جستجوی مقالات مرتبط با کلیدواژه « Alteration » در نشریات گروه « جغرافیا »

Alteration is the simplest, cheapest and most suitable means of mineral exploration. The best way to find changes is to use satellite data processing.
Asadi and Tabatabaei (2007) have used band ratio processing methods and false color images by using selected principal component processing (PCA) to identify the range of variations in different regions on Aster images. Gomez et al. (2005) visualized the lithological units of Namibian using the PCA algorithm on Aster data.
The exposed rock units in Muteh mining area include a series of sedimentary, volcanic, and volcanic-clastic metamorphic rocks that extends from the green schist facies to the border of green schist and amphibolites along the northeast-southwest direction. These units have been repeatedly penetrated by alkaline intrusions, especially acid and granite (Rashidenjad, Omran et al., 2002).
In general, the controlling elements of mineralization in Muteh area include structural factors (faults and fractures), alteration, and deformation. Field observations indicate the occurrence of vein mineralization and gold sulfide deposits in mylonite shear zones and fault zones in felsic to mafic metavolcanic host rocks.
Gold mineralization is mainly concentrated in highly altered metariolites containing iron and copper sulfides and within fractures as veins and deposits. Alterations in silica, sericite, and carbonation are also observed along with these sediments, which are studied as exploration keys (Moritz et al., 2006).
In this area, according to the lithology and distribution of alteration zones and the type of mineralization in Muteh gold mine, gold orogeny-type mineralizations are expected, which can be indirectly identified by recognizing the above alteration.

In this study, Aster satellite images have been used to identify, discover and separate alteration zones in ENVI 5.3 software. Also, Landsat 8 satellite images have been utilized for general investigation and identification of hydrothermal alteration zones and expansion of iron oxide minerals, and Sentinel 2 satellite data due to better spatial and radiometric resolution than the above data has been applied to increase the spatial resolution of these data and the spatial accuracy of the map from the extracted changes.
In order to validate between the field observations and spectral analysis, 24 rock samples were taken from the place of alteration, especially siliceous, argillic, and sercitic alteration around Senjedeh and Chah Khatoon deposits. 11 samples were sent to Zarazma laboratory for XRD analysis, and five samples were sent to Zarkavan Alborz Company’s laboratory for chemical analysis of 41 elements by ICP-MS method and gold element by Fire Assay method.

Considering the relationship between alteration zones and metal mineralization, it is very important to know and map these areas in the exploration of these deposits.
The results and images show that the methods used in determining and separating the altered areas in Muteh exploratory area are acceptable and the optimal and effective methods in this research, SAM and MF, have been introduced.
According to the field observations and surface sampling around Chah Khatoon and Senjedeh mineral deposits, as well as the investigation of changes, it was found that the most important changes in the region are: silicification, kaolinization, sericization, chlorination, alonation, pyrite, carbonation and so forth. This wide range shows the difference in intensity of alteration in different parts of the mineral reserve, which can be attributed to the system of joints, fractures and faults in the region.
According to the available evidence, the metariolite rock is highly silicified in the tensile zones or in places with dense seams, and the pyrite particles in the context of these rocks have turned into iron hydroxide.

By using satellite data processing, various data and information can be identified and extracted. Satellite data processing is done in two ways: visual and digital processing. By combining these two methods, the desired effects can be detected more accurately than the accuracy of satellite images. The visual method consists of preparing images of different color combinations by placing spectral bands in the red, green, and blue channels. Digital satellite image processing methods include band ratio, principal component analysis, least square regression method (Ls-Fit), spectral analysis, spectral angle mapping (SAM), and adaptive MF filter. The selection of the above methods was based on the type of information requested to extract data from images.
Aster sensor images have no blue band (spectral range 0.4-0.5 µm) and the color composition of its VNIR bands is a standard RGB (1,2,3) false color composition. In this color combination, vegetation is seen in red. Since the study area is located in a relatively arid environment without vegetation, vegetation cover was avoided in the spectral analysis.
The use and processing of Aster satellite data is one of the main features of this sensor; the use of unique spectral reflectance curves of alteration indicator minerals helped to identify and highlight these altered areas as well as finding the potential of areas prone to metal mineralization. Due to the high ability of Sentinel-2A images in identifying gossan and iron oxide ranges, the processing of these data was used to highlight these areas better.

