Genesis of the Nuri Cu-W-Mo Deposit,Tibet,China:Constraints from in situ Trace Elements and Sr Isotopic Analysis of Scheelite

The Nuri deposit is the only Cu-W-Mo polymetallic deposit with large-scale WO3 resources in the eastern section of the Gangdese metallogenic belt,Tibet,China.However,the genetic type of this deposit has been controversial since its discovery.Based on a study of the geological characteristics of the deposit,this study presents mineralization stages,focusing on the oxide stage and the quartz-sulfide stage where scheelite is mainly formed,referred to as Sch-A and Sch-B,respectively.Through LA-ICP-MS trace element and Sr isotope analyses,the origin,evolutionary process of the oreforming fluid and genesis of the ore deposit are investigated.Scanning Electron Microscope-Cathodoluminescence(SEMCL)observations reveal that Sch-A consists of three generations,with dark gray homogenous Sch-A1 being replaced by relatively lighter and homogeneous Sch-A2 and Sch-A3,with Sch-A2 displaying a gray CL image color with vague and uneven growth bands and Sch-A3 has a light gray CL image color with hardly any growth band.In contrast,Sch-B exhibits a‘core-rim’structure,with the core part(Sch-B1)being dark gray and displaying a uniform growth band,while the rim part(Sch-B2)is light gray and homogeneous.The normalized distribution pattern of rare earth elements in scheelite and Sr isotope data suggest that the early ore-forming fluid in the Nuri deposit originated from granodiorite porphyry and,later on,some country rock material was mixed in,due to strong water-rock interaction.Combining the O-H isotope data further indicates that the ore-forming fluid in the Nuri deposit originated from magmatic-hydrothermal sources,with contributions from metamorphic water caused by water-rock interaction during the mineralization process,as well as later meteoric water.The intense water-rock interaction likely played a crucial role in the precipitation of scheelite,leading to varying Eu anomalies in different generations of scheelite from the oxide stage to the quartz-sulfide stage,while also causing a gradual decrease in oxygen fugacity(fO2)and a slow rise in pH value.Additionally,the high Mo and low Sr contents in the scheelite are consistent with typical characteristics of magmatic-hydrothermal scheelite.Therefore,considering the geological features of the deposit,the geochemical characteristics of scheelite and the O-H isotope data published previously,it can be concluded that the genesis of the Nuri deposit belongs to porphyry-skarn deposit.

太行山麻棚地区高Ba-Sr花岗质侵入岩的地球化学、锆石U-Pb年龄和Hf同位素特征及其地质意义

华北克拉通经历了长期而复杂的地质过程,中生代时期在太行山地区构造岩浆活动强烈,形成了一系列中酸性岩体。麻棚岩体位于太行山北段,侵位于新太古代片麻岩和表壳岩中,由中心向边缘分别出露似斑状二长花岗岩、花岗闪长岩和石英闪长岩。前人已经对麻棚岩体进行过岩石学、岩石化学、岩体成因类型和年代学等多方面的研究,其花岗岩类型仍存有争议。本文对麻棚岩体进行了系统的岩石地球化学、锆石SHRIMP U-Pb同位素年代学分析和Lu-Hf同位素组成研究,进一步探讨了麻棚岩体的地球化学类型、形成时代和岩浆源区性质。岩石地球化学特征表明麻棚岩体具有较高的SiO_(2)、Na_(2)O+K_(2)O、Ba、Sr、LREE含量和K_(2)O/Na_(2)O值,较低的Al_(2)O_(3)、MgO、Rb、Nb、Ta、Th、U、Y、HREE含量和Mg^(#)值,无明显的Eu异常,明显亏损Nb、Ta、P、Ti等高场强元素,属于高Ba-Sr花岗岩。新获得的3个不同相带岩石的锆石SHRIMP U-Pb同位素206Pb/238U加权平均年龄为129.4±1.4、131.2±2.2和129.5±1.3 Ma,且具有相似主量元素组成及稀土和微量元素分布模式,反映了麻棚岩体为同一期岩浆活动产物。Lu-Hf同位素测试分析数据计算获得麻棚岩体岩浆锆石的εHf(t)值为-27.00~-15.44,二阶段模式年龄t_(DM2)为2 358~1 765 Ma。麻棚岩体是前寒武纪变质基底部分熔融形成的岩浆与幔源岩浆混合作用的结果。

