Mesozoic molybdenum deposits in the East Xingmeng orogenic belt,northeast China: characteristics and tectonic setting

Numerous molybdenum (Mo) ore deposits have been discovered in the East Xingmeng orogenic belt (East Central Asian orogenic belt), over the past 10 years, and this region is becoming one of the world's most important Mo production areas. It contains 6.18 Mt of proven Mo metal reserves, which accounts for 30% of the total proven Chinese Mo reserves. The ore district includes 37 deposits and 15 occurrences, with three major Mo ore types, that is porphyries, skarns, and hydrothermal veins. The latter can be subdivided into quartz- and volcanic hydrothermal-vein types. With the exception of the Ordovician Duobaoshan porphyry Cu–Mo deposit (477 Ma), all the East Xingmeng Mo deposits formed during the Mesozoic. Re–Os dating of molybdenite has documented three episodes of Mo mineralization: Early Triassic (248–242 Ma), Jurassic (178–146 Ma), and Early Cretaceous (142–131 Ma). Early Triassic Mo deposits are distributed along the northern margin fault of the North China Craton (NCC) and include porphyry and quartz vein types. They are characterized by the association of Mo + Cu. Jurassic Mo deposits are mainly distributed in the eastern area and include porphyry, quartz vein, and skarn types. They are typified by Mo alone and/or the association of Mo, Pb, and Zn. Cretaceous Mo deposits are distributed in all areas and include porphyry and volcanic hydrothermal vein types. Similar to the Jurassic ores, they are simple Mo or Mo + Pb + Zn deposits. Volcanic hydrothermal vein deposits are characterized by an association of molybdenum and uranium. The Triassic Mo deposits formed in a syn-collision setting between the Siberian and North China plates. The Jurassic Mo deposits formed in a compressional setting, which was probably triggered by the westward subduction of the palaeo-Pacific plate. The Early Cretaceous Mo deposits are linked to a tectonic regime of lithosphere thinning, which was caused by delamination of thickened lithosphere. However, the Mo deposits in the Erguna terrane of the northwest Xingmeng orogenic belt may be related to the evolution of the Okhotsk Ocean.     

Mesozoic molybdenum deposits in the east Qinling–Dabie orogenic belt: Characteristics and tectonic settings

The East Qinling–Dabie orogenic belt accommodates the largest Mo ore district in the world. It contains 8.43 Mt of proven Mo metal reserves which accounts for 66% of the total proven Chinese Mo reserves. The Mo ore district includes 24 deposits and 12 occurrences, with four major types of Mo mineral systems, i.e., porphyry, porphyry-skarn, skarn and hydrothermal veins. The latter can be further subdivided into quartz vein and carbonatite vein types. Although Mo mineralization in the belt began in the Paleoproterozoic (1680 ± 24 to 2044 ± 14 Ma), all economically significant deposits were formed during the Mesozoic. Re/Os dating of molybdenite has shown that there are three episodes of Mo mineralization, i.e., Late Triassic (233–221 Ma), Late Jurassic to Early Cretaceous (148–138 Ma) and Early to middle Cretaceous (131–112 Ma).Late Triassic Mo deposits developed as molybdenite–quartz veins and carbonatite vein types. Stable isotope systematics (C, O, S) and high contents of Re and Sr indicate that the carbonatite Mo veins are mantle-derived. Porphyry and porphyry–skarn Mo mineral deposits were formed in the Late Jurassic to Early Cretaceous and Early to middle Cretaceous. The Late Jurassic to Early Cretaceous granite porphyries that are associated with the Mo deposits usually occupy less than 1.5 km² at the surface and are situated in the East Qinling area, far west of China's continental margin. On the other hand, the Early to middle Cretaceous batholiths and granite porphyries, , with associated Mo deposits are located in the Dabieshan area and eastern part of the East Qinling area. The Late Jurassic to Early Creataceous granitoids and related Mo deposits possibly formed in a back-arc extensional setting of the Eurasian continental margin, which was probably triggered by the oblique subduction of the Izanagi plate. The Early to middle Cretaceous batholiths and granite porphyries are linked to the tectonic regime of lithospheric thinning, asthenospheric upwelling and partial melting of the crust, induced by a change in Izanagi Plate motion parallel to the continent margin.In the East Qinling–Dabie belt there are vein type Pb–Zn–Ag deposits surrounding porphyry and/or porphyry–skarn Mo (W) deposits, forming well defined ore clusters. The same spatial arrangement (i.e., porphyry Mo stockworks and outlying Pb–Zn–Ag ore veins) is also observed at the deposit scale. Thus, Mo porphyry stockworks and distal polymetallic veins belong to the same ore system and may reflect an outward temperature decrease from the highly fractionated granite plutons. Both, porphyry stockworks and polymetallic veins, can be used as vectors for further prospecting.     

