بررسی زمین‌شناسی و ژئوشیمی رگه‌های منگنزدار بشگز شمال‌شرق بیرجند، خراسان‌جنوبی

نویسندگان

1 دانشگاه تبریز

2 دانشگاه بیرجند

چکیده

رگه­های منگنزدار بشگز در 45 کیلومتری شمال­شرق بیرجند، خراسان­جنوبی و در شرق ایران قرار گرفته­اند. این رگه­ها به ضخامت 1/0 متر تا 5/1 متر و طول 4-7 متر به صورت نا­هم­شیب در حجم وسیعی از سنگ­های آتشفشانی-آذراواری منسوب به پالئوژن (ائوسن-الیگوسن) قرار دارند. سنگ میزبان رگه­های منگنز، توف­های با ترکیب ریوداسیتی- داسیتی است، کانی­های منگنز در منطقه­ی برشی و لاپیلی توف با قطعات آندزیتی نیز دیده می­شوند. عیار منگنز در رگه- رگچه­ها به %45
می­رسد. کانه­های اصلی پیرولوسیت، کریپتوملان و پسیلوملان است، کانی­های کانسنگی بافت­های کلوفورم و پرکننده فضای خالی را نشان می­دهند. مهم­ترین باطله سیلیس­های بی­شکل هستند، مقدار سیلیس بین %41/2 در رگه منگنز تا %98/20 در منطقه­ی سیلیسی می­رسد. براساس یافته­های کانی­شناسی و ژئوشیمیایی، چگونگی تشکیل کانی­های منگنز بدین صورت است­که نخست اکسی­ هیدروکسیدهای منگنز بی­شکل بوجود می­آیند و به مرور پسیلوملان پسین پیرولوسیت تشکیل می­شوند. با توجه به میانگین نسبت Mn/Fe در رگه­های منگنز­دار بشگز که 31/26 است و افزایشZn, U, Sr, Ba  همراه با افزایش Mn در رگه­ها، بیانگر تشکیل منگنز به صورت گرماب و رورانده بوده است

کلیدواژه‌ها


عنوان مقاله [English]

Geology and geochemistry of manganese-bearing veins of Beshgaz inNE of Birjand, Southern Khorasan

نویسندگان [English]

  • behnaz Barghi 1
  • aliasghar Calagar 1
  • mohammadhosain Zarrinkoub 2
  • vartan Simmonds 1
1
2
چکیده [English]

The Beshgaz manganese-bearing veins are located in ~45 km northeast of Birdjand, South-Khorasan, and east of Iran. These veins with 0.1-1.5 m thickness and 4-7 m length are engulfed discordantly within Paleocene (Eocene-Oligocene) volcanic-pyroclastic rocks.  The host of Mn-bearing veins are dacite to rhyo-dacite tuff, lapilli tuff with andesitic and andsi-basaltic fragments in shear zones. The Mn grade reaches up to 45% in the vein/veinlets. The major Mn ore minerals are pyrolusite, cryptomelane, and psilomelane. Ore minerals showing colloform and open-space filling textures. Amorphous silica is the principal gangue mineral in the Mn ores and the SiO2 content of these veins vary from 2.41 in Mn-bearing veins to 20.98 % in silicic zone. Based on mineralographic and geochemical data, the Mn ores were preliminarily precipitated as amorphous Mn-oxide and hydroxide gels, and gradually psilomelane and then pyrolusite were developed in expense of the primary amorphous minerals. The average ratio of Mn/Fe in Beshgaz manganese-bearing veins is 26.31 and positive correlation of manages with Ba, Sr, U, and Zn in Mn-bearing veins indicate that these veins have formed as epigenetic by hydrothermal fluids.

کلیدواژه‌ها [English]

  • Manganese
  • pyrolusite
  • Psilomelane
  • Amorphous silica
  • South-Khorasan
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