滇西北浪都夕卡岩矿床致矿岩体的岩石地球化学、年代学、Sr-Nd-Pb同位素组成及其地质意义

滇西北浪都侵入岩体位于义敦岛弧南段的中甸弧,在空间上属浪都夕卡岩型铜矿床的致矿岩体。本文以浪都致矿岩体中石英二长斑岩为对象,对其开展了锆石SIMS(二次离子质谱)U-Pb定年、岩石地球化学和Sr-Nd-Pb同位素研究。锆石U-Pb定年结果显示浪都石英二长斑岩的成岩年龄为219.2±1.8 Ma(2σ,MSWD=1.3,n=13),与中甸弧中晚三叠世侵入岩体成岩年龄基本一致。浪都石英二长斑岩具有中等SiO2含量(w(SiO_(2))为60.42%~66.44%),高Al_(2)O_(3)(w(Al2O3)为14.56%~16%)和高K2O(w(K_(2)O)为3.49%~4.49%)含量,以富集LREE和Rb、Ba、Sr等大离子亲石元素,相对亏损HREE和Ta、Nb、Ti等高场强元素为特征,在化学成分上属于高钾钙碱性系列。此外,浪都石英二长斑岩的87Sr/86Sr初始值为0.7054~0.7061,εNd(t)值为-3.5~-2.5,且所有样品在Pb同位素构造模式图上均落在造山带演化线附近。结合浪都石英二长斑岩的成岩时代、岩石化学和同位素特征,本文认为浪都致矿岩体形成于晚三叠世甘孜-理塘洋壳西向俯冲增生的构造背景,是交代地幔部分熔融形成的熔体在上升过程中受到下地壳物质混染,并经历分离结晶作用形成的产物。浪都石英二长斑岩的高Sr/Y比值和高V/Sc比值,指示岩浆具有高含量H2O和较高的氧逸度,是该区斑岩-夕卡岩铜矿床形成的关键。

胶东西南部三合山岩体岩石成因和构造背景:年代学、地球化学及Sr-Nd-Pb-Hf同位素约束

【研究目的】胶东地区是中国最大的金矿矿集区,也是山东省最为重要的铜钼多金属矿成矿区。加强中生代花岗岩的岩相学、岩石地球化学和年代学等方面的研究,有利于进一步促进该区金及多金属矿的找矿工作。【研究方法】本文以胶东半岛西南部三合山岩体中细粒二长花岗岩和花岗斑岩为研究对象,开展系统的岩相学、LA-ICP-MS锆石U-Pb年代学、主微量元素地球化学、全岩Sr-Nd-Pb同位素及锆石Lu-Hf同位素研究,旨在探讨其岩石成因、岩浆源区性质和构造背景。【研究结果】LA-ICP-MS锆石U-Pb定年结果表明,中细粒二长花岗岩的成岩年龄为(115.42±0.27)Ma,花岗斑岩的形成年龄为(115.21±0.25)Ma,形成时代均属中生代早白垩晚期;岩石地球化学特征表明,中细粒二长花岗岩和花岗斑岩均属高钾钙碱性I型花岗质岩石,LREE较HREE分馏明显,具弱Ce负异常和明显Eu中等负异常,富集Rb、K、Zr和Hf,亏损Sr、Ba、Nb、P、Ti;全岩Sr-Nd-Pb及锆石Hf同位素分析结果表明,三合山岩体起源于重熔的下地壳,并受到了幔源物质的混染。【结论】三合山岩体形成于早白垩世太平洋板块相对欧亚板块俯冲导致的陆内伸展背景下,为中国东部岩石圈减薄过程中壳幔相互作用的产物。

