مراحل پیدایش کانسار مس پورفیری- اپی‌ترمال نگار، جنوب‌باختری کرمان: بر پایة بررسی‌های زمین‌شناسی، دگرسانی و زمین‌شیمی

کانسار مس نگار در شهرستان بردسیر استان کرمان، در بخش مرکزی پهنة دهج- ساردوییه، در سامانة پورفیری جنوب نگار جای دارد. در این منطقه، کانه‌زایی درون سنگ‌های آتشفشانی، مواد آذرآواری و آندزیت‌های دگرسان با سن ائوسن رخ داده است که با توده‌های آذرین درونی گرانیتوییدی فراگرفته شده‌اند. این توده‌های آذرین درونی شامل گرانیت، گرانودیوریت، دیوریت، کوارتزدیوریت و مونزونیت هستند و از مجموعه کانی‌هایی تقریباً همانند انواع نمونه‌های آتشفشانی تشکیل شده‌اند. بر پایة بررسی‌های میدانی و سنگ‌شناسی، سنگ‌های آتشفشانی از نمونه‌های سنگی تراکیت، تراکی‌آندزیت، داسیت، توف و توف‌داسیتی با داشتن کانی‌های اولیه مانند کوارتز، پلاژیوکلاز± (آلکالی‌فلدسپار (در نمونه‌های اسیدی)) و نیز هورنبلند و بیوتیت با بافت غالب پورفیری تشکیل شده‌اند. الگوی دگرسانی‌ها شامل دگرسانی پروپیلیتیک در پیرامون، دگرسانی فیلیک و آرژیلیک در مرکز سامانة گرمابی و دگرسانی سیلیسی درون پهنة کانه‌دار است. در این کانسار، دگرسانی پتاسیک در ژرفا و در بخش باختری منطقه متمرکز است. از مهم‌ترین کانی‌های سولفیدی درون‌زاد در این منطقه می‌توان کالکوپیریت و پیریت را نام برد که با کانی‌های برون‌زادی مانند گوتیت، هماتیت، لیمونیت، مالاکیت و آزوریت همراه می‌شوند. بررسی‌های زمین‌شیمی و کانیایی نمونه‌های سنگی منطقه، وجود کانسار مس اپی‌ترمال سطحی سولفیداسیون بالا در بخش‌ خاوری و مس پورفیری عمقی در بخش باختری منطقه را نشان می‌دهند که در چندین مرحله متاثر از حضور تودة آذرین درونی ساخته می‌شوند.

an overview of the formation stages of porphyry-epithermal negar copper deposit, southwest of kerman: based on geological, petrological, and geochemical studies of negar area

the negar copper zone with about 1.2 km2 is located in the southern part of the urumieh-dokhtar magmatic belt. the dehaj- sarduiyeh metallogenic belt is considered as a part of the central iranian volcanic belt. the history of the formation of this volcanic belt, which resulted from the subduction of the neotethys ocean under the central iranian microcontinent (alavi, 1991), has been influential in the potential of this deposit and similar deposits. the negar area has not been precisely studied so far; therefore, in this research, efforts have been made to achieve a more detail and comprehensive understanding of ore mineralization and ore formation in this studied area based on geological, alteration, and geochemical studies.regional geologythe southeastern part of the urumieh-dokhtar belt is known as the dehaj- sarduiyeh metallogenic zone or the cenozoic magmatic arc of kerman. in fact, the oligo-miocene-pliocene intrusives in this belt have penetrated into eocene volcanic units and, with the expansion of alteration zones, gave rise to extensive mineralization in the region. the largest porphyry deposits from the kerman magmatic belt are associated with two types of oligocene-miocene granitoid rocks, kuh-panj and jebal-barez (mohammadzadeh et al., 2018). among them, the largest porphyry copper mineralizations are associated with kuh-panj granitoids, which are mostly concentrated in the northern and central parts of this belt. two important volcanic units present in this belt include the razak and hazar volcanic complexes. the razak complex consists of a sequence of volcanic rocks and sediments (nedimovic, 1973). these strongly folded volcanic and pyroclastic rocks intruded by granitoid intrusive masses (oligocene-miocene). the injection of these masses occurred along the major faults and axes of the anticlines in the region, leading to mineralization in the form of porphyry, vein, and regional veins in the area as well.analytical methodsin order to conduct geochemical studies, more than 30 samples from drilling logs, 9 samples from oxidized veins containing malachite mineralization, and approximately 40 samples from breccias, host rocks, alterations, and surface volcanic rocks were collected in trenches and outcrops. a total of 83 samples were collected using the rock chip method from the limited area to analysis by icp-mass method to the iran mineral processing research center in karaj.discussionmineralogical studies and investigations show that in the polished sections of the rocks in the studied area, metallic minerals such as hematite, goethite, pyrite, chalcopyrite, chalcocite, and possibly gold are often observable. the predominant texture is scattered grain texture, vein-like, and filling empty spaces. the sulfide minerals are scattered throughout the background of rock samples.as the field investigation display alteration and mineralization zones ae intimate association showing a specific pattern with propylitic alteration in the surroundings, phyllic and argillic zones in the center of the hydrothermal system, whereas silicic alteration with minor alonitization occupied the ore-bearing zone with abundant fracturing and veins, high levels of copper and mineralization in the inner parts of the hydrothermal system occurred in relation to alterations and the occurrence of boiling phenomena.the bimodal distribution diagram of copper also clearly indicates the abnormality of the entire area and the multiple ore-forming phases in this mineralized zone. probability in the initial stage of the formation of this deposit, deep granitoid masses intruded the upper volcanic rocks and sedimentary sequences in the region. the differentiation of intrusive masses and the accumulation of hydrothermal fluids and mostly magmatic solutions containing various chalcophile elements in their upper levels led to an increase in vapor pressure of fluids and consequently the movement of these solutions along the weak points such as major faults. as the temperature of these solutions reduces their acidic nature changes giving rise to precipitation the primary elements including cu., the temperature of the rocks along the path of the hydrothermal solutions increases. as the passage of hydrothermal solutions continues, thus, hot acidic solutions, produce a high concentration of elements and to deposit these elements as the sulfide veins and advanced argillic alterations.conclusionnegar area in the south (or southwest?) of kerman province indicate the high potential for copper mineralization. according to field and geological evidences, mineralization in this area occurred in volcanic rocks and its pyroclastic materials, and the intrusive bodies played a significant role in the development processes. due to the mineralization area, its formation processes are directly related to subduction of the neotethys ocean during the cenozoic era, particularly the eocene time. the extensional forces resulting from this subduction as well as the movement of faults create fractures and void spaces providing suitable pathways for migration of magma and associated ore-forming fluids. in the negar copper deposit area, two types of significant copper ore reserves are present. one type is the epithermal surface copper ore reserves located in the eastern parts, and the other type is the deep porphyry copper ore reserves found in the western part of the area. the overall geological, mineralogical and the geochemical features document that the negar copper deposit is an epithermal deposit with high sulfidation type.