فهرست مطالب

زمین شناسی اقتصادی - سال هشتم شماره 1 (پیاپی 14، بهار و تابستان 1395)
  • سال هشتم شماره 1 (پیاپی 14، بهار و تابستان 1395)
  • تاریخ انتشار: 1395/06/06
  • تعداد عناوین: 15
|
  • پژوهشی
  • مهدی بمانی، سید حسین مجتهدزاده، امیرحسین کوهساری صفحات 1-20
    منطقه مورد پژوهش در 50 کیلومتری جنوب سبزوار واقع شده است. در این منطقه اثراتی از کانی های بورات دیده می شود. اندیس بور محمدآباد عریان، تنها اندیس بورات شمال شرق ایران است و در واحدهای سنگی مارن کرمرنگ، مارن توفی و ولکانیک برش و توف برش قرار گرفته است. دو گسل از نوع راندگی یا معکوس، محدوده کانسار را در بر می گیرند و دارای امتداد NE-SW هستند. می توان گفت: این گسلها به عنوان معبری برای محلولهای سازنده کانسار و همچنین ایجادکننده فضاهای لازم برای جای گزینی کانسار عمل کرده اند. بررسی های صورت گرفته در ترانشه های حفر شده در منطقه نشان می دهد؛ که از سطح به عمق از شدت کانی سازی کم می شود. وسعت محدوده مورد بررسی، در ابتدا بیش از 600 کیلومتر مربع بوده است؛ که بعد از انجام بررسی های دورسنجی، زمین شناسی، ساختاری و تلفیق این لایه های اطلاعاتی، مناطق امید بخش کانی سازی بورات ها تعیین و این منطقه محدودتر شد. برای انجام بررسی های مفصل تر، بررسی ها و پژوهشهای صحرایی صورت گرفت و تعداد 9 پیمایش انجام شد. در هر یک از پیمایش ها، واحدهای زمین شناسی مورد بررسی قرار گرفت و در مناطقی که چشمه های هیدورترمالی وجود داشت، نمونه های شورابه ای برداشت شد. سرانجام، منطقه مورد بررسی با توجه به محل برداشت نمونه ها به دو منطقه توناکار و برج خارکن محدود و بررسی ها و تجزیه و تحلیل آماری داده های ژئوشیمیایی روی این دو منطقه انجام شد. مجموعه نمونه های برداشت شده از منطقه، بعد از آنالیز با استفاده از روش های آماری مورد تجزیه و تحلیل قرار گرفت. در تجزیه و تحلیل آماری داده ها، برای تعیین مقدار حد آستانه نمونه ها و جداسازی میزان زمینه از آنومالی، از روش های آماری کلاسیک، هندسه فرکتال و EDA و Median+2MAD استفاده شد. با استفاده از هر روش مناطق آنومالی برای انجام بررسی های تفصیلی تر، تعیین شد.
    کلیدواژگان: آمار کلاسیک، هندسه فرکتال، EDA، Median+2MAD، نمونه های شورابه ای، اندیس بور محمدآباد عریان
  • سمیه فلاحتی، موسی نقره ئیان، مرتضی شریفی، قدرت ترابی، همایون صفایی، محمد علی مکی زاده صفحات 21-38
    سنگهای آتشفشانی شوراب با سن الیگوسن زیرین و با ترکیب بازالت، همراه واحدهای مارنی و نمکی سازند قرمز زیرین در 50 کیلومتری جنوب شرق شهرستان قم قرار گرفته اند. کانی های اصلی سازنده این سنگها شامل الیوین، کلینوپیروکسن و پلاژیوکلاز و کانی های فرعی شامل کانی تیره، اسفن و آپاتیت است. آنالیز نقطه ای کلینوپیروکسن های موجود در این سنگها، نشان دهنده ترکیب دیوپسید برای این کانی هاست. ترکیب شیمیایی کلینوپیروکسن های سنگهای مورد بررسی، دمای حدود 1200 درجه سانتی گراد و فشار کمتر از 10 کیلو بار را برای تشکیل این کانی نشان می دهد و همچنین با توجه به ترکیب شیمیایی این کانی ها، سرشت ماگمای سازنده سنگهای منطقه مورد بررسی کالک آلکالن، فوگاسیته اکسیژن آنها در طی تبلور، زیاد و جایگاه تکتونیکی تشکیل آنها، در ارتباط با فرورانش است.
    کلیدواژگان: کلینوپیروکسن، دما، فشارسنجی، تکتونوماگمایی، شوراب، قم
  • منصوره مقصودلو محلی، بهنام شفیعی بافتی صفحات 39-59
    افقهای آرژیلیتی دارنده اووئیدهای آهن، از سازند لشکرک البرز شرقی (اردویسین زیرین- میانی) و بر اساس توالی کاملا آواری کم ژرفا و بدون حضور سنگهای آتشفشانی واقع شده اند. هماتیت و شاموزیت کانی های آهن دار اصلی هستند و گوتیت و گلاکونیت در مقدار جزئی شناسایی شدند. افقهای مورد بررسی، با میانگین 21 درصد وزنی آهن در گروه سنگ آهنهای اوولیتی کم عیار رده بندی شده اند. آهن مورد نیاز برای تشکیل اووئید های آهن در مناطق مورد بررسی، از آب دریای معمولی در دسترس قرار گرفته است و این آهن می تواند به صورت ذرات آواری همراه با رسها، از هوازدگی و فرسایش سنگهای شیلی و از خشکی های مجاور به دریا حمل شود. بالا بودن میزان پتاسیم و سیلیکا در افقهای اوولیت آهن، حضور زیرکن، کوارتز و کانی های رسی در داخل اووئیدها و همچنین در زمینه این سنگها ضمن تایید این الگو، نقش رسهای آهن دار را در پیدایش اووئیدهای اولیه شاموزیتی در محیطی با pH=5-9 و Eh اکسیدان متوسط- ضعیف با اهمیت نشان داده است. فراوان بودن اووئیدهای هماتیتی نسبت به گوتیتی، اووئیدهای متراکم و بیضی شکل و رخ داد فراوان رگه چه های کلسیتی قطع کننده اووئیدها به فرآیند دیاژنز و تبدیل شاموزیت و گوتیت به هماتیت نسبت داده شده است.
    کلیدواژگان: آهن اوولیتی، هماتیت و شاموزیت، توالی پیش رونده، سازند لشکرک، البرز شرقی
  • محمد سیاری، مرتضی شریفی صفحات 61-78
    در منطقه قهرود (شمال اصفهان)، سنگهای آتشفشانی با ترکیب آندزیت تا بازالت به صورت توده هایی با ابعاد مختلف پراکنده اند. از نظر کانی شناسی، سنگهای آتشفشانی بازالتی مورد بررسی از فنوکریست های پلاژیوکلاز به همراه بلورهای کوچکتر کلینوپیروکسن در زمینه ای از میکرولیت، شیشه و کانی های کدر تشکیل شده اند. پلاژیوکلازها ترکیب لابرادوریت- بیتونیت (41-An85-58Ab15) دارند و کلینوپیروکسنها از نوع اوژیت (26-En41-49Di29-38Fs17) هستند. ترکیب کلینوپیروکسن ها نشان می دهد، ماگمای مادر سنگها دارای ماهیت تولئیتی است. بر اساس محاسبات نظام مند زمین دما- فشارسنجی با استفاده از نرم افزار تخصصی SCG، کلینوپیروکسنها در محدوده دمایی حدود 1120-1170 درجه سانتیگراد و محدوده فشار حدود 2-6 کیلوبار متبلور شده اند. پردازشهای آماری نشان می دهد، همگام با صعود ماگما و تبلور هم زمان پیروکسن ها، در قبال هر درجه سانتی گراد کاهش دما، به میزان 6/84 بار از فشار وارد بر ماگما کاسته شده که معادل با 320 متر کاهش عمق در پوسته قاره ای است.
    کلیدواژگان: کلینوپیروکسن، دما، فشارسنجی، سنگهای آتشفشانی، قهرود
  • حجت الله صفری، بهنام شفیعی بافتی، حسن محمدرضایی صفحات 79-92
    کانسار مس سرچشمه و سایر اندیس های مس پیرامون آن در کمربند دهج- ساردوئیه ( استان کرمان) قرار گرفته اند. گسلها گاه با ایجاد شرایط مناسب سینماتیکی و مکانی می توانند الگوی تشکیل رخ داد های مس را کنترل کنند. در راستای بررسی صحت این فرضیه، با استفاده از روش های سنجش از دور، خطواره ها، استخراج و سپس با مشاهدات صحرایی، گسلهای اصلی و فرعی مشخص شدند. بررسی های ساختاری در قالب تهیه نمودار گل سرخی و محاسبه محور فشارش انجام شد. با استفاده از قابلیتهای GIS، اقدام به تهیه نقشه هم شکستگی و فاصله داری رخ دادهای مس از گسلها شد و لایه موقعیت رخ دادهای مس بر روی سایر لایه های خروجی منطبق شد. نتایج بررسی نقشه های خروجی نشان می دهد گسلهای اصلی دخالت مستقیمی در کنترل محل رخ دادهای پورفیری و رگه ای نداشته و رده های دوم این پهنه های گسلش، موقعیت رخ دادها را کنترل کرده اند. همچنین مشخص شد که محل رخ دادهای مس آغشتگی ارتباط نزدیکتری با گسلها داشته و بیشتر رخ دادها نزدیک به گسل رفسنجان قرار دارند.
    کلیدواژگان: منطقه سرچشمه، رخ دادهای مس، سنجش از دور، سیستم اطلاعات جغرافیایی
  • مهری کرمی، محمد ابراهیمی، حسین کوهستانی صفحات 93-115
    رخ داد معدنی آهن لولک آباد، در گوشه شمال باختری زون ایران مرکزی و در فاصله 55 کیلومتری شمال باختر زنجان قرار دارد. کانه زایی آهن در این منطقه، به صورت رگه ای- رگه چه ای و عدسی شکل، درون واحدهای دگرشکل شده شیستی، متاولکانیکی (معادل سازند کهر) و گرانیتی رخ داده است. بر اساس بررسی های میکروسکپی، کانی های معدنی در لولک آباد، شامل اولیژیست، اندکی مگنتیت و پیریت کانی های باطله، شامل کوارتز، کلسیت و کلریت است. بافت کانه ها شامل دانه پراکنده، رگه- رگه چه ای، برشی و پرکننده فضای خالی است. دگرسانی شامل سیلیسی، کلسیتی و کلریتی شدن بخشهای کانه دار است. دو مرحله کانه زایی در رخ داد معدنی آهن لولک آباد قابل تفکیک است. کانه زایی مرحله اول، به صورت مگنتیت های دانه پراکنده و عدسی شکل چینه سان و چینه کران هم زمان با واحدهای آتشفشانی- رسوبی میزبان دیده می شود. مرحله دوم کانه زایی، به صورت رگه و رگه چه های اولیژیستی- پیریتی- کلسیتی رخ داده و برگ وارگی غالب میلونیتی سنگها را قطع کرده است. مقایسه الگوی عناصر نادر خاکی در سنگهای میزبان فاقد کانه زایی و بخشهای کانه دار، بیانگر غنی شدگی عناصر نادر خاکی سنگین نسبت به عناصر نادر خاکی سبک در بخشهای کانه دار است. این امر بیانگر نسبت بالای واکنش سیال به سنگ در لولک آباد است. مقایسه ویژگی های زمین شناسی، کانی شناسی، زمین شیمیایی و ساخت و بافت ماده معدنی در رخ داد معدنی لولک آباد با نوعهای مختلف کانسارهای آهن نشان می دهد؛ که کانه زایی آهن در لولک آباد، در ابتدا به صورت آتشفشانی- رسوبی تشکیل شده و بعد به صورت رگه ای تمرکز دوباره یافته است.
