نشریه علوم زمین خوارزمی

نشریه علوم زمین خوارزمی

زمین‌دماسنجی پهنه‌های اسکارنی در کانسار آهن تپه‌قرمز (A')، منطقۀ معدنی آهن سنگان، شمال‌شرقی ایران

نویسندگان
1 دانشگاه خوارزمی
2 مرکز تحقیقات فرآوری مواد معدنی ایران
چکیده
منطقۀ معدنی سنگان، بزرگترین ناحیه کانسنگ آهن اسکارنی در ایران محسوب می‌­شود. این کانسار در بخش شمال­‌شرقی کمان ماگمایی البرز واقع شده است. مجموعۀ معادن سنگ آهن سنگان (1 میلیارد تن و عیار 35 تا 60 درصد آهن) شامل 14 کانسار است، که در یک روند شرقی- غربی کشیده شده‌­اند و به سه بخش شرقی، مرکزی و غربی تقسیم می­‌شوند. کانسار آهن تپه‌قرمز ('A) در بخش غربی معدن سنگ آهن سنگان واقع شده است. اسکارن­‌زایی و کانه­‌زایی آهن همراه آن در منطقۀ تپه­‌قرمز در مجاورت تودۀ نفوذی سینوگرانیتی سرنوسر با ماهیت پتاسیم بالا تشکیل شده­ است. پهنه­‌های اسکارنی در منطقۀ مورد مطالعه شامل، 1) پهنه­‌های درون ­اسکارن و برون ­اسکارن پیشرونده (زیرپهنۀ کلینوپیروکسن- گارنت اسکارن) و 2) پهنۀ برون ­اسکارن پسرونده (زیرپهنۀ آمفیبول اسکارن) هستند. دماسنجی تشکیل اسکارن، براساس شیمی کانی‌­های سیلیکاتۀ اسکارنی و انطباق آن­‌ها با نتایج حاصل از مطالعات میکروترمومتری میانبارهای سیال انجام‌شده بر روی گارنت و کلسیت، برای پی­ بردن به شرایط فیزیکوشیمیایی و دمای تشکیل پهنه­‌های اسکارنی کانسار تپه‌قرمز، انجام شد. زمین­ دماسنجی زوج‌کانی گارنت-کلینوپیروکسن، دماهای 302 تا 442 درجۀ سانتی­گراد را برای پهنۀ اسکارن پیشرونده نشان داد. برپایۀ زمین­ دماسنجی آمفیبول‌های کلسیمی در پهنۀ پسرونده، دماهای تشکیل 206 تا 333 درجۀ سانتی­گراد بدست آمد. نتایج زمین­ دماسنجی پهنه­‌های پیشرونده و پسروندۀ اسکارنی با نتایج حاصل از میکروترمومتری میانبارهای سیال هم‌خوانی دارد. آندرادیت در دمای بیش از 430 درجۀ سانتی­گراد، حتی در شرایط سولفیداسیون بالای محیط نیز پایدار است. در دماهای کمتر از 430 درجۀ سانتی­گراد و فوگاسیتۀ نسبتاً بالای گوگرد (بیش از 6-10)، آندرادیت به مجموعۀ کلسیت و کوارتز دگرسان می­‌شود. با کاهش fS چنین سیالاتی مجموعۀ مگنتیت را تشکیل می­‌دهند. بنابراین، می­توان نتیجه گرفت که سیالات متاسوماتیک پسرونده در کانسار اسکارن آهن تپه‌قرمز (A')، دارای fS2 حدود 6/5-10 و دمای کمتر از 430 درجۀ سانتی­گراد هستند.
کلیدواژه‌ها

عنوان مقاله English

Geothermometry of skarn zones in the Tappeh Ghermez (A') iron deposit, Sangan iron mining district, NE Iran

نویسندگان English

Hamed Ebrahimi Fard 1
Majid Ghasemi Siani 1
Behrouz Karimi Shahraki 2
Fanoos Sharafi Nia 1
1 Kharazmi University
2 Iranian Mineral Processing Research Center
چکیده English

The Sangan mining district, the largest Fe-skarn district in Iran, is located in the northeastern part of the Alborz magmatic arc. It comprises 14 deposits (1 Gt tons and a grade of 35-60% Fe), which have an east-west trend and are divided into three parts: eastern, central and western where the Tappeh Ghermez iron deposit (A') is located in the western part. The skarnification formed near the Sarnowsar syenogranitic intrusive body, and is composed of: 1) prograde endoskarn and exoskarn zones (clinopyroxene-garnet skarn subzone) and 2) retrograde exoskarn zone (amphibole skarn subzone). Thermometry of skarnification was carried out based on the chemistry of skarn silicate minerals and their agreement with the results of microthermometry studies of fluid inclusion carried out on garnet and calcite in order to determine the physicochemical conditions and temperature of skarnification in the Tappeh Ghermez deposit. Geothermometry of the garnet-clinopyroxene pair minerals, indicated temperatures of 302 to 442°C for the prograde skarn zone. Based on the geothermometry of the calcic amphiboles in the retrograde zone, formation temperatures of 206 to 333°C have been obtained. The results of the geothermometry of the prograde and retrograde skarn zones are consistent with the results of the microthermometry of the fluid inclusions. Andradite is stable at temperatures above 430°C, even under high sulfidation conditions. At temperatures below 430°C and a relatively high fugacity of sulfur (greater than 10-6), andradite altered into calcite, quartz and pyrite. As fS2 decreases (about 10-6), such fluids form the magnetite complex. Itcan therefore be concluded that retrograde metasomatizing fluids in the Tappeh Ghermez iron skarn deposit have a sulfur fugacity of 10-6.5 and temperatures below 430°C.

کلیدواژه‌ها English

Geothermometry
Skarn zones
Tappeh Ghermez iron deposit
Sangan mining district
Eastern Alborz zone
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