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زمین شناسی اقتصادی - سال سیزدهم شماره 2 (پیاپی 29، تابستان 1400)

فصلنامه زمین شناسی اقتصادی
سال سیزدهم شماره 2 (پیاپی 29، تابستان 1400)

  • تاریخ انتشار: 1400/07/11
  • تعداد عناوین: 8
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  • منیره سخدری، مهرداد بهزادی*، محمد یزدی، نعمت الله رشید نژاد عمران، مرتضی صادقی نایینی صفحات 245-265

    محدوده گدارسرخ، در پهنه سنندج-سیرجان، 20 کیلومتری جنوب‌غربی منطقه معدنی موته واقع‌شده است. قدیمی ترین رخنمون واحدهای سنگی، کمپلکس شیست سبز با درجه دگرگونی متوسط تا پایین است که سن آن به پالیوزوییک نسبت‌داده شده است و شامل مجموعه ای از سنگ‌های آتشفشانی-رسوبی دگرگون‌شده‌، واحدکربناته پرمین که به ‌صورت تدریجی یا ناپیوستگی هم‌شیب و گاه گسله بر روی واحدهای قدیمی‌تر قرار‌گرفته است و در نهایت رخنمون واحد های شیل و ماسه ژوراسیک است. دایک های بازیک و فلسیک درون واحدهای سنگی نفودکرده اند. توالی‌های سنگی در مراحل مختلف دگرشکلی، نظم اولیه خود را از دست‌داده است و ساختار‌های جدیدی را نشان می‌دهند. دگرشکلی به ‌صورت پهنه‌های برشی شکل‌پذیر- شکنا تا شکنا در محدوده مشاهده می‌شود. کانی سازی در شکستگی ها و گسل ها رخ‌داده و به ‌صورت ساختاری کنترل‌شده است. بیشترین تمرکز طلا همراه با کانی‌های اکسید-هیدرواکسید آهن در امتداد گسل‌هایی با روند W45N رخ‌داده است. کانی شناسی ساده و به‌طور عمده شامل پیریت و به ‌صورت محلی کالکوپیریت، کالکوسیت، کوولیت، گالن، اسفالریت و کانی‌های ثانویه آهن است. دگرسانی‌های موجود سریسیتی، کربناتی، کلریتی، سولفیدی، سیلیسی و آرژیلیکی است. بالاترین مقدار طلا در نمونه‌های برداشت‌شده، به روش لیتوژیوشیمیایی9/9 ppm و میانگین طلا 3/0 ppm است. بر اساس بررسی‌های میکروسکوپی، طلا به ‌صورت آزاد همراه کانی های ثانویه آهن مشاهده می‌شود و همچنین نتایج تجزیه مایکروپروپ الکترونی نشان‌دهنده حضور طلا در شبکه کانی‌های سولفیدی است. بر اساس بررسی‌های انجام‌شده، عوامل کنترل کننده کانی‌زایی در پهنه‌های شکل‌پذیر-شکنا، ویژگی‌های زمین شناسی و کانی زایی محدوده گدار سرخ، بیشترین شباهت را با کانسار های نوع کوه‌زایی دارد.

    کلیدواژگان: کانه زایی طلا، ژئوشیمی، پهنه شکل پذیر- شکنا، گدارسرخ، موته، سنندج-سیرجان
  • رضوان مهوری*، سید حسن طباطبایی صفحات 267-293

    منطقه سعدآباد در 30 کیلومتری جنوب کاشان و در استان اصفهان قرار‌گرفته است. این منطقه بخشی از پهنه فلززایی ارومیه دختر را تشکیل می دهد. مهم ترین واحدهای سنگ شناختی منطقه شامل سنگ های آتشفشانی ایوسن و توده های نفوذی الیگومیوسن هستند. واحدهای آتشفشانی منطقه به‌شدت دگرسان‌شده و دگرسانی های پروپیلیتیک و آرژیلیک از انواع اصلی دگرسانی در منطقه محسوب می شوند. ‌بررسی‌های آماری بر روی داده های ژیوشیمیایی نمونه های رسوب برای 8 عنصر As، Cd، Fe، Co، Cu، Pb، Zn و S صورت‌گرفت که شامل پردازش و نرمال‌کردن یافته ها، بررسیی تغیرهای تک متغیره و چند متغیره و رسم و تفسیر نقشه بی هنجاری عناصر است. بر اساس نتایج به‌دست آمده، میانگین عامل آلودگی عناصر Fe و Co به ترتیب 05/1 و 27/0، عناصر Cu، Pb و Zn به ترتیب دارای عامل آلودگی 81/0، 33/1 و 99/0 و برای عناصر As و Cd 22/1 و 40/1 است. نتایج به‌دست آمده از عامل غنی شدگی بر روی نمونه های رسوب نشان می دهد که عناصر (74/10) As و (61/0) Co به ترتیب دارای بیشترین و کمترین میزان غنی شدگی هستند. بنابراین نتایج حاصل از عامل غنی شدگی نشان‌دهنده آن است که علاوه‌‌بر عوامل طبیعی (واحدهای سنگی، کانه زایی و دگرسانی)، عوامل انسانی (معدن‌کاری) نیز در تمرکز برخی از عناصر در نمونه های رسوب نقش داشته اند.

    کلیدواژگان: دگرسانی عامل آلودگی، عامل غنی شدگی، عناصر بالقوه سمی، کاشان
  • محمد فلاح، قاسم نباتیان*، سعیده قدیمی صفحات 295-325

    معدن روی-‌سرب انگوران در غرب استان زنجان و شمال غربی پهنه ماگمایی-‌دگرگونی سنندج-‌سیرجان قرار‌گرفته است. در این پژوهش از کانی پلی‌ مورف ورتزیت، به‌عنوان کانی معرف و ردیاب برای شناسایی مکان‌های مستعد غنی شده از عناصر فلزی کمیاب استفاده شد. بر اساس این پژوهش‌، تمرکز اقتصادی عناصر فلزی در معدن انگوران را می توان به دو بخش سولفیدی دارای غنی شدگی از عناصر نقره، کادمیم و سلنیوم (بالاتر از عیار حد خود) و باطله‌های کربناته دارای غنی شدگی از عنصر آرسنیک تقسیم‌ کرد. تمرکز برخی از عناصر در فرو‌دیواره شیست این معدن (مانند آهن و به مقادیر کم‌ آرسنیک، کبالت، مس و آنتیموان) در ارتباط با کانی‌زایی سولفیدی در آنهاست. نتایج به‌دست آمده از تجزیه ژیوشیمیایی در این پژوهش نشان‌دهنده آن است که تمرکز بالای عناصر فلزی (نقره، کادمیم، سلنیوم، قلع، ایندیم، کبالت و غیره) در بخش سولفیدی معدن انگوران است که تاییدی در ارتباط با تشکیل کانی‌های اسفالریت و ورتزیت به‌ صورت همزیست در نتیجه غنی شدگی از عناصر فلزی کمیاب است. انباشت اصولی عناصر فلزی موجود در باطله‌ها و سایر بخش‌های معدنی بر اساس نوع و میزان غنی‌شدگی، نه تنها موجب به حداقل رساندن مخاطرات زیست‌محیطی می‌شود؛ بلکه می‌تواند قدمی برای استخراج و بهره‌برداری این عناصر به ‌صورت محصول جانبی باشد.