胶东大疃刘家铍矿床碱性岩岩石成因及对成矿的制约:锆石U-Pb年代学、地球化学及Sr-Nd-Hf同位素证据

胶东大疃刘家铍矿床位于华北板块东南缘,矿体受NW向断裂控制,圈定的7条矿体呈透镜状产出,赋存于中细粒正长岩中。矿石矿物主要为羟硅铍石,与绢云母、方解石、重晶石、褐铁矿等蚀变矿物密切共生。Be与Mo、Rb、Cs、REE等元素具有良好的正相关性,与CaO呈负相关关系,矿床成矿专属性明显。矿区内正长花岗岩为高硅、富碱、高钾、贫镁铁岩石,为准铝质-弱过铝质岩石;正长岩具有低硅、富碱、高钾特征,为准铝质岩石。两类岩石均具有轻重稀土分馏明显,轻稀土富集,无明显负Eu异常的稀土元素特征,稀土及微量元素配分模式相同,微量元素具有富集大离子亲石元素,亏损Nb、Ta、Ti等高场强元素的特征。正长花岗岩锆石LA-ICP-MS U-Pb定年表明其侵位于200.3±1.3Ma,全岩Sr-Nd同位素组成比较均一,ε_(Nd)(t)值为-15.8~-15.4,Hf同位素组成变化范围较大,ε_(Hf)(t)为-25.5~-7.75;正长岩锆石LA-ICP-MS U-Pb定年表明其侵位于200.9±1.4Ma,ε_(Hf)(t)值为-23.2~-15.7。地球化学研究指示正长岩为经历了华南陆壳交代的华北富集岩石圈地幔低程度部分熔融的产物,正长花岗岩来源于俯冲的华南陆壳,二者为华南板块与华北板块碰撞折返阶段岩浆作用的产物。

桐柏—大别造山带中部娘娘顶花岗岩成因——锆石U-Pb年龄、岩石地球化学及Sr-Nd同位素证据

娘娘顶花岗岩体位于桐柏—大别造山带中部﹐其侵位时代及形成构造环境还不清楚。采集娘娘顶花岗岩样品,开展锆石U-Pb年代学、岩石地球化学及Sr-Nd同位素研究,探讨其岩浆源区特征、岩石成因、构造环境及其与杨新岩铍矿点的关系。结果表明,娘娘顶花岗岩的锆石U-Pb年龄为(752.6±9.0)Ma,属南华纪岩浆作用产物,仅构成杨新岩铍矿点的赋矿围岩;具有高硅(SiO_(2)含量为72.56%~77.26%)、富碱(Na_(2)O+K_(2)O含量为7.37%~8.86%)、过铝质(A/CNK为0.97~1.22)等特征,Rb、K、Th等元素相对富集,Ba、Sr、Ti、P等元素明显亏损,稀土元素配分曲线呈右倾的轻稀土元素富集型,具明显负Eu异常(δEu为0.2~0.7),表明岩石为铝质A型花岗岩;(^(87)Sr/^(86)Sr)i为0.710605~0.710608,εNd(t)为-4.94~-5.05,相应的Nd模式年龄t_(DM)为1.83~1.84 Ga,具有大陆上地壳特征,可能为古—中元古代古老基底部分熔融的产物;主量元素CaO、MgO、TFeO、TiO_(2)与SiO_(2)均显示负相关关系,其岩浆演化机制应以结晶分异作用为主。综合来看,娘娘顶花岗岩形成于新元古代伸展背景。

Magma Origin and Evolution of Tengchong Cenozoic Volcanic Rocks from West Yunnan,China:Evidence from Whole Rock Geochemistry and Nd-Sr-Pb Isotopes

Tengchong Cenozoic volcanics that have record key information on the tectonic evolution and mantle features of the southeast margin of the Tibetan Plateau are of great importance because of its unique eruption history spanning the entire Quaternary period. Magma origin and evolution of Tengchong Cenozoic volcanic rocks were studied on the basis of Nd-Sr-Pb isotope and major and trace element data from different eruptions in the Ma＇anshan area. Different samples within one eruption show relative identical lithologies, chemical and isotopic compositions. However, the geochemical features for the five eruptions are distinct from each other. These volcanic rocks show low Mg# values （〈45）, moderate to high fractionation of LREEs and HREEs, and enrichment of Pb and Ba and depletion of Nb. Tengchong Cenozoic volcanic rocks were derived from an enriched mantle based on Nd-Sr-Pb isotopic studies. And lines of evidence show that crustal contamination should be involved before the eruption of different periods of Tengchong Cenozoic volcanic rocks. Older subducted components may be responsible for adakite recycling at various stages of evolution, which results in the origin of the enriched mantle source magma accounting for the isotopic features of Tengchong Cenozoic volcanic rocks. Segregated primitive magma pulsating injected into magma chamber, fractional crystallized and contaminated with crust component. Finally, magmas with distinct chemical and isotopic compositions for each eruption formed. The extension of the northeast segment of the Yingjiang tectonic belt triggered the pulsating eruption of the Cenozoic volcanics in the Tengchong area.

