زمین شناسی، دگرسانی، کانی سازی، زمین شیمی، بررسی سیالات درگیر، پتروژنز و سن‌ سنجی دایک های دیوریتی محدوده مس رباعی (جنوب دامغان)

محدوده اکتشافی مس رباعی در کمربند ترودچاه شیرین در فاصله 95 کیلومتری جنوب دامغان واقع‌شده است. سنگ ‌شناسی منطقه از واحدهای آتشفشانی ائوسن با ترکیب آندزیت و تراکی ‌آندزبت تشکیل‌شده که دایک ‌هایی با ترکیب دیوریتی در این واحدها نفوذ کرده است. زون ‌های دگرسانی رخنمون‌یافته در این منطقه شامل پروپیلیتیک، سریسیتی، آرژیلیک و کربناتی ‌شدن است. کانی ‌سازی به‌صورت رگه‌ ای با شیب بین 60 تا 80 درجه با روند شمال‌شرقی جنوب‌غربی و عرض 1 تا 5 متر در امتداد شکستگی ‌ها و گسل ‌ها رخ‌داده است. کانی‌ های اولیه شامل کالکوپیریت، بورنیت و پیریت و کانی ‌های ثانویه شامل کالکوسیت، کوولیت، مالاکیت، آزوریت، گوتیت، لیمونیت و هماتیت است. مقدار مس بین 0.01 تا 5.6 درصد متغیر است و همچنین مقدار عناصر سرب، روی، نقره و طلا در منطقه، پایین است. دایک‌ های دیوریتی منطقه غنی ‌شدگی در عناصر لیتوفیل بزرگ یون و عناصر نادر خاکی سبک، و تهی ‌شدگی در عناصر نادر خاکی سنگین و عناصر با شدت میدان بالا نشان می‌ دهند. مقدار 87sr/86sr، 143nd/144nd اولیه و ایزوتوپ ‌های اولیه εndi بیوتیتهورنبلند دیوریت پورفیری به‌ترتیب برابر با 0.705664،  0.518426 و 1.7 است. همه این شواهد با تشکیل‌شدن دایک‌ های دیوریتی محدوده اکتشافی مس رباعی از گوشته اولیه با ذوب‌بخشی گوه گوشته ‌ای در بالای زون فرورانش همسو است. بر اساس داده ‌های upb بر روی کانی زیرکن، سن دایک‌ ها برابر با 0.49±50.49 میلیون سال مربوط به اشکوب ایپرزین (ائوسن زیرین) است. دماسنجی بر روی سیالات درگیر اولیه موجود در کانی کلسیت مرتبط با کانی‌سازی، بیانگر تشکیل این نوع کانی‌ سازی در دمای حدود 165 تا 300 درجه سانتی ‌گراد از سیالی با شوری متوسط (7 تا16  درصد وزنی معادل نمک طعام) است. مخلوط‌‌شدن سیال ‌ها با شوری متفاوت و در نتیجه کاهش شوری مهم‌ترین عامل در ته‌نشست مس در منطقه است. شواهد سنگ‌ شناسی، دگرسانی، شکل و حالت کانی ‌سازی، کنترل ساختاری، سیالات درگیر و ناهنجاری‌ های زمین ‌شیمیایی نشان می‌دهد که کانی ‌سازی مس رگه ‌ای محدوده اکتشافی رباعی از نوع اپی ترمال است.

Geology, alteration, mineralization, Geochemistry, fluid inclusion, petrology, petrogenises and U-Pb zircon dating of diorite dykes in the Robaie copper area (South of Damghan)

