滇东南白牛厂多金属矿床铅同位素组成及铅来源新认识

白牛厂矿床位于滇东南锡多金属成矿带中部,是一个Ag、Pb、Zn、Sn等共生的多金属矿床,但成因争议较大.前人引用早期矿床矿石矿物铅同位素数据得出矿石铅主要来源于基底岩石淋滤,矿床经历了热水沉积+岩浆热液叠加两个成矿阶段的结论.本文采用最新铅同位素数据系统研究了白牛厂矿床的铅同位素组成,其中,白牛厂矿床矿石矿物的铅同位素组成206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为17.264～18.537、14.843～15.862和38.481～39.424;薄竹山花岗岩长石铅同位素组成206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为18.301～18.387、15.611～15.670和38.677～38.904;薄竹山岩体接触带型矿床(点)矿石矿物铅同位素组成206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为18.302～18.417、15.603～15.692和38.596～38.868;区域地层及矿区地层钻孔样品铅同位素组成206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为18.307～19.206、15.622～15.809和38.436～39.932.对比四者铅同位素组成特征,白牛厂矿床矿石矿物、薄竹山花岗岩长石、薄竹山岩体接触带型矿床(点)矿石矿物具有一致的铅同位素组成,与地层铅同位素组成相差甚远,表明白牛厂矿床铅主要来自岩浆作用,在侵入的过程中可能受到了地层的轻度混染.矿床地质特征及近期地球化学和年代学研究成果表明,白牛厂矿床的形成主要受岩浆作用影响,沉积成矿作用在白牛厂矿床很可能是不存在的.     

东昆仑东段那更康切尔银矿硫-铅同位素特征与找矿模型

那更康切尔银矿是东昆仑造山带的大型热液脉型独立银矿床,有望达到超大型规模。以矿区地质特征为研究基础,开展硫化物硫-铅同位素、二长花岗岩和花岗闪长岩铅同位素研究,探讨成矿物质来源及两类岩体与成矿的关系。矿区硫化物样品(黄铁矿、方铅矿和闪锌矿)的δ34S值介于-6.1‰~3.9‰之间,主体δ34 S值介于-4‰~2.1‰之间,数值集中,指示成矿物质硫源具有深源岩浆硫的特征。矿石铅同位素组成中206 Pb/204 Pb、207 Pb/204 Pb、208 Pb/204 Pb的变化范围分别为18.28~18.62、15.6~15.73、38.38~39.1,矿石铅具有壳幔混合源的特点。矿区内二长花岗岩LA-ICP-MS锆石U-Pb年龄为239±1 Ma,(206Pb/204Pb)i、(207Pb/204Pb)i、(208Pb/204Pb)i值分别为18.389~18.585、15.638~15.648、38.288~38.558;花岗闪长岩LA-ICP-MS锆石U-Pb年龄为252±1 Ma,(206Pb/204Pb)i、(207Pb/204Pb)i、(208Pb/204Pb)i值分别为18.348~18.447、15.625~15.629、38.394~38.412,铅同位素组成投图显示成矿与2类岩浆岩关系较弱,与区域上鄂拉山组火山岩呈较明显的线性相关。那更康切尔银矿与邻区哈日扎铅锌银矿床具有相似的成矿物质来源,硫源具有同一性,且矿石铅同位素组成表现出很明显的线性关系,表明2个矿床的成矿物质具有相近或相似的源区或演化过程。成矿地质条件、成矿物质来源及成矿流体特征均表明两者属中-低温热液脉型矿床。综合本文及前人对那更康切尔银矿床的研究,构建了成矿模式和找矿模型,为区域内同类型银矿床的找矿工作提供了指导作用。     