An Isotopic(Sr,Nd and Pb) Tracer Study on the Xiaoxinancha Gold-rich Copper Deposit in Yanbian,China:Implication for the Geodynamic Model of Diagenesis and Metallogenesis

An isotopic study was systemically carried out on the granitic complex,diorite-porphyrite, ores and ore minerals of the 103 Ma Xiaoxinancha gold-rich copper deposit in Jilin province to determine the geodynamic model of diagenesis and metallogenesis.Results show that the initial Nd and Sr isotopic compositions of the granitic complex are in the range of 0.70425-0.70505 for（87Sr/86Sr）i, 0.51243-0.51264 for INd,and -1.31 to ＋2.64 forεNd（t）;those of the diorite-porphyrite are in the range from 0.70438-0.70448 for（87Sr/86Sr）,,0.51259-0.51261 for INd,and ＋1.56 to ＋2.09 forεNd（t）.For ores and sulfides,the（87Sr/86Sr）i,7Nd,andεNd（t） values are in the range from 0.70440-0.70805,0.51259- 0.51279 and ＋1.72 to ＋5.56,respectively.The Pb isotopic ratios of the granitic complex range from 18.2992-18.6636 for 206Pb/204Pb,from 15.5343-15.5660 for 207Pb/204Pb,and from 38.1640-38.5657 for 208Pb/204Pb For diorite-porphyrite,the isotopic ratios of 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb are 18.3919,15.5794 and 38.3566,respectively,whereas those of the ores and ore sulfides vary from 18.2275-18.3770 for 206Pb/204Pb,from 15.5555-15.5934 for 207Pb/204Pb and from 38.1318-38.3131 for 208Pb/204Pb.The results indicate that the mineralization was correlated to the formation and evolution of the granitic complex and the diorite-porphyrite.Combining with the reported data in petrologic characteristics,elemental geochemistry and chronology,conclusions can be drawn that the geodynamic settings of diagenesis and metallogenesis of this deposit were consistent with the subduction of the Izanagi oceanic plate during the Early Cretaceous.The diorite-porphyrite was formed by the emplacement of the adakitic magma triggered by partial melting of the enriched mantle,which originated from the derivative continental lithospheric mantle metasomatized by dehydration fluids from the subducting oceanic crust.The granitic complex was produced by fractional crystallization of the mixture between the adakitic magma and the high-K calc-alkaline acidic magma,which were generated by the remelting of the lower crust in the course of intraplate upwelling of the adakitic magma.The ore-bearing fluid reservoir convened in a late stage of the evolution of the mixed magma chamber.

Geochemistry of trace elements and Sr-Nd isotopes of foraminifera shell from the Okinawa Trough

Trace elemental associations and Sr-Nd isotopic compositions are of important to recognition of biogenic material from mixed marine sediments. The foraminifera shell from the Okinawa Trough strongly enriches Sr,P,Mn and Ba, enriches Li,U,Th,Sc,Co,Cu,Pb,Zn,Cr,Rb,Y,Sb and light rare earth elements,slightly enriches V,Ga,Zr,Nb,Cd and middle rare earth elements,is short of Mo,In,Sn,Cs,Hf,Ta,W,Ti,Bi and heavy rare earth elements. The mechanism of elemental enrichment in forminifera is the concentrations of trace elements in sea water and selective absorption of trace elements during foraminifera living, as well as the geochemical affinity between major elements and trace elements.The REE (rare earth elements)partition pattern of foraminifera shell of the Okinawa Trough shows enrichment of middle rare earth elements with slightly negative Ce anomaly,which are different from those of foraminifera of the Pacific Ocean.The Sr,Nd isotopic ratios of the Okinawa Trough foraminifera are 0 709 769 and 0 512 162,respectively, which are different not only from those of oceanic water, but also from those of river water of China's Mainland, the former is slightly higher than those of oceanic water,but much lower than those of river water;the latter is slightly lower than those of oceanic water,but higher than those of river water,demonstrating that the Okinawa Trough sea water has been influenced by river water of China's Mainland.