    کلیدواژگان: کانه زایی آهن، رگه ای گرمابی، دگرسانی، لولک آباد، زنجان، ایران مرکزی
  • طاهره ربانی، نادر تقی پور، رضا اهری پور صفحات 117-128
    به منظور بررسی گروه های ماسرالی زغا ل سنگ ناحیه زغال دار قشلاق، از 11 لایه زغال سنگی متعلق به چهار معدن در حال استخراج شامل: معدنهای زمستان یورت، نرگس چال، چشمه ساران و شرق کلات، نمونه برداری انجام شد. بررسی پتروگرافی آلی زغال سنگهای قشلاق، بیانگر حضور هر سه گروه ماسرالی است. گروه ویترینیت (vol% 66/2 – 87/2) شامل:ماسرال های کالودترینیت، کالوتلینیت و کورپوژلینیت، گروه اینرتینیت ( vol% 4/9 – 23/2) شامل: ماسرال های فوزینیت، سمی فوزینیت، ماکرینیت، اسکرتینیت، فانگینیت، اینرتودترینیت و میکرینیت و گروه لیپتینیت (vol% 0 – 3/5) شامل: ماسرال های اسپورنیت، کوتینیت، رزینیت و لیپتودترینیت هستند. گروه ویترینیت دارای بیشترین و گروه لیپتینیت دارای کمترین فراوانی در این زغال سنگها هستند. مقدار مواد معدنی این لایه های زغال سنگی در محدوده بین 5 و vol% 24/9 متغیر است.
    کلیدواژگان: ماسرال، زغال سنگ، قشلاق، البرز شرقی
  • منصور عادل پور، ایرج رساء، فریبرز مسعودی، مسعود حسینی صفحات 129-146
    در این پژوهش، سعی شده است تا با تلفیق نتایج به دست آمده از بررسی های زمین شناسی، زمین شیمیایی سطحی و زمین فیزیک، ضمن تکمیل بررسی های یادشده ، با استفاده از روش های جدید زمین فیزیک اکتشافی، موقعیت مکانی زون کانی سازی کانسار مس گرماب (شمال شرق قائن) تعیین شود. بعد از الکترومغناطیس، از متداولترین روش های زمین فیزیکی قابل استفاده در اکتشاف کانسارهای سولفیدی مس، روش های قطبش القایی و مقاومت ویژه الکتریکی است. در این پژوهش، از این روش در حوزه زمان استفاده شد و مولفه های ثابت زمانی ظاهری، وابسته بسامد ظاهری و بارپذیری حقیقی استخراج شد. پس از تفسیر نتایج، نواحی بی هنجاری در مناطق با بارپذیری متوسط و همچنین مقاومت ویژه الکتریکی کم تا متوسط شناسایی شد که این امر را می توان به حضور کانی های سولفیدی در مناطق کانی سازی نسبت داد،. همچنین، با استفاده از نتایج مولفه ثابت زمانی، میانگین دانه بندی دانه های فلزی در منبع تولید کننده قطبش القایی دریافت شد. با توجه به این که نتایج خام اندازه گیری ها، اطلاعات کمی دقیق و مطمئنی درباره عمق و هندسه توده های کانی سازی شده زیر سطحی در اختیار قرار نمی دهند؛ با استفاده از مقاطع حاصل از مولفه های قطبش القایی و مدل سازی معکوس هموار برای تعیین محلهای احتمالی، گسترشهای جانبی و قائم کانی سازی های زیر سطحی استفاده شد. بررسی های زمین فیزیک نشان می دهد، کانی سازی بیشتر به صورت محدوده های کوچک و پراکنده است.
    کلیدواژگان: قطبش القایی، مقاومت ویژه الکتریکی، مدل سازی معکوس، مس، قائن
  • کریم عبدالهی سیلابی، سیدمحسن طباطبایی منش، سمیه کریمی صفحات 147-165
    سنگهای دگرگونی شمال ازنا در زون سنندج – سیرجان قرار دارد و در نتیجه تاثیر حرارتی توده گرانیتی مرزیان بر روی سنگهای پلیتی قدیمی تر به وجود آمده اند. این دگرگونه ها شامل انواع میکا شیست، آندالوزیت شیست و متابازیت با بافتهای لپیدوبلاستی و پورفیروبلاستی هستند. از نظر کانی شناسی، کانی های مهم تشکیل دهنده نمونه های شیست شامل آندالوزیت، گارنت، فلدسپار، مسکویت، بیوتیت، کوارتز و کلریت است. ترکیب شیمیایی کانی های موجود در شیست های آندالوزیت دار این منطقه بیانگر آن است که میکای سفید دارای ترکیب مسکویت، پلاژیوکلاز غنی از عضو انتهایی آلبیت، آندالوزیت با ترکیب شیمیایی %7/8 درصد کاتیونی آلومینا و % 1/3 درصد کاتیونی آهن، جزو ذخایر غنی برای آلومینیوم است. گارنت موجود در این سنگها دارای ترکیب متوسط 68 درصد آلماندین، 25 درصد اسپسارتین و 4 درصد پیروپ است. رسم مقاطع میکروزوندی در گارنت ها نشان می دهد که گارنت های مورد بررسی، منطقه بندی خفیفی نشان می دهند. کلریت های موجود در این سنگها غنی از ریپیدولیت هستند و بیوتیت ها نیز عمدتا از عضوهای انتهایی سیدروفیلیت-آنیت تشکیل شده اند. تغییرات مربوط به Al بیوتیت مربوط به جانشینی چرماک و تغییرات Ti بیوتیت تابعی از دماست.
    سنگهای متاپلیتی ازنا بر اساس بررسی های صورت گرفته در رخساره هورنبلند هورنفلس دگرگون شده و بر پایه بررسی های ترموبارومتری در دمای حدودC° 592-692 و فشار حدود 1/07 تا 4/12 کیلوبار تشکیل شده اند. پس از تشکیل این سنگها ماگماتیسم گرانیتوئیدی دگرگونی مجاورتی این سنگها و تشکیل شیست های لکه ای عمدتا آندالوزیت دار را موجب شده است.
    کلیدواژگان: پتروگرافی، مینرال شیمی، آندالوزیت، ازنا، پهنه سنندج - سیرجان، ایران
  • سید جواد مقدسی، ابراهیم طالع فاضل، عالیه سادات بنی فاطمی صفحات 167-180
    کانسار فلوریت- باریت (± سولفید) آتش کوه در جنوب شهرستان دلیجان، حدود 80 کیلومتری جنوب شرقی اراک واقع شده است. کانی سازی به شکل رگه ای با ماهیت دیرزاد، در سنگهای میزبان کربناتی و شیلی سازند شمشک و بادامو به سن ژوراسیک زیرین تا بالایی روی داده است. فلوریت و باریت فراوانترین کانی های سازنده کانسنگ هستند و کانی های فرعی شامل کوارتز، کلسیت، دولومیت، گالن و کالکوپیریت هستند. شواهد به دست آمده از بررسی های میکروترمومتری نشان می دهد، رگه های فلوریت- باریت (± سولفید) آتش کوه در نتیجه اختلاط اعضای انتهایی یک شورابه Na–K(–Mg–Ca) اولیه و شورابه های سازندی غنی از کلسیم با شوری کمتر، ناشی از تبادلات سیال- سنگ بعدی شکل گرفته است. چهار مرحله کانی سازی در منطقه آتش کوه قابل تشخیص است: 1- تحرک شورابه های حوضه ای غنی از Na–K از افقهای زیرین؛ 2- اختلاط و رقیق شدگی شورابه غنی از نمک با سیالات سازندی با شوری کمتر و تشکیل کانی سازی فلوریت- باریت؛ 3- رخ داد کربن زدایی و افزایش میزان CO2 در محیط و 4- تشکیل بافتهای حفره ای و برشی، ناشی از انحلال سنگهای کربناتی.
    کلیدواژگان: کانسار فلوریت آتش کوه، میانبار سیال، مراحل کانی سازی، تحول سیال کانی ساز، دلیجان
  • محمد کشکویی جهرمی، افشین قشلاقی صفحات 181-199
    تحلیل مولفه های اصلی، یک روش آماری چند متغیره در تحلیل داده های چند بعدی بوده و تفسیر نتایج حاصل از آن با پیچیدگی های خاص خود همراه است. در این پژوهش، روشی جدید در تحلیل و انتخاب مولفه های اصلی تصاویر لندست+ETM، به منظور نقشه برداری دگرسانی هیدروترمال ارائه شده است. در این روش با تجزیه و تحلیل ریاضی و آماری بردارهای ویژه، سطح معناداری بردارهای ویژه بین باند های مختلف هر مولفه اصلی تعیین شد. مولفه ای که حاوی حداکثر معناداری طیفی (مقادیر هدف) برای باندهای 1، 3، 5 و 7 و همچنین 5 و 3 است، به ترتیب، به عنوان مولفه اصلی کارآمد در بارزسازی اکسیدهای آهن، کانی های رسی و کانی های کربناته انتخاب شد. در مرحله بعد، بر اساس اطلاعات طیفی کانی های یاد شده بالا، برتری طیفی مولفه های اصلی تعیین و سهم هر مولفه در بارزسازی این کانی ها محاسبه شد. در مرحله آخر با استفاده از نتایج حاصله از تحلیل مولفه های اصلی، تصاویر اکسید آهن، کانی رسی و کانی های کربناته تهیه شد. هر مولفه حاوی بخشی از اطلاعات طیفی کانی های مختلف است و محاسبه سهم هر مولفه امکان تعیین پتانسیل طیفی هر PC را فراهم می کند. مولفه ای که وزن طیفی بالاتری دارد، اطلاعات طیفی بیشتری را در خود جای داده است. در تصویر مورد بررسی، مولفه پنجم دارای بیشترین وزن طیفی بوده و حاوی اطلاعات طیفی کانی رسی، اکسید های آهن و کانی های کربناته است. دگرسانی پروپلیتیک و تشکیل کلسیت باعث بارزسازی هم زمان این دگرسانی و رگه های کربناته شده است. دگرسانی فیلیک و تشکیل کانی های رسی با زمینه روشن، باعث بارزسازی هم زمان این کانی ها با واحد های کربناته شده است. مناطق منطبق با سنگ شناسی آذرین و دگرسانی هیدروترمال به عنوان مناطق امیدبخش مس پورفیری معرفی شده است.
