نشریه علوم زمین خوارزمی

نشریه علوم زمین خوارزمی

منشأ و تکامل سیال کانه ساز در کانسار مگنتیت±آپاتیت لکه سیاه (بافق): شواهدی از میانبارهای سیال و ایزوتوپ های پایدار اکسیژن

نویسندگان
ابراهیم طالع فاضل
مهین رستمی
دانشگاه بوعلی سینا، گروه زمین‌شناسی
10.29252/gnf.5.2.217
چکیده
کانسار مگنتیت ± آپاتیت لکه­سیاه در شمال­شرق بافق و در زون ساختاری ایران مرکزی قرار دارد. سنگ میزبان کانسار شامل توالی­های ضخیم آتشفشانی-رسوبی به سن کامبرین زیرین است که به‌صورت مجموعه کالدرایی لکه­سیاه رخنمون دارد. کانه­زایی آهن به‌صورت عدسی­های مگنتیت و هماتیت اغلب همراه کانی­های باطله آپاتیت، کوارتز و کلسیت تشکیل شده­ است. براساس شواهد پتروگرافی میانبارهای سیال، پنج نوع میانبار سیال شامل چندفازی (L+V+S1+S2)، سه فازی (L+V+S)، دوفازی غنی از مایع (L+V)، دوفازی غنی از گاز (V+L) و تک فاز گاز (V)، در کانی­های کوارتز و آپاتیت کانسار لکه­سیاه شناسایی شد. میانبارهای سه فازی فراوان­ترین نوع میانبارها هستند که دمای همگن­ شدن برای کوارتز بین 123 تا°C 530 (متوسط C° 344) و در آپاتیت بین 175 تا °C 420 (متوسط C° 385)، به‌دست آمد. هم‌چنین، تغییرات شوری در میزبان کوارتز بین 30 تا 58 درصد وزنی معادل نمک (متوسط 40 درصد وزنی) و در آپاتیت بین 34 تا 53 درصد وزنی معادل نمک (متوسط 6/41 درصد وزنی)، را نشان می­دهد. فشار محاسبه شده در سیستم H2O-NaCl، بین 10 تا 500 بار و معادل عمق 3/0 تا 5/1 کیلومتری، به‌دست آمد. مقادیر δ18Owater در تعادل با کوارتز بین 5/7 تا 11 درهزار است که نشان­دهندۀ سیال با خاستگاه ماگمایی است. براساس تغییرات وسیع دمای همگن­شدن نهایی و شوری و نیز هم‌بستگی مثبت آن‌ها در میانبارهای سیال، اختلاط سیال ماگمایی دما و شوری زیاد با سیال سرد با شوری کم (مشابه سیال جوی)، از عوامل مؤثر در رخداد کانسار لکه­سیاه است.
کلیدواژه‌ها
مگنتیت±آپاتیت
توالی آتشفشانی-رسوبی
ایزوتوپ اکسیژن
مجموعه کالدرایی لکه‌سیاه
بافق

عنوان مقاله English

Origin and Evolution of Ore-Forming Fluids in the Magnetite±Apatite Lake Siah Deposit (Bafq): Evidence of Fluid Inclusions and Oxygen Stable Isotope

نویسندگان English

Ebrahim Tale Fazel
Mahin Rostami
Bu-Ali Sina university
چکیده English

The Lake Siah magnetite ± apatite deposit is situated in the northeastern of Bafq and Central Iran tectonic zone. The host rock of deposit is composed of lower Cambrian volcano-sedimentary sequence that has exposed as caldera complex. The iron mineralization includes magnetite and hematite with apatite, quartz and calcite as gangue minerals. Based on fluid inclusion petrography in quartz and apatite, at least five types of fluid inclusions are recognized including multi-phase solid bearing (L+V+S1+S2), three phase solid bearing (L+V+S), liquid-rich two phase (L+V), vapor-rich two phase (V+L) and monophase vapor (V(. The three phase fluid inclusions are the most abundant of fluid inclusions type and indicate homogenization temperature between 123 to 530°C (avg. 344°C) and salinity content of 30 to 58 wt% NaCl equiv. (avg. 40.60 wt% NaCl equiv.). Three phase fluid inclusions in the apatite are characterized by homogenization temperature of 175 to 420°C (avg. 385°C) and salinity of 34 to 53 wt% NaCl equiv. (avg. 41.58 wt% NaCl equiv.). Estimated pressure on the basis of microthermometric measurements on fluid inclusions in the H2O-NaCl system is between 10 to 500 bar which is corresponding to depth of 0.5 to 1.5 km. The values of δ18O of fluid in equilibrium with quartz are 7.5 to 11 ‰ which indicate magmatic fluid origin. According to wide range of fluid inclusion homogenization temperature and salinity accompanied with positive correlation between salinity and homogenization temperature of fluid inclusions, mixing of hot and high salinity fluid with cold and low salinity water (similar to meteoric waters) is the main factor for occurrence of the Lake Siah deposit.

کلیدواژه‌ها English

Keywords: Magnetite±apatite
Lower Cambrian volcano-sedimentary
Caldera complex
Lake Siah
Bafq
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