静态测量方式的单颗粒锆石蒸发铅同位素定年方法

报道的单颗粒锆石蒸发定年方法是利用新型固体质谱计的多离子接收器配置实现的。改进的锆石蒸发^207Pb／^206Pb定年流程通过静态测量方式，在锆石蒸发过程中直接测定铅同位素比值，获得^207Pb／^206Pb年龄。应用该方法测定了元古代永宁组沉积岩的碎屑锆石，获得6颗锆石的^207Pb／^206Pb年龄值为1965—2590Ma。与传统的蒸发法流程相比，静态测量方法省时简捷，同时可以直观地观测到锆石内部的铅同位素组成变化。这些变化反映锆石结晶历史、后期事件叠加以及锆石成因等地质信息。     

黔中白云岩同化剖面的铅同位素组成及物源的指示

碳酸盐岩上覆红土的形成模式是一个争议的问题,尤其是形成该红土的物质来源争议最大.本文对贵州中部平坝剖面进行了铅同位素的综合分析,结果显示全岩样品的Pb同位素组成显示是以长石矿物为主的"普通铅",下伏三叠纪白云岩样品的n(206Pb)/n(204Pb)为19.29,风化剖面全土样品的n(206Pb)/n(204Pb)约为...     

湖北鸡笼山矽卡岩型金铜矿床铅同位素地球化学研究

湖北鸡笼山金铜矿床是长江中下游铁铜金多金属成矿带鄂东南成矿区中典型的矽卡岩矿床,对其成矿物质来源的专门研究相对贫乏。对鸡笼山矽卡岩带的11件黄铁矿、2件方铅矿和2件闪锌矿样品进行了铅同位素分析,结果显示206Pb/204Pb为17.358～18.589,207Pb/204Pb为15.414～15.745,20 8Pb/204Pb为37.956～39.094,矿石铅属异常铅,其单阶段模式年龄(136.3～707.3 Ma)不能代表成矿年龄,但其分布特征反映了铅的多源混合特征。同位素构造模式图上投点的线性分布特征显示了花岗闪长斑岩、矽卡岩、大理岩中的铅同位素演化具有很好的继承性和相应性,但各类铅同位素组成在20 8Pb/204Pb-206Pb/204Pb图上均落在下地壳和地幔之间,指示其具有来自壳幔边界附近的深源的特点。鸡笼山金铜矿床、丰山洞铜钼矿床、城门山铜金矿床、铜绿山铜铁矿床4个相似矿床的铅同位素组成进行对比,显示整体成矿物质来源在主体相似的背景下也具有局部的差异性。     

中国大陆新生代上地幔铅同位素特征

收集了新生代(含少量晚中生代) 301件幔源玄武岩的Pb同位素数据, 编制了系统的Pb同位素变化趋势(等值线) 图件, 现仅提供“中国大陆新生代上地幔的206Pb/204Pb比值变化趋势图”.图件显示, Pb同位素在南北方向的差异比较显著, 南北的界线大体从合肥-郑州-银川-汗腾格里峰, 结合Nd同位素的资料, 以206Pb/204Pb比值为18~18.5作为分界, 以北小于18~18.5;以南大于该值.此外初步辨认出该时期存在3种类型的地幔: 造山带地幔、裂谷型地幔及“非典型地幔”.与依据不同时代、各种类型的样品铅同位素的比值, 统一编制的“中国大陆岩石圈206Pb/204Pb比值变化趋势图”进行比较, 显示出在东北的西北部的206Pb/204Pb比值、南北向东经104°附近的高206Pb/204Pb比值区是否存在、渤海周边Pb异常区的强度以及华南DUPAL异常区问题等方面都有区别, 表明晚中生代-新生代时期, 中国大陆进入了一个新的软流圈地幔对流体系, 近代地幔并没有完全继承老地幔的全部特征而是被注入了新的软流圈物质.此外, 两张趋势图都显示了南北分块的特征, 而东西向的系统变化, 仅在近代Pb比值趋势图中华南块体的东南沿海地区出现, 暗示太平洋板块俯冲对中国大陆的影响处于次要地位.      

