کانه زایی، شیمی کانه ها و ایزوتوپ های پایدار گوگرد در اندیس طلای چالداغ (شمال تکاب): شواهدی برای دستیابی به سازوکار تشکیل طلا

نوع مقاله : مقاله پژوهشی

نویسندگان

گروه زمین‌شناسی، دانشکده علوم، دانشگاه بوعلی سینا، همدان، ایران

چکیده

منطقه اکتشافی چالداغ با عیار متوسط 5/4 گرم در تن به‌عنوان یکی از اندیس­ های پرعیار کانسار زرشوران، در شمال تکاب واقع‌شده است. از لحاظ ساختاری این منطقه در غرب گسل رانده قینرجه و طاقدیس ایمان­خان (راستای NW) قرار دارد و واحد کربنات آهن­دار چالداغ به سن نئوپروتروزوئیک-کامبرین بالایی، سنگ میزبان اصلی کانه ­زایی است. طبق شواهد ریزکاوالکترونی، طلا به‌صورت محلول جامد با کاتیون Au+ و محتوای 10 تا 80 گرم در تن (ppm) در ترکیب کانه آرسنین­پیریت با فرمول (Fe2+As3+)S2Au2.S0 تمرکز دارد. شواهد ایزوتوپ پایدار گوگرد بر روی کانه ­های سولفیدی رالگار و پیریت گویای مقادیر δ34SCDT بین 5/3 تا ‰ 5/6 (متوسط ‰ 5 در تعداد 6 نمونه)، است. با توجه به مقادیر FeS mol% اسفالریت­، تغییرات LogfS2 در اندیس چالداغ بین 14- تا 16- به‌دست آمد که منطبق با شرایط سولفیداسیون متوسط است. طبق شواهد به‌نظر می­ رسد در اندیس طلای چالداغ، سیال گرمابی غنی از H2S هم‌ زمان با فرایند کربنات­ زدایی و آزاد‌شدن مقادیر بالای Fe2+ و As3+ در محیط، با این کاتیون­ ها واکنش داده و آرسنین­پیریت تشکیل‌ شده است. در پی این فرایند، ضمن کاهش محتوای H2S محیط، کمپلکس­ های بی­سولفیدی Au(HS)2 تحت شرایط خنثی تا اسیدی و ماهیت اکسیدی محیط ناپایدار شده و به دنبال آن ته‌نشینی طلا رخ‌داده است.

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