جستجوی مقالات مرتبط با کلیدواژه "shale" در نشریات گروه "زمین شناسی"

In this study, formation of pyrite framboids was investigated in two Upper Devonian marine black shale intervals in south of the Tabas Block in southeast of central Iran. In order to identify and study the morphology of the pyrite framboids, polished section slides were prepared from pyrite-bearing black shale samples. The section slides from the shale samples were examined and photographed with a scanning electron microscope (SEM). The identified pyrite framboids are spheroid to sub-spheroid in shape and consist of several euhedral and octahedral-euhedral compact microcrystals. Generally, the diameter of the pyrite framboids range from 5 μm to 18 μm. The relative abundance and size distribution of the pyrite framboids in the studied shale intervals show that the identified pyrite framboids were mainly formed during the early diagenesis below the redox boundary, within the sediments of a nearshore marine substrate, under a slightly dysoxic–oxic water column. The absence of pyrite framboids in the other shale intervals in the studied Devonian succession may indicate fully oxic conditions in the water column.

The design of underground or terrestrial structures on the rock bed depends on the physical and mechanical properties. Considering the mining method in Tabas coal mine extraction method is long and destructive, the evaluation of the geomechanical properties of the rocks is more necessary. In this research, the characteristics of the rock units of the eastern tunnel No. 3 of Tabas coal Pervadeh mine were investigated. In this study, 3 samples of shale, sandstone and mudstone were examined.  Considering the importance of the subject in this research, new experimental relations have been proposed, and their application shows desirable results. In order to obtain geomechanical characteristics and empirical relationships, physical tests such as porosity, water absorption percentage, unit volume weight, and mechanical properties such as uniaxial compressive strength, point load index, Brazilian tensile strength, direct cutting test, durability and brittleness index were carried out. To achieve the desired objective, the most appropriate relationships are presented using the regression method. Statistical analysis shows good correlation between different parameters in shale, sandstone and mudstone samples.