铜陵地区老鸦岭层状钼矿床铅同位素组成研究

安徽铜陵老鸦岭矿床中二叠系大隆组(P2d)顶部的含矿(钼矿化)黑色页岩以及附近(立新煤矿)同一层位不含矿黑色页岩的实测铅同位素组成分别为：^206Pb/^204Pb20.20～22.37,^207Pb/^204Pb15.67～15.82,^208Pb/^204Pb38.47～38.60和^206Pb/204Pb18.83～20.80,^207Pb/^204Pb15.65～15.76,^208Pb/^204Pb38．84～39．22。对137Ma的放射成因Pb进行校正后的铅同位素组成表明，含矿黑色页岩和不含矿黑色页岩均与燕山晚期火成岩无关，老鸦岭含矿黑色页岩可能具沉积成因。对沉积(约250Ma)以来的放射成因Pb进行校正后的铅同位素组成表明：不含矿黑色页岩的Pb源自上地壳，而含矿黑色页岩的Pb(因而推测其他成矿金属)可能源于上地壳物质(与不含矿黑色页岩的Pb源相似)与下地壳物质的混合。     

湖北徐家山锑矿床铅同位素组成与成矿物质来源探讨

徐家山锑矿床位于湖北省通山县境内,矿体赋存于上震旦统灯影组和陡山沱组地层中.对采自该矿的辉锑矿进行了系统的铅同位素测定.结果表明,在徐家山矿区范围内存在两组明显不同的铅同位素组成:A组206Pb/204Pb为18.874～19.288,207Pb/204Pb为 15.708～15.805, 208Pb/204Pb为38.642～39.001, 为高放射性成因铅;B组以低放射性成因铅为特征,其同位素组成206Pb/204Pb为17.882～18.171,207Pb/204Pb为15.555～15.686,208Pb/204Pb为37.950～38.340.对应地,相关参数也明显不同,如单阶段模式年龄,A组为负值或极小的正值,而B组为636～392 Ma.铅同位素组成与某些相关参数(Δγ与Δβ、V1与V2)之间呈明显线性正相关关系.根据铅构造模式和矿石铅同位素的Δγ-Δβ成因分类图解等综合分析,A组辉锑矿的铅主要来源于赋矿围岩--震旦系海相碳酸盐岩,B组主要来源于赋矿围岩的下伏基底碎屑岩--中元古界冷家溪群浅变质岩系.研究结果不支持前人沉积-改造成因的观点,成矿物质是多来源的,部分成矿物质来自基底地层.     

西藏北部舍索与拉屋铜矿床硫化物铅同位素特征

本文在系统的野外地质工作基础上,对舍索与拉屋矿床的矿石硫化物铅同位素组成进行综合分析,进而示踪其成矿物质来源。结果显示,舍索矿区矿石硫化物铅的206Pb/204Pb值为18.517~18.776,207Pb/204Pb值为15.671~15.756,208Pb/204Pb值为38.955~39.33;拉屋矿区矿石硫化物铅的206Pb/204Pb值为18.651~18.757,207Pb/204Pb值为15.707~15.823,208Pb/204Pb值为39.183~39.561。研究表明,舍索与拉屋矿床矿石硫化物铅同位素含量比值具有明显的上地壳特征,指示两个矿床成矿物质主要来自上地壳。其中舍索矿床成矿物质富集受燕山期岩浆作用影响,而拉屋矿床部分成矿物质由晚石炭纪地幔物质的喷流沉积作用提供。     

广东北部早白垩世粗面岩的成因:Sr-Nd-Pb同位素制约

广东北部大长沙盆地粗面岩锆石SHRIMP U-Pb年龄为(135.3±1.5) Ma,形成于早白垩世早期,其Sr-Nd-Pb同位素组成为:富放射性成因铅,(206pb/204Pb)i=18.23～18.39,(207pb/204pb )i=15.78～ 15.88,(208Pb/204Pb)i＝38.83～39.14,...     