燕山板内造山带中生代构造演化特征

燕山地区自晚三叠世以来进入了板内造山带形成演化阶段，并具有分期演化的幕式特征。在时间演化序列上，可分出造山前期（T3）、造山主期（J1－J3）和造山后期（K1）等3个阶段。构造变形方面，燕山板内造山带的基本构造格局为一大型逆冲推覆系统组成的构造楔形体，呈前展式扩展，造成的地壳缩短量可达44.1%。动力变质作用以高压动力变质为特征，发育高压动力变质岩（榴辉岩和高压麻粒岩），形成于构造应力集中的逆掩断层上盘，由中－上地壳长英质岩石转变而成。岩浆岩属钙碱性岩石系列、中酸性岩石组合，其中岩石类型、稀土元素配分型式及所反映的构造运动强度均具有一定的特征。在造山带形成过程中伴生3期同造山磨拉石：杏石口期磨拉石（T3x)、后城期磨拉石（J3h)和青石砬期磨拉石（K1q)，它们反映了造山带的幕式演化特点和不同造山时期构造运动强度的不均一性。     

东昆仑阿克楚克塞地区辉长岩地球化学特征、锆石U-Pb年龄及其构造意义

东昆仑地区基性-超基性岩石的研究较薄弱,缺乏对东昆仑幔源岩浆活动及岩浆演化的整体认识。对阿克楚克塞辉长岩进行了地球化学、锆石U-Pb年代学及Hf同位素研究,结果显示,该岩石形成于晚三叠世早期(219.3±1.1Ma,MSWD=0.80);岩石SiO2含量为49.03%~57.26%,Mg#值为49~57,属于钙碱性系列岩石;稀土元素配分曲线为轻稀土元素富集的右倾型,富集大离子亲石元素Rb、Ba、K,相对亏损高场强元素Nb、Ta、Ti;εHf(t)=-1.81~3.25,锆石Hf模式年龄大于锆石结晶年龄。地球化学特征显示,阿克楚克塞辉长岩岩浆源区应为受俯冲板片流体交代的岩石圈地幔。结合区域构造背景分析,阿克楚克塞辉长岩形成于印支期造山后伸展的构造环境,继承了早期板片俯冲改造的地幔源区特征。     

秦岭—大别造山带(湖北段)重力场特征与造山带构造

利用区域重力资料,通过位场分离、转换技术,揭示了造山带深部构造特征。正的线状重磁异常带及各阶小波细节,清晰地反映了桐柏—大别及东秦岭造山带南缘缝合带的位置,特别是重力异常小波四阶逼近,深部构造特征更加醒目。在鄂西北地区岩石圈所呈现出的"立交桥式"双层结构中,自由空间、均衡重力、剩余重力异常及小波各阶细节明显地反映出相对浅部的造山带近东西向延伸的构造特征;各阶逼近结果则反映了相对深部的地壳-岩石圈地幔南北向伸展的构造特征。应用地球物理资料来研究地球岩石圈结构、构造,除深层地震外,区域重力也是最有效方法手段之一。特别是近年来二维小波变换技术日趋成熟,为应用区域重力资料解决诸如造山带深部构造等疑难问题提供了新的手段和工作思路。     

