شناسایی دگرسانی های هیدروترمال در منطقه موته، شمال غرب اصفهان، با استفاده از تصاویر ماهواره ای (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
کانسار طلای موته و نواحی مجاور آن از تیپ طلای کوهزایی است، در این ناحیه در مجموعه متاولکانیک ها و در رابطه با گنایس و میکاشیست هاى متعلق به پرکامبرین، کانی زایی عمدتاً در زون های دگرسانی سیلیسى و سریسیتى و کربناتیزاسیون، در شکستگی ها به صورت رگه و رگچه اى به همراه اکسیدهای آهن متمرکز شده است. طبق بررس ی های انج ام ش ده در ای ن منطق ه، دگرس انی های ت وأم رس ی، اکس یدهای آه ن و سیلیسی شدن سنگ دیواره برای پی جویی ذخایر طلا حایز اهمیت است. در این تحقیق تصاویر ماهواره ای ASTER و لندست 8 به منظور بارزسازی کانی های رسی در رابطه با دگرسانی ها، اکسیدهای آهن و واحدهای سنگی منطقه مطالعاتی و از داده ماهواره ای سنتینل-2 برای افزایش قدرت تفکیک مکانی این داده ها و افزایش دقت مکانی نقشه های دگرسانی استخراج شده مورد استفاده قرار گرفته اند. پس از انجام پیش پردازش های لازم، برای پردازش تصاویر فوق الذکر روش های مختلف پردازش داده هاى ماهواره اى چند طیفى ASTER مانند ترکیب رنگی کاذب، نسبت باندی، روش کمترین مربعات رگرسیون [1](Ls-Fit)، آنالیز مولفه های اصلی [2](PCA)، نقشه بردار زاویه طیفی[3](SAM)، فیلتر گذاری تطبیقی [4](MF)، برای شناسایی و تفکیک کانی های دگرسانی مرتبط با کانی زایی طلا به کار گرفته شدند. در نهایت نقشه پراکندگی زون های دگرسانی شناسایی شده، با نقشه زمین شناسی، مشاهدات میدانی و نتایج آنالیز XRD نمونه های میدانی مقایسه شد. برای مقایسه نتایج و ارزیابی صحت روش های یاد شده از ماتریس خطا و ضریب کاپا استفاده شد. پس از نمونه برداری ها و تجزیه های آماری، مشخص شد که روش نقشه بردار زاویه طیفی، بهترین تطابق را با واحدهای زمین شناسی منطقه نشان می دهد، و با این روش علاوه بر زون های از پیش شناخته شده، محدوده های جدید دگرسان شده قابل شناسایی است. [1] - least square Fit[2]- Principal Component Analysis[3] - Spectral Angle Mapper[4] - Matched FilteringIdentification of hydrothermal alterations in Muteh area, northwest of Isfahan, using satellite images
Extended Abstract 1- IntroductionAlteration 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.2- Materials and methodsIn 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.3- ResultsConsidering 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.4- DiscussionBy 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.5- ConclusionAccording 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.