Ion microprobe U–Pb dating of zircon with a 15 micrometer spatial resolution using NanoSIMS

We developed a ²³⁸U–²⁰⁶Pb and ²⁰⁷Pb–²⁰⁶Pb zircon dating method using a Cameca NanoSIMS NS50 ion microprobe. A 7-to 9-nA O⁻ primary beam was used to sputter a 15-μm crater, and secondary positive ions were extracted for mass analysis using the Mattauch–Herzog geometry. The multicollector system was modified to detect ⁹⁰Zr⁺, ²⁰⁴Pb⁺, ²⁰⁶Pb⁺, ²³⁸U¹⁶O⁺, and ²³⁸U¹⁶O₂⁺ ions simultaneously. A mass resolution of about 4000 at 10% peak height and with a flat peak top was attained, and the sensitivity of Pb was about 4 cps·nA^− 1·ppm^− 1. A multicrystal zircon standard (QGNG) from South Australia with a U–Pb age of 1842 Ma was used as a reference for Pb⁺/UO⁺–UO₂⁺/UO⁺ calibration, and on the basis of the positive correlation between these ratios, we determined the sample ²⁰⁶Pb/²³⁸U ratios. ²⁰⁷Pb/²⁰⁶Pb ratios were measured by magnetic scanning in single-collector mode. The standard zircons 91500, from Canada, and SL13, from Sri Lanka, were analyzed against QGNG. Observed ²³⁸U–²⁰⁶Pb and ²⁰⁷Pb–²⁰⁶Pb ages agreed well with published ages within experimental error. Then, 16 zircon grains in a metamorphic rock from Nagasaki, Japan, were analyzed. Observed ages were compatible with SHRIMP ages, suggesting that the NanoSIMS with a 15-μm probe diameter is suitable for ion microprobe U–Pb zircon dating.     

A Correction Approach to the Common Pb Contribution to ^207Pb／^206Pb Ratios Obtained by the Zircon Evaporation Technique

An approach is recommended for the correction of common Pb contribution to ^207Pb/^206Pb ages obtained by the zircon evaporation technique.A comparison with that by Cocherie et al.(1992)shows that two approaches yield similar results in the ^207Pb*/^206Pb* ratios.But when using the new approach,only two errors of the measured ^204Pb/^206Pb and ^207Pb/^207Pb ratios are introduced to the calculated ^207Pb^*/^206Pb^* ratios.     

Laser ablation coupled with ICP-MS applied to U–Pb zircon geochronology: A review of recent advances

Improvements in the technology of laser ablation and ICP-MS instruments make LA-MC-ICPMS a rapid, precise and accurate method for U–Pb zircon geochronology. In this review we describe the main stages of the evolution of this in situ approach from the early 1990s to the present time. Some key points have been progressively improved. The crater size has been reduced to achieve real in situ measurements. The laser wavelength has been reduced as well as the duration of each pulse in order to lower inter-element fractionation. The blank from the gas has to be lowered as far as possible. Double focusing instruments and magnetic field sectors allow flat-topped peaks required for precise isotope ratio measurement to be obtained. The use of a multi-ion counting system significantly improves the sensitivity of the method and the static mode of integration favours the precision of measurement of the transient signal originating from a noisy laser ablated particle beam.Combining the use of a 213 nm UV laser and a MC-ICPMS equipped with a multi-ion counting system operating in static mode, the common precisions achieved for the key ratios ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁶Pb/²³⁸U are better than 1% and 3% (2σ) respectively, including error propagation associated with standard normalization. Until now, the use of a zircon standard has remained necessary to ensure the accuracy of the calculated age. A strategy for common-Pb correction is proposed according to the age of the zircon and according to the Th/U ratio of the grains. After recording sixteen to twenty spot analyses the precision usually achieved on the age is about 1% and even significantly better for Proterozoic samples.In order to show the performance achieved by modern LA-MC-ICPMS geochronology, we tested four zircon samples covering a wide age range from 290 to 2440 Ma. These new age determinations can be compared in term of precision and accuracy since they have already been dated by reference methods (ID-TIMS and SHRIMP). Further developments in the technology of ion counters equipping modern MC-ICPMS and in laser systems will certainly be applied to a large field of geochronology studies in the near future as an alternative to SIMS for in situ age determination.     

