مطالعات کانی‌شناسی و ژئوشیمیایی عناصر خاکی کمیاب (REE) در نهشته‌ بوکسیتی پرمو- تریاس شمال‌خاوری بوکان، شمال باختری ایران

نویسندگان

1 دانشگاه تبریز

2 دانشگاه پیام نور تبریز

چکیده

نهشته­ بوکسیتی پرمو- تریاس شمال خاوری بوکان، به شکل چینه­سان در مرز بین سازندهای روته و الیکا گسترش و تکامل یافته و شامل 4 واحد سنگی مجزاء ست. این نهشته تحت تاثیر فرایندهای زمین­ساختی و ریخت­شناسی قرار گرفته است. بررسیهای کانی­شناسی و ژئوشیمیایی نشان می­دهند که در طی فرایندهای هوازدگی، دو ساز و کار آهن­زدایی و آهن­زایی نقش بارزی در تشکیل کانیهای دیاسپور، بوهمیت، هماتیت، گوتیت، کائولینیت، پیروفیلیت، کلینوکلر، ایلیت، مونت­موریلونیت، آناتاز، روتیل، آلبیت، سانیدین، کوارتز، و کلسیت در این نهشته ایفا کرده­اند. با توجه به شواهد صحرایی و یافته­های کانی­شناسی و ژئوشیمیایی، بازالتها (که هنوز بقایایی از آنها در طول برخوردگاه این نهشته با سنگ بستر کربناته موجود است) سنگ مادر این نهشته هستند. الگوی توزیع REE (هنجار شده به کندریت و سنگ مادر بازالتی) همراه با تغییرات ناهنجاریهای Eu و Ce و (La/Yb)N، تفکیک HREEها را طی فرایندهای بوکسیتی شدن نشان می­دهند. ملاحظات ژئوشیمیایی بیشتر نشان می­دهند که تمرکزهای LREEها با کانیهای هماتیت، گوتیت، اکسیدهای منگنز، Cerianite و فسفاتهای ثانویه (Rhabdophane، Vitusite، Gorceixite و Monazite)، و تمرکز HREEها با کانی­های رسی، روتیل، آناتاز، زیرکن، Euxenite و Fergusonite رخ داده­اند. تلفیق نتایج حاصل از بررسیهای کانی­شناسی و ژئوشیمیایی پیشنهاد می­کنند که علاوه بر فاکتورهایی چون تغییرات pH آبگونهای عامل هوازدگی، پتانسیل یونی، ترکیب شیمیایی سنگ مادر و تثبیت در کانیهای مقاوم، فرایندهای جذب سطحی نیز نقش مهمی در غنی­شدگی REEها طی لاتریتی شدن متوسط تا شدید در گستره مورد مطالعه ایفا کرده­اند.  

کلیدواژه‌ها


عنوان مقاله [English]

Studies of Mineralogy and Geochemistry of Rare Earth Elements (REEs) in Permo-Triassic Bauxite Deposit, Northeast of Bukan, NW of Iran

چکیده [English]

Bauxite deposit of Permo-Triassic age in northeast of Bukan was developed stratiformly along the boundary between Ruteh and Elika formations, and includes four distinct rock units. This deposit was affected by tectonic and morphological processes. Mineralogical and geochemical investigations showed that during weathering processes, two mechanisms of ferrugenization and deferrugenization played crucial role in formation of minerals such as diaspore, boehmite, hematite, goethite, kaolinite, pyrophyllite, clinochlore, illite, montmorillonite, anatase, rutile, albite, sanidine, quartz, and calcite in this deposit. By taking notice of field evidence and of mineralogical and geochemical data, the basalts (whose remnants are still present along the contact of this deposit with carbonate bedrock) are the potential parent rock of this deposit. The distribution pattern of REEs (normalized to chondrite and basaltic parent rock) along with anomaly variations of Eu, Ce, and (La/Yb)N indicates differentiation of LREEs from HREEs during bauxitization processes. Further geochemical considerations indicate that the concentrations of LREEs were occurred by hematite, goethite, manganese oxides, cerianite, and secondary phosphates (rhabdophane, vitusite, gorceixite, monazite) and of HREEs by clay minerals, rutile, anatase, zircon, euxenite, and fergusonite. Incorporation of the results obtained from mineralogical and geochemical investigations suggests that in addition to factors such as pH of weathering solutions, ionic potential, composition of the parent rock, and fixation by residual minerals, adsorption processes also played crucial role in enrichment of REEs during moderate to intense lateritization in the study area.

کلیدواژه‌ها [English]

  • Bauxite
  • parent rock
  • REEs geochemistry
  • deferruginization
  • host minerals
  • NE Bukan
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