    کلیدواژگان: باطله های معدنی، ورتزیت، عناصر کمیاب، پهنه سنندج- سیرجان، انگوران، زنجان
  • میثم قلی پور، مهرداد براتی*، ابراهیم طالع فاضل، وراتیسلاو هورای صفحات 327-352

    کانسار آهن لکه سیاه 1 در 40 کیلومتری شمال‌شرقی شهرستان بافق در استان یزد و در پهنه زمین‌ساختی کاشمر- کرمان واقع‌شده است. واحدهای سنگی منطقه به کامبرین زیرین تعلق دارند و شامل ریولیت، ‌آندزیت، سنگ های آذرآواری، دولومیت و ماسه‌سنگ هستند. توده های نفوذی با ترکیب مونزونیت تا دیوریت در این واحدهای سنگی نفوذ کرده اند. فرایند دگرسانی، سنگ های منطقه را تحت‌تاثیر قرار داده؛ به طوری که مهم ترین هاله های دگرسانی رخ‌داده در منطقه (سدیک)- کلسیک، کلریتی شدن، اپیدوتی شدن، سریسیتی شدن، سیلیسی شدن و آرژیلیک است. مگنتیت کانه اصلی کانسار است که دارای بافت های توده ای، برشی و مارتیتی است. بر اساس بررسی‌های پتروگرافی، چهار نوع سیال درگیر در کانی کوارتز همراه کانسنگ مشاهده شده که شامل تک‌فاز مایع (L)، تک‌فاز گاز (V)، دوفازی (L+V) و سه فازی (L+V+H) هستند. دمای همگن‌شدن سیالات درگیر دو فازی بین 217 تا 428 و سه فازی بین 384 تا 467 درجه سانتی‌گراد و شوری برای سیالات دو فازی بین 10 تا 27 و برای سه فازی بین 40 تا 44 درصد معادل شوری نمک طعام به‌دست آمد. بر اساس بررسی‌های اسپکتروسکوپی لیزر رامان بر روی سیالات درگیر، میزان گاز N2 و CO2 در سیالات دو فازی به ترتیب 69 و 31 درصد و در سیالات درگیر سه‌فازی به ترتیب 33 و 67 درصد مولی است که منشا آن می تواند گاززدایی از گوشته و واکنش سیالات با سنگ های کربناته باشد. بررسی ترکیب ایزوتوپی O و H سیال در تعادل با کوارتز نشان می دهد که سیال اولیه در این کانه زایی منشا ماگمایی داشته که در مرحله‌های بعدی با سیالات جوی اختلاط حاصل‌کرده که این فرایند با کاهش سیستماتیک دما و شوری همراه بوده است.

    کلیدواژگان: لکه سیاه، دگرسانی، سیال ماگمایی، آب جوی، اسپکتروسکوپی لیزر رامان
  • علیرضا زراسوندی*، زهرا فریدونی، بهرام علیزاده، بهمن سلیمانی صفحات 353-386

    افق فسفریتی زاگرس به سن ایوسن-الیگوسن، به میزبانی سازند پابده، در کمربند زاگرس چین خورده با روند شمال غرب -جنوب شرق واقع است. هدف از این پژوهش، بررسی زمین شیمی عناصر کمیاب برای پایش شرایط نهشت و زایش این عناصر در افق فسفریتی زاگرس است. طبق بررسی‌های میکروسکوپی، اجزای فسفاته و غیرفسفاته اغلب شامل پلت، اایید، اینتراکلاست و باقی‌مانده خرده‌های استخوان ماهی، میکروفسیل ها، گلوکونیت، کلسیت، پیریت، اکسید آهن و کوارتز است. شیل بیتومینه در توالی چینه‌شناسی، حضور پیریت های فرامبوییدال فراوان، الگوی پراکنش REE نرمالیز‌شده به PAAS، آنومالی منفی Ce تمامی نمونه ها، آنومالی مثبت Euدر همه نمونه های مورد بررسی به جز نمونه شیل بیتومینه فسفریت کوه ریش، نسبت Ni/Co و همچنین نمودار (V+Ni) V/ در برابر Ni/Co، همگی نشان‌دهنده تغییر شرایط از اکسیدی در زمان نهشت فسفات تا نیمه احیایی-احیایی در اثر تخریب و تجزیه ترکیبات آلی توسط میکروارگانیسم ها و فراهم شدن شرایط ورود عناصر کمیاب از جمله اورانیوم به ساختار بلوری آپاتیت، در حوضه زاگرس هستند.

    کلیدواژگان: عناصر کمیاب، زمین شیمی، افق فسفریتی، کمربند زاگرس
  • فاطمه حسنی سوقی*، علی اصغر کلاگری، قهرمان سهرابی صفحات 387-409

    منطقه قره‌کند در فاصله 25 کیلومتری جنوب‌شرق شهرستان مراغه در استان آذربایجان شرقی واقع‌شده است. کانی‌سازی در منطقه قره‌کند به صورت رگه- رگچه‌ای در سنگ‌های میزبان رسوبی رخ‌داده است. دو مرحله کانه‌زایی در منطقه قره‌کند قابل‌تفکیک هستند. در مرحله اول، رگه- رگچه‌های کوارتزی هم‌زمان با فرایندهای دگرسانی و کانی‌سازی طی سه زیرمرحله مجزا (پیشین، میانی و پسین) توسعه یافته‌اند. بلورهای کوارتز در رگه- رگچه‌های کوارتزی، بافت‌های برشی، جعبه‌ای، دروزی و شانه‌ای را به نمایش می‌گذارند. طی مرحله دوم، رگه- رگچه‌های باریتی شکل گرفته‌اند. دگرسانی درون‌زاد اغلب به صورت توسعه هاله‌های سیلیسی که جانشین سنگ‌های میزبان رسوبی در دیواره و اطراف رگه– رگچه‌های کوارتزی شده‌اند، توسعه یافته‌اند. کانه‌زایی سولفیدی (گالن، اسفالریت، پیریت و کالکوپیریت) و طلا در رگچه‌ها و ریزرگچه‌های کوارتزی زیرمرحله پسین متجلی می‌شوند. گوتیت، هماتیت، ژاروسیت، مالاکیت و آزوریت در زون اکسیدان و سولفیدهای ثانویه مس (کوولیت، کالکوسیت و دیژنیت) در زون برون‌زاد تشکیل شده‌اند. میان‌بارهای سیال در بلورهای کوارتز زیرمرحله پسین مورد بررسی قرار‌گرفته و بر اساس محتوای فازهای اصلی، به سه نوع دو‌فازی غنی از مایع، تک‌فاز گازی و دو‌فازی غنی از گاز طبقه‌بندی شده‌اند. مقادیر دمای همگن‌شدن میان‌بارهای سیال دو‌فازی غنی از مایع در محدوده دمایی 80 تا 220 درجه سانتی‌گراد قرار می‌گیرند. دماهای ذوب نهایی یخ از 1/9- تا 7/3- درجه سانتی‌گراد متغیر بوده که منطبق با شوری‌هایی بین 6 تا 13 درصد وزنی معادل نمک طعام هستند. بر اساس یافته‌های ریزدماسنجی، رخداد جوشش و سرد‌شدن ساده موثرترین سازوکار‌های نهشت کانی‌های کانسنگی و باطله در قره‌کند تشخیص‌داده شدند. همچنین بررسی‌های ریزدماسنجی نشان دادند که لیگاندهای کمپلکس‌ساز بی‌سولفیدی به احتمال زیاد نقشی مهم در حمل فلزات کانسنگی (به‌ویژه طلا) ایفا کرده‌اند. ویژگی‌های زمین‌شناسی، یافته‌های میان‌بارهای سیال، کانی‌شناسی و بافت کانی‌های کدر و باطله در رگه- رگچه‌های کوارتز و باریت نشان‌دهنده آن است که کانه‌زایی در قره‌کند از قسم اپی‌ترمال نوع سولفید کم است.