Albany K-Feldspar: A New Pb Isotope Reference Material

Lead isotopes are a powerful and versatile tool to elucidate fundamental geological problems related to the formation and evolution of continental crust. K-feldspar is a popular target for Pb isotope measurement as it is prevalent in many rock types and tends to capture the initial Pb isotope composition of its parental magma. We present data for a new Pb isotope reference material: Albany K-feldspar; as well as updated data for Shap K-feldspar. Results of Pb double-spike TIMS for Albany K-feldspar are ²⁰⁶Pb/²⁰⁴Pb = 16.7872 ± 0.0062, ²⁰⁷Pb/²⁰⁴Pb = 15.5640 ± 0.0056, and ²⁰⁸Pb/²⁰⁴Pb = 36.6600 ± 0.0168 (2s). TIMS measurement results for Shap K-feldspar indicate two isotopically distinct Pb populations. LA-MC-ICP-MS, with a spatial resolution as high as 15 μm, indicates a homogeneous Pb isotopic composition in Albany K-feldspar. In accord with previous studies, our results show that scatter in the measured Pb isotope ratios, related to the low natural isotopic abundance of ²⁰⁴Pb, along with the effect of isobaric ²⁰⁴Hg-²⁰⁴Pb interference, increases at lower count rates. However, the mean Pb isotope ratios measured via LA-MC-ICP-MS using a range of spot sizes are in excellent agreement with TIMS results thus highlighting the feasibility of Pb isotope determination via LA-MC-ICP-MS to access geological information preserved in small crystals, including mineral inclusions.     

VizualAge: A Novel Approach to Laser Ablation ICP‐MS U‐Pb Geochronology Data Reduction

VizualAge, a new computer software tool for analysing U‐Pb data obtained by laser ablation‐inductively coupled plasma‐mass spectrometry, was developed. It consists of a data reduction scheme (DRS) for Iolite (a general mass spectrometry data analysis tool) as well as visualisation routines. In addition to the U/Pb and Th/Pb ages calculated by Iolite’s U‐Pb geochronology DRS, VizualAge also calculates ²⁰⁷Pb/²⁰⁶Pb ages and common Pb corrections for each time‐slice of raw data. Importantly, VizualAge allows one to display a live concordia diagram for visualising data on such a diagram as an integration interval is being adjusted. This provides instantaneous feedback regarding discordance, uncertainty, error correlation and common Pb. Several zircon data sets were used to illustrate how the live concordia could be used as a powerful inspection tool, revealing a single analysis to consist of zones of concordance, metamict areas, as well as inherited cores or younger overgrowths. VizualAge also constructs histograms, conventional and Tera‐Wasserburg type concordia diagrams, as well as 3D U‐Th‐Pb and total U‐Pb concordia diagrams. The precision and accuracy of data reduced with VizualAge are demonstrated with examples of the Ple?ovice, Temora‐2 and Penglai zircon reference materials. Data for zircon from the Long Lake Batholith (Wyoming craton) were used to illustrate how VizualAge calculated common Pb corrections and helped to expose as yet unexplained difficulties with accurately determining ²⁰⁴Pb.     

Ore Geology,Fluid Inclusion,and S‐ and Pb‐Isotopic Constraints on the Genesis of the Chitudian Zn‐Pb Deposit,Southern Margin of the North China Craton

