dolomitic and calcitic marble of Ruchun complex is the host rock for Pb-Zn mineralization. Primary mineralization in Seh Chah, Chah Sorbi, and Chah Nar deposits includes galena, sphalerite, and pyrite ± chalcopyrite along with quartz, calcite, and dolomite ± barite. Vein-veinlet, open space filling, brecciated ± disseminated ± laminate structures and textures can be seen in these deposits. The most important alterations in these deposits are silicification and carbonitization (calcitic and dolomitic alterations). Primary sulfide ore in Zardbazi Dar and Chah Sorbi Arjmand deposits has been weathered and mining has been carried out on nonsulfide ore (supergene ore). The nonsulfide ore formed at the expense of sulfides, and mainly consists of smithsonite, hydrozincite, hemimorphite, and cerussite. It seems that these deposits belong to the direct replacement and, to a lesser extent, wall rock replacement nonsulfide zinc deposits. Based on the geological, mineralogical and alteration evidence, the primary mineralization in the region can be divided into two groups of SEDEX type (Chah Sorbi deposit) and vein type (Chah Nar and Seh Chah deposits). It was concluded that under supergene conditions in some deposits, nonsulfide ore was also formed. Moreover, the deposits of this region can be categorized into primary sulfide (hydrothermal) and nonsulfide (supergene).

Shotorsang iron skarn is located in 60 km northwest of Neyshabour (Khorasan Razavi, Iran) in Quchan-Sabzevar magmatic belt. Subvolcanic intrusion rocks have intruded into Cretaceous limestones and created skarnization. These rocks are divided into syenite porphyry and granodiorite porphyry based on their geochemical characteristics. They are I type oxidizing, metaluminous, and tectonic. Setting of the subvolcanic rocks are the subduction zone of the continental margin (VAG). Comparing the mineralization potential of the subvolcanic rocks of this area based on the use of the graph of SiO2 against K2O, MgO, Na2O+K2O, and Ni-V shows that they are fertile in terms of the formation of Fe and Cu skarn. Syenite porphyry is the origin of this mineralization, and magnesium in skarn is taken from hydrothermal fluid. The diagram of Eu/Eu*, Ce/Ce*, (Pr/Yb)n ratios also confirms the presence of meteoric water in the formation of the skarn zone. The primary fluid, which has a positive anomaly of Ce/Ce* and Eu/Eu* had acidic and oxidant conditions and high temperature, and formed pyroxene skarn. A part of magnetite mineralization is formed in this zone, and in this condition, the highest amount of REE entered the pyroxene skarn zone and diluted the fluid in terms of REE. This issue has led to a sharp decrease in the amount of REE in the mineralization zone. Negative Ce/Ce* and Eu/Eu* anomalies indicate alkaline conditions with less concentrated REE content, consistent with chlorite skarn. The highest amount of Fe mineralization is formed in this zone.

Iron mineralization has occurred in Larak Island, located 30 km south of Bandar Abbas, within the Persian Gulf, in the Zagros structural zone. Stratigraphically, Larak Island dominantly consists of the Late Proterozoic Hormuz volcanic-sedimentary series, including rhyolitic lava and tuff, shale, and evaporative sediments. Iron mineralization has occurred in a specific stratigraphic horizon within the volcanic-sedimentary sequence. The orebodies involve four ore facies from bottom to top: vein-veinlets, brecciated, massive, and banded. The ore minerals are dominated by magnetite, oligiste, and hematite with gangue minerals including pyrite, apatite and secondary goethite and limonite, associated calcite, quartz, and anhydrite. Wall rock alterations in this area include silicic-sericitic, carbonatic, chloritic, and secondary argillic. The samples obtained from iron ores in the geochemical diagrams including the Fe/Ti versus Al/(Al+Fe+Mn+Na+K+Ca) diagram and Mg versus V/Ti diagram, were plotted in the range of Banded Iron Formation (BIF) deposits. Due to the volcanic-sedimentary nature of the host sequence, lack of observation of glacial sediments, ore facies, ore textures, structures and mineralogy, alteration and geochemical features, the iron mineralization in Larak Island shows the most similarities with the Algoma-type BIF deposits.