مطالعه دگرسانی، کانه نگاری، سیالات درگیر، اسپکتروسکوپی رامان و ایزوتوپ های پایدار اکسیژن- هیدروژن در کانسار آهن-آپاتیت لکه سیاه 1، استان یزد

کانسار آهن لکه سیاه 1 در 40 کیلومتری شمال‌شرقی شهرستان بافق در استان یزد و در پهنه زمین‌ساختی کاشمر کرمان واقع‌شده است. واحدهای سنگی منطقه به کامبرین زیرین تعلق دارند و شامل ریولیت، ‌آندزیت، سنگ های آذرآواری، دولومیت و ماسه‌سنگ هستند. توده های نفوذی با ترکیب مونزونیت تا دیوریت در این واحدهای سنگی نفوذ کرده اند. فرایند دگرسانی، سنگ های منطقه را تحت‌تاثیر قرار داده؛ به طوری که مهم ترین هاله های دگرسانی رخ‌داده در منطقه (سدیک) کلسیک، کلریتی شدن، اپیدوتی شدن، سریسیتی شدن، سیلیسی شدن و آرژیلیک است. مگنتیت کانه اصلی کانسار است که دارای بافت های توده ای، برشی و مارتیتی است. بر اساس بررسی‌های پتروگرافی، چهار نوع سیال درگیر در کانی کوارتز همراه کانسنگ مشاهده شده که شامل تک‌فاز مایع (l)، تک‌فاز گاز (v)، دوفازی (l+v) و سه فازی (l+v+h) هستند. دمای همگن‌شدن سیالات درگیر دو فازی بین 217 تا 428 و سه فازی بین 384 تا 467 درجه سانتی‌گراد و شوری برای سیالات دو فازی بین 10 تا 27 و برای سه فازی بین 40 تا 44 درصد معادل شوری نمک طعام به‌دست آمد. بر اساس بررسی‌های اسپکتروسکوپی لیزر رامان بر روی سیالات درگیر، میزان گاز n2 و co2 در سیالات دو فازی به ترتیب 69 و 31 درصد و در سیالات درگیر سه‌فازی به ترتیب 33 و 67 درصد مولی است که منشا آن می تواند گاززدایی از گوشته و واکنش سیالات با سنگ های کربناته باشد. بررسی ترکیب ایزوتوپی o و h سیال در تعادل با کوارتز نشان می دهد که سیال اولیه در این کانه زایی منشا ماگمایی داشته که در مرحله‌های بعدی با سیالات جوی اختلاط حاصل‌کرده که این فرایند با کاهش سیستماتیک دما و شوری همراه بوده است.

Alteration, geothermometry, Raman spectroscopy and O-H stable isotopes studies on Lakehsiah 1 deposit, Yazd province, Iran

