یکی از مناطق مستعد جهت پیجویی و اکتشاف اندیسهای فلزی از جمله آهن، در شمال شرق اصفهان واقع شده است. برونزد وسیعی از توده گرانیتوئیدی در محدوده مورد مطالعه و اطراف آن (گرانیتهای کرکس) وجود دارد که بیشتر واحدهای چینه‌شناسی قبل از الیگومیوسن منطقه را قطع کرده است. لیتولوژی منطقه شامل ماسه‌سنگ های ریز تا درشت‌دانه، دولومیتهای تودهای، آهک‌های کرم رنگ فسیلدار و توده‌های نفوذی منطقه به ترتیب فراوانی شامل کوارتزمونزونیت، کوارتزمونزودیوریت، گرانودیوریت و گرانیت میباشد. گرانیتهای منطقه در زون فرورانش و قبل از تصادم تشکیل و از نوع (VAG) هستند و از نظر ماگمایی جزء سری کالکو آلکالن (CAG) میباشند که دمهای داسیتی فراوانی در آن نفوذ کرده است. سنگ‌های آتشفشانی منطقه شامل پورفیروداسیت، آندزیت و کوارتزلاتیت به سن میوسن تا پلیوسن است. منشاء آهن، ماگمای گرانیتی نیمه عمیق با موتور محرکه عظیم گرمایی که ضمن گسیل دادن سیالات حاوی عناصر به افق‌های بالا و حمله به سنگ‌های آهک و دولومیتها اسکارنزایی با ترکیب کانیشناسی آندرادیت، گرسولر، هسونیت، اپیدوت، لیپیدوکرولیت، زوئیزیت و هدنبرژیت شده است. علاوه بر این، سیالات گرمابی سبب تشکیل کانیهای دگرسانی کائولینیت، مونت موریلونیت کلریت و سرسیت گردیده و پدیده سوپر ژن در غنی شدگی کانسار آهن در سطح نقش اساسی داشته است که شاهد اصلی آن کلاهک آهنی (گوسان) است. معدن آهن کامو که بر روی آن واقع است از کانیهای آهن مانند مگنتیت، هماتیت، لیمونیت، گوتیت و پاراژنزهای آن تشکیل شده است. مگنتیت و کانیهای سولفیدی مانند پیریت و کالکو پیریت و با منشاء ماگمایی، نسل اول کانیزایی اسکارنی و دگرسانیهای حاصل از سیالات ماگمایی نسل دوم و پدیده سوپرژن نسل سوم کانیسازی (هماتیت، لیمونیت، کوولیت، گوتیت) منطقه کامو را تشکیل دادهاند. بنابراین ژنز اصلی کانسار آهن کامو به صورت اپی ژنتیک هیدروترمالی میباشد.
The Choghart iron oxide-apatite (IOA) deposit is located 124 km southeast of Yazd, in the Bafq district within the Central Iranian microcontinent.The Choghart deposit is hosted by the rhyolitic rocks of the Early Cambrian volcano-sedimentary sequence (the Esfordi formation).Both host rocks and the orebodies are crosscut by diabase dykes.Tectonically, the Choghart rhyolites represent the continental margin setting and the Choghart diabase dykes formed in the back-arc basin environment, respectively, indicating that the evolution of the Bafq district is associated with subduction of Palaeotethys oceanic crust beneath the Central Iranian microcontinent followed by formation of continental arc related granitoids and rhyolites and then formation of backarc basin diabase dykes.Similar to the other subduction-related rhyolites, the Choghart rhyolite is enriched in Th and LREE compared to Ta, Nb, and HREE.The main host minerals of Th and REE in the Th-REE mineralization zone are thorite and sphene.Albitization is the most important alteration aspect related to Th-REE mineralization (mainly Th, La, Ce, Nd, and Y).In addition to albite, Th-REE mineralization is associated with actinolite, augite, diopside, minor microcline and orthoclase, plus magnetite, calcite, pyrite, rutile, and minor amounts of chalcopyrite.The negative Eu anomaly in Th mineralization zone, as well as the paragenetic occurrence of magnetite, pyrite and chalcopyrite with thorite suggest that Th-REE mineralization formed in relatively reduced condition.The presence of paragenetic calcite accompanied by thorite and sphene in the Th-REE mineralization zone indicates that Th and REE were likely transported by the carbonate complexes in the mineralizing fluids.The similarity between the chondrite-normalized REE patterns of the host rhyolite and the Th-REE mineralization zone suggests that post-magmatic driven fluids of continental margin rhyolitic magma played an important role in Th-REE mineralization.