Re—Os Isotope Ages of Molybdenum Deposits in East Qinling and Their Significance

Dating of metallic ore deposits has been one of the problems concerned with by ore geologists for many years.The establishment of the Re-Os Isotope Laboratory at the Institute of Rock and Mineral Analysis,Chinese Academy of Geological Sciences, has provided us with a new technique to carry out geochronological studies of molybdenum ores.As one of the most important Re-bearing minerals, molybdenite contains almost no common osmium, but ^187Os was derived completely from decay of ^187Re, with ^187Os content as the function of Re content in the mineral .An ID-ICP-MS technique has been used in this study,and Re-Os isotopic ages of several large molybdenum deposits of differ-ent types from the East Qinling molybdenum belt have been determined.It is indicated that the Huanglongpu carbonatite vein-type molybdenum-(lead) deposit has a Re-Os age corresponding to Indosinian,while the rest porphyry-type molybdenum deposits and porphyry-skarn-type molybdenum-(tungsten) deposits have Re-Os ages corresponding to Yenshanian.     

秦岭大别造山带地壳化学结构研究

大陆地壳不同结构层之间化学组成(含元素和同位素组成)的系统性差异可以称为地壳化学结构,地球化学参考模型(GERM)能够作为参照标准进行地壳化学结构(元素组成)的对比分析,据此提出了反映地壳演化特征的蛛网图标准化方法。对秦岭—大别造山带的尝试发现,造山带总体上具有物质组成分异较弱的特点;造山带及邻区太古亩结晶基底太华群、崆岭群的化学组成都不能代表全部的下地壳,可能仅代表了下地壳上部,而大别群可能经历了复杂的构造熟化过程。通过对造山带地壳化学结构的分析,指出铕负异常可能并非为地壳拆沉作用所造成。     

东昆仑拉陵灶火钼多金属矿床地质特征及辉钼矿Re-Os同位素定年

提要：拉陵灶火钼多金属矿床是青海祁漫塔格成矿带新发现的矽卡岩-斑岩型矿床。利用辉钼矿Re-Os同位素定年技术,11件样品和4件重复样品的模式年龄显示2个分段：214.1~223.9 Ma与235.7~240.8 Ma,187Re-187Os等时线年龄分别为（214.5±4.9）Ma和（240.8±4.0）Ma,模式年龄的加权平均值分别为（217.6±3.5）Ma和（238.4±1.2）Ma,等时线年龄与模式年龄加权平均值在误差范围内一致,表明矿床存在2期成矿作用：中三叠世和晚三叠世。辉钼矿样品中铼含量为17.40×10-6~149.52×10-6,绝大多数集中在十几至几十微克,指示其成矿物质来源为壳幔混合源。结合前人及本次研究成果表明,两次成矿作用分别与中三叠世东昆仑地区俯冲结束与碰撞开始时的板片断离作用和晚三叠世岩石圈拆沉作用有关。     

论东天山觉罗塔格造山带的大地构造属性

觉罗塔格造山带位于吐哈盆地和中天山地块之间，长期以来，关于该造山带的大地构造属性争论较多，有晚古生代岛弧带、弧后盆地、裂陷槽、古生代陆缘增生带、石炭纪火山岩型被动陆缘等不同认识。基于晚古生代早期觉罗塔格地区处于板内拉张的动力学背景，而非挤压碰撞环境，结合对带内早石炭世雅满苏组火山—沉积建造较为系统的岩石学、岩石化学及岩石地球化学研究，认为觉罗塔格造山带应为一拉张型构造—岩浆岩带。     

