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1.
对出露东秦岭金堆城大型斑岩钼矿床北部的老牛山黑云二长花岗岩和金堆城含矿斑岩利用单颗粒锆石激光探针LA-ICP-MS定年技术进行了UPb精确定年和岩石地球化学对比研究。LA-ICPMS锆石UPb测年得到老牛山黑云二长花岗岩和金堆城含矿斑岩锆石加权平均年龄值分别为146.35±0.55Ma和140.95±0.45 Ma,与前人多次获得的金堆城钼矿床的辉钼矿Re-Os模式年龄141±4～127±7 Ma下限值一致,显示成矿与成岩同时或略滞后于岩体,成岩成矿发生于侏罗纪-白垩纪的同一成岩成矿系统中,与发生于1  相似文献   

2.
East Qinling is the largest porphyry molybdenum province in the world; these Mo deposits have been well documented. In West Qinling, however, few Mo deposits have been discovered although granitic rocks are widespread. Recently, the Wenquan porphyry Mo deposit has been discovered in Gansu province, which provides an insight into Mo mineralization in West Qinling. In this paper we report Pb isotope compositions for K-feldspar and sulfides, S isotope ratios for sulfides, the results obtained from petrochemical study and from in situ LA-ICP-MS zircon U-Pb dating and Hf isotopes. The granitoids are enriched in LILE and LREE, with REE and trace element patterns similar to continental crust, suggesting a crustal origin. The Mg# (40.05 to 56.34) and Cr and Ni contents are high, indicating a source of refractory mafic lower crust. The εHf(t) values of zircon grains from porphyritic monzogranite range from ? 2.9 to 0.6, and from granitic porphyry vary from ? 3.3 to 1.9. The zircons have TDM2 of 1014 to 1196 Ma for the porphyritic monzogranite and 954 to 1224 Ma for the granitic porphyry, implying that these granitoids were likely derived from partial melting of a Late Mesoproterozoic juvenile lower crust. The Pb isotope compositions of the granitoids are similar to granites in South China, showing that the magma was sourced from the middle–lower crust in the southern Qinling tectonic unit. The Pb isotopic contrast between the Mo-bearing granitoids and ores shows that the Pb in the ore-forming solution was derived from fractionation of a Triassic magmatic system. δ34S values of sulfides are between 5.02 and 5.66‰, similar to those associated with magmatic-hydrothermal systems. LA-ICP-MS zircon U-Pb dating yields crystallization ages of 216.2 ± 1.7 and 217.2 ± 2.0 Ma for the granitoids, consistent with a previously reported molybdenite Re-Os isochron age of 214.4 ± 7.1 Ma. This suggests that the Mo mineralization is related to the late Triassic magmatism in the West Qinling orogenic belt. In view of these geochemical results and known regional geology, we propose that both granitoid emplacement and Mo mineralization in the Wenquan deposit resulted from the Triassic collision between the South Qinling and the South China Block, along the Mianlue suture. Since Triassic granitoid plutons commonly occur along the Qinling orogenic belt, the Triassic Wenquan Mo-bearing granitoids highlight the importance of the Triassic tectono-magmatic belt for Mo exploration. In order to apply this metallogenic model to the whole Qinling orogen, further study is needed to compare the Wenquan deposit with other deposits.  相似文献   

3.
The Mesozoic porphyry assemblage in the Jinduicheng area is a special molybdenum area in China, the Mo deposits, including the Jinduicheng, Balipo, Shijiawan, Huanglongpu, are distributed. The emplacement age and geochemical features of the granites in the Jinduicheng area can provide essential information for the exploration and development of the porphyry molybdenum deposit. In this study, we report LA–ICP–MS zircon U–Pb age and zircon Hf isotopic compositions of granite porphyries from the Jinduicheng area, and provide insights on the petrogensis and source characteristics of the granites. The results show that the zircon U–Pb ages of the Jinduicheng granite porphyry (143±1 Ma) and the Balipo granite (154±1 Ma), agree well with the Re–Os ages of molybdenite in the Jinduicheng molybdenum polymetallic deposit (139±3 Ma) and the Balipo molybdenum polymetallic deposit (156±2 Ma), indicating that the emplacement of granite porphyries occurred between Late Jurassic and Early Cretaceous. Zircons granite from the Jinduicheng area give the εHf(t) values mainly ranging from ?10 to ?16, and ?20 to ?24, respectively, corresponding to two–stage model ages (tDM2: mainly focused on 1.86–2.0 Ga, and 2.2–2.6 Ga, respectively) of zircons of the granite from the Jinduicheng values. The ore–forming materials are mainly derived from crust, with minor mantle substances. Zircons of the granite from the Balipo area give εHf(t) values ranging from ?18 to ?20, ?28 to ?38, and ?42 to ?44, respectively, corresponding to two–stage model ages (tDM2: mainly focused on 1.88–3.0 Ga, and 3.2–3.90 Ga, respectively). the εHf(t) values of the Jinduicheng porphyry more than that of the Balipo porphyry, and two–stage model ages (tDM2) less than that of the Balipo porphyry, shows that he source of the porphyries originated from ancient lower crustal materials in the Jinduicheng area, and mixed younger components, more younger components contributed for the source of the Jinduicheng porphyry.  相似文献   