Abstract Phosphate deposits are found in the Khormuj anticline at the end of the Folded Zagros Zone of Iran and are enriched in REE and trace metals. Field survey, petrography, X-ray diffraction and whole-rock geochemistry were used to determine the petrogenesis of these phosphate deposits and evaluate the mechanisms of trace metal enrichment. Khormuj anticline phosphate layers are hosted by carbonate rocks of the Pabdeh Formation (Lower Paleocene-Oligocene). The phosphatic layers are composed of phosphorus grainstone–packstone with microfossils and contains green glauconite. Whole-rock compositions of phosphates indicate a minimal detrital component and enrichment in U and HREE. These elements are not enriched in the limestone units that overlie and underlie the phosphate layers. Overall, the textures and trace element compositions of phosphate layers are interpreted to represent accumulation on a basin margin carbonate ramp, in the reduced and suboxic-to-anoxic zone, with low detrital input but occasional high-energy erosional events. Upwelling process played a fundamental role in the deposition of the sandy glauconite-bearing phosphate layers. Phosphate mineralization has syngenetic, diagenetic, and epigenetic components. Positive correlations between P 2 O 5 and REE, U and other trace elements suggest that cation substitution into carbonate fluorapatite and not ion adsorption is the dominant mechanism for metal enrichment in these phosphates. REE patterns in these phosphate layers show strong negative Ce anomalies, positive Eu and Y anomalies and high La/Yb ratios (> 10). Yttrium versus (La/Nd) N ratios are in the seawater range and have been affected by diagenesis process. These elevated ratios suggest that the phosphates are relatively enriched in both the LREE and HREE. This enrichment is related to their marine origin, and weathering had no effect on the phosphate horizons. This research show that marine phosphates have high potential to preferentially fractionate the HREE and U and could represent a future source of these metals.
The Bondar Hanza porphyry Cu deposit, hosted by a granitoid stock, is located 120 km south of Kerman city in the elongated NW–SE trending Urumieh‐Dokhtar magmatic arc (UDMA), Iran. The granitoid stock is a multiphase intrusive body, 2 km 2 in surface area, which comprises microdiorite–microquartz diorite and granite–granodiorite. Petrological and geochemical analyses show that granitoids are peraluminous, magnesian, calcic to alkali‐calcic, and non‐adakitic intrusions characterized by negative Eu* anomalies. Thermobarometric and oxygen fugacity calculations indicate that magma emplacement occurred at 719–784°C, <100 MPa, and at a log f O 2 of NNO +1.6 to +3.2. Sulphur isotopic composition of sulphide minerals (δ 34 S = 5.0–6.8 ‰) are similar to other porphyry Cu deposits worldwide. Molybdenite separates yield Re–Os ages of 28.22–28.03 Ma, indicating that the Cu mineralization and associated magmatism occurred during the Oligocene. The Bondar Hanza is one of the several granitoids from small porphyry Cu deposits in the UDMA that is related to island arc sub‐productive granitoids. It seems that the largest ore‐hosting porphyry systems within the UDMA are generally restricted to Miocene intrusions with adakitic affinity (e.g., Sarcheshmeh granitoids) and that the temporally discrete non‐adakitic magmatic systems are sub‐productive to barren. These data are interpreted to show that magmatism in the Bondar Hanza region was likely associated with partial melting of juvenile lower crust induced by north‐eastward subduction of the Neo‐Tethys oceanic lithosphere.