    کلیدواژگان: تحلیل مولفه اصلی، تصاویر لندست، دگرسانی هیدروترمال، نقشه برداری، بافت، کرمان
  • زهرا مهربان، بهنام شفیعی بافتی، غلامحسین شمعانیان صفحات 201-221
    مطالعه زمین شیمی عناصر نادر خاکی در کانسارهای فلوریت سازند الیکا (تریاس میانی)، محتوای پایین عناصر مذکور را در فلوریت ها (REEs 0/5-18 ppm=∑)، کلسیت ها (REEs 0/5-3 ppm=∑) و سنگهای کربناته میزبان (آهک: REEs 1/8-7 ppm=∑، آهک دولومیتی: REEs 6/5 ppm=∑) نسبت به بازالت ها (REEs 43 ppm=∑) و شیل های تریاس بالایی (REEs 261 ppm=∑) آشکار کرد. تهی شدگی فلوریت ها از عناصر سبک (10-La/Sm=2) و غنی شدگی نسبی آنها از عناصر سنگین (0/08-La/Yb=0/01) در مقایسه با سنگ میزبانهای آهکی (4-La/Yb=0/1-1/5 ، La/Sm=2/5 ) و آهک دولومیتی (La/Yb=0/07-0/4 ، La/Sm=4/28 ) همراه با بی هنجاری مثبت Eu در فلوریت ها، تشکیل کانسارهای فلوریت مورد بررسی را 1- بعد از رسوب گذاری و سنگ شدگی سنگهای کربناته میزبان و 2- توسط محلولهای گرمابی رسوبی زاد واجد شرایط احیایی و دامنه دمایی 200-250 درجه سانتی گراد شبیه کانسارهای نوع دره می سی سی پی غنی از فلوریت مانند ایلینویز-کنتاکی (امریکا) و پناین (انگلستان) معرفی کرد. پژوهش حاضر نشان داد، محتوای پایین مجموع غلظت عناصر نادر خاکی در فلوریت های ته نشست یافته از این محلولها می توانسته ناشی از 1- افزایش pH محلول گرمابی کانه ساز طی برهم کنش با سنگ میزبان کربناته؛ 2- کاهش تدریجی غلظت فعال فلوئور در محلول گرمابی ناشی از کانی سازی نسلهای مختلف فلوریت و 3- محتوای پایین عناصر نادر خاکی سنگهای کربناته میزبان بوده باشد.
    کلیدواژگان: عناصر نادر خاکی، فلوریت، الیکا، مازندران
  • سید ابوالفضل عزتی، سید رضا مهرنیا، کیمیا سادات عجایبی صفحات 223-238
    منطقه مورد بررسی، بخشی از نوار ماگمایی ارومیه- دختر در زون ساختاری ایران مرکزی است که در جنوب غرب شهرستان بوئین زهرا و جنوب بخش دانسفهان قرار دارد و فاصله آن تا مرکز استان حدود 60 کیلومتر است. منطقه رامند، عمدتا شامل سنگهای آذرین ریوداسیتی و ریولیتی، توف ریوداسیتی، توف بلورین و گدازه های جریانی ریوداسیتی است. در این منطقه دگرسانی وسیعی به روشنی در پردازش تصاویر ماهواره ای قابل ردیابی و پی گیری است.
    حضورکانی های رسی، بر وجود دگرسانی آرژیلیک در منطقه دلالت دارد؛ که می تواند نشانه خوبی به لحاظ کانی سازی باشد. وجود این دگرسانی در بازدیدهای صحرایی، مطالعه مقاطع نازک و آنالیز XRD نیز به خوبی مشخص است .واحدهای آذرآواری و آتشفشانی توسط گسلهای اصلی این منطقه شامل گسل کورچشمه، گسل حسن آباد و گسلهای فرعی، قطع شده اند. این گسلها در امتداد شمال غرب جنوب شرق در منطقه وجود دارند و دگرسانی های گسترده ای در طول گسلها و در سنگهای دیواره رخ داده است.
    دگرسانی ها شامل دگرسانی آرژیلیک، سریسیتیک، پروپیلیتیک و سیلیسی هستند؛ که به صورت قائم و جانبی منطقه بندی نشان می دهند. بارزسازی زون های احتمالی دگرسانی در محدوده مورد نظر در مراحل اولیه، به کمک پردازش داده های سنجنده ETM به روش کروستا صورت گرفت. همچنین برای تفکیک زون دگرسانی آرژیلیک منطقه، از بین ره یافتهای مختلف، روش مولفه اصلی انتخاب شده است.
    علاوه بر هاله دگرسانی آرژیلیک، پدیده سیلیسی شدن سنگ میزبان دارای اهمیت بالایی بوده است و شرایط میزبانی فلزات پایه و گرانبها در درون این رخساره تامین می شود. برای شناسایی دگرسانی سیلیسی، از داده های سنجنده ASTER استفاده شده که با اعمال روش نسبت باندی، نواحی با احتمال کانی سازی سیلیسی مشخص شده اند. نتایج مبتنی بر آنالیز دستگاهی (XRD)، تاییدکننده بررسی های سنجش از دور است. با توجه به بررسی های انجام شده در این منطقه، دگرسانی های توام رسی، اکسیدهای آهن و سیلیسی شدن سنگ دیواره برای پی جویی ذخایر فلزات پایه و گرانبها حایز اهمیت است.
    کلیدواژگان: دگرسانی، سنجش از دور، تحلیل مولفه اصلی انتخابی (کروستا)، رامند
  • رضا منظمی باقرزاده، محمدحسن کریم پور، جی لنگ فارمر، چارلز استرن، ژوزه فرانسیسکو سانتوس، سارا ریبیرو، بهنام رحیمی، محمدرضا حیدریان شهری صفحات 239-264
    منطقه مورد بررسی، در بخش میانی زون ساختاری تکنار در شمال خرد قاره ایران مرکزی قرار گرفته است. این زون ساختاری از سازند تکنار و کمپلکس پلوتونیک برنورد تشکیل شده است. تشکیلات ولکانوسدیمنت سازند تکنار متشکل از سنگهای آتشفشانی فلسیک (متاریولیت- ریوداسیت و توف ریولیتی) با ضخامت قابل توجه و به همراه مرمر و ماسه سنگ کمی دگرگون شده، فیلیت، اسلیت و شیست است. کانی شناسی و شیمی اولیه این سنگها بر اثر فرآیندهای ثانویه (دگرگونی ناحیه ای و دگرسانی هیدروترمالی) مورد تغییر قرار گرفته است. بیشترین حجم سنگهای آتشفشانی مورد بررسی در بخشهای زیرین و میانی سازند تکنار به همراه توفهای لایه ای سبز روشن تشکیل شده است. در برخی از نقاط، این مجموعه ولکانوسدیمنت در کنتاکت با کمپلکس گرانیتوئید برنورد مشاهده می شود. سن سنجی کانی زیرکن به روش (U-Pb) متاریولیتهای سازند تکنار، سن 6/62- ،4/73+ 552/23 میلیون سال قبل (اواخر نئوپروتروزوئیک) را نشان می دهد. εNd(552) زمان تشکیل متاریولیتهای برنورد (مرکز زون تکنار) در گستره 6/98- تا 1/5- قرار می گیرد. عناصر نادر خاکی سبک (LREE) به جز Eu نسبت به عناصر نادر خاکی سنگین (HREE) با شیب ملایمی غنی شدگی نشان می دهند. همچنین، در این متاریولیت ها، غنی شدگی در بیشتر عناصر کمیاب ناسازگار (Th،U،Y،K،Rb،Pb، Nd) دیده می شود در حالی که عناصر (Ba،P،Ti،Sr،Zr، Nb) فقیرشدگی شاخصی را در مقایسه با گوشته اولیه نشان می دهند. مشخصه -ایزوتوپی (143Nd/144Nd)i متاریولیت های منطقه مقدار عددی 0/511701 تا 0/511855 به دست آمده است. مقدار عددی نسبت i(87Sr/86Sr) متاریولیتهای منطقه برنورد در گستره 0/688949 تا 0/723435، بیانگر دو منشا مختلف برای گدازه های ریولیتی این منطقه است. با توجه به مطالب بالا و همچنین حجم بالای ولکانیسم در منطقه تکنار، می توان تشکیل آنها را به یک محیط ریفت قاره ای مربوط دانست. این ریفت می تواند با ایجاد یک زبانه در گوشته بالایی واقع در زیر پی سنگ شرق ایران در مدت زمان نئوپروتروزوئیک تشکیل شده باشد.
    کلیدواژگان: ایزوتوپ، زیرکن، سن سنجی، نئوپروتروزوئیک، برنورد، بردسکن، تکنار
  • صدیقه زیرجانی زاده، محمدحسن کریم پور، خسرو ابراهیمی نصرآبادی، ژوزه فرانسیسکو سانتوس صفحات 265-282
    محدوده مورد بررسی، در شرق ایران، شمال بلوک لوت و شمال غرب گناباد واقع شده است. این محدوده شامل برون زدهایی از سنگهای آتشفشانی ائوسن با ترکیب آندزیت تا ریولیتی است که واحد های نیمه عمیق و عمیق گرانیتی تا دیوریتی در آنها نفوذ کرده است. در این بررسی پتروژنز واحدهای آتشفشانی که بیشترین گسترش را دارند، مورد بررسی قرار گرفت. واحدهای پیروکلاستیک و گدازه با دامنه، ریولیت، ریوداسیت، داسیت، آندزیت، تراکیت و تراکی آندزیت در منطقه شناسایی شدند. بافت غالب این واحدها پورفیری، هیالوپورفیری و میکرولیتی و شامل کانی های پلاژیوکلاز، آلکالی فلدسپار نوع سانیدین، هورنبلند، بیوتیت و کوارتز هستند. بررسی های ژئوشیمیایی حاصل از این پژوهش، نشان می دهد که این سنگها، ماهیت کالک آلکالن پتاسیم بالا دارد و در محدوده متاآلومینوس و پرآلومینوس قرار می گیرند. سنگهای آتشفشانی غنی شدگی LREE/HREE (LaN/YbN طیفی از 3/53 تا 15/47) و آنومالی منفی Eu. (با متوسط 0/54 =Eu*/EuN) نشان می دهند. پایین بودن نسبت Al2O3/CaO+Na2O+K2O و شواهد ژئوشیمی عناصر نادر خاکی و کمیاب، نشان می دهد که منشا ماگمای اولیه از پوسته بوده که در طی فرورانش شکل گرفته است. بر اساس نسبت ایزوتوپ اولیه 87Sr/86Sr، ماگمای شکل دهنده واحد های آندزیتی و ریولیتی از ذوب بخشی پوسته زیرین نشات گرفته است.
    کلیدواژگان: ایزوتوپ اولیه 87Sr، 86Sr، ژئوشیمی، سنگهای آتشفشانی، بلوک لوت، شرق ایران
|
  • Mahdi Bemani, Seyed Hossein Mojtahedzadeh, Amir Hossein Kouhsari Pages 1-20
    Introduction
    Mohammad-abad Oryan is the only potential source of borate in the North-east of Iran located in 50 km South of Sabzevar. The area is located in tuff marl, tuffaceous marl, volcanic braccia and tuff braccia structures. Remote sensing techniques, geological studies and integration of this data in GIS were applied in an area of about 600 square kilometers to locate the promising areas of borate mineralization for detailed studies (Bemani, 2012). The aim of this detailed geochemical study is to confine the anomaly areas for exploratory drilling and trenching.
    Materials And Methods
    Field studies were carried out in 9 geological traverses, mainly in Tonakar and Borje Kharkan area and 126 brine samples were taken from hydrothermal springs and 13 rock samples were taken from trenches. All the samples were analyzed for four elements, including B, K, Li and Mg. In order to determine the threshold quantities of the samples and isolation of anomaly, the data were analyzed using statistical methods including classical statistics, fractal geometry and EDA methods (Bemani, 2012).
    Result
    Initial data analysis showed that there were no censored data. Also, by applying statistical hypothesis testing, no significant relation was observed between the elements in the two areas (except for Li). Therefore, all the statistical analyses were carried out separately.
