استفاده از روش ترکیبی Ahp-Topsis به منظور مدل‌سازی پتانسیل معدنی مس در ورقه یکصدهزار ابهر، شمال‌غرب ایران

اساساً دلیل تهیه مدل پتانسیل معدنی این است که با شناسایی بهترین نواحی امیدبخش و مناطق اهداف اکتشاف، ناحیه مورد مطالعه محدودتر شده تا با کوچک شدن آن، ریسک عملیات اکتشاف کاهش و با قطعیت بیش تری بتوان نواحی امیدبخش را برای متمرکز شدن در مراحل تفصیلی انتخاب نمود. بر این اساس، هدف از مطالعه حاضر تلفیق لایه های شاهد مختلف با استفاده از روش ترکیبی ahp-topsis، به منظور شناسایی نواحی امیدبخش مس در ورقه یکصدهزار ابهر می‌باشد. بدین منظور، 7 لایه شاهد اطلاعاتی شامل آنومالی ژئوشیمیایی مس حاصل از تحلیل مولفه اصلی، نقشه فاصله از واحدهای سنگی آذرین نفوذی و واحدهای آتشفشانی، نقشه فاصله از گسل‌های منطقه و در نهایت نقشه‌های فاصله از دگرسانی‌های آرژیلیک، فیلیک و پروپیلیتیک در نظر گرفته شد. جهت آماده سازی نقشه های شاهد برای تلفیق، ابتدا مقادیر نقشه‌ها با استفاده از تابع لجستیکی به فضای مناسب با دامنه (1-0) منتقل و سپس توسط روش فرکتالی عیار - مساحت کلاسه‌بندی شدند. در گام بعد معیارها و زیرمعیارهای مختلف توسط روش ahp وزن دهی و در ادامه توسط روش topsis تلفیق شدند. نقشه پتانسیل نهایی توسط نمودار( prediction-area(pa مورد اعتبارسنجی قرار گرفت. بر طبق این نمودار، نقطه تلاقی منحنی های نرخ پیش بینی و مساحت اشغال شده مربوطه، مقدار 78 را نشان داد که توان بالای مدل مذکور را در معرفی نواحی امیدبخش مس ثابت می کند. در مدل پتانسیل معدنی مس ایجادشده، عمده نواحی پرپتانسیل مس در نیمه شمالی ورقه و در زیرزون طارم معرفی شده است که به خوبی با محل کانسارهای قدیمی مس نظیر خلیفه لو، چرگر، الوند، حصار و دوه‌یاتاقی منطبق می باشد.

Application of AHP-TOPSIS method to model copper mineral potencial in the Abhar 1:100000 geological map, NW Iran

Extended abstract Introduction Fulfillment of exploration activities is costly and timeconsuming, which reveals the necessity of mineral prospectivity mapping (MPM) for identifying highly mineral potential zones. MPM as a key procedure, integrates multiple geoscience datasets performed across different scales. In this regard, Various methods have been developed over the past three decades that are basically categorized into either datadriven or knowledgedriven methods. This study aims to represent a new combinatorial MCDM method called AHPTOPSIS to outline highly potential Cu zones in the Abhar area. Material and Methods The Abhar area is located southeast of Zanjan province, NW Iran. From the structural and metallogenic point of view, the study area has been composed of two segregated subzones: Tarom subzone and Soltanieh subzone. Most of the known Cu occurrences are of vein type, the overwhelming of which have outspread in the northern part of the study area (Tarom subzone). A slight body of profoundly eroded leucogranite is partially manifested in the low topography circa Doran village, named Doran granite which affiliates to late Precambrian. The granite and some small sporadic Eocene granites have intruded into Kahar and Soltanieh dolomites, respectively. This could promise the skarn mineralization of iron and copper in this area. The research presented here endeavors to outline Cu potential zones based on subsequent investigations appertaining to the Abhar area using AHPTOPSIS. This method is a hybrid method, in which the task of AHP is to determine the weights of criteria and subcriteria, and thereinafter the TOPSIS method is concerned with order preference of decision alternatives. Despite the ability and competence of each of the foregoing methods, experience has affirmed that the combination of two MCDM methods and the concurrent use of their potentials gives better results and leads to eminent performance for the MPM. The first paramount step in mineral prospectivity mapping is to identify and collect geospatial data pertinent to the deposit typesought. In the present study, aforesaid data is taken into consideration based on the data availability alongside theoretical and empirical analysis of the spatial association between Cu mineral deposit and various data. Hereupon, seven evidential layers, as predictor maps, were propounded to outline Cu potential zones. They consisted of multielement geochemical signatures pertinent to Cu mineralization, closeness to late Eocene intrusive contacts, closeness to late Eocene volcanic rocks, proximity to the faults, and vicinity to argillic, phyllic and propylitic alterations.     Modeling and Discussion The spatial evidence values in the obtained maps do not involve identical maximum and minimum values. Inevitably, the evidential values of mentioned maps were transformed into a new space. Then concentrationarea (CA) fractal model, was applied to classify spatial values of evidential maps. Next, AHPTOPSIS MCDM method was applied to generate Cu prospectivity map. In this regard, AHP method was used to determine the weights of criteria and subcriteria and TOPSIS method was used to rank the alternatives. For this, a decision matrix of 361638×7 was created that comprises 7 criteria (evidential maps) and 361,638 alternatives (each of which corresponds to a particular cell with a certain coordinate in the evidence layers). At the end, the Cu prospectivity map was generated. To evaluate the efficiency of prospectivity map obtained by AHPTOPSIS method, the PredicationArea (P–A) plot was applied. According to the result of this PA plot, the intersection point for this prospectivity model has been appeared in a high place, at about 78%. Thus, this map can be used as target map for subsequent detailed explorations. Conclusion The present study addresses the successful application of a new hybrid MCDM method called AHPTOPSIS to generate a predictive model for Cu mineralization in the Abhar area. Despite the ability of two methods alone, experience has demonstrated that the combination of two or more MCDM methods eventuate to better results. Since the simultaneous use of these two methods will ultimately eventuate to the reduction of the target areas, this could indicate the high precision of the hybrid method in predicting target areas. Consequently, it was decided to use a combination of two methods, which are already mentioned. After generating the overlay prospectivity map, P–A plot was used to evaluate its efficiency in predicting favorable areas. Based on the results, the AHPTOPSIS method can provide a potent tool for quantifying the specifications of geoanomalies and delimiting target areas in mineral exploration programs