Mississippi Valley-Type (MVT) deposits are epigenetic zinc and lead deposits with minor copper hosted by dolostone, limestone, and locally sandstone in platform carbonate sequences inboard of major orogenic belts (Leach and Sangster, 1993; Leach et al., 2010). The Irankuh-Ahangaran Belt, which is the most important Pb-Zn mineralized zone of Iran, is situated within the Sanandaj-Sirjan tectonic zone. This belt is 400 km in length and 100 km in width. Three deposits including Irankuh mininig district, Ahangaran and Hosseinabad deposits were studied in this article (Fig. 1). The aim of this research is study of thermal gradient of subducted slab and age of formation of Pb-Zn deposits at Irankuh-Ahangaran belt, which is contrary information has been published so far on the type and their formation. Also, chemistry of ore-fluid in MVT deposits and impact of dolomitic and shale host rock on paragenesis, alteration, style, reserves and grade of deposits were discussed.These parameters will certainly be useful for exploration of the hidden MVT type deposits in the Irankou-Ahangan belt. Result and Discussion: The Irankuh mineralization is hosted by Cretaceous dolostone and minor Jurassic shale rocks as epigenetic. The constructive thrust fault, which has been cut the Jurassic and Cretaceous host rocks, has played a major role in the rising of fluid and formation of mineralization. Mineralization is occurred as replacement and open space filling (fault breccia, veinlets and cavity of rock) in dolostone and breccia, veinlet and open space filling in shale host rock. The mineral assembelages are Fe-rich sphalerite, Feand Mn-rich dolomite, ankrite, galena, minor pyrite, bituminous, calcite ± quartz ± barite within carbonate host rocks, whereas quartz, pyrite, Ferich sphalerite, galena, minor chalcopyrite, low Fe-dolomite, bituminous, ± barite ± calcite are important primary minerals at clastic hos rocks (Karimpour et al., 2018). The Ahangaran deposit is very similar to Irankuh in host rock, alteration, paragenesis, and form of mineralization. Thrust fault has a constructive role for occurrence of mineralization and later destructive strike slip and normal faults have caused the displacement and destruction of mineralization. The Hosseinabad deposit is hosted by Jurassic shale, siltstone, and sandstone rocks as veinveinlets, breccia and open space filling with structural control. Alteratin consists of silicification, chlorite, bituminous, and minor siderite, dolomite and ankerite similar to mineralization hosted by shale in Irankuh district. The mineral assemblages are galena, Fe-rich sphalerite, pyrite, chalcopyrite and minor phyrotite. Due to the lack of a proper dolostone unit in the Husseinabad deposit, mineralization is concentrated in particular areas with low-grade and low-reserves. Based on lithology, alteration, mineralization style, structural control by thrust faults, mineral paragenesis, and comparison with differnet types of Pb-Zn deposits, all deposits of Irankuh- Ahangaran belt are MVT-type. Deep-seated thrust faults formed during the early stages of subduction (~ 70 to 75 Ma), and played an important role in the upward migration of hydrothermal fluids from the basement to shallow depths. The geochronology of pyrite in Irankuh district based on Re-Os method indicate age of Irankuh Pb-Zn mineralization is 66.5 ± 1.6 Ma (Liu et al., 2019). Since the thrust faults have been cut the Jurassic to Upper Cretaceous rocks, and according to the absoulte age determined in Irankuh, the mineralization of this belt have been formed in the age range of 66 to 56 million years ago, mainly in the Paleocene (Fig. 15). Karimpour and Sadeghi (2018) suggested the hydrothermal fluid originated from the dehydration of a hot and young oceanic subducted slab, which liberated Pb, Zn, and other metals, and may have removed metals from rocks and organic material of the continental crust. More than 90% of all the water within the oceanic slab was released in the depth zone of the forearc region (depth of 30 to 50 km) (Karimpour and Sadeghi, 2018). In the depth zone, Mg-rich silicate minerals (such as antigorite, hornblende, chlorite, talc) have broken and the produced fluid is rich in Mg and Fe (Fig. 17). The ore-fluid of MVT deposits is Si-poor and Feand Mg- rich. Such fluid is mineralized on the hosts of the dolstone (Irankuh and Ahangaran) or Shale-Siltstone (Hossein Abad, and part of Irankuh and Ahangaran). There are significant differences in the type of paragenesis, alteration, shape, dimensions, reserves and grade in the deposits of this belt, which is controlled by the host rock type. Based on all lithological evidence, alteration, shape of mineralization, existence of thrust faults, mineral paragenesis and specific geological and geographic location, it can be used to exploration of the hidden MVT deposits in this belt.

The one of the most important petroleum source rocks in the Zagros basin is the Pabdeh Formation that has been investigated by geochemical techniques. The aim of this study was to assess the quality of organic matter, evaluate thermal evolution and highlight Pabdeh Formation potential as a source rock of Ramin oilfield located in Dezful Embayment. Based on HI versus Tmax and HI versus OI diagrams were used in classifying the organic matter in the formation indicating the presence of Type II kerogen. Most samples of the Pabdeh formation have Tmax values more than 435ºC indicate that the shale of formation is thermally mature with respect to petroleum generation. Hydrogen Index (HI) values range from 150 to 350mgHC/gTOC and S1 S2 yields values ranging from 11.98 to 31.06mgHC/g rock, suggesting that the shale have oil generating potential.The TOC of shale samples of the studied Ramin Well no. 4 ranges from 1.82 to 3.5%, an indication of a very good source rock of terrestrially derived organic matter. So, investigation of the variation S1 S2 and TOC parameters indicated that Pabdeh Formation (in the well) is assessed a good source rocks in producing hydrocarbon. Also with T max examination showed that formation is mature enough to generate hydrocarbon and has yet entered oil generation window.

Introduction The Dash-Aghel area is located about 20 km east of Bukan town, south of West-Azarbaidjan Province, NW Iran. Shales of the Shemshak Formation (Lower Jaurassic) form cap rock of layers and lenses of the iron-rich laterite ores in this area. The propose of the present study is to indentify the source rock characteristics as well as the source-area weathering, tectonic setting, and paleo-oxidation conditions by using major, trace, and rare earth elements geochemistry of shales of the Shemshak Formation exposed in the Dash-Aghel area.

