نشریه علوم زمین خوارزمی

نشریه علوم زمین خوارزمی

بررسی زمین شیمی عناصر اصلی و کمیاب در ترکیب پیریت: رهیافتی برای تکوین ذخایر طلای نامرئی در ناحیه تکاب- انگوران (شمال غرب ایران)

نویسنده
ابراهیم طالع فاضل
دانشگاه بوعلی سینا
چکیده
سولفیدهای آهن و آرسنیک مهمترین کانی­های میزبان­ طلا در کانسارها هستند که در این میان، ذخایر طلای افشان دور از منشاء با سنگ ­میزبان رسوبی و محتوای بالای طلا در ترکیب پیریت، از آن جمله است. در این پژوهش به­طور مشخص خصوصیات بافتی- زمین­شیمیایی ­پیریت با هدف درک نحوه توزیع طلا در قالب ذرات آزاد (Au0) یا مشارکت در شبکه بلوری کانی (Au+) در سه کانسار زرشوران (عیار متوسط 63/2 گرم در تن)، آق­دره (عیار متوسط 7/3 گرم در تن) و عربشاه (عیار متوسط 2/1 گرم در تن)، در ناحیه فلززایی تکاب- انگوران، مورد بررسی قرار گرفته است. طبق نتایج، یک رابطه شیمیایی منفی میان آرسنیک و گوگرد (R2= −0.61) در ترکیب آرسنین­پیریت­ها با فرمول تجربی Fe(AsxS1−x)2 به­دست آمد که گویای حضور سویه As3+ در این ترکیب است. با توجه به وجود شواهدی نظیر همراهی پاراژنتیکی طلا با کانه‌های سولفیدی پیریت و اسفالریت، عدم رخداد کانی‌های اکسیدی نظیر هماتیت و مگنتیت، وجود مجموعه دگرسانی‌ آرژیلیکی± سریسیتی، pH نزدیک به خنثی تا اسیدی و فعالیت بالای سولفور (logaS2) در هنگام رخداد طلا، نقش کمپلکس‌های بی‌سولفیدی –Au(HS)2 در مهاجرت ‌طلا را در کانسارهای طلای ناحیه فلززایی تکاب- انگوران قوی­تر می­نماید. پس از آن، واکنش­های وسیع سیال- سنگ و مصرف H2S موجب کاهش فعالیت S2-، ناپایداری کمپلکس­های بی­سولفیدی و در نهایت ته­نشست طلا شده است.
کلیدواژه‌ها
آرسنین پیریت طلادار
کربنات های آهن دار
دگرسانی کربنات زدایی
ناحیه تکاب-انگوران

عنوان مقاله English

Major and trace elements geochemistry of pyrite: Implications for development of invisible gold deposits in the Takab-Angouran district, NW Iran

نویسنده English

Ebrahim Tale Fazel
Bu-Ali Sina University
چکیده English

Fe-As sulfide minerals are the most important hosts of gold in various deposits, which sedimentary rock-hosted disseminated gold deposits is known by high content of gold in arsenian pyrite composition. In this study, the textural-geochemical charecteristics of arsenian pyrite is specifically aimed at understanding how gold is distributed in the form of nanoparticles (Au0) or participation in the mineral crystal lattice (Au+) in three ore deposits: Zarshuran (average grade: 2.63 g/t), Agdarreh (average grade: 3.7 g/t), and Arabshah (average grade: 1.2 g/t), at Takab-Angouran metallogenic zone, have been studied. According to the results, a negative chemical relationship between arsenic and sulfur (R2 = −0.61) was observed in the arsenian pyrite composition, which indicates the presence of As3+ with the empirical formula of Fe(AsxS1−x)2. Due to the paragenetic association of gold with pyrite and sphalerite ores, the absence of oxide minerals, near-neutral to acidic nature of pH (presence of argillic±sericitic alteration), and the high activity of sulfur, shown that the gold solubility and its transfer were conducted by Au(HS)2– bisulfide complex. Evidence suggests that pervasive fluid-rock interaction is caused decreased S2– activity - has resulted instability of bisulfide complex and gold deposition in the pyrite veins.

کلیدواژه‌ها English

Auriferous arsenian pyrite
Fe-rich carbonate
decarbonation alteration
Takab-Angouran district
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