معیار‌‌های اکتشافی کانسار مس و مولیبدن پورفیری کهنگ در استان اصفهان

در این پژوهش تصویرهای ماهواره‌ای، نقشه‌‌های زمین‌شناسی، داده‌‌های زمین‌شیمیایی و مغناطیسی کانسار مس-مولیبدن پورفیری کهنگ در بخش میانی کمان ماگمایی ارومیه-دختر برای شناسایی معیار‌های اکتشافی بررسی شد. کانی‌سازی به‌صورت افشان، برشی و استوک‌ورک در این کانسار دیده می‌شود. کانی‌سازی اقتصادی در رابطه با دایک‌‌های برشی دارای دگرسانی نوع فیلیک و در ژرفای بیش از 150 متر به‌صورت افشان و استوک‌ورک در رابطه با توده‌‌های آذرین درونی کوارتزمونزونیت پوفیری دارای دگرسانی فیلیک و پتاسیک با ترکیب شیمیایی کالک‌آلکالن است. دگرسانی‌‌های گرمابی از مرکز به حاشیه شامل فیلیک، آرژیلیک و پروپیلیتیک، و در ژرفای بیشتر از 200 متری پتاسیک هستند. نقشه‌‌های زمین‌شیمیایی هالة مرکب سه آنومالی غنی‌شدگی از عنصرهای مس و مولیبدن و تهی‌شدگی از عنصرهای سرب و روی منطبق بر سه مرکز پورفیری را به‌روشنی نشان دادند. بررسی داده‌‌های مغناطیسی این کانسار نشان داد پهنة دگرسانی فیلیک در رابطه با ناهنجاری کم مغناطیسی است. با مقایسه معیار‌‌های اکتشافی ناهنجاری کم مغناطیسی، ناهنجاری بالای هالة مرکب مس و مولیبدن، پهنه‌بندی دگرسانی‌ها، واحد‌‌های سنگی برشی، توده‌‌های نفوذی کوارتزمونزونیتی و همچنین، تقاطع ساختار‌‌های خطی با ساختار‌های حلقوی می‌توان پهنه‌های پر پتانسیل و نقاط حفاری پیشاهنگ موفق را در کانسار کهنگ شناسایی کرد. با بررسی معیار‌‌های اکتشافی معرفی‌شده می‌توان به اکتشاف کانسار‌های پنهان همانند کانسار کهنگ در بخش میانی کمان ماگمایی ارومیه-دختر پرداخت.

exploration criteria at kahang cu-mo porphyry deposit, isfahan province

porphyry deposits are very important as they contain very large reserves of copper and valuable secondary elements such as molybdenum and gold. copper-molybdenum or quartz monzonite porphyry deposits are usually structurally related to the magma arc associated with the upper parts of the subduction zone of the continental margin, and copper-gold or porphyry diorite deposits usually form in association with the subduction zone of the island arc (sillitoe, 2010; park et al., 2021).kahang cu-mo deposit is located in the middle section of the urumieyh-dokhtra magmatic arc. in 2001, kahang was identified by processing satellite imagery data and mapping hydrothermal alteration by rio tinto mining and exploration limited company. then, a detailed exploration was carried out by dorsa mining company from 2002 to 2007 and about 40 million tons of copper ore with a grade of 0.6 percent was established (asadi, 2007). since 2008, extensive deep drilling has been performed by the national iranian copper company to increase the proved reserve. the main focus of the previous researchers at the kahang deposit was mostly based on conceptual studies on magmatic character and hydrothermal alterations (ayati et al., 2008; harati, 2011; azadi et al., 2014; komeili, et al., 2017; aliyari et al., 2020). in the present research, aster satellite imagery data, geological maps, as well as geochemical and magnetic data were processed and used to identify optimum exploration criteria at the kahang porphyry cu-mo deposit and other similar deposits.geology and mineralization near-surface mineralization at kahang deposit is related to altered and brecciated quartz monzonite dykes, and deeper than 200 m is associated with altered quartz monzonite porphyry intrusions showing calk alkaline characteristics. the extensive hydrothermal alteration, from the center to the margin of the kahang deposit, are phyllic, argillic, and propylitic alterations. mineralization is mostly related to strong phyllic and potassic alterations.materials and methodsdetailed geological maps of kahang area were used to identify geological exploration criteria. aster satellite imagery data of the area was used to identify hydrothermal alterations. icp analytical results of elements such as cu, mo, zn, and pb were used to create uni-element and additive index multi-element geochemical anomaly maps to identify geochemical exploration characteristics. in total 16 rock samples were collected for petrographic studies and xrf analysis. a number of 568 magnetic measurements were used to create magnetic anomalies associated with favorable subsurface hydrothermal alterations possibly associated with cu-mo mineralization.geochemical exploration criteriaicp analytical results of the soil samples were used to identify geochemical exploration criteria at kahang deposit. basic statical studies were applied to these data to identify the variation of cu, mo, pb, and zn concentrations in the soil samples that could be associated with subsurface mineralization. mult-elements additive index geochemical maps of the analytical results of the soil samples showed a cu-mo enrichment zone in the central part of the hydrothermal alteration and a pb-zn depletion zone in the margin. based on these additive index maps three porphyry centers were identified at the kahang deposit for further exploration.magnetic signatureby processing ground magnetic data of the eastern porphyry center at kahang deposit, residual total magnetic intensity and upward continuation magnetic maps were created to identify magnetic signatures possibly associated with mineralized hydrothermal alterations. these maps showed an ellipsoid-shaped low magnetic anomaly in the eastern porphyry center associated with phyllic alteration hosting cu-mo mineralization. these low magnetic anomalies can be used to identify zones of subsurface mineralization at kahang deposit.discussionin this research, remote sensing, geological, geochemical, and geophysical studies showed three porphyry centers at kahang deposit. the world-class economic mineralization only occurred in the eastern porphyry center due to the presence of extensively strongly altered and brecciated quartz monzonite porphyry units showing low magnetic signatures and high cu-mo additive index anomalies. by comparing the low magnetic anomalies, high cu-mo anomalies, alteration zonation, brecciated rock units, and favorable structures, successful drilling targets can be identified to test subsurface mineralization at kahang deposit. the integration of this information along with the geochemical and primary drilling information were used to plan systematic drilling. most of the holes drilled in this zone at depths greater than 150 meters encountered economic mineralization of copper (approximately 0.5%) and molybdenum (approximately 700 ppm). the magmatic arc of urmia-dokhtar is considered the most important copper (molybdenum, gold) porphyry province in iran. most of the known large porphyry deposits of iran, such as sarcheshmeh and meidok, are located in the southeast of this magmatic arc, and songun is located in its northwest. in the central part of the urmia dokhtar magmatic arc, which is located in isfahan and central provinces, no similar deposit was reported prior to the discovery of kahang deposit. therefore, these studies have shown that the middle part of this arc may have the potential for many hidden porphyry mineralizations like kahang deposit. therefore, the exploration criteria identified in this study can be used for the exploration of similar deposits in this area at various stages of exploration, from identification to detailed exploration.