According to the agreement of the results of geochemical and XRD studies with the distribution map of the alteration zones identified from the reference spectrum (USGS) and the spectral library (JPL), with the distribution map of lines and structural fractures of Muteh exploratory zone outside the pre-identified areas, new alteration zones were also introduced that require field research to confirm the results of stereo data processing.

The design of Remote Sensing algorithms and the development of various methods of processing satellite images to identify porphyry copper deposits are among the important topics of studies in the field of mineral resource evaluation and their optimal exploitation. To this end, the determination of alteration zones provides a suitable tool for designing acceptable exploratory patterns. In this research with an almost comprehensive strategy and using the determination of alterations related to porphyry copper deposit based on Lowell and Gilbert model with three different strategies (visual, spectral and statistical processing) as well as the extraction of linements in the case area The study suggested the concentration range of the mineral for drilling. The study area in this article is Masjed Daghi porphyry copper deposit in the northeast of East Azerbaijan province, which consists of multispectral satellite images of ASTER, OLI of Landsat-8 and Sentinel-2 sensors for various processes including band ratio combinations, principal component analysis and pixel and subpixels basics spectral processing methods including SAM and MTMF, and statistical processing using the logical operator algorithm. Finally, by fuzzy and combining the layers of satellite image processing with geometric structures of the region (linements) which were extracted on Sentinel-2 data in two automatic and semi-automatic methods, the results were analyzed in GIS space and by comparing the presented results with the analysis of ground samples, the accuracy and conformity of the target areas were confirmed. User and producer accuracy for the area with the first priority were 78.54% and 78.36%, respectively, which are more appropriate criteria for introducing the area of ​​the drilling center.

In this study, processing and interpretation methods in remote sensing such as visual and spectral analysis have been performed on the EO-1, ASTER and ETM+ data from Meshkinshahr North area, and as a result, the alteration zones in the area have been identified. Then result Aeromagnetic data, using geological information, alteration and mineralization from the area.  Development of advanced tools in remote sensing and geophysical exploration during recent decades indicates the necessity and importance of these tools in industry. For this purpose, a variety of image processing methods are used Aeromagnetic methods have an important role for exploration of metallic ore deposits. To achieve good results from these methods. In order to identify alteration zones, image processing methods such as PCA (principal component analysis), SAM (spectral angle mapping) and MTMF (Matched Filtering MF) using ENVI software were applied on the Hyperion EO-1, ASTER and ETM+ images from the study area. After removal of the noise from observed magnetic data, processing steps were considered, including IGRF subtraction for the proper years, reduction to pole, Signal Analytic, Tilt (TDR), THDR, and upward continuation 1000 meters. Identification of alteration zones in the study area using remote sensing and image processing methods, and interpretation of the geophysical Aeromagnetic results using geological and Mineralization and Hot Springs and Faults information in the area have been led to the identification of Alteration zone. Many Anomaly and Alterations Kaolinite and silica located in the Meshkinshahr north area (northwest Sabalan) and the other many situated in the northwest Sarab. For credibility of results, samples were taken and analyzed by XRD methods. Confirmed the results of remote sensing and aeromagnetic processes. Conclusions of this research revealed that applying concurrency both the remote sensing and aeromagnetic data could be led to improve the precision of the results.

Contamination of soil with pathological and carcinogenic toxic elements presents a vitally important challenge for the environment. The dispersed contamination source is one of the important pollution sources, which different elements originate from weathering of rock and alterations zones and diffuse in the environment. The mine lands are considered as one of the dispersed contamination sources. In these locations, excavation, concentration and uncovering of some elements cause contamination of soil, which leads to contamination of the environment. This paper presents the pollution load of toxic elements in 236 soil samples collected around mining zone in north of Meshginshahr, northwest of Iran. Pollution intensity of the soils was calculated based on the pollution index and enrichment factor. Classification of the soils was done by using the factorial and cluster analysis. Soil samples collected in this study contain higher concentrations of harmful elements compared to the target and intervention limits set by international regulatory standards. Concentration of elements such as As (3-3430mg/kg), Mo (0.5-160mg/kg), Sb (0.21-97.6mg/kg), Pb (3.7-518mg/kg), Cu (10-748mg/kg) and Sn (0.5-11.4mg/kg) was found to be very high in the region soils. Some of the soil samples also have a worrying levels of Cr (3-267mg/kg), Mn (27-4120mg/kg) and Co (0.5-211mg/kg) concentrations. As per the pollution index, 19.4-66.7% of the soils on the mineralized and altered zones in the region are considered as contaminated with toxic elements. There is a high variation of concentration of elements in the soil samples. Distribution of the elements have been influenced heavily by both chemical (pH, organic carbon content (%), concentration of Fe + Mn, Al and S) and physical (grain size < 63µm) factors. Emphasis need to be put on control measures of pollution and remediation techniques in the study area.

