بررسی‌های کانی‌شناسی، زمین شیمی و ایزوتوپ پایدار اکسیژن کانسار قشلاق، کمربند فلززایی طارم-هشتجین، شمال‌غرب ایران

نوع مقاله : مقاله پژوهشی

نویسندگان

دانشگاه آزاد اسلامی

چکیده

ذخیره مس قشلاق در کمربند فلززایی طارم-هشتجین (THMB) در شمال‌غرب ایران واقع است. کانه‌زایی با میزبانی سنگ‌های آتشفشانی و آتشفشانی‌آواری سازند کرج در موقعیت کمان ماگمایی صورت گرفته است. زمین شیمی سنگ میزبان موقعیت ماگمای برآمده از فرورانش و ترکیب آندزیت-بازالتی با کانی‌شناسی غالب پلاژیوکلاز-پیروکسن را نشان داد. همبستگی آلومینیوم، آهن، کلسیم و منیزیم را می‌توان به این مجموعه کانی‎‌ها مربوط دانست. همچنین به علت کانه‌زایی غالب سولفیدها، همبستگی قوی بین عناصر گوگرد دوست چون سرب، روی، گوگرد، نقره و مس دیده شد. براساس نتایج کانی‌‌شناسی و روابط همبرزایی، چهار مرحله اصلی کانی‌سازی تشخیص داده شد: مرحله نخست با تشکیل پیریت در شرایط کاهیده در محیط تدفینی کف دریا و دگرسانی پروپلیتی همراه است. این دگرسانی در نتیجه آمیختگی سیال­های ماگمایی با جوی یا آب دریا ایجاد می‌شود که در این پژوهش با نتایج تصحیح شده ایزوتوپ اکسیژن نمونه‌های رگه کوارتز (5/6 - 1/2 در هزار) با دمای همگن‌شدگی 389 درجه سانتیگراد و با فرض مقادیر δ18O برابر با 10-6 درهزار سیال ماگمایی و مقادیر δ18O  برابر با 9/0- تا 8/0- درهزار آب دریای ائوسن تایید شد. با افزایش عمق، مرحله دوم در اثر سخت‌شدگی و نیروی ناشی از فشار سنگ ایستایی و فعالیت آذرین، چرخش سیال­های ماگمایی و بین‌سازندی رخ می‌دهد . سیال­های غنی از مس به سمت بالا مهاجرت کرده و با ورود به واحد بازالتی- آندزیتی پیریت‌دار، کاهیده می‌شوند و در مکان‌های مطلوب کالکوپیریت و کالکوسیت تشکیل می‌شود. در مرحله تدفینی عمیق‌تر (مرحله 3)، کانی‌های برنیت و دیژنیت جانشین کانی‌های پیشین می‌شوند. در مرحله (مرحله 4)، کانی‌های اکسیدی (چون هماتیت، مگنتیت) و نیز مالاکیت در حفره­ها و درزه‌ها ایجاد شده­اند. برپایه این نتایج، می‌توان کانه‌زایی کانسار مس قشلاق را از نوع مانتو در نظر گرفت.     

کلیدواژه‌ها


عنوان مقاله [English]

Mineralogy, geochemistry and oxygen isotope studies of the Gheshlagh Cu-deposit, Tarom-Hashtjin metallogenic zone, Zanjan, northwestern Iran

نویسندگان [English]

  • Baghbanan
  • Jafari Rad
  • Sheikhzakariaee
  • Nezafati
چکیده [English]

The Gheshlagh Cu-deposit is located in the Tarom-Hashtjin metallogenic belt (THMB) of northwest Iran. The mineralization is hosted by Eocene volcanic and volcaniclastic rocks of the Karaj Formation at the subduction-related magmatic arc setting. The geochemistry and petrogenesis analysis confirmed the subduction setting and mineralogically- dominant plagioclase-pyroxene compositions of the host rocks. A good correlation between Al, Fe, Ca, Mg attests to the minerallogic composition, also a strong correlation between chalcophile elements like Pb, Zn, S, Cu and Ag shows sulfide mineralization in the rocks. Based on cross-cutting, the relationship of vein, textural relationship, mineral assemblage and fluid inclusion microthermometry show that alteration and mineralization in the Gheshlagh ore deposit occurred in the fourth main stages. The first stage (stage I) is accompanied by the propyllitic alteration and formation of pyrite (discontinuous) under reducing conditions in the seafloor and very shallow burial environment. The alteration is attributed to magmatic and seawater mixing, which with assuming of the δ18O ranges from 6-10 ‰ for the magmatic fluids and -0.8 to -0.9 ‰ for the Eocene seawater, supported by the values of δ18O quartz (2.1-6.5 ‰) corrected by homogenization temperature of 389 ºC of the related rocks. As the depth of burial increases (stage II), sediments have hardened and also tectonic and lithostatic stress, dykes and floods cause intraformational and magmatic fluids circulation by compaction and heat recharging. These high-temperature fluids are enriched in copper during circulation among volcanic units. Copper-rich fluids migrate upward and are reduced by entering the pyrite-rich andesitic-basaltic unit, and copper is deposited in sulfide forms such as chalcopyrite and chalcocite in the favorable sites. In deeper burial (stage III), the copper mineral formed in the previous stage would be replaced by bornite and digenite. At the supergene condition (stage IV), due to oxidizing conditions, weathering, and leaching, copper sulfides mostly appear as malachite in the joints and voids. According to the results, the mineralization model of the copper in the Qeshlaq deposit can be considered as manto type.
 

کلیدواژه‌ها [English]

  • Cu deposit
  • Manto type
  • metallogenic belt
  • Karaj Formation
  • Geochemistry
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