    کلیدواژگان: میان بار سیال، کانه زایی طلا، اپی ترمال، قره کند، مراغه
  • نسرین صدرمحمدی*، سید رضا مهرنیا، خلیل رضایی، سلما کادی اوغلو، محمود هنرور صفحات 411-439

    معدن روی- سرب کالامین (مهدی آباد، یزد، ایران مرکزی)، یک رخنمون اقتصادی غیرسولفیدی با منشا رسوبی- آتشفشانی است که بر اساس سوابق اکتشافی منطقه، از ویژگی های زمین شناختی و ژیوشیمیایی متناسب با محیط های سوپرژن برخوردار است. در این پژوهش، از سه رهیافت رگرسیون خطی، توزیع پواسونی و تغییرات بعد فرکتال برای بازبینی توزیع های ژیوشیمیایی و معرفی اولویت های اکتشافی منطقه مورد بررسی استفاده‌ شده است. مقایسه ضرایب رگرسیون خطی و توزیع پواسونی عناصر مختلف، بیانگر تمایل نسبی آنها به توزیع غیرخطی است. بنابراین از مدل ‌نمایی پراش- مسافت برای دستیابی به تغییرات بعد فرکتالی 13 عنصر شاخص و ردیاب ذخایر‌ برون‌دمی استفاده شده است. تعیین سطح توزیع براونی هر عنصر، ملاک هندسی جدیدی است که با فرایند خودساماندهی ژیوشیمیایی در سامانه های ماگمایی، گرمابی و آتشفشانی سازگاری دارد. در پیش بینی به روش فرکتال، از الگوی ناحیه بندی ترکیبی شامل 10 عنصر با سطوح آرمانی و 3 عنصر با سطوح نزدیک به سطح براونی برای معرفی اولویت های اکتشافی منطقه استفاده شده است. نتایج پژوهش نشان می دهند که عناصر آرسنیک، روی و آنتیموان از سطوح توزیع براونی مطلوب (FD>2 3>) برای تولید مولفه های متناظر (عیارهای متناظر) برخوردارند. تغییرات بعد فرکتالی سرب، مس، نقره و گوگرد از نوع محدود، اما قابل برازش با سطوح براونی آرسنیک، روی و آنتیموان بوده و بیانگر ناحیه بندی ژیوشیمیایی متناسب با فرایند غنی شدگی در عمق رخساره های دگرسانی است. لذا بر اساس نقشه پیش داوری مبتنی بر تحلیل های واریوفرکتالی، امکان دستیابی به ذخایر هیپوژنیک در برخی از اهداف اکتشافی منطقه کالامین وجود دارد.

    کلیدواژگان: سطح براونی، کالامین، کانی سازی روی و سرب، مدل پراش - مسافت
  • رضا احمدی صفحات 435-462

    به دلیل پیچیدگی های ذاتی زمین شناسی، محدودیت اطلاعات اکتشافی در دسترس، زمان بر و مشکل بودن محاسبات مربوطه، مدل‌سازی داده های اکتشافی کانسارهای فلزی کم عیار با استفاده از نرم افزارهای تخصصی قوی گریزناپذیر است. در این پژوهش‌، مدل‌سازی ریاضی سه بعدی زمین شناسی، عیارسنجی و ذخیره کانسار مس نارباغی شمالی ساوه با استفاده از اطلاعات چاه نگار و عیارسنجی تعداد 23 حلقه گمانه اکتشافی با مجموع متراژ حفاری 2425 متر با استفاده از قابلیت های نرم افزار RockWorks‏ صورت‌گرفت. برای این منظور، واریوگرافی و تجزیه و تحلیل ساختار فضایی کانسار با استفاده از نرم افزار SGeMS انجام‌شد که بر اساس آن کانسار ناهمسان‌گرد بوده و شعاع های بیضوی تجسس (شعاع تاثیر در جهت‌های مختلف) برابر با 50، 130 و 433 متر به‌دست آمد. مدل‌سازی داده های عیارسنجی و تخمین ذخیره کانسار با استفاده از روش های مختلف موجود در نرم افزار همانند بلوک بندی از طریق منوی I-Data، تخمین ذخیره به روش مدل شبکه دوبعدی و انباشتگی دوبعدی برای شش رده عیار حد 1000،1500،2000،2500،3000 و 3500 گرم در تن نشان می دهد که در برخی موارد، نتایج روش های مختلف با یکدیگر بسیار متفاوت است. به‌طورکلی، برای تخمین ذخیره منطقه مورد بررسی، دقت روش بلوک بندی از طریق منوی I-Data و روش انباشتگی دوبعدی از دیگر روش های موجود در نرم افزار بیشتر است. در مجموع، با متوسط‌ گیری از میزان ذخیره و عیار متوسط محاسبه‌شده توسط روش های تخمین ذخیره مورد استفاده، ذخیره کلی کانسار به ازای عیار حد 1/0 درصد (1000 گرم در تن) حدود 500000 تن با عیار متوسط 8/0 درصد برآورد شد. نتایج این پژوهش به ویژه نحوه انتخاب مولفه‌های گوناگون در بخش های مختلف نرم افزار، برای مدل‌سازی دیگر کانسارهای فلزی مشابه با کانسار مورد بررسی در کمان ماگمایی ارومیه- دختر، قابل‌تعمیم است.