4.
Given that the Duobuza deposit was the first porphyry Cu–Au deposit discovered in central Tibet, the mineralization and mineralized porphyry in this area have been the focus of intensive research, yet the overall porphyry sequence associated with the deposit remains poorly understood. New geological mapping, logging, and sampling of an early granodiorite porphyry, an inter-mineralization porphyry, and a late-mineralization diorite porphyry were complemented by LA–ICP–MS zircon dating, whole-rock geochemical and Sr–Nd isotopic analyses, and in situ Hf isotopic analyses for both inter- and late-mineralization porphyry intrusions. All of the porphyry intrusions are high-K and calc-alkaline, and were emplaced at ca. 120 Ma. The geochemistry of these intrusions is indicative of arc magmatism, as all three porphyry phases are enriched in light rare earth elements and large ion lithophile elements, and depleted in heavy rare earth elements and high field strength elements. These similar characteristics of the intrusions, when combined with the relatively high (87Sr/86Sr)i, negative εNd(t), and positive εHf(t) values, suggest that the magmas that formed the porphyries were derived from a common source region and shared a single magma chamber. The magmas were generated by the mixing of upwelling metasomatized mantle-wedge-derived mafic magmas and magmas generated by partial melting of amphibolite within the lower crust.The inter-mineralization porphyry has the lowest εNd(t) and highest (87Sr/86Sr)i values, suggesting that a large amount of lower-crust-derived material was incorporated into the melt and that metals such as Cu and Au from the enriched lower crust were scavenged by the parental magma. The relative mafic late-mineralization diorite porphyry phase was formed by the residual magma in the magma chamber mixing with upwelling mafic melt derived from metasomatized mantle. The magmatic–hydrothermal evolution of the magma in the chamber released ore-forming fluid that was transported mainly by the inter-mineralization porphyry phase during the mineralization stage, which ultimately formed the Duobuza porphyry Cu–Au deposit.These porphyritic intrusions of the Duobuza deposit have high Mg# and low (La/Yb)N values, and show some high LILE/HFSE ratios, indicating the magma source was enriched by interaction with slab-derived fluids. Combined with age constraints on the regional tectonic evolution, these dating and geochemical results suggest that the Duobuza porphyry Cu–Au deposit formed in a subduction setting during the final stages of the northward subduction of the Neo-Tethyan Ocean.  相似文献   

5.
The Chalukou porphyry Mo deposit, located in the Great Hinggan Range, is the largest Mo deposit in northeast China, although the age and genesis of the associated magmatic intrusions remain debated.Here we report zircon U-Pb ages and trace elements, whole rock geochemistry and Sre Nd isotope data with a view to understand the relationship between the magmatism and molybdenum mineralization.Zircon U-Pb analysis yield an age of 475 Ma for rhyolite in the older strata, 168 Ma for the premineralization monzogranite, and 154 Ma for the syn-mineralization granite porphyry. The granite porphyry and quartz porphyry are considered as the ore-forming intrusions. These rocks are peraluminous, alkali-calcic, and belong to high-K to shoshonitic series with a strong depletion of Eu. They also display characteristics of I-type granites. The rocks exhibit wide variations of(87 Sr/86 Sr)iin the range of 0.705426 -0.707363, and ε_(Nd)(t) of -3.7 to 0.93. Zircon REE distribution patterns show characteristics between crust and the mantle, implying magma genesis through crust-mantle interaction. The Fe_2O_3/FeO values(average 1) for the whole rock and EuN/Eu*Nvalues(average 0.45), Ce~(4+)/Ce~(3+) values(average 301)for zircon grains from the granite porphyry are higher than those from other lithologies. These features suggest that the ore-forming intrusions(syn-mineralization porphyry) had higher oxygen fugacity conditions than those of the pre-mineralization and post-mineralization rocks. The Chalukou Mo deposit formed in relation to the southward subduction of the Mongol-Okhotsk Ocean. Our study suggests that the subduction-related setting, crust-mantle interaction, and the large-scale magmatic intrusion were favorable factors to generate the super-large Mo deposits in this area.  相似文献   