    After outlier correction, based on the amount of skewedness and histograms and probability plots of different elements, it became clear that none of the elements in the raw data distribution were normal and required to be transformed to be close to normal. In this study, logarithmic and three-parameter logarithm transformation were used in order to normalize the data . Based on the mean values, standard deviation of the normalized data, and background value and threshold, probable and possible anomalies were obtained and geochemical anomaly maps were drawn to identify the promising areas.
    With the exception of the fractal pattern, anomaly separation methods are based on the differences of fractal dimensions between communities of geochemical data (Hasanipak and Sharafoddin, 2005). In this study, concentration area fractal method was used to separate anomalies from the background. Using fractal geometry, threshold value corresponding to the two areas (Tonakar and Borje Kharkan) were obtained and were plotted separately on geochemical maps.
    Exploratory data analysis (EDA) is an approach to analyze data sets to summarize their main characteristics, often with visual methods (Filliben and Heckert, 2005). Exploratory data analysis is a useful method for analysis of geochemical exploration data. This is a statistical method known as the Robust Statistic classification (Carranza, 2009). In geochemical exploration, box plots, histograms and scatter plot are more practical. According to the box plots, the data of Tonakar and Borje Kharkan areas were classified and threshold levels were determined (Bemani, 2012).
    Discussion
    Using the results obtained from different methods, geochemical maps of each area were prepared for all the elements and thresholds were obtained for each method. Moreover, the geochemical maps of each area were plotted for each element. According to the geochemical maps of Tonakar area, boron anomaly was observed in the East and West zones and the anomaly of the latter is larger. These areas were recommended for further detailed exploration and borehole drilling. Also, geochemical maps of Borje Kharkan showed anomaly in the central zone for all of the elements. The results showed that the highest and the lowest amounts of boron in brines samples vary between 6 ppm to 5930 ppm. Among boron and the three other elements (i.e. lithium, magnesium and potassium) a significant correlation was not observed. In terms of frequency, in most cases brines with high levels of boron (more than 1000 ppm) were concentrated in the South East of the Tonakar area. So, this area was suggested for detailed exploration (Bemani et al., 2014). Generally speaking, for considering the spatial distribution of data the fractal method could better identify the anomalies. Also, EDA is a quick and easy method to detect anomalies.
    Keywords: classical statistics, fractal geometry, EDA, Brine samples, index of Mohammad, abad Oryan
  • Somayeh Falahaty, Moussa Noghreyan, Mortaza Sharifi, Ghodrat Torabi, Homayon Safaei, Mohammad Ali Mackizadeh Pages 21-38
    Introduction
    The study area is located in the Shurab area that is about 50 Km Southeast of Qom. Volcanic rocks of the Shurab area have basaltic composition that is associated with salt and marl units. Igneous rocks of the Shurab area have not been comprehensively studied thus far.
    Clinopyroxene composition of volcanic rocks, and especially the phenocrysts show Magma chemistry and can help to identify magma series (Lebas, 1962; Verhooge, 1962; Kushiro, 1960, Leterrier et al., 1982), tectonic setting (Leterrier et al., 1982; Nisbet and Pearce, 1977) as well as temperature formation and pressure of rock formation. Some geologists have estimated temperature of clinopyroxene formation by clinopyroxene composition (Adams and Bishop, 1986) and clinopyroxene-olivine couple. So, clinopyroxene is used in this study in order to identify magma series, tectonic setting, plus the temperature and pressure of volcanic rocks of the Shurab.
    Material and
    Method
    Clinopyroxene analyses were conducted by wavelength-dispersive EPMA (JEOL JXA-8800R) at the Cooperative Centre of Kanazawa University (Japan). The analyses were performed under an accelerating voltage of 15 kV and a beam current of 20 nA. The ZAF program was used for data corrections. Natural and synthetic minerals of known composition were used as standards. The Fe3 content in minerals was estimated by Droop method (Droop, 1987).
    Discussion
    In the Shurab area, the volcanic rocks area with basaltic composition are located 50 km Southeast of Qom. Their age is the early Oligocene and they are associated with the salty marl units of the Lower Red Formation (LRF). The hand specimens of the studied rocks look green. These rocks are intergranular, microlitic, porphyric, vitrophyric and amygdaloidal and they consist of olivine, pyroxene and plagioclase. Accessory minerals contain sphene, apatite and opaque.
    According to Wo-En-Fs diagram (Morimoto, 1988), clinopyroxenes indicate diopside composition.
    Clinopyroxenes are representatives of magma composition and they are usually used for identifying magma series. There are several diagrams that are used for this purpose as follows.
    1 - Al2O3 – SiO2 diagram (Lebas, 1962): According to this diagram, the studied clinopyroxenes were plotted in sub-alkaline field.
    2 - Al2O3 – TiO2 diagram (Lebas, 1962): In this diagram, the studied clinopyroxenes show to be calcalkaline.
    Some diagrams that are used for determining tectonic setting according to clinopyroxene composition are as follows: 1 - F1 – F2 diagram (Nisbet and Pearce, 1977): Based on this diagram, the Shurab clinopyroxenes rocks lie between volcanic arc and mid ocean ridge basalt fields.
    2 - Al2O3 - SiO2 diagram (Lebas, 1962): Using this diagram, the studied clinopyroxenes are located in the sub-alkaline field.
    Some methods that are used for determining temperature formation and pressure of clinopyroxene are as follows: 1 – Kretz method (Kretz, 1994): Using this method, temperature formation of clinopyroxene is about 1200- 1250oC.
    2 – Soesoo method (Soesoo, 1997): Using this method, pressure formation of clinopyroxene is about 6-10 Kb.
    In Al�븊 against Na diagram, Clinopyroxenes are located above the Fe=0 line (Schweitzer et al, 1979). This case and abundant hematite and magnetite in the Shurab area rocks confirm that oxygene fugasity is high. Based on Helz diagram (Helz, 1973), the content of magma water during clinopyroxene formation is about 2-5 percent.
    Results
    Using various methods, the temperature and pressure of clinopyroxene formation are about 1200 oC and 6-10 Kb, respectively. Clinopyroxene composition and the abundant hematite and magnetite in the studied rocks confirm that oxygene fugasity is high. According to Helz diagram, the amount of water is about 2-5 percent.
    Additionally, the parent magma of the studied area rocks is calc alkaline and tectonic setting is subduction-related based on the clinopyroxene composition.
    Keywords: Clinopyroxene, Thermobarometry, Tectonomagmatic, Shurab, Qom
  • Mansoore Maghsoudloo Mahalli, Behnam Shafiei Bafti Pages 39-59
    Introduction
    Oolitic iron formations are sedimentary rocks with >5 vol.% oolites and >15 wt.% iron, corresponding to 21.4 wt.% Fe2O3 (Young, 1989; Petranek and Van Houten, 1997; Mucke and Farshad, 2005). In Iran, new iron oolite-bearing members have been identified in the Lashkarak Formation (lower-middle Ordovician) in the Abarsej, Dehmola and Simehkuh sections, eastern Alborz (Ghobadi Pour et al., 2011). At present, the mineralogy and geochemistry of these members are not known. Consequently, research reported here was conducted to reveal the mineralogical and geochemical characteristics of Ordovician oolitic iron formationmembers and to discuss their genesis and economic importance.
    Materials and Analyses: Field geology and sampling was carried out to collect 25 samples from the ooliticiron formation members in the Abarsej, Dehmola and Simehkuh section in eastern Alborz. Samples were prepared for polished-thin sections (n=10), XRD analysis (n=15). Whole-rock chemical analysis (n=15) by XRF for major elements and by ICP-ES for trace elements was performed by laboratories at the SarCheshmeh copper mine complex, Kerman, Iran. One sample was analyzed by SEM at the Wales Museum, UK.
    Results
    Microscopic studies show that the oolitic iron formation members are hosted by carbonate argillite rocks. They are mainly composed of oolites rather than pisoliths (small bodies somewhat larger and more irregular than oolites), whereas oolites have mainly ellipsoidal forms and locally spherical shapes. Most (6) oolites show banding with a central core. Simple oolites without a core are scarce. Mineralogically, oolites are mainly chamositic and hematitic in composition; goethite, pyrite and glauconite occur in traces and siderite is absent. Quartz, calcite and zircon are accessory minerals which are present in the groundmass. Geochemically, TFeO % of the oolitic iron formation horizons ranges from 8 to 48 % with an average of 21%. The CaO content ranges from 2 to 37% and SiO2 from 11 to 37 %. Based on TFeO % content, oolitic iron formation horizons are divided into two geochemical groups: 1: Low-grade iron formations ( the Abarsej section) (8) with TFeO
    Keywords: Oolitic iron, Hematite, Chamosite, Transgressive, Lashkarak Formation, Eastern Alborz
  • Mohammad Sayari, Mortaza Sharifi Pages 61-78
    Introduction
    Volcanic rocks with a porphyritic texture have experienced two crystallization stages. The first is slow, resulting in phenocrysts, and the second, which took place at, or near the surface, or during intrusion into a cooler body of rock, result in a groundmass of glass, or fine crystals. The pressure and temperature history of a magma during crystallization is recorded in the chemical composition of the phenocrysts during both stages. These phenocrysts provide valuable data about the physicochemical conditions of the parent magma during the process of crystallization. The composition of clinopyroxene (cpx) reflects not only the chemical condition and therefore the magmatic series, but also the physical conditions, i.e., temperature and pressure of a magma at the time when clinopyroxene crystallized.
    The Ghohrud area lies in the middle part of the Urumieh-Dokhtar Magmatic Arc , which is part of a much larger magmatic province extending in a vast region of convergence between Arabia and Eurasia north of the Zagros-Bitlis suture zone (Dilek et al., 2010). In the Ghohrud area, north of Isfahan, exposed Eocene volcanic rocks belong to the first pulse of Cenozoic volcanism of Iran (Sayari, 2015), ranging in composition from andesitic basalt to basalt. The basaltic rocks of the Ghohrud area are composed mainly of plagioclase phenocrysts surrounded by smaller crystals of clinopyroxene in a groundmass of microlites, glass and opaques. In this study, the clinopyroxene and plagioclase of these rocks were analyzed in order to estimate the physicochemical conditions of the parent magmas.
    Results
    Clinopyroxene and plagioclase phenocrysts of nineteen samples were analyzed with the electron microprobe. The chemical compositions of the clinopyroxenes were used to estimate both the chemical evolution and temperature and pressure conditions of the magmas during crystallization, using SCG, a specialized software for clinopyroxene thermobarometry (Sayari and Sharifi, 2014). Microprobe analyses show that plagioclases in the Eocene basaltic rocks are labradorite-bytownite (An85-58Ab15-41) and clinopyroxenes are augite (En41-49Di29-38Fs17-26). The compositions of the clinopyroxenes indicate a tholeiitic affinity for the magma. After plotting the cpx thermobarometry results on a P-T diagram, and applying a linear regression, an equation of P-T describing the physical conditions of the ascending magma was obtained.
    Discussion
    Several complex thermobarometry equations used to estimate T and P of cpx have been introduced to the Society of Petrology by different researchers (e.g., Sayari, 2012; Sayari and Sharifi, 2014Putirka et al., 1996; Nimis and Ulmer, 1998; Putirka, 2008). Ten well-known barometric and six thermometric equations developed for clinopyroxene were tested for the analyzed samples with the aid of SCG, and then the equations giving the best match were selected and integrated to estimate contemporaneous P and T. According to the systematic cpx-thermobarometry calculations done with SCG software, it was inferred that the clinopyroxenes crystallized over a range of 1120-1170 °C and a range of pressure of 2-6 kbar.
