کانی شناسی عناصر نادر خاکی در فسفریت های معدن جیرود، البرز غربی

نویسندگان

1 استاد گروه زمین‌شناسی، دانشکده علوم‌زمین، دانشگاه شهید بهشتی، تهران

2 کارشناس‌ارشد زمین‌شناسی اقتصادی، دانشکده علوم‌زمین، دانشگاه شهید بهشتی، تهران

3 استادیار پژوهشکده مواد و چرخه سوخت، پژوهشگاه علوم و فنون هسته‌ای، ایران

4 دانشیار گروه زمین‌شناسی، دانشکده علوم‌زمین، دانشگاه شهید بهشتی، تهران

چکیده

افق فسفات­زایی معدن جیرود در بخش مرکزی سازند جیرود در مجاورت ارتفاعات دیزین در شمال تهران قرار دارد. رسوبات این سازند با سن دونین پسین اغلب از سنگ­های آواری نظیر ماسه­سنگ، شیل­ماسه­ای و آهک­های ماسه­ای تشکیل شده است. کانی­سازی فسفریت اغلب­ در بخش شیلی آن متمرکز است. مطالعات میکروسکوپ نوری و طیف­سنج پراش پرتو ایکس (XRD) بر روی نمونه­های فسفریتی معدن جیرود نشان داد که فلوئور آپاتیت کانی­ اصلی فسفاته و کانی­های باطله همراه آن شامل کوارتز، کلسیت، پیریت، اکسیدهای آهن (اغلب گوتیت) و کانی­های رسی هستند. نتایج تجزیه کمی دقیق نقطه­ای (XPMA) نشان داد که کانی فلوئور آپاتیت، میزبان اصلی عناصر نادر خاکی در نمونه­های فسفریتی معدن جیرود است. مونازیت و در مقادیر خیلی کم زیرکن میزبان دیگر عناصر نادر خاکی در این فسفریت­ها به هستند. مقدار Ce (به عنوان نماینده عناصر نادر خاکی) در دانه­های آپاتیتی تجزیه شده از 05/0 تا 08/0 درصد وزنی متغیر است. مقدار حضور Ce و سایر عناصر نادر خاکی در آپاتیت­های رسوبی با عواملی نظیر 1) منشاء اولیه عناصر نادر خاکی؛ 2) میزان ورود این عناصر به محیط رسوب­گذاری؛ 3) مدت زمان تماس آپاتیت­ها با آب دریا در حین و بعد از تشکیل؛ 3) ترکیب شیمی آب­های بین منفذی بعد از تشکیل؛ 4) همراهی مواد آلی به عنوان یک منشا محلی؛ 5) شبکه بلوری آپاتیت­ها و تاثیر رخداد دگرجایی در فسفریت­ها مرتبط است.

کلیدواژه‌ها


عنوان مقاله [English]

Mineralogy of rare earth elements of the Jeirud phosphorites, western Alborz

نویسندگان [English]

  • M. Yazdi 1
  • M. Najafi 2
  • Kh. Khoshnoudi 3
  • M. Behzadi 4
چکیده [English]

The phosphorites horizon related to the Jeirud area is located in the central part of the Jeirud Formation, in the northern Tehran. The Late Devonian sediments of this formation is composed mainly of detrital rocks such as sandstone, sandy shale and sandy limestones. Phosphorite mineralization is mainly concentrated in the sandy shale horizon. Optical microscopy and X-ray diffraction (XRD) results showed that fluoroapatite is the main phosphate mineral and other gangues minerals composed of quartz, calcite, pyrite, iron oxides (mostly goethite) and clay minerals. The X-Ray Probe Micro Analysis (XPMA) results showed that fluoroapatite is the main host mineral for REEs. Other REE-bearing minerals include monazite and very rarely zircon. The Ce concentration (as representative of REEs) is highly variable in the decomposed apatite grains and the amount of Ce and other REEs in sedimentary apatite originating from primary rare earth elements. The concentration of REE in this phosphorites are related to the deposition environment, duration of seawater interaction during and after apatite formation, chemical composition of pore-water, organic source, apatite crystal network and the effect of the allogenic events.

کلیدواژه‌ها [English]

  • Rare earth elements
  • Phosphorite
  • Jeirud formation
  • Northern Iran
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