6.
《China Geology》2018,1(1):36-48
The Truong Son Fold Belt, located at the northeastern margin of the Indochina Block, is considered to be tectonically linked to the subduction of the Paleotethys Ocean and subsequent collision. Sepon is one of the most important super large deposits of the Truong Son Fold Belt. Our LA-ICP-MS zircon U-Pb dating results show that granodiorite porphyry samples from the Sepon deposit have ages of 302.1±2.9 Ma, which is a crucial phase for magmatic-tectonical activities from the Late Carboniferous to Early Permian and has avital influence on the mineralization of copper and gold. Zircon from granodiorite porphyry yields εHf (t) values of 4.32 to 9.64, and TDM2 has an average age of 914 Ma, suggesting that the source of the granodiorite porphyry in the region were mainly mantle components but underwent mixing and contamination of crust materials. The Ce4+/Ce3+ value of zircon in the granodiorite porphyry varys greatly from 2.4 to 1438.29, which shows magma mixing might occur. Considering the characteristics of trace elements in the zircon and the whole rock geochemical characteristics of intrusion rocks as well as the characteristics of regional volcanic-sedimentary association, it is indicated that the tectonic setting may be the continental arc environment. The Sepon Au-Cu deposit is derived from emplacement of calc-alkaline intermediate-acid magma with coming from deep sources in the subduction process of the Paleotethys Ocean, forming porphyry Mo-Cu, skarn Cu-Au mineralization and a hydrothermal sedimentary-hosted Au mineralization in the wall rocks.  相似文献   

7.
The geodynamic setting of Mesozoic magmatic rocks and associated mineralization in eastern Tianshan, Northwest China, are attracting increasing attention. The newly discovered giant Donggebi molybdenum deposit (0.508 Mt at 0.115% Mo) is located in the central part of eastern Tianshan, Xinjiang. The molybdenum mineralization was genetically associated with the Donggebi stock, comprised of porphyritic granite and granite porphyry. Secondary ion mass spectrometry (SIMS) zircon U–Pb dating constrains that the porphyritic granite and granite porphyry emplacement occurred at 233.8 ± 2.5 Ma and 231.7 ± 2.6 Ma, respectively. The Re–Os model ages of six molybdenite samples range from 235.2 to 237.0 Ma, with a weighted mean age of 236.1 ± 1.4 Ma, which is roughly consistent within errors with the zircon U–Pb ages, suggesting a Middle Triassic magmatic–mineralization event at Donggebi. Geochemically, the Donggebi granitoids are characterized by high SiO2 and K2O contents, with low MgO contents, belonging to high-K calc-alkaline granites. These rocks show pronounced enrichment in K, Rb, U, and Pb, and depletion in Sr, Ba, P, and Ti, with negative Eu anomalies (Eu/Eu* = 0.20–0.38). In situ Hf isotopic analyses of zircon from the porphyritic granite and granite porphyry yielded εHf(t) values ranging from +6.6 to +10.5, and from +5.5 to +10.1, respectively. The geochemical and isotopic data imply that the primary magmas of the Donggebi granitoids could have originated by partial melting of a juvenile lower crust that involved some mantle components. Combined with the regional geological history, geochemistry of the Donggebi granitoids, and new isotopic age data, we thus propose that the Donggebi molybdenum deposit was formed in the Middle Triassic, and occurred in an intracontinental extension setting in eastern Tianshan.  相似文献   