    کلیدواژگان: کانسار مس نارباغی شمالی ساوه، مدل سازی زمین شناسی- اکتشافی، واریوگرافی، تخمین ذخیره، بلوک بندی، مدل شبکه دوبعدی، انباشتگی دوبعدی، RockWorks
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  • Monire Sakhdari, Mehrdad Behzadi *, Mohammad Yazdi, Nematollah Rachidnejad Omran, Morteza Sadeghi Naeini Pages 245-265
    Introduction

    Gold deposits formed during mountain-building processes in Phanerozoic terranes that formed in metamorphic environment have a great dispensation in the world (Goldfarb et al., 2001). They constitute an economically important type of gold mineralization called orogenic gold deposits (Groves et al., 2003). The Sanandaj-Sirjan zone is one of the most important areas for orogenic gold exploration and it hosts several orogenic gold deposits (Aliyari et al., 2012).  This zone is characterized by regionally metamorphosed and deformed Paleozoic and Mesozoic sedimentary, volcanic and volcanoclastic rocks under green schist and amphibolite facies conditions. (Rashidnejad-Omran, 2001; Abdollahi et al., 2009; Kouhestani et al., 2014(. The Godar Sorkh area is locatedin the central part of the Sanandaj-Sirjan zone, 20km southwest of the Muteh region. The rocks sequence of the Godar Sorkh area comprise of the volcano-sedimentary rocks of the greenschist complex with Paleozoic age rock units intruded by basic and felsic dikes. These country rocks are affected by a NW-SE-trending shear zone and are highly deformed. Rock units illustrate ductile-brittle to brittle shear zones and had been under poly-phase metamorphism. In other words, Godar Sorkh has the most similarity with orogenic gold.

    Methods

    In this study after field observations, rock samples were collected from mineralized and altered zones that included 26 thin sections, 47 polished sections and 10 polished thin sections which were prepared for petrography, mineralization and alteration studies, 10 samples were prepared for XRD analyses, 21 samples were analyzed for Au  content by the Fire Assay method and 21 samples were analyzed by the ICP-MS method for REE and trace element amounts in the Iran Minerals Research and Processing Center, and 9 samples  were selected  for XRF analyses  in the Kansaran Binaloud laboratory.  According to the petrographic studies and the results of chemical analysis 7 polished double sections were selected to determine the amount of gold and other elements by electron-microprobe analysis.

    Discussion and Results

    The rocks sequence of the Godar Sorkh area comprise of greenschists complexes including limestone, dolomitic, marbles, micaschists, black schist, greenschist, intercalations of quartzite, calc schist, phyllites and slate, metamorphosed under greenschist facies grade. These units are considered to belong to the Paleozoic age. Rock unites have been intruded by basic and felsic dikes. Rock assemblages are characterized by several phases of deformation and generation of various fabrics and structures. Gold mineralization occurs in ductile and brittle shear zones, along N45W trending and controlled by structures. The main alterations are sericitization, carbonization, chloritization, silicification and sulphidization. Ore-mineralogical paragenesis mainly includes pyrite and locally chalcopyrite, arsenopyrite, covellite, sphalerite, galena and Fe Oxide-Hydroxide secondary minerals such as goethite, hematite and limonite. The results show that the maximum grade of gold in the mineralization zone has been reported to be 9.9 ppm and the average value of gold in the area is about 0.3 ppm. The microscopic studies show native gold minerals in the range of 15 to 30 micrometers.  Also, electron-microprobe analysis indicates Au in the lattice of sulfide minerals. Based on geochemical studies, rocks have characteristics peraluminous range and the granodiorite intrusion belongs to S type granitoids. LREE are enriched. Controlling parameters for mineral concentration in Godar Sorkh area are shear zone. Therefore, regarding the development of Paleozoic metavolcanic-sedimentary sequences and the formation of multistage extensional structures including the normal faults, and fractures, texture and structure investigation, mineral paragenesis, alteration and geochemistry, gold mineralization in the Godar Sorkh area can be classified as orogenic gold mineralization.

    Keywords: Gold mineralization, Geochemistry, Ductile-brittle, Godar Sorkh, Muteh, Sanandaj-Sirjan
  • Rezvan Mehvari *, Seyed Hassan Tabatabaei Pages 267-293
    Introduction

    Soil and sediments are considered to be the main places for absorption of heavy metals in contaminated environments (Priju and Narayana, 2007; Øygard and Gjengedal, 2009; Ahmed and Al-Hajri, 2009). Therefore, they are used in Heavy Metals Pollution Index in geochemical studies.Saadabad area that is a part of the Urumieh-Dokhtar magmatic belt is located at 30 km south of Kashan. The natural processes along with hydrothermal processes, altered areas and mineral activities on mineralization areas have potential for releasing toxic elements in the environment. Therefore, the presence of toxic elements in sediments of the Saadabad is expected.The purpose of this study is to evaluate the concentration of toxic elements and determine their source in the sediments of the Saadabad region.

    Material and Methods

    To investigate the status of environmental pollution of sediments, 174 samples were collected from the surface of sediments in the Saadabad area. The samples were analyzed by ICP-MS spectroscopy for determination of elements such as As, Cd, Pb, Zn, Cu, Co in the Zarazma Laboratory, Tehran, Iran.

    Discussion and Results

    Geochemical studies are carried out using various statistical techniques to map the various elemental abnormalities. These maps play an important role in determining high- risk areas. The results of preliminary investigations showed that according to the correlations between the various elements studied the patterns of dispersion of various elements in the sediments of the Saadabad region are similar to each other. The anomalies observed of As and Cd in the southwest of the region can be attributed to the presence of travertine in this part of the region (Smedley and Kinniburgh, 2005).Maximum concentrations of Co and Fe in the central part of the Saadabad region are consistent with the location of igneous and sedimentary rocks, skarnification and hydrothermal alterations. The enrichment of elements Cu, Pb, and Zn in sediments of the Saadabad region, emphasizes the effective role of sulfide mineralization and hydrothermal alteration processes in the region.Several methods that are applied for the assessment of trace elements contamination as follows:1- Contamination Factor (CF) is defined as follows (Reboredo, 1993): 1) CF=Cm Sample/Cm.

    Keywords: Alteration, Contamination Factor, Enrichment Factor, Potentially toxic Elements, Kashan
  • Mohammad Fallah, Ghasem Nabatian *, Saideh Ghadimi Pages 295-325
    Introduction

    Increasing demand for ore minerals needed for economic development and the desire to find a suitable rank in the international community has forced developing countries such as Iran employ more mining activities which has led to creation of a large amount of waste minerals. Given the existing equipment establishing the necessary situation and economic solutions for the exploitation of valuable elements from these waste minerals can be considered as a source for economic development of the country. The Angouran Zn-Pb mine is located west of the Zanjan province and northwest of the magmatic- metamorphic Sanandaj-Sirjan zone. The wurtzite mineral can be used as an indicator mineral for trace elements such as IGG (indium, gallium, germanium) in this mine. The economic concentration of metal elements in the Angouran mine can be divided into two parts of sulfide and gangue carbonate. The sulfide part of this mine is enriched with silver, cadmium and selenium (higher than their cut-off grade) and the gangue carbonate part is enriched in arsenic element. The foot-wall schists show some concentration of elements which are related to sulfide mineralization.

