شناسایی کانه زایی سرب و روی بر اساس بررسی های ژئوشیمیایی رسوبات آبراهه در کمربند فلززایی ملایر-اصفهان

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشکده زمین‌ شناسی، پردیس علوم، دانشگاه تهران، تهران، ایران

2 گروه زمین‌ شناسی، واحد اهواز، دانشگاه آزاد اسلامی‌، اهواز، ایران

چکیده

کمربند فلززایی ملایر-اصفهان با روند شمال­ غربی-جنوب­ شرقی بزرگ‌ ترین و مهم‌ترین کمربند کانه ­زایی سرب و روی نوع MVT موجود در ایران به‌شمار می ­رود که بیش از 170 کانسار با توانایی معدنی بسیار بالا در آن شناسایی‌شده است.
مهم‌ترین بحث در تحلیل داده­ های ژئوشیمیایی تعیین حد مقدار زمینه برای هر عنصر در منطقه مورد بررسی و جدا کردن زمینه از بی­ هنجاری­ های عنصر مربوطه است. هدف از این پژوهش، بررسی کانه­ زایی و جداسازی بی­ هنجاری ژئوشیمیایی فلزات سرب و روی با استفاده از روش­های آمار کلاسیک، انحراف مطلق از میانه، روش­های مولتی­ فرکتال عیار-تعداد و عیار-مساحت، شاخص سینگولاریتی و نمودار شواهد وزنی در منطقه مورد بررسی است. به‌طور کلی در مجموع 19946 نمونه ژئوشیمیایی از رسوبات آبراه ه­ای که توسط روش ICP-MS و XRF مورد تجزیه و تحلیل قرار‌گرفته، استفاده شده است. ابتدا از طریق روش آمار کلاسیک و انحراف مطلق از میانه با محاسبه مؤلفه‌های آماری به جداسازی جوامع ژئوشیمیایی پرداخته‌شد. پس از آن با استفاده از روش­ های فرکتالی عیار-تعداد و عیار-مساحت و با توجه به خط برازش هر فلز بر روی نمودارهای لگاریتمی و همچنین با استفاده از روش سینگولاریتی و تلفیق آن با نمودار شواهد وزنی، بی­ هنجاری ژئوشیمیایی دو فلز سرب و روی در منطقه مورد بررسی تفکیک شدند. روش فرکتال عیار-مساحت نشان‌داد که مقدار کمینه و بیشنیه عیار برای فلز سرب به‌ترتیب 11/25 ppm و 25/141ppm  و برای فلز روی 09/63 ppm و 68/446 ppm است که بیانگر عیار بیشتر فلز روی در این منطقه است. در نقشه ­های حاصل از روش شاخص سینگولاریتی، دقت بالاتر این روش نسبت به سایر روش­ها، آشکارسازی بی­ هنجاری ­های پنهان و همچنین انطباق بالای بی­ هنجاری­ ها و موقعیت کانسارهای سرب و روی موجود در پهنه مورد‌نظر مشخص‌شد. به‌طور کلی نتایج این روش­ها نشان داد عیار فلزات سرب و روی در جنوب­ شرق و شمال­ غرب منطقه مورد بررسی، بیشترین میزان بی­ هنجاری را دارا هستند و در این مناطق احتمال وجود مناطق امیدبخش کانساری بسیار بالاست.

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