    The results of the cpx-thermobarometry were then plotted on a P-T diagram and a linear regression was used to find a function describing P and T for clinopyroxenes. The equation of the regression line is: P (kbar) = 0.0846T (°C)-93.128
    The equation has a high coefficient of determination parameter (R2), making it reliable to determine the rate of T-loss against P-reduction. By assuming that the pressure on the magma was lithostatic due to the weight of overlying rocks, and considering the density of continental crust of about 2.7 gr/cm3, this equation shows that while magma was ascending while the clinopyroxenes were crystalizing, pressure was decreasing at a rate of about 84.6 bar per 1 °C temperature loss. This pressure loss indicates a rise of about 320 m in the continental crust.
    Keywords: Clinopyroxene, Thermobarometry, Volcanic rocks, Ghohrud
  • Hojjat Ollah Safari, Behnam Shafiei Bafti, Hassan Mohamadrezaei Pages 79-92
    Introduction
    The Sar Cheshmeh copper deposit and indications of other deposits are located in the Dehaj-Sarduieh belt in the Kerman region (Khadem and Nedimovic, 1973). This belt is one of the most important provinces of Cu mineralization in Iran, with approximately 300 Cu deposits and prospects, includingtwenty of the porphyry copper type (Ghorbani, 2013). This belt, 300 km in length and 30–45 km width, is situated in the southern part of the Uramia-Dokhtar volcanic belt in central Iran (Shafiei, 2010). Zarasvandi (2004) has proposed that faulting has played a role in the location of copper deposition in this area.
    Methods of Investigation: In order to check Zarasvandi’s hypothesis, the spatial relationship between faults and Cu deposits was investigated using remote sensing and GIS techniques together with field investigations in the Sar Cheshmeh area. The the following steps were used in this research: 1. Review of available data
    2. Surface geology field studies
    3. Preparation of digital overlay of Copper occurrences
    4. Analysis of the relationshipof faulting to Copper occurrences
    Using remote sensing techniques, a geometrically corrected satellite image was filtered with high pass and Sharpen Edge filters to detect possible lineaments (Lillesand and Keifer, 2008; Sabins, 1996). Directional filters (45º, 90º, 135º and 180º) were then applied to the processed image to enhance the linear structures. Subsequently,the major lineaments were documented in the field as major and minor faults (Safari et al., 2011). Four main faults, designated as the Rafsanjan, Mani, Gaud-e-Ahmar and Sar Cheshmeh faultswere determined to be major. These faults were digitized and overlaid on other data layers in GIS environment. The strikes, dips, striae and directions of movementof the faultswere measured at 20 locations in the field. Structural analyses were done with Rose diagrams, calculation of P-axes and preparation of a structural map.
    Copper occurrences on the mineral distribution map of Lotfi, et al. (1993) were used in this study and the locations of somecopper occurrences were determined in the field using GPS. The locations and main characteristics of the copper occurrences were entered into a GIS map. Finally, aniso-fracture map, was prepared using the GIS environment based onfault lengths within a 1000 ×1000 mgrid and on the buffer map of ore occurrences relative to faults. The copper occurrence locations were overlaid on these prepared maps and the relationship between faults and ore occurrences locations was analyzed.
    Results
    This research indicates that: 1.The faults in the Sar Cheshmeh area trend predominantly 090°-110°, 130°-150°, 050°-070° and 170°-190°.
    2.The data show that three major NW- trendingfaults, the Mani, Gaud-e-Ahmar and Rafsanjan faults show right-lateral strike-slip movement and the two major E-W trending Sar Cheshmeh and Darreh Zar faults have left-lateral strike-slip displacements.
    3. The control of the calculated P-axes shows that at least two older movements have happened along these faults.
    Discussion
    The results show that the main faults did not directly control the locations of the mineralized porphyries and veins, but that rather the locations are due tothe second-order faults. Also, the saturated occurrence locations have the closer relationship with main faults and most indexes are located near the Rafsanjan fault and its second-order faults.
    Keywords: Sar Cheshmeh Area, Copper Occurrences, Remote Sensing (RS), GIS
  • Mehri Karami, Mohammad Ebrahimi, Hossein Kouhestani Pages 93-115
    Introduction
    The Lulak Abad iron occurrence is located in the northwestern part of the Central Iran, 55 km west of Zanjan. Mineralization at the Lulak Abad area was originally identified by Zamin Gostar Company (2007), during a geophysical exploration. The present paper provides an overview of the geological framework, the mineralization characteristics, and the results of a geochemical study of the Lulak Abad iron occurrence with an application to the ore genesis. Identification of these characteristics can be used as a model for exploration of this type of iron mineralization in the Central Iran and elsewhere.
    Materials And Methods
    Detailed field work was carried out at different scales (give scales in parentheses) in the Lulak Abad area. About 16 polished thin and thin sections from host rocks and mineralized and altered zones were studied by conventional petrographic and mineralogical methods at the Department of Geology, University of Zanjan. In addition, a total of 7 samples from ore zones at the Lulak Abad occurrence were analyzed by ICP-OES for minor and trace elements and REE compositions at Geological Survey of Iran, Tehran, Iran.
    Result
    Rock units exposed in the Lulak Abad area consist of schists and metavolcanic units the Kahar Formation; Lotfi, 2001) that were intruded by granite and microdiorite bodies. The schist units consist of chlorite-biotite-muscovite schist and muscovite schist that show granolepidoblastic texture with foliation-parallel disseminated magnetite. The metavolcanic units consist of metadacite, rhyolitic metatuff and meta-andesite with porphyritic textures. They are marked by dominant mylonitic foliation surrounding feldspar and quartz porphyroclasts. Alkali feldspar and quartz are the principal minerals of the granite. The intrusion is characterized by intense deformation features and is highly mylonitized. Based on field and microscopic studies, the microdiorite postdated metamorphic and deformation events and shows neither schistosity nor mylonitic foliation. It is composed principally of plagioclase with minor disseminated magnetite and a microgranular texture. Two deformation events are recognized at the Lulak Abad area, one principally ductile, the other brittle.
    Iron mineralization at Lulak Abad occurs as veins, veinlets and lens-shaped bodies in schist units, mylonitic metavolvanic rocks and mylonitic granite. The main ore vein extends up to 100 m in length and averages 3 m in width, reaching a maximum of 6 m. It trends NE, dipping steeply SE. The ore lenses are parallel to the mylonitic foliation and variably boudinaged, about 10 m in length and vary in thickness up to 5 cm. Two stages of mineralization can be distinguished at Lulak Abad. Stage 1 mineralization is recognized as stratiform and stratabound lenses, laminated and disseminated crystals of magnetite in volcano-sedimentary host rocks. Stage 2 is characterized as hematite-pyrite-calcite veins and veinlets cutting the mylonitic foliation of the host rocks. Hydrothermal alteration is restricted to silicified, calcitic and chloritic altered parts of the ore zones.
    The ore minerals at Lulak Abad formed as vein and hydrothermal breccia cements, and show vein-veinlet, brecciated, disseminated and open space filling vein and veinlet textures. Hematite is the main ore mineral, accompanied by minor magnetite and pyrite. Goethite occurs as a supergene mineral. Quartz, calcite and chlorite are present in the gangue minerals that represent vein-veinlet and vug filling textures.
    The Lulak Abad mineralized veins and breccias show lower concentrations of LREE and HREE (i.e., Pr, Er, Ho, Dy and Yb) relative to barren granitic host rocks but higher Tm, Gd, Eu and Lu concentrations. Chondrite-normalized REE patterns (Sun and McDonough, 1989) of host barren granite and the mineralized samples at Lulak Abad indicate that mineralized samples are depleted in LREE (except Ce) but enriched in most HREE (beside depletion in Dy and Ho). These signatures indicate high wall rock interaction (e.g., Lottermoser, 1992; Liegeois et al., 2003).
    Comparison of the geological, mineralogical, geochemical, textural and structural characteristics of the Lulak Abad occurrence with different types of iron deposits reveals that iron mineralization at Lulak Abad was originally formed as volcano-sedimentary, and then reconcentrated as vein mineralization (Karami et al., 2012; Karami et al., 2013).
    Keywords: Iron mineralization, hydrothermal vein, alteration, Lulak Abad, Zanjan, Central Iran
  • Tahereh Rabani, Nader Taghipour, Reza Aharipour Pages 117-128
    Introduction
    Maceral is a term to introduce organic components visible under a microscope (Stopes, 1935). The physical and chemical characteristics of macerals such as elemental composition, moisture content, hardness, density and petrographic characteristics differ. The differences in the physical and chemical characteristics of macerals are reflected in their industrial behavior.(Parkash, 1985). Petrographic analysis provides information on the various physical components of coals (Suwarna and Hemanto, 2007) and determination of quality of coal, coalification rate, composition and characteristics of coke and paleoenvironmental deposition (Taylor et al., 1998).
    Sampling and
    Methodology
    Coal samples were collected from freshly mined coal from 11 coal seams of 4 active coal mines (Cheshlagh, Zemestan Yourt, Narges Chal and Cheshmehsaran) for organic petrography in the Gheshlagh coal deposits. All samples were collected and stored in plastic bags to prevent contamination and weathering.
    Samples were prepared for microscopic analysis by reflected light following ASTM Standard procedure D2797-04. For microscopic study, coal samples were crushed to1-mm size fraction (18 mesh size), mounted in epoxy resin and polished. Three polished samples were prepared for each coal seam. The petrographic composition was obtained by maceral analyses under standard conditions (ISO 7404/3, 2009, for maceral analysis). Maceral point counting (based on 400 points) analyses were performed using an Olympus BX51 reflected light microscope. The terminology used to identify and describe the organic matter particles is the one proposed by the International Committee for Coal and Organic Petrology (ICCP, 1998; ICCP, 2001; Scott and Glasspool, 2007; Taylor et al., 1998; Stach et al., 1982; Hower et al., 2009; Hower and Wagner, 2012).
    Organic petrography of theGheshlagh coal seams: The vitrinite maceral group is dominant in all coal seams (66.2 to 87.2 vol.%) and includes collodetrinite, collotelinite, and corpogelinite macerals. Collodetrinite maceral (20 to 65.6 vol.%) is the most abundant maceral in the vitrinite group and is associated with inertodetrinite and microspornite macerals. Callotelinite (8.4 to 46.7 wt%) occurs as a structureless, homogeneous mass in the Gheshlagh coal seams. The inertinite group (4.9 to 23.3 vol%) includes fusinite, semifusinite, macrinite, secretinite, funginite and inertodetrinite macerals. Fusinite (1.7 to12.7 vol.%) is present in all coal seams in the Gheshlagh area. Cell cavities of fusinite are filled mostly by corpogelinite and clay minerals. Semifusinite occurs in appreciable concentrations (2.1to 14.3vol.%) and Cell lumens of this maceral are filled with mineral matter, pyrite and clay.
    The liptinite group (nil to 3.5 vol%) includes sporinite, cutinite and resinite macerals. Sporinite is the dominant maceral in the liptinite group (nil to 2.3 vol.%) and occurs as elongated thread-like or spindle-shaped bodies and occurs as microspores and megaspores. Resinite (nil to 0.1 vol.%) occurs as round to oval bodies and as fillings of the cell cavities of fusinite, semifusinite and funginite.
    The mineral matter content of most of the Gheshlagh coal seams varies between 3.1 and 24.9 vol.%. Mineral matter occurs in primary ground mass or secondary cavity filling form and includes clay minerals, carbonate and sulphide.