8.
The Tiegelongnan Cu (Au) deposit is the largest copper deposit newly discovered in the Bangong–Nujiang metallogenic belt. The deposit has a clear alteration zoning consisting of, from core to margin, potassic to propylitic, superimposed by phyllic and advanced argillic alteration. The shallow part of the deposit consists of a high sulphidation‐state overprint, mainly comprising disseminated pyrite and Cu–S minerals such as bornite, covellite, digenite, and enargite. At depth porphyry‐type mineralization mainly comprises disseminated chalcopyrite, bornite, pyrite, and a minor vein molybdenite. Mineralization is disseminated and associated with veins contained within the porphyry intrusions and their surrounding rocks. The zircon U–Pb ages of the mineralized diorite porphyry and granodiorite porphyry are 123.1 ± 1.7 Ma (2σ) and 121.5 ± 1.5 Ma (2σ), respectively. The molybdenite Re–Os age is 121.2 ± 1.2 Ma, suggesting that mineralization was closely associated with magmatism. Andesite lava (zircon U–Pb age of 111.7 ± 1.6 Ma, 2σ) overlies the ore‐bodies and is the product of post‐mineralization volcanic activity that played a critical role in preserving the ore‐bodies. Values of ?4.6 ‰ to + 0.8 ‰ δ34S for the metal sulfides (mean ? 1.55 ‰) suggest that S mainly has a deep magmatic source. The H and O isotopic composition is (δD = ?87 ‰ to ?64 ‰; δ18OH2O = 5.5 ‰ to 9.0 ‰), indicating that the ore‐forming fluids are mostly magmatic‐hydrothermal, possibly mixed with a small amount of meteoric water. The zircon εHf(t) of the diorite porphyry is 3.7 to 8.3, and the granodiorite porphyry is 1.8 to 7.5. Molybdenite has a high Re from 382.2 × 10?6 to 1600 × 10?6. Re and Hf isotope composition show that Tiegelongnan has some mantle source, maybe the juvenile lower crust from crust–mantle mixed source. Metallogenesis of the Tiegelongnan giant porphyry system was associated with intermediate to acidic magma in the Early Cretaceous (~120 Ma). The magma provenance of the Tiegelongnan deposit has some mantle‐derived composition, possibly mixed with the crust‐derived materials.  相似文献   

9.
铜厂沟大型斑岩型Mo-Cu多金属矿床位于扬子西缘义敦岛弧带南端,钼矿化与花岗闪长斑岩紧密相关。花岗闪长斑岩LA-ICP-MS锆石U-Pb年龄为84.57±0.29Ma(MSWD=0.73),侵位于晚白垩世。岩石的Si O2为63.03%~69.60%,Na2O+K2O为6.97%~9.11%,具高钾钙碱性和准铝质-弱过铝质(A/CNK=0.88~1.05)特征。岩石富集轻稀土元素和大离子亲石元素(Rb、Ba、Pb等),相对亏损重稀土元素和高场强元素(Ti、Nb、P等),并且具有较高的Sr/Y和La/Yb比值,及较低的Y、Yb及Mg O含量。这些地球化学特征表明铜厂沟花岗闪长斑岩具有埃达克质岩石的特征,可能起源于加厚下地壳岩石的部分重熔。地球化学投图显示,铜厂沟岩体呈现出晚碰撞-碰撞后花岗岩特征,指示着岩体可能形成于陆内碰撞造山后由挤压转换为伸展构造环境;岩浆上侵过程中含矿热液沿构造发育部位运移,在酸性岩体内形成细脉浸染状钼(铜钨)矿化,在构造破碎带、层间滑动带和玄武岩与碳酸盐岩接触带交代形成矽卡岩型Cu、Pb、Zn多金属矿体和热液脉型Pb、Zn、Ag多金属矿体,构成钼(铜钨)→铜钼→铁铜金→铅锌的成矿元素分带和斑岩成矿系统。  相似文献   

10.
马厂箐钼铜金多金属矿床是滇西地区金沙江-哀牢山构造带内与新生代富碱斑岩有关的典型矿床之一。根据赋矿斑状花岗岩中锆石的阴极发光图像、LA-ICP-MS微量元素分析和U-Pb定年以及辉钼矿Re-Os法测年研究等,结合前人研究成果,应用透岩浆流体成矿理论,进一步讨论了马厂箐矿床的成因机制。研究表明：该矿床的多金属成矿与赋矿斑状花岗岩的成岩基本同时,其成岩成矿过程统一受制于与该区大规模活动的新生代富碱岩浆和深部地壳重熔的花岗质岩浆同步运移的成矿流体作用。这种成矿流体是包含于岩浆并与其互不混溶的含矿地幔流体。但在上侵运移过程中,伴随岩浆的成岩作用,流体与岩浆发生不同程度分离,表现为：产于富碱斑状花岗岩体内,形成正岩浆成矿的斑岩型钼矿;产于岩体与围岩接触带,形成接触交代成矿的矽卡岩型铜（钼）矿;产于地层围岩中则形成构造破碎蚀变岩型金矿。在这一成岩成矿过程中,地幔流体可以运载和沿途活化成矿物质至适宜容矿部位集中,并随其对地壳岩石的交代蚀变以及深度和环境变化引起的物理化学条件变化,其流体属性由熔浆流体→超临界流体→热液流体转化,促使壳幔物质相互作用而叠加成矿,导致在不同部位形成不同矿种和不同类型的系列成矿效应。  相似文献   