秦岭—大别造山带北缘新生代的构造特征及动力学探讨

秦岭－大别造山带北缘新生代的推覆构造带位于宜阳、鲁山、确山、六安一线,由SW→NE依次逆冲叠置。滑脱面主要发育在上古生界软弱岩层或差异岩性的接触面上。在推覆构造的南侧、发育有东西向串珠状分布的变质核杂岩、NE向延伸的垒－堑构造组合、北宽南窄的楔形新 生代盆地和正断层等。地球物理资料表明,宜阳、鲁山、确山、六安一为向南倾斜的地球物理异常带。北部的华北地壳与南部的秦岭－大别地壳在视电阻率、地震反射波组、地震波速、流变学分层、地壳类型和岩石圈结构等方面,均有明显的差别。秦岭－大别造山带北缘新生代不同性质、有规律展布的构造,是中生代末期以来,华北板块相对于秦岭－大别造山带作巨型陆内俯冲的结果。     

东昆仑造山带早中生代镁铁质岩墙群LA-ICP-MS锆石U-Pb定年、元素和Sr-Nd-Hf同位素地球化学

东昆仑造山带白日其利镁铁质岩墙群以苏长辉长岩为主,含少量含斑辉绿岩,LA-ICP-MS锆石U-Pb年代学指示该套岩墙群结晶侵位年龄为251±2Ma.岩石具有中等的Mg#(31～50)和高铝(16.25％～19.49％)的特征,整体属于钙碱性玄武岩系列岩石(Na2O+ K2O =2.75％～3.51％;FeOT/MgO=1.02～2.22);微量和稀土元素方面,岩石具有较低的稀土总量、轻稀土轻微富集和Eu正异常特征(ΣREE =52.16×10-6～99.81×10-6,(La/Yb)N =2.08～5.49,δEu=1.0～1.3),所有岩石富集LILE(如Rb、Ba和Pb等)而亏损HFSE(如Nb、Ta、P和Ti等),且具有显著不同于地壳的不相容元素组成(如Nb/Ta比值).岩墙具有富集的Sr-Nd同位素组成((87Sr/86 Sr)i=0.71103～0.71502,εNd(t)=-7.4～-3.6),具有相对集中且显著不同于地壳岩浆的Hf同位素组成(εHf(t)=-2.37～1.07).元素地球化学和同位素研究指示镁轶质岩浆起源于流体交代的富集地幔Ⅱ,并未受到显著的地壳混染.构造环境分析表明,岩石具有岛弧和洋中脊玄武岩双重特征.结合区域构造演化分析,我们认为,在晚二叠世-早三叠世时期,在俯冲环境下,板片流体交代使上覆地幔楔发生富集,形成富集地幔Ⅱ,随着该区伸展作用的加强,在早三叠世,进一步诱发了富集地幔的部分熔融并产生镁铁质岩浆,最终侵位结晶就形成了白日其利镁铁质岩墙群.     

安徽省金寨县沙坪沟钼矿辉钼矿Re-Os年龄——兼论东秦岭-大别山中生代钼成矿作用期次划分

安徽省金寨县沙坪沟钼矿是新发现的超大型斑岩型钼矿床.文章介绍了该矿床的基本地质特征,并对其进行了精确的辉钼矿Re-Os同位素年代学测定.结果表明,沙坪沟钼矿辉钼矿模式年龄为(112.2±1.7)～(113.9±1.7) Ma,加权平均年龄为(113.18±0.54) Ma,MSWD - 0.39;等时线年龄为(113....     

东秦岭石窑沟斑岩钼矿床地质特征及辉钼矿Re-Os年龄

在东秦岭钼成矿带最近探明的石窑沟大型钼矿床位于近东西向马超营断裂带与北东向石窑沟-焦园断裂带的交汇部位,获得钼金属储量10余万吨,平均品位0.068%。钼矿化呈细脉-网脉状分布于花岗斑岩体及其围岩熊耳群火山岩中,与矿化有关的围岩蚀变有钾长石化、硅化、绢云母化、黄铁矿化等,具有斑岩型钼矿床的一些基本特点。在矿床中选取5件不同矿化类型的辉钼矿样品,采用ICP-MS法进行Re-Os同位素定年,获得模式年龄131.3±2.4～134.3±2.6Ma,等时线年龄135.2±1.8Ma(MSWD=0.18),形成于早白垩世,与豫西熊耳山地区雷门沟、鱼池岭等钼矿床形成时代相近。据辉钼矿Re含量(8.242×10-6～30.24×10-6)推测,矿床成矿物质主要来自于下地壳。矿床为东秦岭-大别山地区中生代第三期钼成矿作用产物,形成于早白垩世中国东部岩石圈伸展环境。     

