با توجه به نتایج بررسی‌های صحرایی(شکل، ابعاد، توزیع مکانی و وضعیت انکلاوها و بیگانه‌سنگ‌ها در سنگ میزبان و در رخنمون‌های قابل دسترس) و آزمایشگاهی(بررسی‌های سنگ‌نگاری، ریزساختاری انکلاوهای ماگمایی و بیگانهسنگهای متاپلیتی و شیمی سنگ کل انکلاوهای ماگمایی)، انکلاوهای ماگمایی از نوع مافیک و فلسیک و بیگانهسنگهای دگرگونی از نوع هورنفلسی هستند. طویل‌شدگی انکلاوهای ماگمایی و بیگانهسنگهای هورنفلسی در امتداد محور طولی ظاهری خود در بخش‌های حاشیه‌ای توده نفوذی به عملکرد تنش‌های زمین‌ساختی در حالت مذاب یا نیمه جامد روی انکلاوها و حالت خمیری برای بیگانه‌سنگ‌ها و همچنین نیروی بالای جریان ماگمایی در منطقه تماس با سنگ‌های دگرگونی منطقه، نسبت داده شده و اشاره‌ای است به این‌که منشأ این بیگانه‌سنگ‌ها، سنگ‌های دگرگونی مجاور توده نفوذی است. انکلاوهای مافیک موجود در میزبان جهت یافته، افزون بر شواهد تغییر شکل پلاستیک (در مقیاس میکروسکوپی)، ریزساختارهای جریانی هم نشان می‌دهند که این حالت را می‌توان به تحمیل جریان حالت جامد(Solid-State Flow) بر جریان ماگمایی نسبت داد. اشکال کروی، بیضوی، دوکی انکلاوهای ماگمایی مافیک، به دلیل عدم مشاهده شواهد تغییر شکل پلاستیک حالت جامد، وجود معیارهای جریان ماگمایی و مرز مشخص با سنگ میزبان در مقیاس ماکروسکوپی و میکروسکوپی به حضور آنها به صورت گلبول‌ها یا بسته‌های ماگمایی در ماگمای فلسیک میزباننسبت داده و با توجه به اختلاف ظاهری، نزدیکی کانی‌شناسی، بافتی و ژئوشیمیایی با سنگ میزبان، به منشأ متفاوت آنها و در واقع با وقوع آمیختگی ماگمایی مرتبط است. انکلاوهای ماگمایی فلسیک که به طور عمده شکل خاصی نداشته و قرابت کانی‌شناسی، ژئوشیمیایی آشکاری با میزبان نشان می‌دهند و در بخش‌های حاشیه‌ای و سقف توده دیده می‌شوند به گسیختگی حاشیه‌ای در فازهای اولیه تزریق، در فشار ناشی از ضربان‌های تزریق بعدی و جایگزینی ماگمای جدید نسبت داده شده‌اند.
سخن سردبیر
Biotite is the most frequent ferromagnesian phase in granitoids from the Malayer-Boroujerd Plutonic complex (MBPC), Zagros Orogen. The abundance of biotite decreases from granitoids towards dioritic intrusions, dioritic and gabbroic dykes to gabbroic intrusions coincident with increase in hornblende/biotite ratio. Primary magmatic biotite composition in the MBPC granitoids (Fe-rich type) changes from annite to siderophyllite, while Fe-depleted secondary biotites from the altered gabbros and gabbroic-dioritic dykes approximate to the phlogopite-eastonite series, and those from least-altered gabbros display average composition of these groups, however, extend towards high-Al end-members. Using Ti-in-biotite geothermometer, the crystallization temperature varies between 550 °C to 750 °C in MBPC granitoids (P 10–15 bars). Mode-III: biotite crystallized at higher oxidizing conditions (f(O2) > 10–10 bars) in gabbroic and dioritic dykes as well as gabbroic intrusions. The progressive decreases in f (O 2)–values and oxidizing conditions from I-type to S-type granites (above HM-to below QFM-buffer) reflect increasing incorporation of less-oxidized upper crustal materials during magmagenesis. In addition, the highest f (O2) in MBPC mafic intrusive rocks is consistent with a modest crustal contamination, if any. There is lack of evidence for porphyry type alteration zoning and subvolcanic porphyritic intrusions associated with porphyry copper system. The small patches of calc-silicate rocks from the NW-MBPC formed in contact with less oxidized and highly fractionated, crustal-derived granular granitoids and are less predisposed to develop Cu-Au mineraliza- tion. However, given the relatively higher f (O2)-values, the Middle Jurassic mafic intrusive rocks originated from the meta- somatised mantle-wedge beneath SaSiZ, appears to be the best candidate for further ore exploration programs in the area.
Abstract Regolith-hosted rare-earth-element (REE) deposits are the world’s primary source of heavy REEs (HREEs) critical to the global clean-energy transition. Previous studies suggested that REEs in regolith-hosted deposits are largely inherited from their parent granites. However, several HREE-dominated deposits occur in the weathering crusts of LREE-enriched granites, where the mechanisms of REE fractionation remain poorly understood. Also, the conventional mining method of regolith-hosted REE deposits has limited efficiencies in REE recovery while causing enormous environmental contaminations. Herein we have investigated the distribution and speciation of Y and REEs in three representative regolith-hosted REE deposits (i.e., Gucheng and Shangyou, HREE-dominated; and Renju, LREE-dominated) as well as Y-sorbed birnessite from batch experiments. Our results show that birnessite in all three deposits is a minor constituent but contains anomalously high REE concentrations, and contributes to 25.3%, 23.4%, and 26.5% of the HREE contents of mineralized saprolites. Measured Y K-edge X-ray absorption spectroscopic data suggest that Y3+ (representing HREE3+) is adsorbed on birnessite as YO8 complexes in all three deposits but via different linkages: i.e., the bidentate corner-sharing mode in the HREE-dominated deposits but a mixture of both bidentate corner-sharing and edge-sharing modes in the LREE-dominated deposit. These binding mechanisms are also observed in Y-sorbed birnessite prepared at different ionic strengths. Therefore, different binding mechanisms of Y and HREE sorption on birnessite together with its preferential adsorption of HREE not only are responsible for the formation of HREE-dominated deposits from LREE-enriched granites but have important implications for the sustainable development of regolith-hosted REE deposits.
Abstract. The occurrence of jadarite (LiNaSiB3O7OH) as a major ore mineral in the world-class lithium–boron deposit of the Miocene Jadar lacustrine basin (western Serbia) raises interesting questions about its formation conditions and potential associations for lithium mineralization in other sedimentary basins. This contribution reports on the first successful synthesis of jadarite in the Li2O–Na2O–B2O3–SiO2–NaCl–H2O system at temperatures from 180 to 230 ∘C and pH values from 6 to 12. Synthetic jadarite has been characterized by powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, laser Raman spectroscopy, and synchrotron Li and B K-edge X-ray absorption near-edge structure (XANES). First-principles theoretical calculations reproduce the measured FTIR and Raman spectra and allow definitive assignments of vibration modes. Similarly, the measured Li and B K-edge XANES spectra are reasonably reproduced by first-principles theoretical calculations. Our synthesis results, together with its association with searlesite in the Jadar basin, suggest jadarite forms in deep sediments derived from Li-rich alkaline brines under high-temperature diagenetic conditions.
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