11.
泉子沟斑岩钼矿床位于内蒙古丰镇市,地处华北克拉通北缘内蒙古台隆凉城断隆内。矿区出露一套燕山期花岗质杂岩体——红娘山杂岩体,主要由中粗粒花岗岩、似斑状花岗岩和石英斑岩组成,钼矿体主要赋存于似斑状花岗岩中。文章在详细的野外地质调查基础上,对泉子沟矿床的成岩成矿时代进行了详细研究,并探讨了地质意义。5件辉钼矿样品的Re-Os模式年龄介于(158.8±2.2)Ma~(161.5±2.2)Ma之间,其加权平均值为(159.8±1.0)Ma(MSWD=0.92),等时线年龄为(161.7±3.1)Ma(MSWD=1.40)。红娘山杂岩体LA-ICP-MS锆石U-Pb年龄分别为:中粗粒花岗岩结晶年龄为(173±1)Ma(MSWD=0.88),似斑状花岗岩侵位年龄为(162±1)Ma(MSWD=0.40),石英斑岩结晶年龄为(160±2)Ma(MSWD=1.90)。辉钼矿Re-Os和锆石U-Pb定年结果表明,泉子沟钼矿床形成于晚侏罗世早期,成矿与似斑状花岗岩关系密切。泉子沟钼矿床的辉钼矿w(Re)介于16.49×10~(-6)~32.87×10~(-6),暗示成矿物质主要来自下地壳。  相似文献   

12.
霍吉河钼矿是小兴安岭地区于近年发现的大型斑岩型钼矿床。本文在对矿化特征分析的基础上,采用LA-ICP-MS锆石U-Pb技术对霍吉河成矿花岗质杂岩测年,获得中细粒花岗闪长岩和斑状花岗岩成岩年龄分别为181.0±1.9 Ma(n=15, MSWD=4.7) 和193.6±1.4 Ma(n=25, MSWD=2.3)。通过辉钼矿Re-Os同位素分析,获得等值线年龄176.3±5.1 Ma(n=5, MSWD=1.3)和加权平均年龄为181.2±1.8 Ma (n=5, MSWD=1.3)。两种方法获得的年龄大致相近,表明成岩与成矿于同一系统形成,成岩大致始于193.6±1.4 Ma,成矿于岩浆期后181.2±1.8 Ma。霍吉河钼矿成岩成矿年龄与乌奴格吐山铜钼矿、兰家沟钼矿和杨家杖子钼矿等矿床辉钼矿Re-Os同位素年龄相近,表明中国东北地区广泛存在早侏罗世岩浆成矿作用。微量元素和同位素显示,霍吉河花岗闪长岩和斑状花岗岩属A型花岗岩,形成于地壳挤压向拉伸转换的构造环境,成矿物质主要来自岩浆。  相似文献   

13.
The Miocene porphyry Cu–(Mo) deposits in the Gangdese orogenic belt in southern Tibet were formed in a post-subduction collisional setting. They are closely related to the Miocene adakite-like porphyries which were probably derived from a thickened basaltic lower crust. Furthermore, mantle components have been considered to have played a crucial role in formation of these porphyry deposits (Hou et al. Ore Geol Rev 36: 25–51, 2009; Miner Deposita doi:10.1007/s00126-012-0415-6, 2012). In this study, we present zircon Hf isotopes and molybdenite Re–Os ages on the newly discovered Gangjiang porphyry Cu–Mo deposit in southern Tibet to constrain the magma source of the intrusions and the timing of mineralization. The Gangjiang porphyry Cu–Mo deposit is located in the Nimu ore field in the central Gangdese porphyry deposits belt, southern Tibet. The copper and molybdenum mineralization occur mainly as disseminations and veins in the overlapped part of the potassic and phyllic alteration zones, and are predominantly hosted in the quartz monzonite stock and in contact with the rhyodacite porphyry stock. SIMS zircon U–Pb dating of the pre-mineral quartz monzonite stock and late intra-mineral rhyodacite porphyry yielded ages of 14.73?±?0.13 Ma (2σ) and 12.01?±?0.29 Ma (2σ), respectively. These results indicate that the magmatism could have lasted as long as about 2.7 Ma for the Gangjiang deposit. The newly obtained Re–Os model ages vary from 12.51?±?0.19 Ma (2σ) to 12.85?±?0.18 Ma (2σ) for four molybdenite samples. These Re–Os ages are roughly coincident with the rhyodacite porphyry U–Pb zircon age, and indicate a relatively short-lived episode of ore deposition (ca. 0.3 Ma). In situ Hf isotopic analyses on zircons by using LA-MC-ICP-MS indicate that the ε Hf(t) values of zircons from a quartz monzonite sample vary from +2.25 to +4.57 with an average of +3.33, while zircons from a rhyodacite porphyry sample vary from +5.53 to +7.81 with an average of +6.64. The Hf data indicate that mantle components could be partly involved in the deposit formation, and that mantle contributions might have increased over time from ca. 14.7 to 12.0 Ma. Combined with previous works, it is proposed that the Gangjiang deposit could have resulted from the convective thinning of the lithospheric root, and the input of upper mantle components into the magma could have played a key role in the formation of the porphyry deposits in the Miocene Gangdese porphyry copper belt in the Tibetan Orogen.  相似文献   