燕山中段盘山花岗岩体锆石SHRIMP U-Pb年龄测定及其构造意义

位于燕山陆内造山带中段南缘的蓟县盘山花岗岩体由狼家峪、官庄、东罗庄和小盘山4个侵入单元组成,并发育侵入期后含斑石英二长岩脉,发育环绕岩体分布的周缘向斜并侵蚀早期东西向蓟县断裂.对前3个侵入单元及岩体西侧围岩中的顺层侵入的含斑石英二长岩脉等4件样品的锆石U-Pb（SHRIMP）定年结果为,年龄值界于203～207Ma,表明盘山花岗岩体侵位于三叠纪末期.这个年龄结果进一步限定了燕山陆内造山带东西向褶皱、逆冲/逆掩断层系统形成时代的上限,显示其形成时代为印支期.     

Tectonic Subdivision of Dabie Orogenic Belt,Central China：Evidence from Pb Isotope Geochemistry of Late Mesozoic Basalts

It has long been debated that the Dabie orogenic belt belongs to the North China or Yangtze craton. In recent years, eastern China has been suggested, based on the Pb isotopic compositions of Phanerozoic ore and Mesozoic granitoid K-feldspar (revealing the crust Pb) in combination with Meso-Cenozoic basalts (revealing the mantle Pb), being divided into the North China and Yangtze Pb isotopic provinces, where the crust and mantle of the Yangtze craton are characterized by more radiogenic Pb. In this sense, previous researchers suggested that the pro-EW-trending Dabie crogenic belt with less radiogenic Pb in the crust was part of the North China craton. In this paper, however, the Late Cretaceous basalts in the central and southern parts of the Dabie orogenic belt are characterized by some more radiogenic Pb (²⁰⁶Pb/²⁰⁴Pb=17.936−18.349,²⁰⁷Pb/²⁰⁴Pb=15.500−15.688,²⁰⁸Pb/²⁰⁴Pb=38.399−38.775) and a unique U-Th-Pb trace element system similar to those of the Yangtze craton, showing that the Mesozoic mantle is of the Yangtze type. In addition, the decoupled Pb isotopic compositions between crust and mantle were considerably derived from their rheological inhomogeneity, implying a complicated evolution of the Dabie orogenic belt. The study was funded by the National Natural Science Foundation of China (No. 49794043) and the Open Laboratory of Constitution, Interaction and Dynamics of the Crust-Mantle System, China.     

大别山造山带中生代构造演化特征

大别山陆内造山带形成于早侏罗世晚期至早白恶世（J^31-K1），并具有分期演化特征。在构造演化序列上，可分出造山前期（J^21-J2）和造山主期（J3-K1）2个阶段。构造变形方面，基本构造格局为一大型逆冲推覆系统组成的构造楔形体，呈后展式扩展，造成的地壳短缩量可达46.8%，动力变质作用以高压动力变质为特征，发育高压动力变质岩（榴辉岩、蓝片岩和高压麻粒岩），形成于构造应力集中的主干逆掩断层上盘。岩浆岩属钙碱性岩石系列，中酸性岩石组合，其中岩石类型，稀土元素配分型式等所反映的构造运动强度均具有一定的特点。在陆内造山带形成过程中伴生了3期同造山磨拉石，朱集期磨拉石（J2z），段集期磨拉石（J3d）和下符桥期磨拉石（K2x），它们反映了不同造山时期构造运动强度的差异。     

Geochemical Characteristics and Implications of Eclogite Gravels from Mesozoic Strata at the Northern Margin of Dabie Orogenic Belt