    Conclusion
    Based on organic petrographic studies carried out on four active coal mines in the Gheshlagh area, the presence of three maceral groups were determined. The vitrinite group (66.2 to 87.2 vol%) is the dominant maceral group, and callodetrinite maceral (20 to 65.6 vol%) is also abundant. The inertinite group contenthas a range of 4.9 to 23.3 vol% while the fusinite and semifusinite macerals are the most abundant of this group. The lowest volume percentage of macerals belongs to the liptinite group (0 to 3.5 vol%) with 2.3 vol% espornitebeing the most abundant Maceral of this group. The presence of espornite maceral at megaspore size in the S2 and K5 coal seams is very noticeable. The content of mineral matter of these coal seams varied from 5 to 24.9 vol%.
    Keywords: Maceral, Coal, Gheshlagh, Eastern Alborz
  • Mansour Adelpour, Iraj Rasa, Fariborz Masoudi, Masoud Hosseini Pages 129-146
    Introduction
    The Garmab copper deposit is located northeast of Qaen (South Khorasan province) in the1:100,000 scale map of Abiz in the eastern tectonic zone of Iran. It is hosted by Late Paleocene-Eocene lava flows consisting mainly of andesite, trachy andesite, andesite-basalt and basalt lavas, as well as pyroclastic rocks, including tuffs and ignimbrites. The Lut Block has undergone intense magmatic activitywith a variety of geochemical characteristics due to changing tectonic conditions (e.g., compression during subduction followed by tensional conditions; Karimpour et al., 2012; Zarrinkoub et al., 2012). The Lut Block has a great potential for the discovery of new mineral deposits, like the Mahrabad and Khonik porphyry copper-gold deposits (Malekzadeh shafarodi, 2009), the Dehsalam porphyry copper deposit (Arjmandzadeh, 2011), high sulfidation epithermal gold deposits such as Chah Shalghami (Karimpour, 2005) and IOCG deposits such as Kuh-E-Zar and Qaleh Zari (Mazlomi et al., 2008).
    Materials And Methods
    After field studies of the Garmab area, 32 thin sections and 21 polished sections were prepared for petrological and mineralogical studies.In addition, 10 least-altered and fractured samples of volcanic rocks were selected for geochemical studies. Major oxides were determined using XRF analyses at the Zarazma laboratory. Induced polarization and resistivity geophysical data were collected and correlated with geological and alteration maps. The geophysical datawere collectedfrom 420 individual points, using a dipole-dipole arrangement along five profiles separated 60m apart.This covered the study area entirely. After a change in the mineralization trend was observed,additional profileswere designed, twoon bearings of 25º and three on 75º.
    Results
    The Garmab volcanic rocks exhibit typical geochemical characteristics of subduction zone magmas including strong enrichment in LILE and depletion in HFSE. Based on the discrimination plot of Irvine and Baragar (1971), all samples belong to the calc-alkaline series, and based on the TAS diagram of Cox et al., 1979, the volcanic ore host rocks of Garmab range from andesite to basaltic andesite to trachyandesite.
    Hydrothermal alteration, associated with deposition of copper sulfide mineralization, occursmostly along the fault zones. .Mineralization also occurs disseminated and as veinlets, restricted to uppermost parts of the volcanic sequences. The deposit has the form of a layer of supergene enrichment characterized principally by chalcocite as the main ore mineral accompanied by digenite, covellite, bornite and chalcopyrite.
    The locationof the anomalies has been determined from their medium chargeability and low to medium resistivity values. This can be attributed to the presence of sulfide minerals in the mineralized zones. The average sulfide mineral grain size was determined using the results of time constant parameter. Since the results of raw data do not indicate accurate information about the depth and geometry of mineralization, smooth inverse modeling was applied to determine probable zones and vertical and horizontal extension of mineralization.Geophysical studies show that zones of mineralization are small and scattered.
    Keywords: Induced polarization (IP), Resistivity, Smooth inverse modeling, Copper, Qaen
  • Karim Abdollahi Silabi, Seyed Mohsen Tabatabaei Manesh, Somaye Karimi Pages 147-165
    Introduction
    The area studied is located north of Azna (Lorestan Province) in a small portion of the Sanandaj – Sirjan structural zone (Mohajjel et al., 2003).This area is part of the Zagros orogenic belt, formed by the opening and closure of Neotethyan ocean. From NE to SW, it consists of three parallel tectonic regions: the Orumieh-Dokhtar magmatic belt, the Sanandaj-Sirjan structural zone and the Zagros thrust-fold belt (Ghasemi and Talbot, 2005).
    The Sanandaj-Sirjan structural zone is a metamorphic belt composed mostly of greenschist, amphibolite and eclogite facies rocks. The development of the zonetook placeduring the opening of the Tethys ocean and its subsequent closing during the Cretaceous and earlyTertiary convergence of the Afro-Arabian and Eurasian plates (Mohajjel and Fergusson, 2000). The second stage of metamorphism and deformation of the zone, designated D2, is the most important, resulting from the opening and closure of the Neotethyan ocean and the collision of the Arabian plate with the southwestern part of central Iran in the Late Cretaceous to Tertiary (Laramideorogenic phase) (Ghasemi and Talbot, 2005; Aghanabati, 2004; Mohajjel et al., 2003; Mohajjel and Fergusson, 2000; Alavi, 1994). In the Sanandaj-Sirjanzone, which includes the Azna area, Cretaceous granitic intrusions into the schists were followed byfolding and faulting. The intrusions produced contact metamorphism, and have lens-shaped outlines, trendingNW-SE. Consequently, the Azna area has a varied petrologic assemblage with polyphase metamorphism and deformation, including schists, metabasites and mylonitic granites. The phases include: 1. Deformation D1, and dynamothermal metamorphism (M1),a result of the subduction of Neotethysoceanic crust beneath the Iranian plate in the Late Jurassic. 2.Deformation D2, and thermal metamorphism (M2),a result of Paleocene continental collision and 3. Deformation D3, and dynamic metamorphism (M3). This deformation is a progressive deformation that hasproduced the current morphologyof the Sanandaj-Sirjan zone (Shabanian Borujeni, 2008).
    In this paper we focused on petrography and mineral chemistry and thermodynamic conditions of the metapelites.
    Materials And Methods
    The chemical compositions of minerals were determined by a CAMECA SX100 electron microprobe (EMP) at Universität Stuttgart (Germany). The instrument is equipped with five wavelength dispersive spectrometers. The beam current and acceleration voltage were 15 nA and 15 kV, respectively.
    Discussion and
    Results
    The Azna regional metamorphic rocks include quartz-feldspar schists, mica schists, andalusite-bearing schists and quartzites.
    The Azna metapelites are schists, containing quartz, feldspars, andalusite, muscovite, biotite, muscovite, chlorite and garnet, in variable proportions, characterized byporphyroblastic and lepidoblastic textures. Based on mineralogy, minerals of these rocks contain andalusite, garnet, feldspar, muscovite, biotite, quartz and chlorite. Microprobe analyses show that the mineral compositions are as follows: White micas in the andalusite-bearing schists are muscovite, plagioclases are albite-oligoclase, garnets are almandine-spessartine with weak chemical zoning and biotites are siderophylite-annite.
    Based on geothermobarometry, these rocks formed in the hornblende-hornfels facies and the low pressure part of the amphibolite facies,with temperatures about 562-692 °C and pressures1.07-4.12 kbar. After the regional metamorphism of these rocks,granitoidintrusions causedthermal metamorphism of these rocks and the formation of andalusite-bearing schists.
    Keywords: Petrography, Mineral chemistry, Andalusite, Azna, Sanandaj, Sirjan Zone, Iran
  • Seyed Javad Moghaddasi, Ebrahim Tale Fazel, Aliyeh Sadat Banifatemi Pages 167-180
    Introduction
    More than 30 fluorite occurrences with approximately 1.35 million tons of reserves have been recognized in Iran (Ghorbani, 2013). The Atashkuh fluorite-barite (±sulfide) deposit is one of four occurrences located south of the city of Delijan in Markazi province, about 80 km SE of Arak city. The Atashkuh deposit occurs between the central Iran structural zone on the north and the Sanandaj-Sirjan structural zone on the south. The geology of the area is dominated by folded and faulted Jurassic carbonates and shales (Thiele et al., 1968). The lower Jurassic shale and calcareous sandstone of the Shemshak Formation and the Middle to Upper Jurassic dolomite of the Badamu Formation are the main host rocks for the fluorite veins.
    In this study, 40 samples from fluorite veins and host rocks were collected, from which 25 thin sections and 8 doubly-polished thin sections were prepared. Micro-thermometric studies were conducted on primary fluid inclusions using the Linkam THM600 heating-freezing stage. In addition, 10 samples were analyzed by XRD.
    Results
    Fluid inclusion data indicate that the Atashkuh fluorite-barite (±sulfides) veins were deposited as a result of mixing a primary multi-component Na-K(-Mg-Ca) high-salinity brine (SH type inclusions) with less saline calcium-rich connate water (LVHH type inclusions) and pressure reduction of ore bearing fluids. Fluid inclusions containing halite in high-salinity brine, and hydrohalite in connate water show suggest a high-salinity brine and connate water before mixing. The main mineralization stage was followed by circulation of low temperature meteoric water, responsible for the late stage mineralization. The micro-thermometry results suggest that the main fluorite mineralization occurred at 250 °C and 150 Mpa pressure.
    Dolomitization and silicification are the main alteration types associated with the Atashkuh mineralization. The occurrence of chlorite, talc, illite and dolomitized host rock all suggest Mg metasomatism associated with the main stage of fluorite mineralization.
    As a result of these observations, three stages of mineralization were recognized in the Atashkuh area: (1) Mobilization of a primary multicomponent Na-K(-Mg-Ca) high-salinity basinal fluid from the underlying rocks and its migration to the upper horizons. This stage is corresponds with the multi-phase SH inclusions with salinity of 31 wt% NaCl equivalent and 220 to 350 °C temperature.
    (2) Mixing and dilution of the basinal saline fluid with low-salinity formation or connate water resulted in deposition of fluorite-barite (±sulfide) mineralization and the formation of ferruginous dolomites. This stage contains Ca-Na rich inclusions with hydrohalite (LVHH).
    (3) Carbonate dissolution and increase in CO2 content of solutions due to oxidation of pyrite, formation of sulfuric acid. This stage is supergene oxidation and deposition of supergene minerals.
    The dissolution of carbonate rocks by acidified meteoric water produced permeable structures and breccias, by followed by of supergene mineralization in the later stages and formation of cerussite, malachite and goethite.
    Discussion
    The Atashkuh fluorite-barite (±sulfide) mineralization is mainly associated with dolomitized and silicified Jurassic carbonates and shales of Shemshak and Badamu Formation. The mineralization is in the form of two veins about 1 km apart. The epigenetic vein mineralization mainly consists of fluorite and barite with subordinate quartz, calcite, dolomite, galena, chalcopyrite, pyrite, hematite, goethite, malachite and cerussite. The main ore textures are replacements, open-space fillings, breccias and veins. The petrographic studies suggest three paragenetic suites: fluorite/quartz/calcite, barite/dolomite/sulfides and hematite/cerussite/goethite as early, middle and late stages.
