ذخیره روی- سرب شهرستانک، جنوب‌شرق قم: ملاحظاتی بر کانه‌زایی، زمین‌شیمی ایزوتوپ‌های پایدار و توزیع عناصر خاکی نادر

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه زمین‌شناسی، دانشکده علوم، دانشگاه ارومیه، ارومیه، ایران

2 گروه زمین‌شناسی، دانشکده علوم، دانشگاه محقق اردبیلی، اردبیل، ایران

3 دانشکده مهندسی معدن، دانشگاه صنعتی اصفهان، اصفهان، ایران

چکیده

ذخیره روی - سرب شهرستانک، به عنوان بخشی از کمان ماگمایی ارومیه - دختر، در 50 کیلومتری جنوب‌شرق شهرستان قم واقع است. نفوذ توده­های آذرین مونزودیوریتی تا کوارتزدیوریتی به سن میوسن به درون توالی‌های آتشفشانی- رسوبی ائوسن (به طور عمده بازالت آندزیتی)، عامل اصلی گسترش دگرسانی­های کربناتی، سیلیسی و کلریتی به همراه رخداد کانه‌زایی روی - سرب به شکل رگه­ای و برشی در منطقه شهرستانک بوده است. بررسی­های سنگ‌نگاری و کانه‌نگاری نشان می‌دهند که اسفالریت، گالن، پیریت، تنانتیت، سروزیت، پلانتریت، هیدروزینکیت، هماتیت و لیمونیت در این ذخیره با کانی­های باطله چون کلسیت، باریت و کوارتز همراهی می­شوند. بافت‌های غالب در کانسنگ‌ها شامل دانه پراکنده، رگه‌ای، برشی، جانشینی و بازماندی هستند. الگوی توزیع عناصر خاکی نادر (REE) بهنجار شده به کندریت در بازالت‌های آندزیتی با تک‌کانی‌هایی چون گالن، اسفالریت و کلسیت کانسنگ‌ها تا حدی متفاوت هستند، با این حال نزدیکی مقادیر Y/Ho آنها نشان می­دهد که شستشوی فلزها از سنگ‌های میزبان بازالت آندزیتی نقش مهمی در تشکیل و گسترش این ذخیره داشته است. رخداد بی­هنجاری مثبت Eu و Ce در گالن (83/2- 18/2 = Eu/Eu* و 54/1- 35/1 Ce/Ce* =) و اسفالریت (28/2-92/1 = Eu/Eu* و 63/1- 36/1 Ce/Ce* =) بیانگر طبیعت احیایی سیال­های کانسنگ­ساز است. مقادیر ایزوتوپ δ34S در نمونه­های گالن و اسفالریت به ترتیب گستره تغییراتی از 3- تا 1+‰ و 2- تا 9/0+‰ را نشان می­دهد که نشانگر خاستگاه ماگمایی این دو کانی سولفیدی است. رسم مقادیر 18Oδ نسبت به 13Cδ در نمونه­های کلسیت نشان­دهنده آمیختگی سیال های ماگمایی با سیال­های جوی طی تکامل و گسترش این ذخیره است. تلفیق نتایج به دست آمده از بررسی­های صحرایی، کانی­‌شناسی، ساخت و بافت، نوع دگرسانی‌های گرمابی، زمین­شیمی REE و بررسی­های ایزوتوپ­های پایدار نشان می­دهد که کانه­زایی رخ داده در منطقه شهرستانک شباهت زیادی به کانسارهای فراگرمایی سولفیدشدگی حدواسط دارد.

کلیدواژه‌ها


عنوان مقاله [English]

The Shahrestanak Zn-Pb deposit, southeastern Qom: Considerations on ore mineralization, geochemistry of stable isotopes, and distribution of rare earth elements

نویسندگان [English]

  • Soheila Hasanzadeh Mahalleh 1
  • Ali Abedini 1
  • Ghahraman Sohrabi 2
  • Maryam Khosravi 3
1 Department of Geology, Faculty of Sciences, Urmia University, Urmia, Iran
2 Departement of Geology, Faculty of Sciences, University of Mohaghegh Ardabili, Ardabil, Iran
3 Department of Mining Engineering, Isfahan University of Technology, Isfahan, Iran
چکیده [English]

The Shahrestanak Zn-Pb deposit, as a part of Urmia-Dokhtar magmatic arc, is located about 50 km southeast of Qom City. Intrusion of monzodiorite to quartzdiorite igneous masses of Miocene age into Eocene volcano-sedimentary sequences (mainly andesi-basalt) has been the main factor in the development of carbonatic, silicic, and chloritic alterations along with the occurrence of Zn-Pb ore mineralization in the form of veins and breccia in the Shahrestank area. Petrographic and mineralographic observations show that sphalerite, galena, pyrite, tennantite, cerusite, planetrite, hydrozincite, hematite, and limonite are accompanied by ganque minerals such as calcite, barite and quartz. Dominant textures in ores include disseminated, vein, stockwork, replacement, and remnant. Although the distribution pattern of rare earth elements (REE) normalized to chondrite in andesi-basalts with monominerals, such as galena, sphalerite, and calcite, of ores are somewhat different, however, the close ratio of Y/Ho values ​​between them indicates that the leaching of metals from andesi-basalt host rocks have played an important role in the formation and development of this deposit. The occurrence of positive anomaly of Eu and Ce in galena (Eu/Eu* = 2.18-2.83 and Ce/Ce* = 1.35-1.54) and sphalerite (Eu/Eu* = 1.92-2.28 and Ce/Ce* = 1.36-1.63) indicates the reduction nature of ore-forming fluids. The δ34S isotope values ​​in galena and sphalerite samples show the range of changes from -3 to +1‰ and -2 to +0.9‰ respectively, which indicates the magmatic origin of these two sulphide minerals. Plotting the values ​​of δ18O against δ13C in calcite samples shows the mixing of magmatic solutions with meteoric solutions during the evolution and development of this deposit. Combining the results obtained from field observations, mineralogy, structure and texture, type of hydrothermal alterations, REE geochemistry, and stable isotope show that the mineralization occurred in the Shahrestanak area is very similar to intermediate sulfidation epithermal ore deposits.

کلیدواژه‌ها [English]

  • Zn-Pb deposit
  • intermediate sulfidation epithermal
  • stable isotopes
  • REE
  • Shahrestanak
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