The Chitudian Zn‐Pb ore deposit, Luanchuan, Henan province, was recently discovered in the southern margin of the North China Craton. The Zn‐Pb orebodies are hosted in the Proterozoic Guandaokou and Luanchuan Groups, occurring as veins in interbedding fracture zones mainly in a WNW‐ and partially in a NS‐direction. The Zn‐Pb ores are characterized by banded, massive, and breccia structures, coarse crystal grains, and a simple mineral composition mainly of galena, sphalerite, pyrite, quartz, dolomite, and calcite. In addition to the vein type orebodies, there are Mo‐ and Zn‐bearing skarn orebodies in the northwest of the Chitudian ore field. Four types of primary fluid inclusions in quartz and calcite were recognized in the Chitudian Zn‐Pb ores, including aqueous, aqueous‐CO₂, daughter‐mineral‐bearing aqueous, and daughter‐mineral‐bearing aqueous‐CO₂ inclusions, with aqueous inclusion being most common. The homogenization temperatures of the fluid inclusions from the main mineralization stage are from 290°C to 340°C, and the salinities mainly from 3.7 to 14.8 wt% NaCl equivalent. In addition to CO₂, CH₄ and H₂S were detected in the vapor phase and HS^‐ in the liquid phase of the fluid inclusions by Laser Raman spectroscopy. The δ³⁴S_V‐CDT values of ore sulfides from the Chitudian deposit range from ?0.32‰ to 8.30‰, and show two modal peaks in the histogram, one from 1‰ to 4‰, and the other from 5‰ to 7‰. The former peak is similar to that of porphyry‐type Mo‐W deposits in the area, whereas the latter is relatively close to the sulfur in the strata. The ore sulfur may have been derived from both the magma and the strata. The Pb‐isotopic compositions of the ore minerals from Chitudian, with ²⁰⁶Pb/²⁰⁴Pb from 17.005 to l7.953, ²⁰⁷Pb/²⁰⁴Pb from 15.414 to 15.587, and ²⁰⁸Pb/²⁰⁴Pb from 37.948 to 39.036, are similar to those of Mesozoic porphyries in the Chitudian ore field, suggesting that the ore‐forming metals were mainly derived from the Mesozoic magmatic intrusions. The Chitudian Zn‐Pb deposit is interpreted to be a distal hydrothermal vein‐type deposit, which was genetically related to the proximal, skarn‐type Mo ore deposits in the region.     

Genesis of the South Zhuguang Uranium Ore Field,South China: Pb Isotopic Compositions and Mineralization Ages

U–Pb isotopic analyses indicate that ores from the South Zhuguang uranium ore field, south China, have high common (non‐radiogenic) Pb contents, with variable and relatively radiogenic initial Pb contents. The U–Pb isochron method was used to date these ores, with plots of ²⁰⁸Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb versus ²⁰⁶Pb/²⁰⁴Pb being used to identify sample suites with similar initial Pb isotopic ratios and to normalize variable initial Pb isotopic ratios. The resulting U–Pb isochrons indicate two substages of uranium mineralization at ~57 and 52 Ma, with a later hydrothermal reformation at ~49 Ma, which homogenized Pb isotopic compositions. Initial Pb isotopic systematics indicate that the ore‐forming fluid was characterized by high ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb ratios and low ²⁰⁸Pb/²⁰⁴Pb ratios, suggesting that the ore‐forming fluid was sourced from Cretaceous–Paleogene red‐bed basins, rather than from magma or the mantle, with consideration of mineralization ages.     

Petrogenesis of the Bao'anzhai granite and associated Mo mineralization,western Dabie orogen,east-central China: Constraints from zircon U–Pb and molybdenite Re–Os dating,whole-rock geochemistry,and Sr–Nd–Pb–Hf isotopes

Recently, many Mo deposits genetically related to emplacement of Early Cretaceous granites have been found in the Dabie–Qinling belt. A typical intrusion that combines magmatism and metallogenesis, the Bao'anzhai granite, yields a zircon ²³⁸U–²⁰⁶Pb age of 123.2 ± 1.1 Ma and a molybdenite Re–Os isochron age of 122.5 ± 2.7 Ma. This granite is characterized by high silica and alkali, but low Mg, Fe, and Ca. It is enriched with light rare earth elements (REEs) and large-ion lithophile elements (LILEs, Rb, K, Th, U) but depleted of heavy REEs, high field strength elements (HFSEs, Nb, Ta, Ti, and Y), and Sr. This high-K granite has medium initial ⁸⁷Sr/⁸⁶Sr ratios (0.706518–0.707116) and low initial Pb isotopic ratios [(²⁰⁶Pb/²⁰⁴Pb)_i, 16.423–16.699; (²⁰⁷Pb/²⁰⁴Pb)_i, 15.285–15.345; (²⁰⁸Pb/²⁰⁴Pb)_i, 37.335–37.633], and is characterized by low ?_Nd(t) and ?_Hf(t) values (?14.92 to??14.22 and??21.67 to??19.19, respectively). These data indicate that this pluton is a high-K calc-alkaline fractionated I-type granitite. It was generated by partial melting of the Yangtze lower crust, which is probably similar to Neoproterozoic TTG-like magmatic rocks at the north Yangtze Block under a non-thickened lower crust environment (<35 km). The ores also have low radiogenic Pb isotopes (²⁰⁶Pb/²⁰⁴Pb, 16.592–17.674; ²⁰⁷Pb/²⁰⁴Pb, 15.300–15.476; ²⁰⁸Pb/²⁰⁴Pb, 37.419–37.911) and low Re content in molybdenite (5.693–10.970 ppm), suggesting a crustal magmatic source for the metallogenic minerals in the Mo deposit.     