IntroductionThe Lakehsiah mining district is hosted in Early Cambrian volcanosedimentary units (CVSU) of the Kashmar–Kerman zone, Central Iran. The KashmarKerman belt is located between the Yazd block in the west and the Tabas block in the east and it is parallel to the Poshed badam, Tabas and Kalmard faults in the north and Koh Banan and Zarand faults in the south of the area (Ramezani and Tucker, 2003). Compositions of the volcanogenic rocks in this area vary from felsic to mafic and include rhyolitic, rhyodacitic tuff and spilitic lava and diabase. The sedimentary rocks include dolomites, dolomitic limestones and evaporites. Lakehsiah 1 deposit is one of three IOA outcrops in the Lakehsiah district which have been studied in this research. Materials and Methods The mineralogical study of alteration zones was carried out by light microscope with transmission light and Xray diffraction (XRD) analysis, at the Mineralogical Laboratory of BuAli Sina University and Iran Minerals Processing Research Center, respectively. Fluid inclusion and Raman spectroscopy studies were also performed to determine temperature, composition and evolution of the oreforming fluid at the Institute of Earth Sciences SAS, Slovakia. Stable isotope geochemistry of quartz (OH) was performed at the Cornell University, USA. DiscussionIron deposits hosted in the Tashk Group show hydrothermal alteration. The major minerals of the SodicCalcic alteration are the crystals of calcic amphiboles (tremoliteactinolite), pyroxene, calcite, magnetite and apatite. Propylitic alteration (chloritization and epidotization) is very widespread and affects volcanic and intrusive rocks. It consists of chlorite, epidote, calcite, and magnetite with minor amounts of sericite. Silicification alteration, occurs as distal alteration in both hanging wall and footwall host rocks, forming finegrained to coarse grained quartz aggregates, veins and veinlets. Sericiticargillic alteration occurs mainly in intrusions. Feldspar (plagioclase and Kfeldspar) was altered to sericite and clay minerals. Minor quartz occurs as veinlets in this alteration zone. Na Ca alteration in volcanic and intrusion rocks is exposed in the center of the area. Amphiboles mainly occur as replacements of plagioclase. Plagioclases were altered to chlorite, epidote, and calcite. Additionally, veinlets of quartzepidotechlorite, chloriteepidote, epidotequartz, quartzcalcite, calcite, chloritecalcite, and epidotecalcite are observed. Quartz and carbonates (calcite) are widespread and veins of these minerals crosscut all the rocks described above.Lakehsiah 1 deposit, hosted within highsilica rhyolitic tuffs and domes, forms a steeply dipping tabular lens and it includes massive magnetite ± apatite ± quartz ± specular hematite ± FeMg silicates. Fluid inclusion PetrographyFour major types of fluid inclusions are observed based on proportions of vapor, liquid, and solid phases present at room temperature in quartz mineral. They are described as follows:1liquidrich inclusions (L)2vaporrich inclusions (V)3Twophase liquid rich fluid inclusions (L+V)4three phase inclusions with halite solid phase as daughter mineral (L+V+H). Study of inclusions petrography shows that most of the inclusions present within this mineral are primary in origin, although secondary or pseudosecondary types have been identified. They have different sizes (typically 5–15 μm). Fluid inclusion shapes are rounded, elliptical, irregular, negative crystal shapes and square. ResultsMicrothermometry and Raman spectroscopyFreezing and heating experiments were performed on Types 3 and 4 fluid inclusions. Stretching of inclusions was noted during heating of large fluid inclusions in quartz from mineralized quartz veins. In such samples, homogenization temperatures range from 217–428 °C for type 3 and 384467°C   for type 4.Microthermometric data were obtained from both Types 3 and 4 inclusions. The data obtained revealed variation in salinity of the trapped fluids. The final ice melting temperature in Types 3 and 4 inclusions varies from −4° to 18 and 9 to 19 °C with a mode at around 12 °C. Final icemelting temperatures are lowest in the mineralized quartz veins. The first melting temperatures in multiphase Types 3–4 inclusions are also in a similar range which varies from 21 to 34°C. Based on their final ice melting temperatures, it varies between 10 to 27 and 40 to 44 wt. % NaCl equivalent for type 3 and 4 inclusions. T°C vs. salinity plots of inclusions show mixing of magmatic hot fluids with cold meteoric waters. Raman spectroscopy revealed presence of 69 mol % N2 and 31 mol % CO2 and 33 mol % N2 and 67 mol % CO2 in types 3 and 4 inclusions. These gases can be derived from mantle degassing (Wang et al., 2018) and chemicalreactions during ascent of fluids. HO isotopesIsotopic studies are among the most common methods for identifying the primary composition of oreforming fluids in deposits (Barati and Gholipoor, 2014). In the study area, five quartz samples in quartz grains and veins were used for HO isotope analyses, with the aim of determining the source(s) of oreforming fluids. The δDH2O and δ18OH2O values of the oreforming fluids in quartz samples vary from 60‰ to 80‰, and 4.71‰ to 1.42‰, respectively. The above observations reveal that the early oreforming fluids are magmatic in origin and is characterized by high temperature and moderate to high salinity, and gradually evolve to low temperature, low salinity meteoric water. The Lakehsiah 1 Fe deposit is associated with the magmatism induced by the protracted subduction. The decrease in temperature, salinity and f(O2), as well as fluidrock interactions, are the main factors controlling Fe deposition. ReferencesBarati, M. and Gholipoor, M., 2014. Study of REE behaviors, fluid inclusions, and O, S stable Isotopes in Zafarabad iron skarn deposit, NW Divandarreh, Kordestan province. Journal of Economic Geology, 6(2): 235–‌275. (in Persian with English abstract) https://doi.org/10.22067/ECONG.V6I2.20257Ramezani, J. and Tucker, R.D., 2003. The Saghand region, central Iran: UPb geochronology, petrogenesis and implications for Gondwana tectonics. American Journal of Science, 303(7): 622–665. https://doi.org/10.2475/ajs.303.7.622‏‏Wang, Y., Wang, K. and Konare, Y., 2018. N2rich fluid in the veintype Yangjingou scheelite deposit, Yanbian, NE China. Scientific Reports, 8(1): 5662. https://doi.org/10.1038/s41598018222277