Geochronology, Geochemistry and Sr-Nd-Pb-Hf Isotopes of No. I Complex from the Shitoukengde Ni–Cu Sulfide Deposit in the Eastern Kunlun Orogen, Western China: Implications for the Magmatic Source, Geodynamic Setting and Genesis

The Shitoukengde Ni-Cu deposit, located in the Eastern Kunlun Orogen, comprises three mafic-ultramafic complexes, with the No. I complex hosting six Ni-Cu orebodies found recently. The deposit is hosted in the small ultramafic bodies intruding Proterozoic metamorphic rocks. Complexes at Shitoukengde contain all kinds of mafic-ultramafic rocks, and olivine websterite and pyroxene peridotite are the most important Ni-Cu-hosted rocks. Zircon U-Pb dating suggests that the Shitoukengde Ni-Cu deposit formed in late Silurian （426-422 Ma）, and their zircons have ~Hf（t） values of-9.4 to 5.9 with the older TDMm ages （0.80-1.42 Ga）. Mafic-ultramafic rocks from the No. I complex show the similar rare earth and trace element patterns, which are enriched in light rare earth elements and large ion iithophile elements （e.g., K, Rb, Th） and depleted in heavy rare earth elements and high field strength elements （e.g., Ta, Nb, Zr, Ti）. Sulfides from the deposit have the slightly higher ~34S values of 1.9-4.3%o than the mantle （0 ~ 2%o）. The major and trace element characteristics, and Sr-Nd-Pb and Hf, S isotopes indicate that their parental magmas originated from a metasomatised, asthenospheric mantle source which had previously been modified by subduction-related fluids, and experienced significant crustal contamination both in the magma chamber and during ascent triggering S oversaturation by addition of S and Si, that resulted in the deposition and enrichment of sulfides. Combined with the tectonic evolution, we suggest that the Shitoukengde Ni-Cu deposit formed in the post-collisional, extensional regime related to the subducted oceanic slab break-off after the Wanbaogou oceanic basalt plateau collaged northward to the Qaidam Block in late Silurian.

Geochemistry and Sr-Nd-Pb Isotopes of the Granites from the Hashitu Mo Deposit of Inner Mongolia, China： Constraints on Their Origin and Tectonic Setting

The Hashitu molybdenum deposit is located in the southern part of the Great Hinggan Range, NE China. Molybdenum mineralization is hosted by and genetically associated with monzogranite and porphyritic syenogranite. Sr-Nd-Pb isotopes of the intrusions show that the porphyritic syenogranite has initial ^87Sr/^86Sr ratios of 0.70418-0.70952, ENd（t） values of 1.3 to 2.1 （t=143 Ma）, ^206Pb/^204Pb ratios of 19.191-19.573, ^207Tpb/^204pb ratios of 15.551-15.572, and ^208Pb/^204Pb ratios of 38.826-39.143. The monzogranite has initial 87Sr/86Sr ratios of 0.70293-0.71305, εNd（t） values of 1.1 to 2.0 （t=-147 Ma）, ^206Pb/^204pb ratios of 19.507-20.075, ^207Pb/^204Pb ratios of 15.564-15.596, and ^208Pb/^204Pb ratios of 39.012-39.599. The calculated Nd model ages （TDM） for monzogranite and porphyritic syenogranite range from 866 to 1121 Ma and 795 to 1020 Ma, respectively. The granitic rocks in the Hashitu area have the same isotope range as granites in the southern parts of the Great Hinggan Range. The isotope composition indicates that these granites are derived from the partial melting of a juvenile lower crust originating from a depleted mantle with minor contamination by ancient continental crust. The integrating our results with published data and the Late Mesozoic regional tectonic setting of the region suggest that the granites in the Hashitu area formed in an intra-continent extensional setting, and they are related to the thinning of the thickened lithosphere and upwelling of the asthenosphere.

Zircon LA-ICP-MS U-Pb dating and Sr-Nd isotope study of the Guposhan granite complex, Guangxi, China

Zircon U-Pb dating by the LA-ICP-MS method was applied to determining the ages of different units of the Guposhan granite complex, among which the East Guposhan unit is 160.8±1.6 Ma, the West Guposhan unit is 165.0±1.9 Ma, and the Lisong unit is 163.0±1.3 Ma in age. Much similarity in ages of the three units has thus proved that the whole Guposhan granite complex was formed in the same period of time. They were the products of large-scale granitic magmatism through crust-remelting in the first stage of the Middle Yanshanian in South China. However, the three units have differences both in petrology and in geochemistry. Besides the differences in major, trace and rare-earth elements, they are distinct in their Rb-Sr and Sm-Nd isotopic compositions. The East Guposhan unit and Lisong unit and its enclaves have a similar (87Sr/86Sr)i value of 0.7064 with an average of εNd(t)=-3.03, indicating that more mantle material was evolved in the magma derivation; whereas the West Guposhan unit has a higher (87Sr/86Sr)i value of 0.7173 but a lower εNd(t) value of -5.00, and is characterized by strong negative Eu anomalies and higher Rb/Sr ratios, suggesting that its source materials were composed of relatively old crust components and new mantle-derived components. In addition, an inherited zircon grain in the East Guposhan unit (GP-1) yielded a 206Pb/238U age of 806.4 Ma, which is similar to the ages of the Jiulin cordierite granite in northern Jiangxi and of the Yinqiao migmatic granite in Guangxi in the HZH granite zone. All this may provide new evidence for Late Proterozoic magmatism in the HZH granite zone.