    Material and methods

    More than 30 rock samples were collected from cross sections in the open-pit part of the Angouran mine which covers all different parts such as foot-wall schist, sulfide mineralization, carbonate mineralization and hanging-wall carbonate (marble). About 30 samples were prepared for petrographic studies and geochemistry analysis which were analyzed at the Zarazma laboratory (Tehran, Iran). The ArcGIS, Geosoft Oasis Montaj and Excel software packages were also used for interpretation of data.

    Geology of the study area:

    The Angouran Zn-Pb mine is located west of the Zanjan province and northwest of the magmatic- metamorphic Sanandaj- Sirjan zone. The rock units in the study area include foot-wall quartz schist and hanging-wall marble with Precambrian age, Mesozoic diorite and granite, Cenozoic pyroclastic units such as white tuffs and Quaternary travertine sediments. It should be mentioned that the white tuffs and, in some cases older units are crosscut by younger diabetic sills and dikes (Ghorbani, 2008; Pirkharrati and Farhadi, 2014; Fallah et al., 2019).

    Results

    The Angouran deposit has been formed as breccia structure on the boundary between thrusted hanging-wall marble and foot-wall quartz schist. According to this study, mineralization in the Angouran deposit has occurred during two hypogene and supergene stages. Hypogene mineralization in the Angouran deposit has been formed as successive phases of sulfide and carbonate. The hypogene mineralization continued by the formation of supergene mineralization. According to the geochemical analysis, a high concentration of trace elements such as silver, cadmium and selenium was detected in the Angouran deposit. These elements are concentrated in the sulfide ore mainly in the sphalerite mineral with poor lead minerals. The carbonate part of the Angouran mine which is considered to be waste contains enrichment of arsenic. The foot-wall schists are not enriched with trace elements and just concentrate in some elements such as iron, antimony, cadmium, cobalt and selenium, which are related to sulfide mineralization.

    Discussion

    Based on the geochemistry analysis and microscopic studies, the economic concentration of metal elements in the Angouran mine can be divided into two parts of sulfide and carbonate. The sulfide part of this mine has been enriched with silver, cadmium and selenium (higher than their cut-off grade) and the carbonate part has been enriched with arsenic. This element can be considered to be a major threat to human health, along with its numerous uses, such as pesticides, medicine, electronics, etc.The wide distribution of arsenic in the open pit mine along with the other toxic elements such as cadmium and selenium (mainly related to the sulfide mineralization and host quartz schist) are too dangerous for the villagers who live near the mine due to the seepage of these toxic elements to underground water aquifers and their surrounding environment. It should be mentioned that, in the Angouran mine, the waste minerals are abandoned as deserted mountains irrespective of their relationship to groundwater and the surrounding environment.It is hoped that with the continuation of the exploitation process in the Angouran mine, the waste minerals are classified according to their type and element enrichment in a suitable manner by environmental standards. This could help prevent seepage of toxic elements (As, Cd, Se) to groundwater. Furthermore, the economic elements such as Ag, Cd, Se can be used as byproducts and be sold as raw material for other uses or extracted by using the necessary equipment. This is due to the fact that what is considered to be waste minerals for a mine, can be considered as useful material for another mine, either now or in the future.

    Keywords: Waste minerals, wurtzite, trace elements, Sanandaj- Sirjan zone, Angouran, Zanjan
  • Meisam Gholipoor, Mehrdad Barati *, Ebrahim Tale Fazel, Vratislav Hurai Pages 327-352
    Introduction

    The Lakehsiah mining district is hosted in Early Cambrian volcano-sedimentary units (CVSU) of the Kashmar–Kerman zone, Central Iran. The Kashmar-Kerman belt is located between the Yazd block in the west and the Tabas block in the east and it is parallel to the Poshed badam, Tabas and Kalmard faults in the north and Koh Banan and Zarand faults in the south of the area (Ramezani and Tucker, 2003). Compositions of the volcanogenic rocks in this area vary from felsic to mafic and include rhyolitic, rhyodacitic tuff and spilitic lava and diabase. The sedimentary rocks include dolomites, dolomitic limestones and evaporites. Lakehsiah 1 deposit is one of three IOA outcrops in the Lakehsiah district which have been studied in this research.

    Materials and Methods

    The mineralogical study of alteration zones was carried out by light microscope with transmission light and X-ray diffraction (XRD) analysis, at the Mineralogical Laboratory of Bu-Ali Sina University and Iran Minerals Processing Research Center, respectively. Fluid inclusion and Raman spectroscopy studies were also performed to determine temperature, composition and evolution of the ore-forming fluid at the Institute of Earth Sciences SAS, Slovakia. Stable isotope geochemistry of quartz (O-H) was performed at the Cornell University, USA.

    Discussion

    Iron deposits hosted in the Tashk Group show hydrothermal alteration. The major minerals of the Sodic-Calcic alteration are the crystals of calcic amphiboles (tremolite-actinolite), pyroxene, calcite, magnetite and apatite. Propylitic alteration (chloritization and epidotization) is very widespread and affects volcanic and intrusive rocks. It consists of chlorite, epidote, calcite, and magnetite with minor amounts of sericite. Silicification alteration, occurs as distal alteration in both hanging wall and footwall host rocks, forming fine-grained to coarse grained quartz aggregates, veins and veinlets. Sericitic-argillic alteration occurs mainly in intrusions. Feldspar (plagioclase and K-feldspar) was altered to sericite and clay minerals. Minor quartz occurs as veinlets in this alteration zone. Na- Ca alteration in volcanic and intrusion rocks is exposed in the center of the area. Amphiboles mainly occur as replacements of plagioclase. Plagioclases were altered to chlorite, epidote, and calcite. Additionally, veinlets of quartz-epidote-chlorite, chlorite-epidote, epidote-quartz, quartz-calcite, calcite, chlorite-calcite, and epidote-calcite are observed. Quartz and carbonates (calcite) are widespread and veins of these minerals crosscut all the rocks described above. Lakehsiah 1 deposit, hosted within high-silica rhyolitic tuffs and domes, forms a steeply dipping tabular lens and it includes massive magnetite ± apatite ± quartz ± specular hematite ± Fe-Mg silicates.

    Fluid inclusion Petrography:

    Four major types of fluid inclusions are observed based on proportions of vapor, liquid, and solid phases present at room temperature in quartz mineral. They are described as follows:1-liquid-rich inclusions (L) 2-vapor-rich inclusions (V) 3-Two-phase liquid rich fluid inclusions (L+V) 4-three phase inclusions with halite solid phase as daughter mineral (L+V+H). Study of inclusions petrography shows that most of the inclusions present within this mineral are primary in origin, although secondary or pseudosecondary types have been identified. They have different sizes (typically 5–15 μm). Fluid inclusion shapes are rounded, elliptical, irregular, negative crystal shapes and square.

