بررسی نقش سولفیداسیون سنگ های کربناته آهن دار در افزایش عیار طلای کانسار زرشوران (شمال تکاب)، ناحیه فلززایی تکاب- انگوران

نوع مقاله : مقاله پژوهشی

نویسندگان

1 کارشناسی ارشد، گروه زمین‌شناسی، دانشکده علوم پایه، دانشگاه بوعلی سینا، همدان، ایران

2 استادیار، گروه زمین‌شناسی، دانشکده علوم پایه، دانشگاه بوعلی سینا، همدان، ایران

3 دانشجوی دکتری، گروه زمین‌شناسی، دانشکده علوم پایه، دانشگاه بوعلی سینا، همدان، ایران

چکیده

سولفیدهای آهن و آرسنیک به­ عنوان مهم‌ترین میزبان طلا در ذخایر طلای افشان نامرئی با سنگ میزبان رسوبی محسوب می ­شوند. کانسار طلای زرشوران (ذخیره قطعی 155 تن طلا و عیار متوسط 63/2 گرم در تن)، در میزبان شیل و سیلتستون سیاه (واحد زرشوران) و کربنات ­های آهن ­دار (واحد چالداغ) به سن کامبرین زیرین شکل‌گرفته است. کانه ­های سولفید آرسنیک (نظیر رآلگار و ارپیمنت) و ­پیریت­ های آرسنی ک­دار مهم‌ترین میزبان طلا در این کانسار هستند. بر اساس شواهد تجزیه ریزکاوالکترونی، پیریت با محتوای آرسنیک زیر حد تشخیص تا 99/3 درصد وزنی در شش نوع مختلف به ­ترتیب شامل Py0 (محتوای طلاppm  01/0)، Py1 (محتوای طلاppm  02/0)، Py2 (محتوای طلا ppm 03/0)، Py3 (محتوای طلاppm  02/0)، Py4 (محتوای طلاppm  04/0) و Py5 (محتوای طلاppm  01/0) شناسایی شد. طبق نتایج به ­دست آمده، طلا اغلب به ­صورت مشارکت شیمیایی در شبکه کانی (Au1+ یا Au3+) یا ادخال­ های نانوذرات آزاد (Au0) حضور دارد. همبستگی زمین‌شیمیایی ضعیف میان عناصر As و S (6/0- R2 =) در پیریت­ ها نشان می­ دهد که پیریت با ترکیب پیچیده [Fe(S,As)2Au2S0] وجود دارد که در آن As جانشین S2− شده است. بررسی‌های کانی­ شناسی و فراوانی آهن و گوگرد در واحدهای سنگی کانسار زرشوران نشان می ­دهد که رخداد طلا اغلب با فرایند سولفیداسیون همراه است. سولفیداسیون زمانی رخ می­ دهد که سیالات کانه ­ساز غنی از H2S با سنگ­ میزبان کربناتی آهن ­دار واکنش داده و کانه ­های پیریت، مارکاسیت یا پیروتیت را تشکیل دهد.

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