Abstract The Kangan anticline in the Folded Zagros Zone contains phosphate deposits enriched in trace metals. Field observations, petrography, X-Ray Diffraction, Scanning Electron Microscopy, and whole-rock geochemistry are used to determine the petrogenesis of this phosphate deposit, evaluate the mechanisms of deposition, and assess the implications for trace metal enrichment. Phosphatic layers are grainstone–packstone with microfossils and contain green glauconite. Carbonate rocks of the Early–Middle Eocene Pabdeh Formation host the phosphate units. Glauconite, calcite, and fluorapatite are the primary minerals of the marine sedimentary phosphate deposit in the Kangan anticline. Whole-rock compositions of phosphate layers indicate negligible clastic components and show enrichment in U and HREE. Limestone and pelagic limestone units in the Pabdeh Formation do not display enrichment of these elements. Carbonate fluorapatite is the host mineral for REEs and uranium. Cation substitution into carbonate fluorapatite is considered to be the main mechanism of trace element enrichment due to positive correlations between P2O5 and trace metals; ion adsorption did not play a crucial role in the metal enrichment in these phosphates. Strong negative Ce anomalies, slight positive Eu anomalies and low ΣLREE/ΣHREE ratios of phosphate layers indicate enrichment of the HREE relative to their marine origin. The depositional environment of the phosphate units is interpreted as a basin margin carbonate ramp in the reduced and suboxic-to-anoxic zone that had low detrital input but occasionally high-energy erosional events. Ocean upwelling had an essential role in depositing the sandy glauconite-bearing phosphate layers.
Copper mineralization in Nahand-Ivand area, NW Iran, appears as disseminated copper sulfides along a redox boundary between gray sandstone and microconglomerate and hematitic sandstones, siltstones and shaly marl. Geochemical analyses of the Nahand-Ivand deposits show as much 35 wt.% Cu and 730 ppm Ag in the gray sandstone. Electron probe micro-analysis (EPMA) was used to determine the mineralogical composition and distribution patterns of copper and silver-bearing phases mainly in pyrite and Cu-bearing sulfides. The EPMA data were essential for evaluating the distribution and partitioning of potential economically-valuable components between co-existing minerals. Furthermore, they contribute to a better understanding of the genesis of the NahandIvand copper deposits and will guide further exploration in the region. The EPMA results from different types of pyrite reveal Cu contents as high as 0.32 wt.%, 1.10 wt.%, and 2.88 wt.% for framboidal pyrite (PyI), overgrowths on framboidal pyrite (PyII), and diagenetic pyrite (PyIII), respectively. This successive increase of copper from PyI to PyIII is attributed to a continuous supply of copper that replaces framboidal pyrite in turn by the more copper-rich digenetic pyrite. Because of hydrothermal overprinting, pyrite has been replaced by djurleite, roxbyite, and other nonstoichiometric Cu–S minerals that include covellite. The EPMA study indicates that covellite contains significant concentrations of Ag (locally > 1 wt.%). In contrast. only trace amounts of silver have been detected in pyrite and other copper sulfides, indicating that covellite is the major Ag-carrier in the ore. According to textural relationships, such open space filling, impregnation, and replacement textures, and the EPMA results, later stage copper-bearing fluids were responsible for the silver enrichment in the Nahand-Ivand deposits.
The Ti- Fe mineralization in the Bafq 15 anomaly is located in 35 Km NW of Bafq city, and is part of Poshte Badam Block in the central Iran. The syngenetic Fe- Ti mineralization was hosted by gabbro and pyroxenite intrusions. Mineralization is including magnetite, titanomagnetite, ilmenite and minor pyrite. Based on the whole rock chemistry, FeOt, TiO2, CaO, Ni Cr and V show positive correlation with MgO, whereas Al2O3, Na2O+K2O and SiO2 show negative correlation. These correlations are in agreement with crystallization of clinopyroxene, amphibole, plagioclase and oxide minerals in intrusion. The positive correlation of V, Cr and Ni with Fe indicates concentration of these elements in Fe minerals. The chemical composition of ore minerals mostly plots in the solid solution of magnetite- ulvospinel (titanomagnetite) and magnetite- ilmenite fields. In QFM+1> conditions, the high Fe-Ti contents along high H2O content (>2 Wt. %) of parental magma are the most prominent factors controlling Fe- Ti mineralization. According to the proposed model for mineralization, as new pulse of magma enters chamber, the high H2O content sufficiently depressed the crystallization temperature of silicates comparing oxides, so that caused the early crystallization of Fe-Ti minerals. Increasing of H2O content and magmatic volatiles during magma fractionation, consequently may induce immiscibility and separation of oxide from residual melt in late magmatic stage whereas this dense oxide melt flow through pre-crystalized silicates and solidified as intercumulus phase.
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