14.
Berzina AN  Berzina AP 《岩石学报》2008,24(12):2657-1668
The Aksug deposit, located in Altay-Sayan region of Russia, is one of the largest porphyry Cu-Mo deposits in Southern Siberia. The ore-bearing porphyries of the Aksug porphyry Cu-Mo system were formed in post-collisional environment. Geochemically they belong to calk-alkaline and high K-calk-alkaline series. Rocks are characterized by enrichment of LILE and depletion of HSFE and HREE, showing the importance of subduction-related components in magma generation. Large plutonic intrusions that host porphyry systems have been formed during collision. The origin of porphyritic rocks is dominantly the mantle with lower crustal contribution. The mainly economically important Cu-Mo mineralization is closely related to a porphyry series in time and space, being emplaced towards the end of magmatic activity. Though the emplacement of plutonic and ore-bearing porphyry complexes took place in different geodynamic environments, both complexes are characterized by certain similarity in geochemical composition, alkalinity, trace element content, Sr isotopic composition. This fact evidently indicates a common deep-seated magmatic source (at the lower crust-upper mantle level). Low initial 87 Sr/86 Sr, sulfur isotopic characteristics and presence of PGE-Co-Ni mineralization in associated pyrite-chalcopyrite ores suggest that mantle source of chalcophile elements was of high importance in porphyry Cu-Mo mineralization of the Aksug deposit.  相似文献   

15.
The newly discovered Zhunuo porphyry Cu-Mo-Au deposit is located in the western part of the Gangdese porphyry copper belt in southern Tibet, SW China. The granitoid plutons in the Zhunuo region are composed of quartz diorite porphyry, diorite porphyry, granodiorite porphyry, biotite monzogranite and quartz porphyry. The quartz diorite porphyry yielded zircon U-Pb ages of 51.9±0.7 Ma(Eocene) using LA-ICP-MS, whereas the diorite porphyry, granodiorite porphyry, biotite monzogranite and quartz porphyry yielded ages ranging from 16.2±0.2 to 14.0±0.2 Ma(Miocene). CuMo-Au mineralization is mainly hosted in the Miocene granodiorite porphyry. Samples from all granitoid plutons have geochemical compositions consistent with high-K calc-alkaline series magmatism. The samples display highly fractionated light rare-earth element(REE) distributions and heavy REE distributions with weakly negative Eu anomalies on chondrite-normalized REE patterns. The trace element distributions exhibit positive anomalies for large-ion lithophile elements(Rb, K, U, Th and Pb) and negative anomalies for high-field-strength elements(Nb and Ti) relative to primitive mantlenormalized values. The Eocene quartz diorite porphyry yielded εNd(t) values ranging from-3.6 to-5.2,(~(87)Sr/~(86)Sr)i values in the range 0.7046–0.7063 and initial radiogenic Pb isotopic compositions with ranges of 18.599–18.657 ~(206)Pb/~(204)Pb, 15.642–15.673 ~(207)Pb/~(204)Pb and 38.956–39.199 ~(208)Pb/~(204)Pb. In contrast, the Miocene granitoid plutons yielded ε_(Nd)(t) values ranging from-6.1 to-7.3 and(87Sr/86Sr)i values in the range 0.7071–0.7078 with similar Pb isotopic compositions to the Eocene quart diorite. The Sr-Nd-Pb isotopic compositions of the rocks are consistent with formation from magma containing a component of remelted ancient crust. Zircon grains from the Eocene quartz diorite have ε_(Hf)(t) values ranging from-5.2 to +0.9 and two-stage Hf model ages ranging from 1.07 to 1.46 Ga, while zircon grains from the Miocene granitoid plutons have ε_(Hf)(t) values from-9.9 to +4.2 and two-stage Hf model ages ranging from 1.05–1.73 Ga, indicating that the ancient crustal component likely derives from Paleo- to Mesoproterozoic basement. This source is distinct from that of most porphyry Cu-Mo-Au deposits in the eastern part of the Gangdese porphyry copper belt, which likely originated from juvenile crust. We therefore consider melting of ancient crustal basement to have contributed significantly to the formation Miocene porphyry Cu-Mo-Au deposits in the western part of the Gangdese porphyry copper belt.  相似文献   