Materials and Methods For the identification of mineralogical phases in the shales, four samples from a selective section were chosen for X-ray diffraction (XRD) analyses. XRD analyses were carried out using diffractometer model D5000 SIEMENS in Geological Survey of Iran (Tehran). The chemical compositions of the shales (#10) were determined at the ACME Analytical Laboratories Ltd. , Vancouver, Canada. The values of major and trace elements were determined by inductively coupled plasma emission spectrometry (ICP-ES). Rare earth element (REEs) contents were determined by inductively coupled plasma mass spectrometry (ICP-MS). Loss on ignition (LOI) was determined by weight loss of 1 g sample after heating at 950 °C for 90 min. The REE contents were normalized relative to chondrite and PAAS (Taylor & McLennan, 1985). Additionally, the geochemical data were evaluated by correlation coefficient analysis, elemental ratios, and plot of binary and ternary diagrams.

Discussion The result of XRD analyses revealed that quartz, kaolinite, illite, montmorillonite, calcite, albite, plagioclase, and goethite are the main mineral constituents of the studied shlaes. The positive correlations of K2O, TiO2, and Na2O with Al2O3 indicate that these elements are associated entirely with detrital phases in the samples. The Dash-Aghel shales show lower TiO2 values than the PAAS, which suggests more evolved (felsic) material in the source rocks. The depletion of P2O5 may be explained by the lesser amount of accessory phases such as apatite and monazite compared to PAAS in the studied samples. The high Sr content in shales indicates that Sr may be associated with calcite minerals. Correlation coefficients of positive and strong between K with elements such as Cr, U, Th, Ba, Hf, Nb, Rb, V, Sc, Co, and Ni suggest that illite have played the important role in distribution and concentration of these trace elements in the studied shales. The distribution pattern of REEs normalized to chondrite shows differentiation and strong enrichment of LREEs relative to HREEs and Eu and Ce negative anomalies in the studied shales. The geochemical signatures of clastic sediments have been used to find out the provenance characteristics (Armstrong-Altrin et al. , 2004). Al2O3/TiO2 ratios of most clastic rocks are essentially used to infer the source rock compositions, because the Al2O3/TiO2 ratio increases from 3 to 8 for mafic igneous rocks, from 8 to 21 for intermediate rocks, and from 21 to 70 for felsic igneous rocks (Hayashi et al. , 1997). In the studied shales, the Al2O3/TiO2 ratio ranges from 23. 57 to 44. 62, which suggests felsic rocks must be the probable source rocks for the shales of the Shemshak Formation. This interpretation is further supported by the TiO2 vs. Ni and Al2O3 vs. TiO2 bivariate plots, which also indicate that these shales were mainly derived from felsic source rocks. Ratios such as La/Sc, Th/Sc, Th/Cr, and Cr/Th are significantly different in felsic and basic rocks and may allow constraints on the average provenance composition. La/Sc, Th/Sc, Th/Cr, and Cr/Th ratios of shales from this study are compared with those of sediments derived from felsic and basic rocks (fine fraction) as
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well as to upper continental crust (UCC) and PAAS values. This comparison suggests that these ratios are within the range of felsic rocks. The REEs pattern and europium anomaly in the sedimentary rocks will provide important clues regarding the source rock characteristics. Higher LREEs/HREEs ratios and negative Eu anomalies are generally found in felsic igneous rocks, whereas the mafic igneous rocks exhibit lower LREEs/HREEs ratios and no or small Eu anomalies (Cullers, 1994). The Dash-Aghel shales show enrichment of LREEs relative to HREEs pattern with strong negative Eu anomalies. This pattern suggests that these sedimentary rocks were mainly derived from the felsic source rocks. Geochemical parameters such as U (0. 1-2. 6), authigenic U (0. 00-0. 28), Mn* (0. 41-1. 11), Ni/Co (3. 04-4. 92), Cu/Zn (0. 12-0. 47), U/Th (0. 33-0. 43), and Ce/Ce* (0. 44-0. 86) suggest that Dash-Aghel shlaes were deposited under oxic environmental conditions (Rimer, 2004). Alteration of rocks during weathering results in depletion of alkalis and alkaline earth elements and preferential enrichment of Al2O3. Therefore, weathering effects can be evaluated in terms of the molecular percentage of the oxide components by using the geochemical indices such as chemical index of alteration (CIA= [Al2O3/(Al2O3 + CaO* + Na2O +K2O] × 100) (Nesbitt & Young, 1982), chemical index of weathering (CIW = [Al2O3/( Al2O3 + CaO* + Na2O] × 100) (Harnois, 1988) and plagioclase index of alteration (PIA = (Al2O3–K2O) /[ (Al2O3–K2O) + CaO* +Na2O)] ×100) (Fedo et al. , 1995). However, samples having highly variable CaO contents due to variation in calcite abundance (such as those included in this study), may produce misleading conclusions if the CIA, PIA, and CIW are used to infer the degree of weathering (Cullers, 2000). Therefore, in this study we used a modified chemical index of weathering (CIW´ = molecular [Al2O3/ (Al2O3 + Na2O] × 100, in which CaO is left out of the CIW; Cullers, 2000). The CIW´ value of the Dash-Aghel shale samples vary from 96. 18-97. 07 %, which refer to intense weathering of source material of the shales. Based upon geochemical data such as ternary diagrams of (K2O+Na2O) (TiO2+Fe2O3+Al2O3) (Kreonberg, 1994) and Th-Sc-Zr/10 (Bhatia & Crook, 1986), the potential tectonic setting for Dash-Aghel shales is the passive continental margin environment.

