زمین‌شناسی و ژئوشیمی ایزوتوپی کانسار Cu-Mo پورفیری هفت‌چشمه با تکیه بر نتایج ایزوتوپ‌های Sr–Nd–Pb-S-O-H

کانه‌زایی cumo پورفیری در کانسار هفت‌چشمه واقع در شمال‌غربی زون فلززایی ماگمایی ارسباران، شمالغرب ایران مرتبط با نفوذ توده نفوذی گرانودیوریتی به ‌درون توده پورفیری گابرودیوریتی می‌باشد. براساس مطالعات کانی‌شناسی، روابط بافتی و متقاطع رگه‌های کوارتز سولفیددار، فرایندهای دگرسانی و کانه‌زایی هیپوژن cumo در این کانسار به سه مرحله کانه‌زاییi  وii  همراه با دگرسانی پتاسیک و مرحله کانه‌زایی iii همراه با زون دگرسانی سریسیتی تقسیم‌بندی شده‌اند. مقادیر محاسبه‌شده سیالδ18o و سیالδd کانی‌های بیوتیت در تعادل با سیال گرمابی به‌ترتیب 8.3+ تا 6+ پرمیل و 76- تا 74- پرمیل نشان‌گر منشاء ماگمایی سیالات سازنده هاله‌های دگرسانی پتاسیک احاطه‌کننده مرحله ii کانه‌زایی می‌باشد. مقادیر محاسبه‌شده سیالδ18o و سیالδd کانی‌های سریسیت در تعادل با سیال گرمابی به ‌ترتیب 7.9+ تا 5.6+ پرمیل و 100- پرمیل تا 84- پرمیل نشانگر مشارکت بسیار کم آب‌های سطحی با سیالات ماگمایی در تشکیل هاله‌های دگرسانی سریسیتی می‌باشد. محدوده تغییرات مقادیر δ34s ایزوتوپ‌های گوگرد کانه‌های پیریت و کالکوپیریت در مراحل کانه‌زایی ii و iii کانسار هفت‌چشمه به‌ترتیب بین 5.4- تا 3.2- پرمیل و 3.1+ تا 0.7+ پرمیل نشان‌دهنده منشاء ماگمایی گوگرد در کانه‌های سولفیدی و تغییرات فیزیکوشیمیایی سیالات کانه‌زا در این مراحل کانه‌زایی می‌باشد. مقادیر همگن و محدوده باریک تغییرات نسبت‌های ایزوتوپی سنگ‌کل 143nd/144nd، 87sr/86sr، εnd و 206pb/204pb، 204pb/204pb و 208pb/204pb توده‌های پورفیری گابرودیوریت و گرانودیوریت به‌ترتیب 0.512773-0.512776، 07046-.7044/0، 2.6+ 2.7+، 18.93-18.82، 15.60-15-16 و 39-38.90 نشانگر تشکیل این توده‌ها در اثر ذوب بخشی پوسته زیرین ضخیم‌شده منشاء گرفته از گوشته تهی‌شده، در رژیم تکتونیکی فشارشی و سپس آغشتگی با مواد پوسته بالایی در طی صعود و تبلور ماگما می‌باشند.

Geologiy and isotopic geochemistry of the Haftcheshmeh Cu-Mo porphyry deposit, implication of the Sr-Nd-Pb-S-O-H isotopes

