فصلنامه زمین شناسی ایران
پیاپی 59 (پاییز 1400)

The magnetic data collected from airborne surveys need to be interpreted after processing. The most important information gathered from the interpretation stage, is the depth and horizontal position of anomalies. Various methods are developed for gathering these data. One of these methods is Euler deconvolution that is based on Euler’s homogenous equation. Euler's method is one of the fastest semi-automatic methods for determining the depth of buried magnetic and gravity anomalies. Its results are highly dependent on the structural index, Euler window size, and depth calculation error. This method identifies the depth and trend of changes in the depth of anomalies very well. The geological information of the study area is important for the application of this method. In this method, the potential field and its first-order derivatives are used in different directions to determine the position and depth of the potential field source. In this paper, by using this method, the depth, and boundaries of anomalies in the Lake Blatchford area of Canada are investigated. The obtained results indicate that most anomalies in this region have shallow to medium depth.

In this study, the velocity deviation log was derived from routine wireline logs to determine the pore types of Kangan and Dalan carbonate formations in one of the central Persian Gulf fields. To achieve this purpose, core information from one well including porosity and permeability and petrography of thin sections along with wireline logs from 12 other wells were used.By using a velocity deviation log reconstruction based on density, neutron and acoustic logs, three velocity zones representing distinct porosity and one nonporous zone were identified. The three-dimensional model of velocity deviation log showed that K1 zone is mainly a dense and non-porous zone and, in some cases, it contains moldic and rarely intercrystaline porosity. This porosity was created due to sea-level fall during deposition of the upper part of this unit because of dissolution and dolomitization. K2 reservoir zone contains major intercrystaline and minor moldic porosities due to dolomitization in shallow sea-level conditions in most parts of this unit. Unit K3 mainly hosts dense and nonporous rocks, in cases moldic porosity and also randomly shows fractures in its lower part. K4 is more likely contain intercrystaline and interparticle porosities at the upper part which was deposited in a shallow environment. Moldic porosities were formed in lower parts in response to meteoric diagenetic environment. Fractures are also detected in some cases. The results of presented study show high correlation with other reservoir evaluations that prove the ability of velocity deviation modeling in predicting large-scale reservoir variations.

Neogene igneous rocks of the Quchan-Esfarayen magmatic belt (north of Sabzevar) represent post collisional magmatism in the northeast of Iran suture zone. This NW-SE igneous complex occurs as sporadic dome, stock, dyke and lava flow in the belt. The basic lava flows (basalt) and dykes croped out in the Miocene marls around the adakitic domes. The studied rocks include olivine basalt to trachy andesitic basalt in composition with microlitic porphyry, hyallomicrolitic porphyry, glomeroporphyry and flow textures which are composed of olivine, clinopyroxene and plagioclase phenocrysts and microcrysts as main minerals in a glassy or microlitic groundmass.
The basalts are sodic in nature, enriched in large ion lithophile elements (LILEs), light rare earth elements (LREEs), high field strenght elements (HFSEs) specially in Nb (20-30 ppm) and depleted in heavy rare earth elements (HREEs). Parental magma of the basaltic rocks originated from 10-15% partial melting from a garnet lherzolitic mantle plume in an intra-arc extensional basin in Miocene time then ascended and extruded in Neogene sedimentary basin via fault and fracture systems. This mantle plume formed by detachment of oceanic slab window and invasion of hot asthenospheric mantle into the mantle wedge over the Sabzevar Neotethyan oceanic subduction zone.

In the present research, to identify potential and existence of possible iron ore-bearing in the Maragh district of Bandar- e- Charak in Hormozgan province, remote sensing studies using Aster sensor data through ENVI were conducted. Afterwards, the preliminary exploration of promised regions was performed by magnetometry method. Remote sensing operation of the region data comprises preprocessing sequences of geometric correction by image-to-image method and atmospheric correction as well as processing techniques containing false color composite, banding ratio, least square-fit, directed principal component analysis and finally supervised classification through spectral angle mapper method. Because of this process, alteration-zoning map associated with iron mineralization in the studied region was prepared. Magnetic data was acquired from 1913 measuring stations using a proton magnetometer in an area of approximately 11.2 km2. Geosoft Oasis montaj software was employed for processing operation and qualitative interpretation of magnetic data via applying various corrections and filters including reduce to pole, upward continuation up to the variety of elevations, low-pass filter, derivative filters containing total horizontal derivative and analytical signal. At the end, to investigate the trend of magnetic anomalies observed on the surface, determination of approximate shape of the deposit and estimation of its depth, a 3-D inverse modeling of the data was carried out. Results of this research through integrating two methods of remote sensing and magnetometry with 3-D inverse modeling of magnetic data, reveal that Maragh district has a high potential of iron ore-bearing. The results of this research is suitable for all geoscienists especially geologists and exploration engineers.