    Results

    Microthermometry and Raman spectroscopy Freezing and heating experiments were performed on Types 3 and 4 fluid inclusions. Stretching of inclusions was noted during heating of large fluid inclusions in quartz from mineralized quartz veins. In such samples, homogenization temperatures range from 217–428 °C for type 3 and 384-467°C   for type 4. Micro-thermometric data were obtained from both Types 3 and 4 inclusions. The data obtained revealed variation in salinity of the trapped fluids. The final ice melting temperature in Types 3 and 4 inclusions varies from −4° to -18 and -9 to -19 °C with a mode at around -12 °C. Final ice-melting temperatures are lowest in the mineralized quartz veins. The first melting temperatures in multiphase Types 3–4 inclusions are also in a similar range which varies from -21 to -34°C. Based on their final ice melting temperatures, it varies between 10 to 27 and 40 to 44 wt. % NaCl equivalent for type 3 and 4 inclusions. T°C vs. salinity plots of inclusions show mixing of magmatic hot fluids with cold meteoric waters. Raman spectroscopy revealed presence of 69 mol % N2 and 31 mol % CO2 and 33 mol % N2 and 67 mol % CO2 in types 3 and 4 inclusions. These gases can be derived from mantle degassing (Wang et al., 2018) and chemical reactions during ascent of fluids.

    H-O isotopes:

    Isotopic studies are among the most common methods for identifying the primary composition of ore-forming fluids in deposits (Barati and Gholipoor, 2014). In the study area, five quartz samples in quartz grains and veins were used for H-O isotope analyses, with the aim of determining the source(s) of ore-forming fluids. The δDH2O and δ18OH2O values of the ore-forming fluids in quartz samples vary from -60‰ to -80‰, and -4.71‰ to -1.42‰, respectively. The above observations reveal that the early ore-forming fluids are magmatic in origin and is characterized by high temperature and moderate to high salinity, and gradually evolve to low temperature, low salinity meteoric water. The Lakehsiah 1 Fe deposit is associated with the magmatism induced by the protracted subduction. The decrease in temperature, salinity and f(O2), as well as fluid-rock interactions, are the main factors controlling Fe deposition.

    Keywords: Lakehsiah, Alteration, Magmatic fluid, Meteoric water, Laser Raman spectroscopy
  • Alireza Zarasvandi *, Zahra Fereydouni, Bahram Alizadeh, Bahman Soleimani Pages 353-386
    Introduction

    Phosphorites are marine sediments of biogenic origin containing 15–20 wt% P2O5 and between 50 and 120 ppm U (Boggs, 2009; Tzifas et al., 2014; Zarasvandi et al., 2019). The study of phosphorites, especially trace elements geochemistry, confirms the importance of deposition conditions and diagenesis on the elemental composition of phosphatic minerals. Even more importantly, marine phosphorites are considered to have an economic potential for elements such as REE, Sc, U and Th (Altschuler, 1980). Some trace elements, including Sr, Ba, Se, Mo, Ag, Pb, Zn, V, Cr, Ni, Cu, Cd, and U are commonly found in phosphorites and sediments rich in phosphorus related to the crystal structure of apatite and carrier organic ligands (Tzifas et al., 2014; Zarasvandi et al., 2019). In general, more than seven horizons with an extent of ∼400 to 100km have been delineated in the Zagros Mountains. The Zagros phosphorite horizon of Eocene-Oligocene age hosted by the Pabdeh Formation is located in the Zagros fold belt with NW-SE trend (Halalat and Bolourchi, 1994; Zarasvandi et al., 2019). The aim of this study is to investigate the geochemistry of trace elements in order to obtain the deposition and genesis conditions of these elements in the Zagros phosphorite horizon.

    Materials and methods

    A total of 29 samples were taken from phosphorite, hydrocarbon-bearing shale, phosphorite and limestone and oxide zone of the studied phosphorites of Zagros. Hence, based on stratigraphy, different samples from Zagros phosphorite horizons were collected from the phosphorites of Kuh-e-Sefid (n=9), Kuh-Rish (n=12) and Sheykh-Habil (n=8). Mineralogical and geochemical studies were carried out using ICP-MS analyses. 20 polished-thin sections were prepared. Mineralogy and petrography of the samples was determined and examined using polarizing-reflected light optical microscopy at the Shahid Chamran University of Ahvaz in Iran. Geochemical studies on mineralized and host rocks of Zagros phosphorite horizon were performed by the ICP-MS technique (Thermo Scientific- X Series II; DL= 0.001 ppb) at the Department of Earth Sciences, Pondicherry University in India.

    Results

    According to the petrographic studies, phosphorite components and non-phosphorite components mainly consist of pellets, Ooids, intraclasts, fish skeletal fragments, micro-fossils, glauconite, calcite, pyrite, iron-oxide and quartz. Several elements that substitute Ca including rare earth elements and trace elements are suitable for contribution in the carbonate-rich fluorapatite (francolite) crystalline structure. Thus, some oxo-anions such as VO4, As2O4, SO2, SO4 and CO3 can be substituted into PO4 structure in apatite group lattices (Tzifas et al., 2014; Zarasvandi et al., 2019). Consistently, the Zagros phosphorite horizon exhibits different concentrations of elements such as Sr, REE, Zn, V, Mo, Cr, Cd, Se, As and U. Trace element distribution patterns in the studied phosphorites are similar to phosphorite in Iran and worldwide, especially in terms of concentration of U, Se, and Cd that can be related to apatite group minerals crystal lattice (Tzifas et al., 2014; Zarasvandi et al., 2019). Due the low entrance rate of detrital components from continental to the basin, the most probable source for trace elements is hydrocarbon-bearing shale in the stratigraphic column as a result of activities of microorganisms.

    Discussion

    Field observation and microscopic studies showed that the phosphorite components occur as authigenic apatite with sparite cement, abundant pellets, ooids of symmetrical to elongated shape due to pressures caused by diagenesis, oval shape intraclasts, fish skeletal fragments and abundant microfossils. In additions to phosphorite and biogenic components, non-phosphorite minerals such as calcite, glauconite, pyrite, iron oxide, and microcrystalline quartz are present.There are many indications of change in conditions. They include bituminous shale in stratigraphic sequence, presence of abundant framboidal pyrites, PAAS-normalized patterns of REEs, negative Ce anomaly of all samples and positive Eu anomalies of all samples except bituminous shale sample of Kuh-e Rish phosphorite, the Ni/Co ratio and also the diagram of V/(V+Ni) vs. Ni/Co. These indicate changes in conditions from oxides during phosphate deposition into dysoxic to anoxic due to degradation and decomposition of organic compounds by microorganisms and the entry of trace elements such as uranium into the crystalline structure of apatite in the Zagros Basin.The significant economic potential of organometallic elements especially U and REE is observed in the Zagros phosphorite horizon due to favorable conditions of dysoxic to anoxic as a result of decomposition of organic compounds and then the entry of the elements into the apatite crystal structure.

