@article { author = {Ghorbani, Afsaneh and Kouhestani, Hossein and Mokhtari, Mir Ali Asghar}, title = {Genesis of the Varmazyar Pb-Zn (Ag) occurrence, Tarom-Hashtjin metallogenic belt: Insights from ore geology, geochemistry and fluid inclusion studies}, journal = {Journal of Economic Geology}, volume = {14}, number = {1}, pages = {1-38}, year = {2022}, publisher = {Ferdowsi University of Mashhad}, issn = {2008-7306}, eissn = {2423-5865}, doi = {10.22067/econg.2021.51947.86716}, abstract = {IntroductionVarmazyar Pb–Zn (Ag) occurrence, 65 km north of Zanjan, is located in the Tarom–Hashtjin metallogenic belt (THMB). The THMB has been recognized as one of the most important epithermal metallogenic belts in Iran (Kouhestani et al., 2018b) that host numerous small- to medium-sized epithermal deposits (i.e., Gulojeh, Aqkand, Aliabad–Khanchy, Chodarchay, Khalyfehlou, Chargar, Zajkan, Marshoun, Abbasabad, Zehabad, and Shah Ali Beiglou). These epithermal deposits are temporally and spatially related to late Eocene granitoids (Mehrabi et al., 2016; Kouhestani et al., 2018b).Although the general geological characteristics of the region, where the Varmazyar occurrence is located, were determined (Faridi and Anvari, 2000), no detailed studies have been conducted on the mineralogy, geochemistry, and the ore-forming fluids characteristics of the Varmazyar occurrence. In this paper, we investigate the geology, mineralogy, geochemistry, fluid inclusions, and alteration styles of the Varmazyar occurrence to constrain its ore genesis. These results may have implication for the regional exploration of epithermal deposits in the THMB. Materials and methodsDetailed field work has been carried out at different scales in the Varmazyar area. A total of 70 samples were collected from various parts of ore veins and breccias, host tuff units and granitoid intrusion. The samples prepared for thin (n=15) and polished-thin (n=27) sections in the laboratory of University of Zanjan, Zanjan, Iran. Representative 7 samples from the mineralized veins and breccias, 1 sample from host intermediate tuff unit and 1 sample from barren and fresh granite intrusion, were analyzed for rare and rare earth elements using ICP–MS in the Zarazma Analytical Laboratories, Tehran, Iran.Fluid inclusion measurements have been conducted on 4 doubly polished thick (~150 μm) sections including crystalline quartz, and sphalerite from the second, and third stages of ore formation. Microthermometric measurements were performed using a Linkam THMSG-600 heating–freezing stage attached to a ZEISS microscope in the fluid inclusion laboratory of Iranian Mineral Processing Research Center, Tehran, Iran. Results and DiscussionThe geological units hosting the Varmazyar occurrence are mainly Eocene volcanic and volcaniclastic rocks that were intruded by late Eocene granitoids. The volcaniclastic rocks can be divided into two units as acidic (lithic tuff, lithic crystal tuff and crystal tuff) and intermediate (lithic crystal tuff, crystal tuff, and lithic tuff) units. They are metamorphosed to clinopyroxene hornfels facies near contact intrusions. The granodiorite intrusion is the main rock units in the Varmazyar area. It crops out mainly in the south, southwest and northeast of the Varmazyar occurrence. It ranges in composition from monzogranite to syenogranite and shows porphyritic and granular textures.Mineralization at Varmazyar occurs as epithermal base metal quartz-sulfide brecciated vein that occupy NS-trending faults in the Eocene acidic and intermediate tuff units.  The ore vein extends up to 300 m along, from several cm to 2–3 m wide, and generally dip steeply (65–80°) to the west. Wall-rock alterations developed at the Varmazyar occurrence include silicification, intermediate argillic, carbonate, and propylitic alteration; the first three are closely related to the Pb–Zn (Ag) mineralization. The alteration styles show a systematic zonation pattern, from the silica, via intermediate argillic, to propylitic alteration. Four stages of mineralization can be distinguished at Varmazyar. Stage 1 is represented by silicification of host rocks along with minor disseminated pyrite. This stage is a pre-ore stage and usually crosscut by later stages. Stage 2 is the main ore-stage at the Varmazyar occurrence. It is characterized by up to 5 cm wide quartz veins and breccias that contain variable amounts of disseminated galena, sphalerite, and minor pyrite. Clasts of this stage and associated wall-rock alteration