کانی شناسی، زمین شیمی و نحوه تشکیل کانسار اسکارن آهن گوزل دره، جنوب شرق زنجان

کانسار آهن گوزل­‌دره در 44 کیلومتری جنوب­‌شرق زنجان، در پهنه البرز غربی آذربایجان قرار دارد. نفوذ توده گرانیتوئید گوزل­‌دره به درون سنگ­‌های کربناتی منطقه مورد بررسی، موجب دگرگونی مجاورتی، تشکیل اسکارن و کانی‌­سازی آهن همراه آن شده است. گرانیتوئید گوزل­‌دره شامل گرانیت، گرانودیوریت و کوارتز مونزونیت و از نوع i است. این گرانیتوئید در محیط زمین­‌ساختی کمان آتشفشانی و حاشیه فعال قاره‌­ای تشکیل‌شده است و در محدوده سنگ­‌های کالک­‌آلکالن پتاسیم بالا و دسته شوشونیتی قرار می­‌گیرد. کانی­‌سازی آهن اغلب به شکل توده‌­های نامنظم، عدسی و رگه‌­ای با خلوص زیاد یافت می­‌شود. مگنتیت فراوان­‌ترین کانه سازنده کانسار است و هماتیت، پیریت و کالکوپیریت کانی­‌های فرعی هستند. با توجه به ویژگی­‌های سنگ­‌شناختی، کانی­‌شناختی و زمین­‌شیمیایی، کانسار اسکارن آهن گوزل­‌دره در سه مرحله تشکیل‌شده است: 1 جای‌گیری توده گرانیتوئید گوزل­‌دره و دگرگونی همبری سنگ­‌های میزبان کربناتی و تشکیل مرمر با بافت گرانوبلاستیک و کانی­‌های سیلیکات کلسیم (منیزیم) بدون آب، 2 متاسوماتیسم و جانشینی که در ادامه مرحله قبلی رخ‌داده و با کانی­‌سازی جزئی مگنتیت در زون پیش‌رونده اسکارن همراه است و 3 سرد‌شدن توده گرانیتوئید گوزل­‌دره و سامانه گرمابی ماگمایی وابسته به آن که با تشکیل کانی­‌های اپیدوت، ترمولیت (اکتینولیت)، سرپانتین، تالک، کلریت، کلسیت و کوارتز در زون پس‌رونده اسکارنی همراه بوده و مسئول کانی­‌سازی اصلی آهن است. عملکرد فرایندهای سوپرژن و هوازدگی بر روی سامانه بالا موجب تشکیل کانی­‌های هماتیت، گوتیت، لیمونیت، مالاکیت و آزوریت شده و کانی‌ها و بافت­‌های اولیه از پیش موجود را متلاشی‌ کرده است.

Mineralogy, geochemistry and genesis of Gozaldarreh iron deposit, southeast Zanjan