    Keywords: Trace elements, Geochemistry, Phosphoritic horizon, Zagros belt
  • Fatemeh Hassani Soughi *, AliAsghar Calagari, Ghahraman Sohrabi Pages 387-409
    Introduction

    The Gharehkand area is located in the southeast of Maragheh city and in Takab metallogenic district. According to the structural divisions of Iran, this area is situated south of the volcanic Mount Sahand in the Central Iran zone (Stocklin, 1968). This paper aims to investigate the characteristics of gold-bearing vein-veinlets and physicochemical conditions of ore-forming fluids in the Gharehkand area.

    Materials and methods

    About 40 rock samples were collected from mineralized zones and host rocks. The thin and thin-polished sample sections were studied in the geology department of the Mohaghegh Ardebili University, Ardebil. Microthermometric data were obtained from fluid inclusions using the Linkam THMS600 stage at the Payame Noor University of Tabriz.

    Results

    1) The mineralization in the Gharehkand area took place principally as vein-veinlets within the host sedimentary rocks during two main stages. Mineralization occurred in quartz vein-veinlets during the first stage. The quartz crystals within the quartz vein-veinlets display brecciated, boxwork, drusy, and comb textures. During the second stage barite mineralization occurred as vein-veinlets. The mineralization of sulfides (galena, sphalerite, pyrite, and chalcopyrite) and gold occurred within the quartz vein-veinlets of the first stage.2) The values of homogenization temperature (Th) and salinity of fluid inclusions vary from 80°C to 220ºC and 6 to 13 wt.% NaCl eq., respectively.3) The study of fluid inclusions demonstrated that boiling and simple cooling were the most important mechanisms in the ore deposition at Gharehkand, and the sulfide complexing ligands played an effective role in transporting metals within the ore-forming hydrothermal fluids.4) The quartz crystals textures (brecciated, boxwork, and comb) in quartz vein-veinlets and microthermometric data (low salinity and Th) of the ore-forming fluids indicate that mineralization at Gharehkand is of epithermal type with low-sulfidation style.

    Discussion

    The mineralization in the Gharehkand area took place principally as vein-veinlets within the host sedimentary rocks. Two main stages of mineralization were distinguished at the Gharehkand area. Stage-1 mineralization is represented by the quartz vein-veinlets. The quartz crystals within the quartz vein-veinlets display brecciated, boxwork, drusy, and comb textures. The formation of quartz crystals in quartz veinlets and micro-veinlets were temporally divided into three sub-stages: early, middle, and late. Stage-2 mineralization is represented by barite vein-veinlets. The hypogene alteration is mainly observed as the development of silicic halos around quartz vein-veinlets within the host sedimentary rocks. The mineralization of sulfides (galena, sphalerite, pyrite, and chalcopyrite) and gold have occurred within the late sub-stage quartz veinlets and micro-veinlets. Oxidized processes have caused formation of goethite, hematite, jarosite, malachite, and azurite. Copper sulfides (covellite, chalcocite, and digenite) are formed in the supergene zone. Based upon phase content, the studied fluid inclusions in late sub-stage quartz crystals may be classified into three types: liquid-rich two-phase (L+V), mono-phase vapor (V), and vapor-rich two-phase (V+L). The values of homogenization temperature (Th) and salinity of the analyzed liquid-rich two-phase fluid inclusions vary from 80°C to 220ºC and 6 to 13 wt.% NaCl eq., respectively (Fig. 11A, C). Given the Th and salinity values of the fluid inclusions, ore-forming hydrothermal fluids during development of the quartz vein-veinlets at Gharehkand experienced hydrostatic pressures within the range of 20-25 bars. This is almost equivalent to depths of 200-250 meters below the underground water table level. It is consistent with the estimated depths of most epithermal deposits (Bodnar et al., 2014). The Gharehkand microthermometric data points on the bivariate plot of Th versus salinity (Wilkinson, 2001) show that the densities of fluid inclusions vary from 0.9 to 1 g/cm3. The occurrence of boiling and simple cooling are the most effective mechanisms in deposition of ore and gangue minerals at Gharehkand.  The Gharehkand microthermometric data points on the bivariate plot of Th versus salinity (Pirajno, 2009) indicate that the bisulfide complexing ligand most likely played the important role in transporting ore metals (particularly gold).

    Keywords: Fluid inclusion, Gold mineralization, Epithermal, Gharehkand, Maragheh
  • Nasrin Sadrmohammadi *, Seyed Reza Mehrnia, Khalil Rezaei, Selma Kadioğlu, Mahmood Honarvar Pages 411-439
    Introduction

    Calamine Zn-Pb deposit (Mehdiabad, Yazd, Central Iran) is a mineable nonsulfide mineralization, located in the upper part of a volcano-sedimentary basin at intersection with erosion surfaces. From statistical viewpoint, geochemical distributions of trace elements due to volcanic-exhalative processes, may naturally be predominated by self-organized zonation in ore mineralized regions (Cheng et al., 2000; Mehrnia, 2017). Therefore, attention is paid to nonlinear distribution of particular elements to finding their spatial relations with concealed ore mineralization for prospecting sedimentary-hosted exhalative deposit (SEDEX). In this way, calculation and analysis of statistical coefficients is a necessary stage for prospection of the inter-relation of typomorphic elements. In cases where the erosion surfaces result in redistribution of supra ore elements, the approach of linear regression coefficient is not recommended, because progressive weathering usually hides the natural zonality of elements, as an expected criterion for hypogenic mineralization (Hassani-Pak, 2012). Our research approach which is to find a proper zonality of elements is based on nonlinear assessment of geochemical distributions for a case of epigenetic mineralization that seems to be related to deep/concealed SEDEX deposits.

    Material and method

    Current research uses a variance-distance equation to modify the linear regression results as follows:  (1)where Log (Vx) and Log (Dvx) are the logarithms of variances and distances respectively; and FD is the fractal dimension. A log-log plot is used to illustrate Vx and Dvx changes on horizontal (X) and vertical (Y) axes to obtain a distribution’s density function. By statistical concepts, FD is an independent variable from the central tendencies as well as distribution parameters. Meanwhile, a self-organizing property of geochemical distributions is geometrically dependent on fractal dimension changes on power-law’s log-log plots. For obtaining the natural geochemical zonation of Calamine’s path-finder elements, a set of lithogeochemical data has been used. Consequently, a total of 180 litho-samples of Calamine region were collected and interpolated to find the anomalous populations. A GIS-based software (Spatial Analyst) was used here to obtain geometric and statistical quantities which are necessary for variance-distance equation (Teymoorian-Motlagh et al., 2012). This soft-package works on ArcMap with the ability to export summarized data to other supplementary software packages such as Excel which are used to complete and present V-D log-log plots.At the second step, we used fractal dimension changes to identify the Brownian surfaces of elements. This surface usually contains a set of paragenetic elements which are found together within several correlated zonations with respect to their rate of activities in magmatic environments. A Brownian surfaces is formed of particular geometric locations of self-similar populations. When it changes between 2.5>FD>2, it represents scale-invariant continuity of distributions (Thorarinsson and Magnusson, 1990). In other word, this surface denotes the tendency of trace-elements to nonlinear distributions and it is geometrically related to a probable phase of mineralization in some epigenetic ore deposits.