Separation and mapping of alteration zones in the exploration of porphyry copper types is of particular importance. Aster sensor of Terra satellite image is used to show these alteration zones. There are different alteration in the Sarkuh area,include potassic, propylitic, phyllic, argillic, siliceous veins, and secondary effects to iron oxide-hydroxides that are reflected in the development of Aster images. Using methods such as color composition, band ratio, false color composition from band bonding and spectral analysis methods(Matched Filtering ، Ls-fit), was used. In argillic alteration, iron oxides and propylitic processes, Matched Filtering ، Ls-fit And the bandwidth ratio method is used among these methods, the MF algorithm and bandy's ratio is well answered. Potassic alteration has a close connection with mineralization. propylititic alteration includes calcite + chlorite + epidote + actinolite + sericite + pyrite in the surroundings of Stock and also volcanic rocks around it.. Phyllic alteration contains sericite and quartz. The results obtained in this section are also consistent with the results of the XRD analysis. In survey field, the set of alteration zones shows a relatively regular zoning with the north-east-southwest process with the center of the porphyry-type Sarkuh porphyry mass.

The study area is part of the Alborz Mountains and the western part of the Central Alborz Zone Aster image processing have been used for mapping hydrothermal alteration zones in studied area. We have combinated hybrid algorithm of banding and false color with logical operators and thereshold setting that have been based on field, Laboratory and experimental studies. In this paper we present algorithm of logical operators mapping that was distinguished by propylation alteration of Calcite and Epidote– Chlorite minerals which was confirmed by the results of alterations. Separate altered zones by using the bandeag ratio method. Detect hydrothermal alteration (Argilic and Flick) according to the sampling and field observations results.

Remote sensing technology has become one of the most efficient tools in geological explorations due to exploiting a broad spatial coverage along with a wide range of spectral resolution. Hence, it has been used widely for geological objects, such as identification and extraction of alteration zones during the recent decades. This research aimed to recognize alteration zones using shortwave infrared radiations of ASTER data and methods of spectral analysis including Crosta, spectral angle mapper (SAM) and mixture tuned matched filtering (MTMF) techniques. To implement the research goal, Siah Kooh area in Kerman Province of Iran was defined as a case study. Then, argillic, sericite (phyllic) and propylitic alteration zones were recognized via the proposed approach. To compare the obtained results with ground control samples for error estimation, Kappa index was used. Error evaluating of methods show that combined approach of MTMF with Kappa index of 64.62 and the total accuracy of 97.12 is the most efficient method to recognize and explore the alteration zones. MTMF method as an integrated approach shows the compliance with field samples and can be used as a suitable method to recognize and map the altered sedimentary zones.

Metamorphic basic rocks are exposed in the west of Esfahan, Shahrekord-Dehsard terrane with Jurassic age. That is part of the structural zone of Sanandaj- Sirjan. These rocks in green schist and most important rock outcrops in this area. The whole rocks chemistry indicates a basalt to basaltic andesite composition for the rocks with sub alkaline and tholeiitic trend. These results indicated this rocks generated back arc basin volcanic subduction. This is mainly composed of plagioclase, amphibole, quartz, epidote, garnet, chlorite and opaque and indicated green schist facies regional metamorphic paragenesis. Amphibole is mainly minerals in metamorphic basic rocks as well as phenocryst and fine crystal in thin section these rocks can be seen. frequency amphibole crystals between 40 to 50 percent rock volume is changed.The most alteration halo are sericitization, chloritization, epidotization and silicification. With this hydrothermal alteration veins iron is present. NW-WS trend Fe-silicified veins cut this rock. These veins are diagnosed with a gossan from other outcrops. Field and laboratory evidence indicates a high potential of the region economically.This mineralized type is likely Au load quartz type in Precambrian green schist belts and Au mineralization probability in this region are increase.