    Micro-thermometric measurements were carried out on primary fluid inclusions of fluorite, barite and quartz crystals from both mineralized veins of the Atashkuh deposit. Fluid inclusions are of several types: (1) two-phase, liquid-vapor (LV), two- phase aqueous with hydrohalite (LVHH), multiphase (SH), H2O-CO2 with clathrate (C1) and without clathrate (C2) were recognized and analyzed.
    The first ice melting temperature (Te) of fluorite, barite and quartz two-phase aqueous (LV) inclusions varies between -22°C and -25°C, representing a H2O ± NaCl ± KCl multiphase solution (Van den Kerkhof and Hein, 2001). The last ice melting temperatures of three samples (Tmice) vary between -4.9°C to -9.7°C, -3.2°C to -7.2°C and -2°C to -4.8°C which indicate salinities of 7.7-13.6, 5.2-10.7 and 3.2-7.5 wt% NaCl equivalent for fluorite, barite and quartz. The final homogenization temperatures (Thtotal) of these inclusions vary between 90 and 205 °C for fluorite, 130 to 270 °C for barite and 110 to 193 °C for quartz. The CO2 melting temperatures (TmCO2) of fluorite and quartz C1 inclusions show ranges of -57.1 to -58.5 °C which suggest the presence of CH4 and/or N2 impurities (Burruss, 1981). The clathrate melting temperature (Tmclath) varies between 4.8 and 8.5 °C representing a salinity of 5.3 to 9.2 and 3 to 6.7 wt% NaCl equivalent for fluorite and quartz. The CO2 homogenization temperature (ThCO2) in these inclusions is 7.4 to 18.8 °C for fluorite and 13.4 to 27.5 °C for quartz. The homogenization temperature (Thtotal) for these inclusions is 170-210 °C for fluorite and 195-280 °C for quartz.
    Keywords: Atashkuh fluorite deposit, fluid inclusion, mineralization stages, fluid processes, Delijan
  • Mohammad Kashkoei Jahroomi, Afshin Qishlaqi Pages 181-199
    Introduction
    In remote sensing studies, especially those in which multi-spectral image data are used, (i.e., Landsat-7 Enhanced Thematic Mapper), various statistical methods are often applied for image enhancement and feature extraction (Reddy, 2008). Principal component analysis is a multivariate statistical technique which is frequently used in multidimensional data analysis. This method attempts to extract and place the spectral information into a smaller set of new components that are more interpretable. However, the results obtained from this method are not so straightforward and require somewhat sophisticated techniques to interpret (Drury, 2001). In this paper we present a new approach for mapping of hydrothermal alteration by analyzing and selecting the principal components extracted through processing of Landsat ETM images.
    The study area is located in a mountainous region of southern Kerman. Geologically, it lies in the volcanic belt of central Iran adjacent to the Gogher-Baft ophiolite zone. The region is highly altered with sericitic, propyliticand argillic alterationwell developed, and argillic alteration is limited (Jafari, 2009; Masumi and Ranjbar, 2011).
    Multispectral data of Landsat ETM was acquired (path 181, row 34) in this study. In these images the color composites of Band 7, Band 4 and Band 1 in RGB indicate the lithology outcropping in the study area. The principal component analysis (PCA) ofimage data is often implemented computationally using three steps: (1) Calculation of the variance, covariance matrix or correlation matrix of the satellite sensor data. (2) Computation of the eigenvalues and eigenvectors of the variance-covariance matrix or correlation matrix, and (3) Linear transformation of the image data using the coefficients of the eigenvector matrix.
    Results
    By applying PCA to the spectral data, according to the eigenvectors obtained, 6 principal components were extracted from the data set. In the PCA matrix, theeigen vector differences between the means of the level of significance between two bands (or spectral significance of the PC). The higher value is regarded as the Target Value of the bands which show a lower correlation. The components having maximum spectral significance of PCs, in bands 1 and 3, 5 and 7 and 5 and 3, were selected for enhancement of iron oxides, clay minerals and carbonate minerals, respectively. In each PC matrix, the sum of the significances is regarded as the spectral weight of that PC.
    The spectral weight of the extracted PCs, was found to be as follows: PC5> PC4>PC2>PC3>PC7>PC1
    The inverse PC4 and –PC3 provide valuable information on vegetation mapping. In order to map the alteration zones and igneous rocks outcropped in the study area, the color composites of the PC5, -PC4 and average of each PC are included in RGB, respectively. The spectral proportion of each PC pertaining to each mineral was calculated as spectral significance in the two bands (e.g. Bands 5 and 7 for clay minerals and Bands 3 and 1 for Fe oxide minerals) divided by spectral weight of that PC. Based on the obtained results, the selectivity of the extracted components for enhancement of clay minerals and Fe oxide minerals was calculated and images of these minerals were produced using the following expressions: Fe oxide minerals: Clay minerals: For carbonate minerals, the proportion of each PC is calculated in terms of the eigenvectors of bands 5 and 3. The selectivity of the PCs used in enhancing of spectral data of carbonate minerals is as follows: PC5>PC2>PC1>PC3>PC4>PC7
    In the remotely sensed image, PC5 with high spectral weight was selected as the informative PC for clay minerals, iron oxides and carbonate minerals. This is becausepropylitic alteration and the formation of carbonate minerals can be easily enhanced in the processed images. Eventually, overlapping of the processed images provides patterns of hydrothermal alterationwhich indicate the areas to be prospected. In order to validate the obtained results of the image processing with geological evidence,petrographic studies of rock samples collected from major outcrops in the study area were made. It was found that quartz, calcite, epidote, sericite and chlorite are the main constituents of sericiticand propylitic alteration assemblages in the study area. The minerals are virtually enhanced in Landsat ETM using the proposed methods and confirm the results obtained from multispectral data analysis.
    Conclusion
    This study provides a new and improved approach to obtain the most meaningful spectral data for oxides, carbonates and clay minerals in multispectral images. As these minerals are typically found in hydrothermal alteration, the method presented in this article can be used for enhancement of such mineral spectral data, which can be very helpful in prospecting and exploration for hidden mineral deposits.
    Keywords: Principal component analysis, Landsat ETM+, Hydrothermal alteration, Mapping, Baft, Kerman
  • Zahra Mehraban, Behnam Shafiei Bafti, Gholam Hossein Shamanian Pages 201-221
    Introduction
    The Central Alborz in eastern Mazandaran province is host to the most important carbonate-hosted fluorite deposits in Iran, such as Pachi-Miana, Sheshroodbar, Era and Kamarposht. In these deposits, mineralization occurs in the upper parts of the middle Triassic Elika formation (Vahabzadeh et al., 2009 and references therein). These deposits have long been studied, and various models are presented for ore genesis. Nevertheless, ore genesis in these deposits is still unclear. The present study of the geochemistry of the REEs of these deposits is intended to improve genetic models.
    Materials And Methods
    Three hundred samples were taken from above mentioned deposits. Samples were categorized into 5 groups: (1) fluorite ore types, (2) ore-stage calcite, (3) carbonate host rocks, (4) basaltic rock around the deposits, and (5) shale of the Shemshak formation. Fourteen pure fluorite samples, 4 samples of pure calcite, 4 samples of carbonate host rock, 1 sample of basalt and 1 sample of shale were analyzed for REEs by ICP-MS at West Lab in Australia.
    Results
    Analytical data on fluorite from the Elika deposits show very low REE concentrations (0.5-18ppm), in calcite(0.5-3ppm) in carbonate host rocks – limestone (1.8-7ppm), and in dolomitic limestone 6.5ppm, compared with upper Triassic basalt (43ppm) and shale (261ppm). REE in fluorite of these deposits are strongly enriched (10 3 to 10 6 times) relative to normal sea water, ore stage calcite and carbonate host rocks, especially for mid-REEs (Eu, Gd) and heavy REEs (Lu, Yb, La/Yb=~0.05).
    Also, LREEs depletion (La/Sm= 2-10) and HREEs (La/Yb=0.01-0.08) relatively enrichment of fluorites compared with limestone (La/Sm=2.5-4, La/Yb=0.1-1.5) and dolomitic limestone (La/Sm=4.28, La/Yb=0.07-0.4) host rocks as well as positive Eu anomaly are the most important REEs signatures in fluorites.
    Fluorite elsewhere in the world with low total REE conten thas been interpreted to have a sedimentary origin (Ronchi et al., 1993; Hill et al., 2000; Sasmaz et al., 2005). Strong enrichment of REEs in fluorite and carbonate host rocks worldwide, relative to normal sea water indicates that diagenetic and/or hydrothermal processes have contributed to the process. Depletion of LREEs and moderately strong HREE enrichment in fluorite relative to carbonate host rocks is interpreted to be post-sedimentation (Ronchi et al., 1993;Hill et al., 2000). Thisis supported by the hydrothermal character of the fluorite in the Elika deposits and similarity between REE profiles and those of fluorine-rich MVT deposits with hydrothermal origin (Chesley et al.,1994; Bau et al., 2003). Positive Eu anomalies in fluorite elsewhere suggest deposition reduced conditions and temperatures~250°C (Bau et al., 2003; Sverjensky, 1989). The present study indicates that low total REEcontents in fluorite precipitated from reduced hydrothermal solutions could be caused by (1) increasing pH of the ore-forming solution during interaction with carbonate host-rock, (2) gradually decreasing F concentration in hydrothermal solutions due to different generations of fluorite mineralization, and (3) low REE contents of carbonate hostrocks.
    Keywords: Rare Earth Elements (REEs), Fluorite, Elika, Mazandaran
  • Seyed Abolfazl Ezzati, Seyed Reza Mehrnia, Kimiya Sadat Ajayebi Pages 223-238
    Introduction
    The Ramand area, southwest of Buin- Zahra, about 60 kilometers from Qazvin, lies in the igneous belt of the Urmieh-Dokhtar region, the main structural zone of north-central Iran. Rhyodacite and rhyolite lava flows are the principal host rocks of mineralization and alteration of the area, most of which occurs in faulted and brecciated zones alongmaj or northwest-trending fault systems (such as Kour-Cheshmeh, Hassan Abad and their branches). Clay minerals determined from satellite images indicated principally argillic hydrothermal alteration before laboratory mineralogical analysis. According to instrumental analyses, mineralized alteration with greater amounts of argillic halos and lesser amounts of sericitic-propylitic minerals contains quartz veinlets in the vertical and lateral sections. Initially, alteration in the Ramand area was revealed in ETM images by using the SPCA technique of Crosta and Moore, 1990 (Selective Principle Component Analysis). Compared with other techniques, SPCA results have reliable spectral signatures for identifying argillic minerals and Fe-oxides as the main mineralogical association in hydrothermal environments. Subsequently, multispectral images (ASTER) were analyzed using band ratios.The results indicated silicification alteration along the faulted regions in the Ramand area. Later, areas of silicification alteration were prospected for precious and base metal mineralization.Sampling results suggested that the altered areas have some potential for epithermal mineralization, according to instrumental analyses and micrographic evidence.
    Materials And Methods
    1- Collecting satellite images, geological evidence and related documents
    2- Image processing to reveal and identify the mineralized alteration.
    3- Sampling of the mineralized zones indicated by the remote sensing.
    4- Thin- and polished section microscopic studies.
    5- X-ray diffraction analysis (XRD) (19 samples), inductively coupled plasma mass spectrometry analysis(ICP- MS)for determining the major and trace elements (4 samples) and 4 samples were analyzed for the gold content by using atomic absorption (AA).
    Discussion and
    Results
    Most of the hydrothermal alteration in the Ramand region was mapped by processing the ETM and ASTER satellite images. The Crosta and Moore (1990) technique indicated the facies of alteration, and increased the correlation between altered and mineralized regions.