    Discussion

    Based on a variance-distance model for Calamine’s indicative and path-finder elements, six target areas are presented in a contoured prognostic map, which contains As, Zn, Cr, Sb, S, Co, Cu, Pb, Ni and Ag in a sequent. Order of this sequent is based on geometry of their Brownian surfaces.  The largest surface belongs to As while the smallest one belongs to Ag and Cd. Among the elements which have reached the Brownian surface, As, Sb and Zn shared similar fractal parameters and extended at the background of other elements. Cr was the only element which did not follow the As, Sb and Zn backgrounds, because its geometrical location is independent of other elements. The mentioned target-areas which are marked on the prognostic map, have different scoring of mineralization potentials that is prioritized by considering zonation peculiarities of elements on fractal surfaces.  

    Results

    Fractal relationship of elements is conceptually different from what is generally stated in statistical models. Therefore, many elements which have desirable linear correlation with each other (relatively good condition for path-finding), are unfavorable as V-D models and vice versa. From a nonlinear perspective, a Poisson distribution is the most important criterion for analyzing coherency of elements in hypogenic environments. As a final result, we have illustrated that Brownian surfaces in As, Zn and Sb are extended well in the central and southeastern parts of Calamine, marking a proper relation of the structures with the host units during exhalative activities of the region. The high amount of these elements compared to the background indicates the effect of fluid flows and the penetration of mineralizing solutions under a supergene condition of the mine as well opening the fractures and fault systems.

    Keywords: Brownian Surface, Calamine, Zn-Pb mineralization, Variance-Distance model
  • Reza Ahmadi * Pages 435-462
    Introduction

    Deposit modeling includes various types of descriptive-genetic, geometric, geostatistical modeling-simulation, economic, and mathematical analyses (Erickson, 1992). In the present study, 3-D geological, mineralization and ore deposit mathematical modeling of the North-Narbaghi copper deposit, Saveh were carried out using various capabilities of the Rockworks software package. The North-Narbaghi exploration area is located in the northeast of the Markazi province, ~26 km northeast of Saveh city, at 1:100,000 Zavieh sheet. The monzogranite-quartzmonzodiorite intrusive bodies are the main host rocks for mineralization in the area. Two main porphyry copper mineralization zones consisting of phyllic and potassic alterations have been recognized in the area by applying systematic explorations including 23 boreholes (i.e., NNB1 to NNB23) with the total depth of 2425 meters. Five boreholes have been drilled in the eastern stock whereas 18 boreholes are located in the western part. The drillholes range in depth from 52 (e.g., NNB9 borehole) to 224 meters (e.g., NNB1 borehole). A total of 558 drill cores collected from different boreholes were analyzed for their copper and associated elements. The ore grades typically range from 2ppm to 12.2%.

    Materials and methods

    The RockWorks software package calculates the volume of minerals in two ways; one through the borehole manager window, the I-data menu, the volumetrics submenu, and four other paths in the utilities window called Ez-volume, 2D (grid model), grade block model grade thickness (GT) grid, and compute grade-thickness volume & mass which comprise subsets of volumetrics main menu. In all cases, the average density of the mineral was considered to be 2.65 g/cm3. Also, the SGeMS software (Remy et al., 2009) outputs were used in order to obtain more accurate estimation of grade and tonnage of the deposit, if required, for estimation of parameters such as search radius. In this research, the values of the search radius corresponding to the measured, indicated and inferred reserve categories were assumed to be 50, 130 and 433 m, respectively. For the North-Narraghi copper deposit, six cutoff grades of 1000, 1500, 2000, 2500, 3000 and 3500ppm were defined. In the 2D (grid model) method, the volume of the mineral deposit was calculated by gridding the thickness of the deposit. The cell size of 20*20*2m was selected and the number of data involved to estimate each cell was chosen to be 3 based on the borehole distances and depth of drill cores by trial and error.To evaluate ore deposits, sometimes accumulation parameter grade-thickness (GT) was used instead of cutoff grade. In this operation, for each column of cells within the primary grade model, the sum of the GT values of the cells were calculated and stored as GT values within the grid model. These values of cellular GT are calculated by multiplying grade by thickness (height) of the cell. If the grade value of a cell is less than the threshold value defined by the user, the value for this cell will not be taken into account in the total summation. If the value of the final sum is lower than the threshold defined by the user, the program will set the value of the relevant grid to zero. The minimum acceptable values for the studied ore grade for the six defined cutoff grades of 0.1%, 0.15%, 0.2%, 0.25%, 0.3% and 0.35% and also, accumulation threshold corresponding to the minimum acceptable values of grade multiplied by the minimum core length (0.1 m) was defined to be 0.01, 0.015, 0.02, 0.025, 0.03 and 0.035(m%), respectively.            

    Results

    The ore reserve calculated by 2D GT method shows that the software output is slightly different from that of other techniques. This method calculates the net ore reserve for three categories of "measured", "indicated" and "inferred" categories. In this algorithm, reserve calculations for the study area has not assigned any values for the "inferred" reserve category. Moreover, no reserve has been calculated for the "indicated" category by increasing the cutoff grade value. In other words, there is no reserve in the "inferred" category for the various cutoff grades. There is no reserve even in the "indicated" category for the upper limits cutoff grade. This indicates the sensitivity of the applied algorithm to the degree of reliability of the reserve.Assay data modeling and ore reserve estimation using the variety of methods that exist in Rockworks for 6 cutoff grades of 1000, 1500, 2000, 2500, 3000 and 3500ppm show that in some cases the results of various methods are very different. In general, blocking through I-Data menu and 2-D accumulation (2D GT) methods are more accurate than the others available in Rockworks to estimate the ore reserve of the study area. Overall,reserve value was calculated about 500000 tonnes with an average grade of 0.8% for cutoff grade of 0.1% (1000ppm) by averaging the ore reserve and average grade of the deposit and using conventional ore reserve estimation methods.

    Discussion

    The findings of the current investigation confirm that the feasibility of achieving reasonable, valid, and reliable results using a specialized software is highly dependent on the knowledge and experience of the user and the high degree of validity of results is only obtained by the choice of appropriate modeling methods as well as selecting suitable parameters.The results of this research study especially how to select parameters in different parts of the software can be generalized for modeling other metallic deposits similar to the study area. However, validation of modeling operation and the produced models are highly dependent on the type and amount of available exploration information.

    Keywords: North-Narbaghi copper deposit Saveh, Geological-exploration modeling, Varigraphy, Ore reserve estimation, Blocking, 2D grid model, 2D accumulation, RockWorks