کانی شناسی و ژئوشیمی کانسنگ‌های لاتریتی پرمین در شرق شاهین‌دژ، استان آذربایجان غربی

نویسندگان

1 دانشگاه ارومیه

2 دانشگاه تبریز

چکیده

شرق شاهین­دژ (جنوب استان آذربایجان غربی)، به عنوان بخشی از کمربند بوکسیت کارستی ایرانو- هیمالیا، در بردارنده لایه­ها و عدسی­های منفصل بوکسیت، لاتریت و کائولن در درون تشکیلات کربناتی روته (پرمین میانی- بالایی) است. آنالیزهای پراش پرتو X نشان می­دهند که کانسنگ­های لاتریتی از کانی­شناسی نسبتاً ساده­ای برخوردار بوده و شامل کانی­های هماتیت، بوهمیت، و کائولینیت به عنوان فازهای اصلی همراه با فازهای فرعی نظیر گوتیت، مونت­موریلونیت، دیاسپور، ایلیت، کلریت، و روتیل می­باشند. بر طبق ملاحظات سنگ­نگاری، چنین استنباط می­شود که کانسنگ­ها طبیعت چند چرخه­ای داشته و تکامل آنها تا حد زیادی بوسیله عملکرد فرایندهای دیاژنتیک و اپی­ژنتیک تحت تاثیر قرار گرفته است. سیماهای پتروگرافیکی همراه با تجمعات کانیایی آشکار می­سازند که کانسنگ­های لاتریتی اغلب در یک محیط هوادار (vadose) نهشته شده­اند. بر اساس شیمی عناصر  اصلی، کانسنگ­ها به سه نوع، (1) فریت بوکسیتی، (2) لاتریت و (3) لاتریت فریتی طبقه­بندی می­شوند. الگوی توزیع REEهای به هنجار شده به کندریت، درجه پایین تفریق LREEها از HREEها و همچنین آنومالی منفی ضعیف برای Eu  را در طی لاتریت­زایی نشان می­دهند. این سیماها همراه با روابط صحرایی، و مقادیر تمرکز Al، Ti و Zr  دلالت بر پروتولیت دیابازی کانسنگ­ها دارند. بررسی آنومالی­های Eu و Ce آشکار می­سازند که شدت لاتریت­زایی به­طور مستقیم به افزایش pH آب زهکشی شده، تغییرات Eh، و نوسانات سطح سفره آب زیرزمینی مرتبط است. نتایج حاصل از یافته­های ژئوشیمیایی شواهد قانع کننده­ای را فراهم می­آورند­ که خنثی­سازی محلول­های هوازده کننده اسیدی فرورو، اختلاف در درجه پایداری در برابر هوازدگی ما بین کانی­های اولیه، تفاوت در درجه پایداری لیگندهای کمپلکس­ساز، و ویژگی­های شیمیایی عناصر، چهار فاکتور کلیدی کنترل کننده برای توزیع و رفتار عناصر اصلی، فرعی، جزئی و نادر خاکی در طی لاتریت­زایی در شرق شاهین­دژ هستند. 

کلیدواژه‌ها


عنوان مقاله [English]

The mineralogy and geochemistry of Permian lateritic ores in east of Shahindezh, West-Azarbaidjan province

چکیده [English]

East of Shahindezh (south of West Azarbaidjan province), as a part of Irano-Himalayan karst bauxite belt, comprises discontinuous layers and lenses of bauxite, laterite, and kaolin within the Ruteh carbonate formation (Middle- Upper Permian). The XRD analyses show that the lateritic ores have rather simple mineralogy, and consist of hematite, boehmite, and kaolinite as major phases accompanied by minor phases such as goethite, montmorillonite, diaspore, illite, chlorite, and rutile. According to petrographical considerations, it can be deduced that the ores have polycyclic nature and their evolution being largely affected by the function of diagenetic and epigenetic processes. Petrographical features along with mineral assemblages reveal that the lateritic ores were deposited almost in a vadose environment. Based on chemistry of major elements, the ores are categorized into three types; (1) bauxitic ferrite, (2) laterite, and (3) ferritic laterite. Distribution pattern of REEs normalized to chondrite displays a low degree of differentiation between LREEs and HREEs and also a weak negative anomaly for Eu during the lateritization processes. These features along with field relations and concentration values of Al, Ti, and Zr indicate a diabasic protolith for the ores. Consideration of Ce and Eu anomalies unveil that the intensity of lateritization is directly related to the pH increase of drained water, Eh variations, and fluctuation of water table. Results from geochemical data have furnished compelling evidence that buffering of underground descending acidic weathering solutions, dissimilaritis in degree of resistance against weathering among primary minerals, discrepancies in degree of stability of complexing legands, and chemical characteristics of elements are four key controlling factors for the distribution and behavior of major, minor, trace, and rare earth elements during lateritization in east of Shahindezh.

کلیدواژه‌ها [English]

  • West-Azarbaidjan
  • Shahindezh
  • lateritization
  • protolith
  • distribution pattern of elements
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