Introduction The Haftcheshmeh porphyry Cu–Mo deposit is located in the NW part of the Arasbaran Metallogenicmagmatic zone (AMZ), NW Iran. The (AMZ), located in the southernmost of Lesser Caucasus subduction zone, extends from NW Iran to Armenia and Azerbaijan (Hassanpour et al., 2015). The Haftcheshmeh Cu–Mo porphyry deposit was developed synchronously with the emplacement of the OligoMiocene Haftcheshmeh porphyries, ranging in composition from gabbrodiorite to granodiorite. Based on the detailed field and petrography studies, four alteration zones from center to outward have been recognized in the Haftcheshmeh deposit, including early potassic and peripheral propylitic alterations, successively followed by sericitic and locally argillic alteration zones. According to the mineralogical, textural, and crosscutting relation of the quartz veins, three hypogene hydrothermal alterationmineralization have been recognized. Stages I and II are associated with potassic alteration zone; and stage III is associated with sericite alteration zone. The purpose of this paper is to determine the characteristics and origin of the orebearing fluids, with particular focus on the results of SOH stable isotopes of the hydrothermal sulfide ores, phyllosilicate minerals (biotite and sericite) given from potassic and sericite alteration zones. The whole rock SrNdPb radiogenic isotopes were undertaken to elucidate the possible origin of the parental magma of the orebearing Haftcheshmeh porphyries. Materials and methodsMore than 100 polished and thin sections from mineralized gabbrodiorite and granodiorite porphyries bore hole samples were studied by petrographic and mineralogical methods at the Shahid Beheshti University, Tehran. Two biotites from stage II; and five sericites from stage III and ten sulfide minerals (eight pyrite and two chalcopyrite) were separated from quartz–sulfide veinlets of II and III mineralization stages. They were used for δ18O, δD and δ34S stable isotope analysis; which was performed at the geochemistry and isotopic research Laboratory of British Colombia, Canada, using a Finnigan MAT 252 mass spectrometer. Wholerock SrNdPb isotopic compositions of the two least altered gabbrodiorite and granodiorite porphyries were performed at the geochemistry and isotopic research Laboratory of British Colombia, Canada, using Nu MultiCollector Thermal Ionization Mass Spectrometer; (TIMS).Results and discussionThe calculated aqueous fluids δ18OH2O and δDH2O values of water in equilibrium with biotite samples range from +8.3‰ to +6 and from –76 to –74‰ respectively. The calculated δ18OH2O and δDH2O values of water in equilibrium with sericite samples range from 5.6 to 8.3 ‰ in δ18OH2O and from –100 to –84‰ in δDH2O, respectively. The δ34S values of pyrite and chalcopyrite from stage II range from 5.4 to 3.7 (n=4), and 3.2‰ (n=1) respectively, and δ34S values of pyrite and chalcopyrite from stage III range from +0.9 to +3.1 (n=3) and +0.7 (n=1), respectively. Gabbrodiorite and granodiorite samples at Haftcheshmeh have an initial 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb ratios, and εNd (t) values between 0.70440.7046; 0.51280.51277; 18.818.93; 15.6015.61; 38.839 and +2.7 to +2.6, respectively.The δ18OH2O and δDH2O1 values of the biotite samples from stage II with potassic alteration halo and sericite samples from stage III, indicate that the initial oreforming fluids were from a magmatic dominated origin and then mixed with a low component of the meteoric water. The δ34S values of pyrite and chalcopyrite minerals reflected a homogeneous magmatic and mantledominated sulfur source. The Pb isotopic compositions of the Haftcheshmeh porphyries show a relatively uniform magmatic origin during the compressional regime. Wholerock initial 87Sr/86Sr, 143Nd/144Nd isotopic ratios and positive ɛNd(t) values indicated that the adakitelike Haftcheshmeh porphyries were generated from a dominantly depleted mantlederived, thickened lower crust source, which was consequently contaminated by upper crustal materials during the ascent and crystallization of magma.ConclusionsThree alteration and CuMo mineralization stages associated with potassic and sericite alteration zones of the gabbrodiorite to granodiorite phases have been recognized in the Haftcheshmeh porphyry deposit. The measured and calculated δ18O and δD values of the potassic to sericite minerals from stage II to III reflected that the magmatic hydrothermal fluids were progressively mixed with a meteoric water influx. The δ34S and the calculated δ34SH2S values of pyrite and chalcopyrite sulfides from stage II and III reflected that the magmatic sulfur and physicochemicals contributed to sulfide mineral formation. The homogenous whole rocks 143Nd/144Nd, 87Sr/86Sr and initial Pb isotopes ratios of the gabbrodiorite to granodioritic porphyries indicated that the primary magmas were generated from a dominantly depleted mantlederived, thickened, lower crust source. It was consequently contaminated by upper crustal materials either at the magma source or during the ascent and crystallization of magma during the compressional regime.