The eclogite gravels, which were found in the Mesozoic Fenghuangtai and Maotanchang formations on the northern margin of the Dabie orogenic belt, are rich in K2O(1.21%),∑REE (278μg/g) ,and LILE(such as Rb, Ba, K, Th, etc.) , with high (La/Yb)N ratios(14.4),on the basis of the analyses of major elements, rare-earth elements (REE) and trace elements. Their enrichment in LILE, notable Nb-Ta depletion through, and depletion in HFSE relative to REE in comparison with the primitive mantle and N-MORB indicate that the protoliths of the eclogite gravels were formed in an island-arc setting. According to the Th-Hf-Ta discrimination diagram, the protoliths of the eclogite gravels are characterized by volcanic arc basalts.Trace element data indicate that the subducted marine sediments were assimilated in the magma chamber, resulting in the enrichment of LILE in the protoliths. Therefore, the protoliths of the eclogite gravels are considered to have been formed in an inland-arc setting, indicating that there had developed a paleo-inland arc before Triassic collision between the North and South China blocks in the Dabie orogenic belt. There is a marked difference between the eclogite gravels and the eclogites developed along the Dabie orngenic belt, solely based on their geochemical data,especially REE. Therefore, the eclogite gravels may not be derived from eclogite terrains preserved in the Dabie orogenic belt.     

秦岭拉鸡庙镁铁质岩体锆石LA-ICP-MS年代学研究

秦岭拉鸡庙镁铁质岩体位于北秦岭南缘,主要由辉长岩(80%)、苏长辉长岩(15%)和少量闪长岩等侵入杂岩组成。对采自该岩体闪长岩的锆石进行阴极发光图像、微区原位LA-ICP-MS微量元素分析和U-Pb定年。CL图像显示这些锆石可以分为两类,一类锆石呈长柱状,具有明显的岩浆生长环带;另一类则呈浑圆状,阴极发光图像复杂,部分颗粒岩浆生长环带较模糊,个别样品外围存在一窄的亮色环边,推测为后期地质事件影响的结果。对26颗锆石核部和生长边进行28次U-Pb同位素分析,获得两组²⁰⁶Pb/²³⁸U年龄,分别为973±60Ma和422±7Ma。分析结果显示,所有样品具有高的Th, U, REE含量,明显富集HREE,其Th/U比值普遍高于0.6,表明这些锆石应属于岩浆成因。其中,422±7Ma应该代表拉鸡庙镁铁质岩体的成岩时代,这可能与古生代扬子陆块或者是具有扬子板块属性的微陆块和华北陆块的碰撞有关,该碰撞导致了秦岭洋的闭合;而973±60Ma应为捕获锆石年龄,代表北秦岭早期与Rodinia超大陆拼合有关的岩浆事件。考虑到没有检测到典型的华北克拉通的年龄,推测元古代北秦岭更接近华南板块。     

东秦岭-大别造山带北侧中新生代差异构造变形

受多期非均衡造山作用以及多构造体制的叠加,东秦岭-大别造山带北侧中新生代发生差异构造变形.基于区域构造动力学机制,将中新生代构造变形分为4个期次:印支期(T2-T3)、早燕山期(J1)、中燕山期(J2-K1)和晚燕山-早喜马拉雅期(K2-E).通过野外地质剖面和地震剖面的构造解析,认为印支期-中燕山期主体变形方式为逆冲...     

福建福安赤路钼矿床辉钼矿Re-Os同位素年龄及其地质意义

本文使用电感耦合等离子体质谱仪TIAX-series ICP-MS对赤路钼矿床中的辉钼矿进行同位素年龄测定,获得了赤路钼矿床中辉钼矿的Re-Os同位素模式年龄为105～106Ma.这一年龄与研究区内与钼矿床成矿关系密切的似斑状花岗岩、二长花岗岩、钾长文象花岗岩形成时代较为吻合,均属燕山晚期岩浆活动的产物.这项研究为在浦城-宁德北西向成矿带燕山晚期岩浆活动、成矿作用以及浦城-宁德与上杭-云霄两条北西向成矿带的对比研究及找矿工作,提供了直接的年代学证据.