    Evaluating the potential for ore-grade mineralization requires mapping the location and probable zonal location of the quartz veins indicated by band ratios in the ASTER image (Kruse et al., 1993; Honarmand et al., 2012). Our studies showed that volcanic rocks in the Ramand area are intensively altered by hydrothermal processes. The micrographic results confirmed that argillic and silicification alteration occurred within calcitized-oxidized masses. The study has shown that the mineralized region significantly contains quartz veinlets usually surrounded by argillic halos and Fe-oxides as two components of the alteration.
    In conclusion, our remotely sensed prognostic mapindicates a strongly altered epithermal system along faulted structures and breccia zonesclearly apparent at the surface (Akbari, et al., 2012).The altered zones probably extend at depth with probable zones enriched in gold and base metals. Considering the zonalpatterns indicated by image processing, besides the ore genesis peculiarities of the epithermal systems (micrographic results), this article introduces reliable data indicating the nature of mineralization in the Ramand area based on analysis of satellite images and mineralogical and chemical analyses of samples which encourage detailed exploration for discovery of orebodies in a deeper prospect.
    Keywords: Alteration, Remote Sensing, Crosta PCA, Ramand
  • Reza Monazzami Bagherzadeh, Mohammad Hassan Karimpour, G. Lang Farmer, Charles R. Stern, Jose Francisco Santos, Sara Ribeiro, Behnam Rahimi, Mohammad Reza Haidarian Shahri Pages 239-264
    Introduction
    The Bornaward area is located in the Northeastern Iran (in the Khorasan Razavi province) 28 km northwest of the city of Bardaskan at 57˚ 46΄ to 57˚ 52΄ N latitude and 35˚ 21΄ to 35˚ 24΄E longitude. The Taknar structural zone, situated in the North central Iranian micro continent, is part of the Lut block (Forster, 1978). The Taknar zone is an allochthonous block bounded by the Darouneh and Taknar major faults. Much of this zone consists of metarhyolite-rhyodacite volcanic rocks, and rhyolitic tuff with interlayers of sandstone and dolomite (Taknar Formation).
    Analytical
    Results
    ICP-MS analysis of REE and minor elements of samples of the Bornaward metarhyolites was carried out at the ACME Laboratory in Vancouver, Canada. U-Pb dating of the metarhyolites was performed on isolated zircons in Crohn's Laser Lab, in Arizona (Gehrels et al., 2008). Measurement of Rb, Sr, Sm and Nd isotopes and (143Nd/144Nd)i and (87Sr/86Sr)i ratios took place in the radioisotope laboratory of the University of Aveiro in Portugal.
    Petrography
    The volcanic rocks are porphyritic, commonly containing phenocrysts of orthoclase and rarely sanidine, quartz and intermediate plagioclase in a groundmass of fine-grained quartz and feldspar. An alteration has produced oriented needles of sericite and clay minerals, clusters of fine-grained green biotite and clots of epidote and chlorite.
    Geochemistry
    The compositions of the volcanic rocks are calc alkaline and high K- calc alkaline. The obtained Shand index (Al2O3/( CaO㖭軸궎) is above 1.1, in the peraluminous S-type granite field (Chappell and White, 2001). Plotted on the TAS diagram (Middlemost, 1994), all the metarhyolite-rhyodacite samples are located in the sub-alkaline field and the majority fall into the rhyolite group. The metarhyolite-rhyodacites show enrichment of LREE with a moderately ascending pattern ((La/Yb)N=2.51-10.11 and La=46.45-145.48). Europium shows a negative anomaly (Eu/Eu*=0.23-0.71).
    U-Pb zircon geochronology
    Measurement of U-Pb isotopes of the Bornaward metarhyolite zircons of sample BKCh-103, indicates an age of 552.23.73,-6.62 Ma (Upper Precambrian).
    Sr-Nd isotopes
    The Sr ratios of the metarhyolites (87Sr/86Sr) were found to fall in the range of 0.688949 to 0.723435 and the Nd ratios (143Nd/144Nd)i were in the range of 0.511701 to 0.511855. These values indicate that the metarhyolites of samples BKCh-12, BKCh-103 and BKCh-177 were affected by hydrothermal alteration since their (87Sr/86Sr)I ratios are high. The Sr ratios suggest that the more negative Nd anomaly and the more negative ɛNd(552) of the samples BKCh-12, BKCh-103 and BKCh-177 indicate that these lavas originated in an enriched upper mantle source and/or lower continental crust. In contrast, two recent examples (Xua et al., 2005) can be related to sialic continental crust with significant contamination.
    Petrogenesis : The Bornaward metarhyolite- rhyodacites show an enriched pattern for Rb, Th, U, K, Pb, Nd and Y relative to the primitive mantle, while Ba, P, Ti, Sr, Zr and Nb show a reduction as a result of fractional crystallization. Based on isotopic correlations of207Pb/204Pb vs 206Pb/204Pb, the primitive source of the Bornaward metarhyolite- rhyodacites is the lower continental crust. This part of the continental crust is only slightly depleted in Pb. Consequently, it has a low 87Sr/86Sr ratio (Samples BKCh-138 and BKCh-198). In contrast, the samples of BKCh-12, BKCh-103 and BKCh-177 have high 87Sr/86Sr ratios that could be the result of significant contamination to parts of the continental crust with very high 87Sr/86Sr (Karimpour et al., 2011).
    Results and
    Conclusions
    The calc-alkaline compositions of samples BKCh-12, BKCh-103 and BKCh-177, the high K- calc alkaline of samples BKCh-138 and BKCh-198 of the Bornaward metarhyolites and the higher temperature overgrowth of plagioclase on lower temperature microcline phenocrysts can be a reason for entrance lavas with different generations. The distinct isotopic characteristics of the two groups of rhyolitic samples are the reasons for two different sources for the production of these lavas: 1) partial melting of an enriched mantle reservoir or lower continental crust, and 2) sialic continental crust with high contamination. With respect to the Bornaward metarhyolite- rhyodacites with (143Nd/144Nd)i ratios from 0.511701 to 0.511855, geochemical characteristics and the high volume of volcanic rocks in the area, their formation can be attributed to a continental rift environment. This rift system can be formed by initiation of a plume in the upper mantle beneath East Iran during Neoproterozoic time.
    Keywords: Isotope, Zircon, Geochronology, Neoprotrozoic, Bornaward, Taknar, Bardaskan
  • Sedigheh Zirjanizadeh, Mohammad Hassan Karimpour, Khosrow Ebrahimi Nasrabadi, Jose Francisco Santos Pages 265-282
    Introduction
    The study area is located in NW Gonabad, Razavi Khorasan Province, northern Lut block and eastern Iran north of the Lut Block. Magmatism in NW Gonabad produced plutonic and volcanic rock associations with varying geochemical compositions. These rocks are related to the Cenozoic magmatic rocks in Iran and belong to the Lut Block volcanic–plutonic belt. In this study, petrogenesis of volcanic units in northwest Gonabad was investigated.
    The volcanic rocks are andesites/trachyandesites, rhyolites, dacites/ rhyodacites and pyroclastics.These rocks show porphyritic, trachytic and embayed textures in phenocrysts with plagioclase, sanidine and quartz (most notably in dacite and rhyolite), hornblende and rare biotite. The most important alteration zones are propylitic, silicification and argillic.Four kaolinite- bearing clay deposits have been located in areas affectedby hydrothermal alteration of Eocene rhyolite, dacite and rhyodacite.
    Analytical techniques: Five samples were analyzed for major elements by wavelength dispersive X-ray fluorescence (XRF) and six samples were analyzed for trace elements using inductively coupled plasma-mass spectrometry (ICP-MS) in the Acme Laboratories, Vancouver (Canada).Sr and Nd isotopic compositions were determined for four whole-rock samples at the Laboratório de GeologiaIsotópica da Universidade de Aveiro, Portugal.
    Results
    Petrography. The rocks in this area are consist of trachyte, andesite/ trachyandesite, dacite/ rhyodacite, principally as ignimbrites and soft tuff. The textures of phenocrysts are mainly porphyritic, glomerophyric, trachytic and embayed textures in plagioclase, hornblende and biotite. The groundmasses consist of plagioclase and fine-grainedcrystals of hornblende. Plagioclase phenocrysts and microlitesare by far the most abundant textures in andesite - trachyandesites (>25% and in size from 0.01 to 0.1mm). Euhedral to subhedral hornblende phenocrysts areabundant (3-5%)and 0.1 to 0.6mmin size.
    Trachyte is characterized by trachytic texture. Ninety percent of the rock consists of sanidine. In trachytes, 3 to 5% hornblende ( 0.3 mm) is replaced by carbonates. Rhyolites contain quartz, plagioclase, sanidine, and biotite phenocrysts in a microcrystalline to glassy groundmass. Rhyodacitehas phenocrysts, some glomerophyric, consisting of quartz, 2 to 3% (0.1-0.5 mm), plagioclase 7 to 10% (0.2- 0.8 mm), hornblende 5% and biotite 1%. Up to 15% of sanidineis altered to clay minerals. Crystal tuff and lithic-crystal tuff are distributed overa large area.
    Using the Zr/TiO2 and Nb/Y diagram of Winchester and Fold (1977), samples are designated as rhyolite, dacite and sub-alkaline basalt. In the Co vs. Th diagram of Hastie et al. (2007), samples plot in the shoshonitic and high calc-alkaline, rhyolite, dacite and andesite-basalt fields.
    The REE patterns and trace element contents of the volcanic samples show: (1) LREE/HREE enrichment ((La/Yb) N = 0.3 to 15.27), (2) Low negative Eu anomaly (ave.Eu*/Eu=0.2-0.85), (3) depletion in Ba, Sr, K2O, Zr and Ti (Lower continental crust-normalized spider diagram from Taylor and McLennan, 1985 and Chondrite-normalized diagram from Nakamura, 1974. Rhyolites show the most extreme negative Eu anomaly (Eu/Eu* = 0.2-0.3) compared with 0.65–0.85 for volcanic elsewhere and also show considerably differences in the contents of Rb,Sr,K,Ti,Zr,Hf,Ce. These differences are related to greater magmatic differentiation or derivation from the other sources. The Sr and Nd isotopic ratios of these volcanic rocks are: 87Sr/86Sr = 0.70699 to 0.71014 and 143Nd/144Nd =0.512144 to 0.512539. Assuming an age of 60 Ma, the initial 87Sr/86Sr ratios vary from 0.70671 to 0.71066 and initial 143Nd/144Nd values vary from 0.512098 0.51249 (εNdi = -9.1) to 0.51249 (εNdi = -1.4).In the εNdi versus (87Sr/86Sr)i diagram, the samples plot in the field typical of magmas that are of crustal origin or, at least, that underwent important processes of crustal assimilation/contamination.
    Andesitic rocks displays lightly lower rangesof87Sr/86Sr (0.7067-0.7068) and εNdi values from -1.44 to -2.34, than rhyolite. Distinct Sr and Nd isotopic compositions are seen between rhyolitic rocks and andesitic rocks. The geochemical data suggest that the rhyolitic magmas probably represent the final differentiates of parental magmas, resulting from partial melting of mafic lower crust. Generally, the magmas from this area have low Sr (less than 400 ppm), high K2O/Na2O and negative Eu anomalies.
    Keywords: 87Sr, 86Sri, geochemistry, volcanic rocks, Lut block, Eastern Iran