Geochemistry, U-Pb Geochronology and Sr-Nd-Hf Isotopes of the Early Cretaceous Volcanic Rocks in the Northern Da Hinggan Mountains

Whole-rock geochemical, zircon U-Pb geochronological and Sr-Nd-Hf isotopic data are presented for the Early Cretaceous volcanic rocks from the northern Da Hinggan Mountains. The volcanic rocks generally display high SiO2 （73.19-77.68 wt%） and Na20＋K20 （6.53-8.98 wt%） contents, with enrichment in Rb, Th, U, Pb and LREE, and depletion in Nb, Ta, P and Ti. Three rhyolite samples, one rhyolite porphyry sample, and one volcanic breccia sample yield weighted mean 206pb/23SU ages of 135.1±1.2 Ma, 116.5±1.1 Ma, 121.9±1.0 Ma, 118.1±0.9 Ma and 116.9±1.4 Ma, respectively. All these rocks have moderate （STSr/S6Sr）i values of 0.704912 to 0.705896, slightly negative eNd（t） values of -1.4 to -0.1, and positive Cur（t） values of 3.7 to 8. Their zircon Hf and whole-rock Nd isotopic model ages range from 594 to 1024 Ma. These results suggest that the Early Cretaceous volcanic rocks were originated from melting of subducted oceanic crust and associated sediments during the closure of the Mongol-Okhotsk Ocean.

Ore Genesis for Stratiform Ore Bodies of the Dongfengnanshan Copper Polymetallic Deposit in the Yanbian Area, NE China:Constraints from LA-ICP-MS in situ Trace Elements and Sulfide S–Pb Isotopes

The Dongfengnanshan Cu polymetallic deposit is one representative deposit of the Tianbaoshan ore district in the Yanbian area, northeast(NE) China. There occur two types of ore bodies in this deposit, the stratiform ore bodies and veintype ones, controlled by the Early Permian strata and the Late Hercynian diorite intrusion, respectively. Due to the ambiguous genetic type of the stratiform ore bodies, there has been controversy on the relationship between them and veintype ore bodies. To determine the genetic type of stratiform ore bodies, laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS) in situ trace elements and S–Pb isotope analysis have been carried on the sulfides in the stratiform ore bodies. Compared with that in skarn, Mississippi Valley-type(MVT), and epithermal deposits, sphalerite samples in the stratiform ore bodies of the Dongfengnanshan deposit are significantly enriched in Fe, Mn, and In, while depleted in Ga, Ge, and Cd, which is similar to the sphalerite in volcanic-associated massive sulfide(VMS) deposits. Co/Ni ratio of pyrrhotites in the stratiform ore bodies is similar to that in VMS-type deposits. The concentrations of Zn and Cd of chalcopyrites are similar to those of recrystallized VMS-type deposits. These characteristics also reflect the intermediate ore-forming temperature of the stratiform ore bodies in this deposit. Sulfur isotope compositions of sulfides are similar to those of VMS-type deposits, reflecting that sulfur originated from the Permian Miaoling Formation. Lead isotope compositions indicate mixed-source for lead. Moreover, the comparison of the Dongfengnanshan stratiform ore bodies with some VMStype deposits in China and abroad, on the trace elements and S–Pb isotope characteristics of the sulfides reveals that the stratiform ore bodies of the Dongfengnanshan deposit belong to the VMS-type, and have closely genetic relationship with the early Permian marine volcanic sedimentary rocks.