Introduction;The Zanjan area hosts several iron deposits with small reserves which are currently active. This extended abstract describes the geology, mineralogy and geochemistry of the Gozaldarreh iron deposit located 44 km south of Zanjan. To further clarify the origin of Gozaldarreh mineralization, the associated Gozaldarreh granitoid intrusion and skarn were also subjected to detail petrography and geochemical studies including the granitoid type and genesis.; ;Materials and Methods;During several field works, fiftyeight samples were collected from different rock types exposed in the area including granitoid intrusion, skarn unit and the iron ore body. Thirtyfive thin, thinpolished and polished sections were prepared and studied in order to study the mineralogy, texture and paragenetic sequences. Based on the petrography and microscopy results, seen granitoid samples and eight ore samples were selected for chemical analysis. The major oxides were analysed by xray fluorescence (XRF) at the Geological Survey of Iran and the FeO was measured using wet chemical methods (titration). Trace elements and rare earth elements were measured by inductively coupled plasma mass spectrometry (ICPMS) at the West Lab in Australia.; ;Results;The intrusion of the Gozaldarreh granitoid into the carbonaceous rocks of the Soltaniyeh and Barout Formations generated a contact methamorphism with a skarn developed and ironoxide mineralization in the Gozaldarreh area. The Gozaldarreh granitoid is an Itype granite to granodiorite and quartzmonzonite. The geochemistry of the Gozaldarreh granitoid suggests that this intrusion belongs to highK calcalkaline and shoshonite series of the volcanic arc of an active continental margin. The serisitic, argillic, silicacarbonate and chloritic alterations are the major alterations affected by the Gozaldarreh granitoid.;The garnet, clinopyroxene and wollastonite are the major minerals generated in the prograde skarn phase in the iron oxide mineralization area. The major ironoxide mineralization stage has happened during the retrograde skarn phase along with epidote, tremoliteactinolite, chlorite, serpentine, talc, calcite and quartz. The ironoxide mineralization is generally in the form of high grade irregular lenses and veins of magnetite with minor hematite, pyrite and chalcopyrite. A small volume of magnetite has also been deposited during the prograde skarn phase.;The evidences show that the Gozaldarreh ore mineralization took place in three stages: (1) intrusion of the Gozaldarreh granitoid and contact methamorphism of the carbonate host rocks and generating a marble with granoblastic texture and CaMg silicates. The paragenetic sequence at this stage is garnetwollastonite calcite for carbonate rocks and garnetclinopyroxenecalcite for dolomitic rocks, (2) metasomatism and replacement phase which created CaMg silicates and minor magnetite as part of a prograde skarn phase, (3) the Gozaldarreh granitoid cooling stage and generation of the hydrothermalmagmatic system. This retrograde skarn phase has generated the main magnetite ore along with epidote, chlorite, tremoliteactinolite, serpentine, talc, calcite and quartz. The poor Casilicates, Feoxides, Fesulfides and carbonates were also generated as final stages of this retrograde phase. The later reactions and weathering affected these primary mineral assemblages and created the secondary minerals such as hematite, goethite, limonite, malachite and azurite.; ;Discussion;As a result of the intrusion of the Gozaldarreh granitoid into the carbonates of Soltanieh (PЄЄs) and Barout Formations (Єb), a skarn unit has developed at the contact metamorphic zone. The petrography of the Gozaldarreh granitoid shows a granular to microgranular texture with alkali feldspar, plagioclase, quartz and biotite as major rock forming minerals and amphibole, zircon and sphene as accessory minerals. Epidot, calcite and chlorite are also present as secondary minerals. The sericitic, argilic, silicacarbonate and chlorite assembleges are presenting the major alterations of the Gozaldarreh granitoid. The analyses of the granitoid samples classify the intrusion as an Itype granite to granodiorite and quartzmonzonite. The YNb and (Nb+Y)Rb plots (Pearce et al., 1984) suggest that the Gozaldarreh granitoid is part of the volcanic arc granitic intrusions. The ThCo plot (Hastie et al., 2007) is placing Gozaldarreh granitoid in the highK calcalkaline and Shoshonite series.;The comprehensive field work shows that the iron mineralization in the Gozaldarreh area is spatially associated with the granitoid skarn zone. The exoskarn is well developed in the region and is the major host for Femineralization. The endoskarn which is mainly exposed at the vicinity of the granitoid, is less developed and consists of clinopyroxene, epidote, chlorite, calcite and garnet. The clinopyroxene and garnet are recognized as prograde and epidote, chlorite and calcite are retrograde minerals. The exoskarn mainly consists of retrograde minerals such as epidote, chlorite, tremoliteactinolite, serpentine, talc, calcite, chrysotile and quartz. These retrograde minerals are mainly replaced the residue of prograde minerals such as clinopyroxene, garnet and wollastonite. The other major skarnrelated phenomena in the area are the carbonate rocks recrystalization and pyritechalcopyriteironoxide mineralization.;The Gozaldarreh iron ore exhibits different forms including massive, veintype and disseminated ironoxide mineralization. The ore bodies are mainly located in the exoskarn. Magnetite is the most abundant ore mineral followed by hematite, pyrite, chalcopyrite, limonite, malachite and azurite as minor minerals. The major gangue minerals are calcite, quartz, epidote, serpentine and chlorite.;The magnetite chemistry plot in the Ni/(Cr+Mn) vs Ti+V and Ca+Al+Mn vs. Ti+V diagrams (Dupuis and Beaudoin, 2011) showing the skarn origin for the Gozalarreh deposit. The TiO2V2O5 diagram plot (Hou et al., 2011) for these samples also points to the skarn and hydrothermal origin.; ;References;Dupuis, C. and Beaudoin, G., 2011. Discriminant diagrams for iron oxide trace element fingerprinting of mineral deposit types. Mineralium Deposita, 46(4): 319–335.;Hastie, A.R., Kerr, A.C., Pearce, J.A. and Mitchell, S.F., 2007. Classification of altered volcanic island arc rocks using immobile trace elements: development of the ThCo discrimination diagram. Journal of Petrology, 48(12): 2341–2357.;Hou, T., Zhang, Z.C. and Kusky, T., 2011. Gushan magnetiteapatite deposit in the Ningwu basin, Lower Yangtze River Valley, SE China: hydrothermal or Kirunatype? Ore Geology Reviews, 43(1): 333–346.;Pearce, J.A., Harris, N.B.W. and Tindle, A.G., 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology, 25(4): 956–983.;