16.
邦铺斑岩型钼(铜)矿床位于甲玛铜多金属矿床北东约30 km处,与钼(铜)成矿有关的岩体主要为二长花岗斑岩,次为花岗闪长斑岩及闪长(玢)岩.通过对二长花岗斑岩体进行LA-ICP-MS锆石U-Pb年龄测试,获得了含矿母岩的年龄,二长花岗斑岩的26颗锆石206Pb/238U加权平均年龄为(16.23±0.19)Ma(MSWD...  相似文献   

17.
Based on the systematic elemental and isotope geochemical study on the Guojialing granite that is closely related to the gold mineralization in the Jiaodong ore-cluster region, further understandings have been made regarding its genetic mechanism, source material and gold mineralization conditions of the Guojialing granites. The (87Sr/86Sr)i values of Guojialing granite range from 0.7106 to 0.7120, and the εNd(t) from −18.1 to −13.2, respectively, which are similar to the initial SrNd isotopic compositions of those Late Jurassic-Early Cretaceous granites widely distributed in the Sulu orogenic belt, indicating similar sources of these intrusions in both Jiaodong and Su-Lu regions. The values of (206Pb/204Pb)i and(207Pb/204Pb)i of Guojialing granite are from 17.158–17.316, 15.453–15.478, respectively, indicating that the source of granites could be originated from mantle mixed with orogenic belt. The zircon Hf isotope of the Guojialing granite is decoupled from the Nd isotope of the whole rock, it has a zircon Hf model age(1979–3202 Ma) older than the full-rock Nd model age (1928 Ma). Compared to the full-rock Nd model age, the zircon Hf model age provides a more reliable age of crust-mantle differentiation and crust formation, suggesting that there is extensive crust deep-melting in the source area before the granitic magma activity, which was accompanied by strong Sm/Nd differentiation. Guojialing granite has similar characteristics to adakite, indicating that garnet is an important residual phase during magma formation. The formation of the Guojialing granite magma may be the partial melting of lithospheric mantle and thickened lower crust under eclogite facies, mixed with significant Neoarchaean crust or even Linglong granites when the magma upwelling. The Guojialing granite has high zircon Ce4+/Ce3+ ratios with the average values of 1151.7 and 811.4 respectively, indicating that the Guojialing granite was formed in a high oxygen fugacity environment, where sulfur is mainly present in the form of SO or SO2, which prevents the immiscibility of sulfides in the magma and avoids the removal of the sulfide metal elements. With crystallization differentiation, high oxygen fugitive magma will become a magma-hydrothermal fluid which is rich in sulfide metal elements, providing favorable material and environmental conditions for gold mineralization, thus favorably formed such giant gold deposit.  相似文献   