Devonian alkaline magmatism in the northern North China Craton:Geochemistry,SHRIMP zircon U-Pb geochronology and Sr-Nd-Hf isotopes

The Wulanhada pluton is among the rare suite of Devonian alkaline plutons occurring along the northern margin of the North China Craton（NCC）.The intrusion is mainly composed of quartz-monzonite.Here we report zircon SHRIMP U-Pb data from this intrusion which shows emplacement age of ca.381.5 Ma.The rock is metaluminous with high（Na2O ＋ K2O） values ranging from 8.46 to 9.66 wt.%.The REE patterns of the rocks do not show any Eu anomaly whereas the primitive-mantle-normalized spider diagram shows strong positive Sr and Ba anomalies.The Wulanhada rocks exhibit high initial values of（87Sr/86Sr）t = 0.70762-0.70809,low εNd（t） =-12.76 to-12.15 values and negative values of εHf（t） =-23.49 to-17.02 with small variations in（176Hf/177Hf）,（0.281873-0.282049）.These geochemical features and quantitative isotopic modeling results suggest that the rocks might have been formed through the partial melting of Neoarchean basic rocks in the lower crust of the NCC.The Wulanhada rocks,together with the Devonian alkaline rocks and mafic-ultramafic complex from neighboring regions,constitute a post-collisional magmatic belt along the northern NCC.

Trace Elements and Sr, Nd Isotope Geochemistry of the Lajimiao Norite-Gabbro from the North Qinling Belt

The Lajimiao norite-gabbro complex, as a part of the ophiolites on the southern side of the North Qinling belt, consists of gabbro and norite-gabbro. They were derived from different magma series: the gabbro was derived from tholeiitic magma series with higher TiO2, REE abundance and Fe3+/Fe2+ ratio ; norite-gabbro was derived from calc-alkali magma series with lower TiO2, Fe3+/Fe2+ ratio and REE abundance and much lower HREE abundance, which suggests that the source of the norite-gabbro magma was deeper and controlled by eclogite facies. Geochemical characteristics of both plutonic rocks are similar to those of island-arc basalts, such as relatively high contents of Ba, Pb and Sr and relatively low contents of Nb, Zr and N j.The Sr, Nd isotopic characteristics of the Lajimiao norite-gabbro complex are similar to those of ophiolites. Its εNd values are constant, about+2; whereas εst values have wide variation from - 6.4 to +31.2 and positively correlate with Na2O, H2O+ and CO2 contents and the Fe3+/Fe2+ ratio. The εNd- Nd/Th, εNd- La/Nb and εNd-Ba/Nb diagrams clearly show that there were significant components of terrigenous sediments in the mantle source of the Lajimiao norite-gabbro complex. It suggests that large amount of sediments had been carried into the mantle by the subducted ancient Qinling sea plate during the Palaeozoic.

华北克拉通南缘大庄铌-稀土矿床地质、地球化学和Sr、Nd、Pb同位素特征

碱性岩型铌-稀土矿床是重要的铌-稀土矿资源类型。河南省方城县大庄铌-稀土矿位于华北克拉通南缘,是近年来新发现的一例赋存于霞石正长岩中的,具有中型规模的碱性岩型矿床。大庄矿区内共圈定17个NW—SE向带状展布的,呈囊状、不规则状、透镜状产出的铌-稀土矿体。铌-稀土矿石主要赋存于角闪霞石正长岩和黑云母正长岩中。矿石矿物主要为烧绿石、氟碳铈镧矿、褐钇铌矿和富铌榍石等。矿石的结构主要有斑状结构、他形粒状结构、半自形粒状结构、包含结构、交代结构、共生结构、伟晶结构等。矿石构造分为块状、脉状和片麻状构造等。热液蚀变包括萤石化、绢云母化、绿帘石化和绿泥石化等。碱性岩样品具有低SiO2、富碱、高铝的特征,稀土元素总量较高,轻重稀土分异明显,具有明显的负Eu异常,富集Nb、Ta、Th、U、Zr、Hf等高场强元素,明显亏损Ba、Sr、P、Ti等元素。碱性岩全岩(87Sr/86Sr)i=0.68158~0.71090,εNd(t)=―1.11~―0.37,两阶段模式年龄(tDM2)为1601~1540 Ma,(206Pb/204Pb)i=16.018~17.502、(207Pb/204Pb)i=15.358~15.489、(208Pb/204Pb)i=36.684~40.340。地球化学特征显示方城地区碱性岩的岩石类型为A型岩套A1亚型,岩浆演化主要受分离结晶控制,其原始岩浆形成于富金云母的地幔源区。总体上看,华北克拉通南缘大庄铌-稀土矿成矿主体受岩浆结晶分异控制,Nb、REE在岩浆结晶晚期大量富集,后期热液活动对铌-稀土成矿有一定的制约作用。方城地区碱性岩形成于板内拉张的构造背景,推测是Rodinia超大陆裂解的响应。

