منشا سیال کانه‌ ساز در کانسار مگنتیت-آپاتیت چغارت، شمال‌ شرق بافق: شواهدی از کانی‌ شناسی، زمین‌ شیمی، ریزدماسنجی و ایزوتوپ‌ های پایدار (o-c و o-h) و ناپایدار (u-pb و nd-sm)

بررسی‌های سنگ‌شناسی، زمین‌شیمی و ایزوتوپی بر روی کانسنگ مگنتیت آپاتیت و دگرنهادی‌های آلبیت‌دار کانسار چغارت بیانگر تنوع کانی‌زایی با منشا متفاوت است. بررسی‌های ایزوتوپ‌های پایدار oh و ایزوتوپ‌های ناپایدار ndsm بر روی کانی‌های آپاتیت نسل اول مرتبط با کانسنگ مگنتیت و نسبت‌های sr در مقابلmn  در هر دو نسل آپاتیت، منشا رسوبی آنها را نشان می‌دهد. از طرف دیگر، بررسی‌های ریزدماسنجی بر روی میان‌بارهای سیال در آپاتیت نسل اول و ایزوتوپ‌های پایدار oc بر روی کلسیت‌های هم‌یافت با آلبیت‌های نسل دوم و سوم در پهنه‌های دگرنهادی و وجود بافت‌های برون‌رستی ایلمنیت در کانی مگنتیت، تلفیقی از فرایندهای ماگمایی و گرمابی دما بالا را به نمایش می‌گذارد. تفاوت سنی آپاتیت‌های نسل اول و مونازیت‌های مرتبط با این آپاتیت‌ها به روش 238u/206pb و 207pb/206pb نشان‌دهنده عملکرد سیالات کانی‌زا در بازه‌های زمانی مختلف است. بر اساس پژوهش، کانی‌زایی در کانسار مگنتیت آپاتیت چغارت منشا چندزادی دارد. این مسئله نقشی مهم در درک فرایندهای کانی‌زایی و مدل‌های اکتشافی کانسارهای آهنفسفات گستره معدنی بافق دارد.

Origin of Mineralizing Fluids in the Choghart Magnetite-Apatite Deposit, NE of Bafq: Evidence from Mineralogy, Geochemistry, Microthermometry, Stable (O-H and O-C) and Unstable Isotopes (U-Pb and Nd-Sm)

IntroductionThe Bafq mining district (BMD) in the KashmarKerman tectonic zone hosts ~34 magnetitehematiteapatite ore deposits with about 1500 Mt of reserves in the central Iran (Torab, 2008). The mineralization has predominantly occurred in the Early Cambrian volcanosedimentary rocks of Esfordi Formation. It consists of rhyolite, rhyodacite, spilitic basalt, and dolostone, which are intruded dominantly by the Early Cambrian granitoid intrusions (Torab, 2008). Metasomatism has not only affected vastly the ore deposits and their host rocks, but it has also controlled ore mineralization. This issue has caused ambiguity and a paradox in determining the genesis of these ore deposits. In this research study, sources of mineralization are determined in the Chogart magnetiteapatite ore deposits. The results of this research study constrain the genesis of the Choghart deposits. Moreover, they shed new light on oreforming processes in similar ore deposits of the Bafq mining district. MethodologyIn this research study, 87 rock and ore samples were collected from the Choghart magnetiteapatite ore deposits. Mineralogy characteristics of 10 apatite samples and 13 magnetiteapatite ore samples were determined by using the LEO1400 Scanning Electron Microscope, with a voltage of 1917 kV and a beam diameter of 20 nA. Moreover, three apatite and three albite samples were examined by using Xray powder diffraction in the Iran Mineral Processing Research Center. Seventeen magnetitehematite ore samples were also analyzed using ICPMS in the Zarazma Company. For microthermometry, one sample of the 1stgeneration apatites was analyzed for fluid inclusions in the Geological Survey and Mineral Exploration of Iran.Four apatite samples were studied by the OH isotope method in the Hungarian Laboratory in Hungary, seven calcite samples were studied by the OC method in Ottawa, Canada, two apatite sample were studied by the NdSm method in Queensland, Australia, and four apatite samples were studied by the Inductively Coupled Plasma Mass SpectrometryLaser ablation method in Tasmania University in order to determine the origin of the mineralizing fluid. ResultsThe petrography, geochemistry, and isotope studies on the host rock and magnetiteapatite ores of the Choghart deposit indicate various forms of mineralization, which is associated with extensive metasomatism. The OH and NdSm isotopes on the 1stgeneration apatites and the ratios of Sr relative to Mn of these apatites demonstrate a sedimentary origin, while the presence of ilmenite exsolution texture in the 1stgeneration magnetites shows a magmatic origin of the oreforming processes. In addition, microthermometry of the fluid inclusions in the 1stgeneration apatites in the magnetiteapatite ore and the evaluation of the OC isotopes on the paragenetic calcites with the 2nd and 3rdgeneration albites of host albitebearing metasomatites indicate a combination of magmatic and hightemperature hydrothermal processes. The results of 206Pb/238U and 206Pb/207Pb isotopic studies on the 1stgeneration apatites and 1st and 2ndgeneration monazites inclusions of the 1stapatites illustrate that monazites are younger than the apatites, which could indicate separation of UPb by hydrothermal fluids or formation of apatite ores during a separate phenomenon. DiscussionIn this research study on the Choghart magnetiteapatite ores and its albitebearing metasomatic host rocks, three generations of albites, two generations of apatites, two generations of monazites and two generations of magnetite have been identified. The geochemical evaluation of the albites indicates lower REEYTi of the 1stgeneration albites, which are sterile in terms of ThU, compared to the 2nd and 3rdgeneration albites. The OC isotope analysis of the paragenetic calcites demonstrated albitization due to the magmatic and hightemperature hydrothermal fluids. In addition, the OH isotope studies on fluid inclusions of the apatites demonstrate atmospheric origin of the fluids, while the microthermometry results of the apatite fluid inclusions indicate magmatic and hydrothermal origins of these fluids. On the other hand, presence of ilmenite exsolutions in the magnetites and OH isotope of the magnetites, conducted by Moore and Modabberi (2003) and Majidi et al. (2021) have shown the magmatic origin of the fluids. The NdSm isotopic results of 1stgeneration apatites, rhyolitic host rock, and ironapatite ores indicate different initial contents of their Nd isotope ratios. The similarity of εNd in the 1stgeneration apatites with phosphorite of the Soltanieh Formation, along with Sr versus Mn amounts of the apatites reinforce the idea that the apatites could have been derived from these sedimentary phosphorites, whose εNd contents increased due to the hightemperature magmatic and hydrothermal fluids, derived from the granitic intrusions, rhyolitic lavas and magnetite melts. The 206Pb/238U and 206Pb/207Pb dating demonstrate 490561 million years for the 1stgeneration apatites, 511543 million years for the 1stgeneration monazites, 503528 million years for most of the 2ndgeneration monazites, and 112153 million years for a limited number of 2nd generation monazites. The different isotopic ages of the apatites and monazites shows their formation during longterm and extensive oreforming processes during later effects of hydrothermal and magmatic fluids. This has resulted in enrichment of apatites in REE, formation of monazite inclusions along the fractures and on the surface of the apatites. AcknowledgementsThe authors would like to express their appreciation of managers and staff of the Iranian Central Iron Ore Company for their assistance during this research.