18.
Adakitic rocks and related Cu–Au mineralization are widespread along eastern Jiangnan Orogen in South China. Previous studies have mainly concentrated on those in the Dexing area in northeastern Jiangxi Province, but information is lacking on the genesis and setting of those in northwestern Zhejiang Province. The Jiande copper deposit is located in the suture zone between the Yangtze and Cathaysia blocks of South China. This paper presents systematic LA–ICP–MS zircon U–Pb dating and element and Sr–Nd–Hf isotopic data of the Jiande granodiorite porphyry. Zircon dating showed that the Jiande granodiorite porphyry was produced during the Middle Jurassic (ca. 161 Ma). The Jiande granodiorite porphyry is characterized by adakitic geochemical affinities with high Sr/Y and LaN/YbN ratios but low Y and Yb contents. The absence of a negative Eu anomaly, extreme depletion in Y and Yb, relatively low MgO contents, and relatively high 207Pb/204Pb ratios, indicated that the Jiande granodiorite porphyry was likely derived from partial melting of the thickened lower continental crust. In addition, the Jiande granodiorite porphyry shows arc magma geochemical features (e.g., Nb, Ta and Ti depletion), with bulk Earth‐like εNd (t) values (?2.89 to ?1.92), εHf (t) values (?0.6 to +2.8), and initial 87Sr/86Sr (0.7078 to 0.7105). However, a non‐arc setting in the Middle Jurassic is indicated by the absence of arc rocks and the presence of rifting‐related igneous rock associations in the interior of South China. Combined with the regional Neoproterozoic Jiangnan Orogeny, it indicates that these arc magma geochemical features are possibly inherited from the Neoproterozoic juvenile continental crust formed by the ancient oceanic crust subduction along the Jiangnan Orogen. The geodynamic environment that is responsible for the development of the Middle Jurassic Jiande granodiorite porphyry is likely a localized intra‐continental extensional environment along the NE‐trending Jiangshan‐Shaoxing Deep Fault as a tectonic response to far‐field stress at the margins of the rigid South China Plate during the early stage of the paleo‐Pacific plate subduction. In terms of Cu mineralization, we suggest that the metal Cu was released from the subducted oceanic slab and reserved in the juvenile crust during Neoproterozoic subduction along the eastern Jiangnan Orogen region. Partial melting of the Cu rich Neoproterozoic juvenile crust during the Middle Jurassic time in the Jiande area caused the formation of adakitic rocks and the Cu deposit.  相似文献   

19.
恰功矽卡岩型Fe(Cu)-PbZn(Ag)矿床的形成与二长花岗斑岩关系密切。该矿床与查藏措、斯弄多、加多捕勒、青都、那扎等矿床已初步在冈底斯中段勾勒出1条矽卡岩成矿带,但目前对这些矿床的研究还较少。本文对发育于西藏恰功矿区南部的2种斑岩的锆石采用CL和LA-ICP-MS进行了成因矿物学和微区微量元素及U-Pb年代学研究,获得石英斑岩的侵位时代为66.83±0.72Ma (MSWD=2.4,n=9),与成矿关系最为密切的二长花岗斑岩侵位时代为67.42±0.80Ma (MSWD=3.8,n=15)。2种斑岩锆石的U/Yb-Hf及U/Yb-Y在微量元素图解中均显示结晶于陆壳环境。二长花岗斑岩中锆石的矿物结构和Zr/Hf、Th/U、Nb/Ta、Nd/Yb值等微量元素特征和根据Ti含量估算的TTiz显示,其是源于上地幔基性岩浆脉动上涌过程中同化、混合地壳物质后形成的岩浆熔体,伴随围岩压力降低在上侵过程中结晶、分异,最终于近地表冷却形成的。这些结果暗示恰功矿床的形成与印亚陆陆初始碰撞时回卷的新特提斯洋壳撕裂诱发的壳幔混源岩浆活动有关,代表了一种尚未充分认识的陆陆初始碰撞阶段壳幔混源岩浆活动有关的成矿作用。在冈底斯中段中北部针对该时代矿床的勘查工作有一定的找矿潜力。  相似文献   

20.
Whole‐rock geochemistry, zircon U–Pb and molybdenite Re–Os geochronology, and Sr–Nd–Hf isotopes analyses were performed on ore‐related dacite porphyry and quartz porphyry at the Yongping Cu–Mo deposit in Southeast China. The geochemical results show that these porphyry stocks have similar REE patterns, and primitive mantle‐normalized spectra show LILE‐enrichment (Ba, Rb, K) and HFSE (Th, Nb, Ta, Ti) depletion. The zircon SHRIMP U–Pb geochronologic results show that the ore‐related porphyries were emplaced at 162–156 Ma. Hydrothermal muscovite of the quartz porphyry yields a plateau age of 162.1 ± 1.4 Ma (2σ). Two hydrothermal biotite samples of the dacite porphyry show plateau ages of 164 ± 1.3 and 163.8 ± 1.3 Ma. Two molybdenite samples from quartz+molybdenite veins contained in the quartz porphyry yield Re–Os ages of 156.7 ± 2.8 Ma and 155.7 ± 3.6 Ma. The ages of molybdenite coeval to zircon and biotite and muscovite ages of the porphyries within the errors suggest that the Mo mineralization was genetically related to the magmatic emplacement. The whole rocks Nd–Sr isotopic data obtained from both the dacite and quartz porphyries suggest partial melting of the Meso‐Proterozoic crust in contribution to the magma process. The zircon Hf isotopic data also indicate the crustal component is the dominated during the magma generation.  相似文献   

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