A Study of REE and Pb, Sr and N d Isotopes in Garnet-Lherzolite Xenoliths from Mingxi, Fujian Province

The REE and Pb ,Sr,Nd isotopes in three xenoliths from limburgite and scoria-breccias,including spinel-lherzolite,spinel-gamet-1herzolite and phlogopite-gamet-1herzolite,were analysed.The REE contentso of the xenoliths are 1.3 to 3.3 times those of the chondrites with their REE pattems characterized by weak LREE depletion.The ^143Nd/^144Nd values of whole rocks and minerals range from 0.51306 to 0.51345 with εNd=+8.2-+15.8,^206Pb/^204Pb<18.673,and ^207Pb/^204Pb<15.574,All this goes to show that the upper mantle in Mingxi at the depth of 67-82km is a depleted mantle of MORB type,with ^87Sr/^86Sr ratios 0.70237-0.70390.In Nd-Sr diagram the data points of whole rocks are all out of the mantle array,implying that the xenoliths from Mingxi have more radiogenic Sr isotopes than those of the mantle array.

CHARACTERISTICS OF Nd AND Sr ISOTOPES AND TRACE ELEMENTS FOR LATE CRETAEOUS VOLCANIC ROCKS IN KING GEORGE ISLAND, ANTARCTICA: IMPLICATIONS FOR SOURCE OF THE VOLCANICS FROM DEPLETED MANTLE

Rb -Sr isotopic isochron dating of the volcanic rock samples from the Upper Cretaceous Half Three Point Formation on the King George Island is 71. 33±0. 3 Ma. Correlative study of εND(T)-147Sm/144Nd, 143Nd/144Nd-87Sr/86Sr, 87Sr/86Sr-Sr and 87Sr/86Sr-K2O/(K2O+Na2O) indicated that the volcanic rocks were chiefly derived from the depleted mantle source and generally were not mixed crust materials. Of the samples 6 were given the mean Sm -Nd model age (TDM) of 443. 3±20. 6 Ma possibly indicating the age of chemical variation event in the magma source of the study area. Features of the trace elements indicated that the rocks from the Half Three Point Formation are of typical calc-alkaline volcanic suite and similar to those from the Tertiary volcanic rocks of the Fildes Peninsula, being the same products of the island-arc volcanic activity.

滇东南马卡铅锌钨矿床成因:闪锌矿Rb-Sr、锡石U-Pb定年和硫化物原位硫、铅同位素制约

马卡铅锌钨矿床地处云南省马关县与麻栗坡县的南温河交界处,位于燕山晚期老君山复式花岗岩体北缘。野外地质调查发现,该矿床主要发育矽卡岩型、石英脉型铅锌矿化和萤石石英脉型白钨矿化,但它们的形成机制仍缺乏系统研究。本文通过闪锌矿Rb-Sr、锡石原位U-Pb同位素定年和硫化物原位S、Pb同位素分析,厘定了马卡矿床不同类型铅锌矿化年龄,并探讨了其成矿物质来源及成因机制。矽卡岩型和石英脉型铅锌矿石中闪锌矿分别获得了88.9±1.9Ma(MSWD=4.5)和85.18±0.72Ma(MSWD=1.2)的Rb-Sr等时线年龄,同时获得石英脉型铅锌矿石中锡石LA-ICP-MS U-Pb年龄为84.3±4.7Ma(MSWD=0.66)。结果指示锌、锡矿化时代为晚白垩世,矽卡岩型和石英脉型铅锌矿化分别与该区广泛出露的老君山花岗岩(-90Ma)和花岗斑岩年龄(80-86Ma)一致。矿石硫化物原位硫同位素测试结果显示,δ34S值范围为2.53‰-9.65‰,均值为4.7‰,与老君山花岗岩中硫化物硫同位素组成(4.07‰)相似,表明硫主要来源于老君山花岗岩,少部分源自沉积地层;原位铅同位素组成特征也表明矿石铅主要源自老君山花岗岩。综合研究认为,老君山花岗岩体南北缘地区具有相似的成矿地质条件。马卡矿床的形成主要与燕山晚期老君山复式花岗岩体有关,可能经历了与花岗岩有关的矽卡岩型矿化和与花岗斑岩有关的热液充填、交代成矿过程。