زمین‌شیمی و ویژگی‌های گوهرشناسی کروندوم‌ در پگماتیت‌های خاکو، شمال شرق باتولیت الوند (غرب ایران)

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشگاه آزاد اسلامی واحد تهران شمال

2 دانشگاه خوارزمی

چکیده

کانسار خاکو در جنوب و جنوب شرق شهر همدان و در نزدیکی روستای خاکو در غرب ایران قرار دارد. در این منطقه کروندوم‌هایی به رنگ آبی درون رگه‌های پگماتیتی و بدنه گرانیتی وجود دارند. داده‌های سن‌سنجی مطلق با روش‌های گوناگون پرتوسنجی نشان می‌دهد که سنگ‌های دگرگونی در گستره زمانی ژوراسیک تا کرتاسه تشکیل شده و سپس در ژوراسیک میانی تا کرتاسه پیشین، مورد هجوم توده‌های نفوذی قرار گرفته‌اند و فازهای جوانتر و رگه‌های پگماتیتی درون آن­ها نفوذ کرده‌اند. فعالیت‌های گرمابی سیال های داغ تراوش یافته از توده گرانیتی همبری­های ویژه شامل بلورهای کروندوم + کیانیت+ میکا ± پلازیوکلاز را به وجود آورده­اند. کانی‌های آلومینوسیلیکاتی و کروندوم در این رگه ها و توده های کوچک پگماتیتی و لبه توده گرانیتی دیده می‌شوند. برپایه بررسی­‌های انجام شده، فرآیندهای دگرگونی دگرنهادی و ترکیب قلیایی غنی از آلومین توده نفوذی منجر به یک مدل زایشی بر اساس تبادل دوطرفه سیال های داغ در دمای بالا و فشار متوسط شده که در آن پدیده سیلیس‌زدایی گسترده، افزایش نسبت Al/Si و تبدیل بلورهای آلومینوسیلیکات و پلاژیوکلاز به کروندوم طی فرآیندهای پیشرونده در یک سامانه زمین شیمیایی باز صورت گرفته است. بنابراین خاستگاه کانسار خاکو با یک مدل ماگمایی دگرنهاده قابل توجیه است. نتایج نشان می‌دهد، که مقدار عناصر کمیاب کروندوم‌های منطقه خاکو گستره تغییرات وسیعی دارند. بلورهای کروندوم طبیعی کانسار خاکو از نظر عمق رنگ در گروه­های 6 و 7، از نظر میزان درخشندگی در گستره 2 و 3 رنگ سرد و از نظر رنگ مایه در گروه بنفش آبی (VB)  و آبی (B)  قرار دارند. کروندوم‌‌های مورد بررسی در منطقه خاکو دارای کمتر از 1 درصد وزنی عنصر آهن، ppm 10 تا 47 گالیوم، ppm 83 تا 690 تیتانیوم و 30 (ppm) عنصر وانادیوم هستند و شباهت شیمیایی با نمونه‌های معادن همنشین با سینیت‌ها در تانزانیا دارند.

کلیدواژه‌ها

عنوان مقاله [English]

Geochemistry and gemology characteristics of corundum in the Khakoo pegmatites in the southeast of Alvand batholith (west Iran).

نویسندگان [English]

  • Sadeghi 1
  • Mahmoudi 2
  • Reza Jafari 1
  • Arian 1
1
2
چکیده [English]

The Khakoo deposit is located in south and southeast of Hamedan city, near the Khakoo village, in western Iran. In this area, blue corundum formed inside the pegmatite veins and granite body. Geochronological data, using various radiometric methods, show that metamorphic rocks formed during the Jurassic to Cretaceous. Then during the Middle Jurassic to Early Cretaceous time, a massive intrusive masses as well as younger phases and pegmatite vines penetrated into this body. The hydrothermal activity of hot fluids driving from the granite mass has created specific paragenesis including corundum crystals. Aluminosilicate and corundum minerals are formed in the pegmatite filons and the margin of granite body. Based on recent studies, the metamorphic–metasomatic process and per-alumnus alkaline composition of intrusive body made a genetic model which based on the bimodal exchange of hot fluids at high temperature and medium pressure are the phenomenon of extensive desilicification and increases of the Al/Si ratio. Metasomatic progressive processes have changed aluminosilicate and plagioclase minerals to corundum in an open geochemical system. Therefore, the Khakoo deposit in a metasomatic magmatic model can be justified. According to the results obtained in this study, natural corundums have a large variation in most trace elements. The collected crystals are in the 6th- 7th rank in terms of tone, from the Saturation terms in the range of 2 and 3 cool colors and based on the Hue termsour samples fill in the Violet Blue (VB) and Blue (B) groups. The Khakoo corundum deposit contain less than 1% (Wt) Iron, 10 to 47 (ppm) Gallium, 83 to 690 (ppm) Titanium, and 30 (ppm) Vanadium. Finally, the Khakoo deposit has resembled associated deposits with the alkaline syenite in Tanzania mines.

کلیدواژه‌ها [English]

  • corundum
  • metasomatism
  • gemology
  • Khakoo
  • Hamedan

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سابقه مقاله

  • تاریخ دریافت: 25 آذر 1400
  • تاریخ بازنگری: 29 بهمن 1400
  • تاریخ پذیرش: 11 اسفند 1400

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