Shear strength is one of the most important properties of mudrocks and shales in rock engineering and engineering geology. Because of the difficulty to obtain undisturbed samples of shales as required for determination of shear strength parameters, it is also the most difficult to evaluate. This research investigated properties that can be used to predict the shear strength parameters of Shemshak formation shales. Thirty samples of shales from various depths were collected from boreholes in Shemshak formation in the site of Siahbishe pumped storage powerhouse. Shear strength parameters (c and φ), tensile strength (TS), quartz percent (Qz %), porosity (n) and density (ρ) were determined in lab for each sample. Data were analyzed statistically and with fuzzy inference system to determine the relationships between shear strength parameters with other properties. Results show that cohesion and friction angle of shales can be meaningfully predicted from a few engineering properties by fuzzy inference system. The adjusted R2 values between measured and predicted values for cohesion and friction angle are 0.95 and 0.84 respectively. Also the variation of regression coefficient (R2), performance indices (VAF) and root mean square error (RMSE) with were calculated as for the shear strength parameters, obtained from the multiple regression modeland the fuzzyinference system, revealed that the prediction performance and accuracy of the fuzzy models are high and multiple regression equations not have performance in prediction of shear strength parameters of shales.

Metamorphic rocks are two groups of contact and regional in North West of Aligudarz. Regional metamorphic rocks in this area are composed from slate, phyllite, schists and contact metamorphic rocks are spotted schists and hornfels respectively. Petrographic studies of this rocks show that andalusite, cordierite and sillimanite minerals formed during of contact metamorphism. The geochemistry of theses rocks suggested that shale or greywacke is parent sedimentary rocks. The major and trace element show that igneous rocks (almost andesite) were primary rocks for these sediments. In comparison with average of upper continental crust, the rocks of studies area indicate of Rb, Sr, K negative anomalies cause to replacements of these elements during metamorphism and alteration. Discriminations diagrams of tectonic setting indicate a subduction zone (OIB). Based on the P-T pseudo sections and Bt-Sil- Cord, Bt-Sil and Sil-Cord paragenesis, for contact metamorphism estimated T and P were 650-670 ˚C and 3.5 Kbar respectively.

The uniaxial compressive strength and modulus of deformability of intact rocks are highly important parameters for rock engineering and engineering geology projects. Because of the difficulty of measuring these parameters and the need for laboratory equipments for their prediction, indirect methods are often used. In this study, some predictive models using regression analysis and fuzzy inference system have been developed for the Shales cropping out in the Shemshak formation in Siahbishe area. For this purpose, a series of easy measurable parameters such as density, porosity and point load index were applied. Both multiple regression analyses and the fuzzy inference system exhibited good performance in prediction of the uniaxial compressive strength and modulus of deformability. The variation of regression coefficient (R2), performance indices (VAF) and root mean square error (RMSE) were calculated as for the uniaxial compressive strength and the modulus of deformability obtained from the multiple regression model and the fuzzy inference system revealed that the prediction performances and accuracy of the fuzzy model are higher than those of multiple regression equations in prediction of uniaxial compressive strength and modulus of deformability.