have been recognized in the hydrothermal cements of stage 3 breccias. Stage 3 is marked by quartz-calcite-manganese oxides (psilomelane, pyrolusite, braunite) veins and breccia cements. It is usually crosscut previous mineralization stages and, in turn, is cut by stage 4 calcite veinlets. Stage 4 is a barren post-ore stage represented by < 1 mm wide calcite veinlets. This stage usually crosscuts previous ore stages. No sulfide minerals are recognized with stage 4. The ore minerals at Varmazyar formed as vein-veinlet and hydrothermal breccia cements, and show disseminated, vein-veinlet, brecciated, comb, crustiform, colloform, cockade, bladed, plumose, and vug infill textures. Galena, sphalerite, pyrite, psilomelane, and pyrolusite are the main ore minerals; smithsonite, cerussite, goethite, secondary pyrolusite, and braunite are supergene minerals. Quartz, calcite, and sericite are present in the gangue minerals. Comparison of Chondrite–normalized rare elements and REE patterns of host intermediate tuffs, barren and fresh granite intrusion, and the mineralized samples at Varmazyar indicate that mineralization is probably genetically related with granite intrusions. In this case, leaching of some elements from the host tuff units may have involved in mineralization. Ore-forming fluids associated with the quartz-sulfide veins are represented by two-phase aqueous inclusions and by H2O–NaCl fluids with moderate-temperature (135–249 °C) and low-salinity (0.2–6.4 wt.% NaCl equiv.). Fluid inclusion data indicates that fluid boiling and mixing were important processes in the evolution of the ore-forming fluids at Varmazyar. Our data suggest that Varmazyar is an example of intermediate-sulfidation type of epithermal base metal mineralization. ReferencesFaridi, M. and Anvari, A., 2000. Geological map of Hashtjin, scale 1:100,000. Geological Survey of Iran.Kouhestani, H., Mokhtari, M.A.A., Chang, Z. and Johnson, A.C., 2018b. Intermediate-sulfidation type base metal mineralization at Aliabad–Khanchy, Tarom–Hashtjin metallogenic belt. NW Iran. Ore Geology Reviews, 93: 1–18. https://doi.org/10.1016/j.oregeorev. 2017.12.012Mehrabi, B., Ghasemi Siani, M., Goldfarb, R., Azizi, H., Ganerod, M. and Marsh, E.E., 2016. Mineral assemblages, fluid evolution and genesis of polymetallic epithermal veins, Gulojeh district, NW Iran. Ore Geology Reviews, 78: 41–57. https://doi.org/10.1016/j.oregeorev.2016.03.016}, keywords = {Epithermal mineralization,Intermediate-sulfidation,fluid inclusion,Tarom–Hashtjin,Varmazyar,Zanjan}, title_fa = {تعیین منشأ رخداد معدنی سرب- روی (نقره) ورمزیار، کمربند فلززایی طارم- هشتجین: بر اساس داده‌ های زمین‌ شناسی، زمین‌ شیمی و میان بارهای سیال}, abstract_fa = {کانه‌زایی سرب- روی (نقره) در رخداد معدنی ورمزیار به‌صورت رگه کوارتز- سولفیدی‌ درون توالی توف‌های حدواسط و اسیدی ائوسن رخ داده است. گالن، اسفالریت، پیریت، پسیلوملان و پیرولوزیت، کانه‌های فلزی و کوارتز، سریسیت و کلسیت، کانی‌های باطله می‌باشند. بافت‌های کانسنگ شامل دانه‌پراکنده، رگه- رگچه‌ای، بِرشی، شانه‌ای، پوسته‌ای، کاکلی، پرمانند، گل‌کلمی، تیغه‌ای و پُرکننده فضای خالی است. چهار مرحله کانه‌زایی در ورمزیار قابل تشخیص است. مرحله اول کانه‌زایی با سیلیسی‌شدن سنگ‌های میزبان همراه با اندکی پیریت اکسیده مشخص می‌شود. مرحله دوم شامل رگه- رگچه‌های کوارتزی و بِرش‌های گرمابی است که حاوی مقادیر متغیری گالن و اسفالریت همراه با میزان اندکی پیریت می‌باشند. مرحله سوم با حضور کوارتز، کلسیت و اکسیدهای منگنز (پسیلوملان، پیرولوزیت و براونیت) در رگه‌ها و سیمان گرمابی بِرش‌ها مشخص می‌شود. مرحله چهارم شامل رگه- رگچه‌های کربناتی تأخیری است. دگرسانی‌های گرمابی شامل سیلیسی، آرژیلیک متوسط، کربناتی و پروپیلیتیک می‌باشد. شباهت الگوهای به‌هنجارشده عناصر کمیاب و کمیاب خاکی برای نمونه‌های کانه‌دار و نمونه‌های گرانیتی و توف‌های حدواسط، بیانگر ارتباط سیالات کانی‌ساز با توده گرانیتی و مشتق‌شدن آنها از این توده و همچنین شسته‌شدن عناصر از واحدهای توفی منطقه است. براساس داده‌های ریزدماسنجی، سیالات مسئول کانه‌زایی در ورمزیار، یک سیستم H2O-NaCl با دمای متوسط (249-135 درجه سانتی‌گراد)، شوری پایین (4/6-2/0 درصد وزنی معادل نمک طعام) و چگالی پایین (1-8/0 گرم بر سانتی‌متر مکعب) بوده است. بر اساس این داده‌ها، روند تکامل سیال کانه‌ساز با فرایندهای اختلاط سیالات و جوشش سیال هم‌خوانی دارد. ویژگی‌های رخداد معدنی ورمزیار با کانسارهای اپی‌ترمال فلزات پایه (نقره) نوع سولفیداسیون حدواسط قابل مقایسه است.}, keywords_fa = {کانه‌زایی اپی‌ترمال,سولفیداسیون حدواسط,میانبار سیال,طارم- هشتجین,ورمزیار,زنجان}, url = {https://econg.um.ac.ir/article_41498.html}, eprint = {https://econg.um.ac.ir/article_41498_20a363ac9944b91b698c1f3fafc20cf6.pdf} }