The Manto-type copper deposits of the Qom-Saveh region are located in the central part of the Urumieh-Dokhtar magmatic arc and occurred in the Eocene volcano-sedimentary sequence. The most important deposits in the studied area are East Narbaghi, Khankishi, Veshnaveh, and Kahak. The geometry of mineralization is stratabound and hosted in the silty tuff, tuff breccia, andesite, lithic crystal tuff, and amygdaloidal andesite basalt. The hypogene ore minerals include chalcocite, bornite, and minor chalcopyrite with vein-veinlet, open space filling, disseminated, and replacement textures. Based on geological studies, two major stages are distinguished for hypogene mineralization. Disseminated and framboidal pyrite formed during the first stage of mineralization which occurred simultaneously with volcanism, sedimentation, and early diagenesis. The second stage of mineralization took place during late diagenesis when copper-bearing oxidized fluids entered into the reduced pyrite-bearing host rock, causing the replacement of the first stage pyrites by copper sulfides. The sulfur isotope composition of sulfide minerals from the East Narbaghi deposit varying from -10.2 to -4.4 ‰ (averaging -6.7 ‰VCDT) indicates the presence of a reduced environment resulting from activation of sulfate-reducing bacteria. The geology, ore mineralogy, alteration characteristics, and sulfur isotopic compositions suggest that the studied ore deposits may be classified as Manto-type mineralization.

The NW-SE trending Tarom Metallogenic Zone is located in the northwest of the Urumieh- Dokhtar Zone, from the tectonics viewpoint. This zone has been cut by main NW- SE trending faults and minor NW- SE, N-S, NE- SW, E-W as second-order faults. In this zone, some dyke swarms with different strikes and compositions are exposed and structurally have not paid sufficient attention. For these reasons, geo-information techniques including: Landsat-5 Thematic Mapper (TM) satellite images which were used to facilitate recognition and delineation of the different dykes; investigation of Google Earth™ with Being images for preparing an initial map of the dyke swarms and detailed structural analysis were also performed at the mesoscopic and outcrop scale. The results reveal that the shear zone between the Tarom and Zanjan faults with their Riedel (R) and anti- Riedel shear fractures were recognized as the main structural controls on dyke swarms of the area. Based on rose diagrams, the main sub-vertical dykes have a mean N120o trend which corresponds to the trend of one of the main fault- joint sets. Four sets of intermediate and mafic dykes, with Azimuth trend of, ≈ N030o, N060o, N120o and N150o and two sets of acidic dykes, N120o, N150o are exposed. Based on field studies and faults cross-cutting relationship, NE−SW mafic dykes are the youngest trend in the studied region.

Kushk sulfide Zn-Pb ore deposit is located in the Posht-e-Badam block, in the central Iranian tectono-magmatic zone. The host rocks of the ore deposit include shale, sandstone and dolomite. In order to investigate the physicochemical condition controlling the formation of the sulfide ore, a number of fluid inclusions were gathered from silicic thin layers. The silicic contents of the samples have contemporaneously been deposited with shale and sulfide minerals mainly in the footwall and the main mineralized horizon. In this research, the general properties of fluid inclusions in the ore-forming system are taken into account and the interpretation of these data in terms of fluid evolution processes is discussed. Considering the syngenetic formation of the silicic thin layers and the mineralized shale, a similar formation condition can be considered for both of these units.  Based on the results, two types of fluids were involved in the formation of the silicic thin layers, including fluid 1 that is characterized by higher salinity (av. 38.8% NaCl.eq) and is thought to transport the metals chloride complexes and fluid 2 with lower salinity (av. 4.46% NaCl.eq) and is thought to carry sulfide species. Part of sulfide in this type of fluid could be originated from bacterial activity. Isothermal mixing of the two fluids sequencially resulted in destabilization of chloride complexes of chalcophile elements, the reaction between the elements and sulfur originated from the low salinity fluid and formation of the sulfide ore.