Introduction The Robaie copper area is located 95 kilometers South of Damghan in the Semnan province. The study area has coordinates between 54˚30΄37˝to 54˚30΄42.71˝ latitude and 35˚22΄29.41˝ to 35˚23΄47.54˝ longitude. Geotectonically, the study area is located in the central Iran and in the northern part of the TorudChahshirin volcanicplutonic belt (Houshmandzadeh et al., 1978). The TorudChahshirin volcanicplutonic belt is a Tertiary magmatism in central Iran which is composed of volcanic rocks with dominant andesite composition and granodiorite intrusive with dominant diorite composition (Fard et al., 2001). TorudChahshirin volcanicplutonic belt has created a favorable geological situation for base metals such as copper, lead, zinc, gold, silver and other precious and base metals, such as the Robaie copper area, Chah Messi (Cu±PbZn; Imamjome et al., 2009), KuhZar (CuAu; Rohbakhsh et al., 2018) and other instances. The main objective of this study is geology, petrography, UPb zircon dating and SrNd isotope and also alteration, mineralization, geochemistry and fluid inclusion in the study area.   Materials and methods 60 samples were collected from the study area. Petrographic studies were done on 40 thin sections. Mineralization and paragnesis of the system were studied based on 10 polishedthin sections and 6 polished sections. The measurements were conducted on a Linkam THMSG 600 at the Ferdowsi University of Mashhad. REE (ICPMS methodACME Laboratory in Vancouver, Canada) elements were analyzed for 3 samples of diorite dykes. Eight  sampels for geochemistry and four samples for fire assay were analyzed at the Zar Azma Company. UPb dating in zircon of diorite dyke was conducted by the ICPMS method in the Arizona LaserChron Center. Sr and Nd isotopic compositions were determined at the Laboratório de Geologia Isotópica da Universidade de Aveiro, Portugal.   Results The geology of the area is dominated by volcanic rocks (andesite and trachyandesite), which were intruded by diorite dykes. Alteration zones are propylitic, argillic, sericitic and carbonate. The Copper deposit in the study area occurs as ore veins situated along fault zone with NSSW trending. Vein thickness varies from 15m. Vein thickness varies from 15m. The primary minerals are chalcopyrite, pyrite and chalcocite, covellite, bornite, malachite, azurite, hematite, goethite and limonite are secondary minerals. The amount of Cu is between 0.01 to 5.6 % and amount of Ag, Sb, Pb, Zn, As elements is low. The homogenization temperature (Th) values ranged from 165 to 300 oC. Salinities of oreforming fluids ranged from 7 to 16 wt. % NaCl equivalents. Diorite dykes in the Robaie area have characteristics of enrichment in LREE versus HREE, enrichment of LILE and depletion in HFSE. The initial 87Sr/86Sr and 143Nd/144Nd ratios of biotitehornblende diorite are 0.705664 and 0.512486, respectively. The εNdI value is 1.7. In the εNdI versus initial 87Sr/86Sr diagram diorite dykes of the Robaie area plot to the right part of the mantle array. The mean age of diorite dyke is 50.49±0.49 Ma. Therefore, the UThPb zircon dating indicates that diorite dyke formed in the early Eocene (Ypresian) era.   Discussion Diorite dykes originated from mantlederived magmas. The parental melt would have originated in a nondepleted mantle source. Isotopic data from diorite dykes show that subduction source with contamination to continental crust. In tectonic setting diagrams (Pearce et al., 1984) diorite dykes plot on the fields of the volcanic arc granites (VAG). In the Dy/Yb vs. Dy system (Shaw, 1970) diorite dykes of Robaie area were formed by 1520% partial melting of spinelphlogopite lherzolite. According to Yh/Yb vs. Ta/Yb (Pearce et al., 1984) and Ba/La vs. Th/Nd diagrams (Shaw, 1970) diorite dykes were formed from slabdrive fluid in the active continental margins. Fluid inclusions data of the Robaie area manifest that the oreforming fluids were medium to low temperature and medium to low salinity. The pressure determined for the Robaie area was approximately < 10 MPa, which is equivalent to a depth of approximately < 1 km assuming lithostatic pressure. Fluid inclusion studies indicate that there is a positive correlation between homogenization temperature and fluid salinity, similar to the process of fluid mixing. The decrease in salinity has been the most important factor in the precipitation of copper in the area. All of evidence shows that mineralization in the Robaie area is of epithermal type deposit.   Acknowledgment The financial support provided by grant no. 42842.3, date: 3 Jan 2017 is greatly appreciated. We would like to thank Mr. Ehsan Azizian of the Zamin Pouyan Fraz Assia Company for the generous support and the access to mine data.   References Fard, M., Rastad, E., RashidnejadOmran, N. and Ghaderi, M., 2001. Mineralization and potential of gold in Torud Chahshirin volcanoplutonic complex (south Damghan). 5th Symposium of Geological Society of Iran, Tehran University, Tehran, Iran. Houshmandzadeh, A.R., Alavi Naini, M. and Haghipour, A.A., 1978. Evolution of geological phenomenon in Torud area. Geological Survey of Iran, Tehran, Report 5H, 138 pp. Imamjome, A., Rastad, E., Bouzari, F. and Rashidnezhad, N., 2009. An introduction to individual disseminated veinlet and vein mineralization system of Cu (PbZn) in the Chah Messi and Ghole Kaftaran mining district, eastern part of the TroudChah Shirin magmatic arc. Scientific Quarterly Journal, Geosciences, 18(70): 112–125. Pearce, J.A., Harris, N.B.W. and Tindle, A.G., 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology, 25‌(4): 956–983. Rohbakhsh, P., Karimpour, M.H. and Malekzadeh Shafaroudi, A., 2018. Geology, mineralization, geochemistry and petrology of intrusive bodies In KuhZar CUAu deposit, Damghan. Journal of Economic Geology, 10(1): 1–23. (in Persian with English abstract) Shaw, D.M., 1970. Trace element fractionation during anataxis. Geochimica et Cosmochimica Acta, 34(2): 237–243.