湘东南铜山岭铅锌多金属矿床成矿时代与成矿物质来源——Sm-Nd等时线年龄和Pb同位素证据

铜山岭铅锌多金属矿床位于扬子地块湘南-桂东北坳陷与华夏地块粤北坳陷的拼贴部位,是中国南岭多金属成矿区代表性矿床之一。为确定矿床成矿时代,挑选铜山岭铅锌多金属矿床中含矿矽卡岩的石榴子石进行Sm-Nd同位素定年,获得的等时线年龄为173±3Ma,指示成矿作用发生于燕山早期。对金属硫化物矿物进行了Pb同位素分析,其~(206)Pb/~(204)Pb、~(207)Pb/~(204)Pb、~(208)Pb/~(204)Pb平均值分别为18.602、15.701、38.729,表明成矿物质来源于相对富集铀铅、略微亏损钍铅的上地壳源区。从(~(207)Pb/~(204)Pb)i-(~(206)Pb/~(204)Pb)i铅同位素演化模式图可知,寄主花岗闪长岩是铜山岭铅锌多金属矿床的重要物质来源,且成矿物质中可能含有寄存在花岗闪长岩中的地幔组分。     

Early Cretaceous A-type granites and Mo mineralization,Aershan area,eastern Inner Mongolia,Northeast China: geochemical and isotopic constraints

The Jiazishan porphyry-type molybdenum deposit is located in the eastern Inner Mongolia Autonomous Region in China. Mineralization occurs mainly as veins, lenses, and layers within the host porphyry. To better understand the link between mineralization and host igneous rocks, we studied samples from underground workings and report new SHRIMP II zircon U–Pb and Re–Os molybdenite ages, and geochemical data from both the molybdenites and the porphyry granites. Seven molybdenite samples yield a Re–Os isochron weighted mean age of 135.4 ± 2.1 Ma, whereas the porphyry granite samples yield crystallization ages of 139 ± 1.5 Ma (Jiazishan deposit) and 133 ± 1 Ma (Taolaituo deposit). The U–Pb and Re–Os ages are similar, suggesting that the mineralization is genetically related to Early Cretaceous porphyry emplacement. Re contents of the molybdenite range from 21.74 ppm to 52.08 ppm, with an average of 35.92 ppm, whereas δ³⁴ S values of the sulphide vary from 1.3‰ to 4.2‰. The ores have ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios of 18.178–18.385, 15.503–15.613, and 37.979–38.382, respectively. We also obtained a weighted mean U–Pb zircon age of 294.2 ± 2.1 Ma for the oldest granite in Jiazishan area. All granites are A-type granites. These observations indicate that the molybdenites and the porphyry granites were derived from a mixed source involving young accretionary materials and enriched subcontinental lithospheric mantle. A synthesis of geochronological and geological data reveals that porphyry emplacement and Mo mineralization in the Jiazishan deposit occurred contemporaneously with Early Cretaceous tectonothermal events associated with lithospheric thinning, which was caused by delamination and subsequent upwelling of the asthenosphere associated with intra-continental extension in Northeast China.