岩石学报  2014, Vol. 30 Issue (7): 2081-2091   PDF    
引用本文
孙振明, 任云生, 鞠楠, 赵华雷, 陈聪, 孙宇超. 2014. 吉林延边天宝山矿集区的叠加成矿——来自同位素年代学证据. 岩石学报,30(7): 2081-2091  
Sun ZM, Ren YS, Ju N, Zhao HL, Chen C, Sun YC. 2014. Superimposed mineralization of the Tianbaoshan metallogenic region in Yanbian area (eastern Jilin Province), northeastern China：Indicated by the isotopic dating. Acta Petrologica Sinica,30(7): 2081-2091 (in Chinese with English abstract)  
吉林延边天宝山矿集区的叠加成矿——来自同位素年代学证据
孙振明1, 任云生1 , 鞠楠2, 赵华雷1, 陈聪1, 孙宇超3    
1. 吉林大学地球科学学院, 长春 130061;
2. 沈阳地质矿产研究所, 沈阳 110034;
3. 吉林省龙井市瀚丰矿业有限公司, 龙井 133400
2013-11-2 收稿, 2014-1-17 改回.
基金项目：本文受国家重点基础研究发展计划项目（2013CB429802）和中国地质调查局项目（1212011085485）联合资助.
第一作者简介：孙振明，男，1987年生，博士生，矿产普查与勘探专业，E-mail：sunzhenming.9040@163.com
通讯作者：任云生，男，1969年生，教授，博士生导师，主要从事矿床学与区域成矿规律的教学与研究工作，E-mail：renys@jlu.edu.cn
摘要：天宝山大型多金属矿集区位于兴蒙造山带东缘，西拉木伦-长春断裂带与敦（化）-密（山）断裂带交汇部位的北东侧，已发现矽卡岩型Pb-Zn-Ag矿化（如立山和选厂后山）、隐爆角砾岩中的Pb-Zn-Ag矿化（如新兴）、沉积变质-热液改造型Cu-Pb-Zn矿化（如东风南山）和热液脉型Mo矿化（如东风北山）等多种矿化类型。为建立该区的成岩成矿年代学格架，采用LA-ICP-MS单颗粒锆石U-Pb法，对立山成矿闪长岩与东风北山含矿黑云母石英闪长岩开展了同位素测年研究；并对东风北山钼矿床开展了辉钼矿Re-Os法测年。结果表明，立山闪长岩体与东风北山黑云母石英闪长岩体中锆石的加权平均年龄分别为266.2±3.9Ma（MSWD=14）和278.4±1.8Ma（MSWD=2.9），两岩体均属海西晚期岩浆事件的结果；东风北山钼矿床中6件辉钼矿样品的Re-Os模式年龄介于190.3±3.1Ma~194.6±2.8Ma，等时线年龄为192±3.1Ma，表明钼的成矿作用发生于燕山早期。立山铅锌矿化属接触交代型，成矿岩体的年龄基本代表成矿时代，所以立山铅锌矿床形成于海西晚期；东风北山钼矿床为热液脉型，虽然含矿岩体的侵位时代为海西期，但钼矿化发生于燕山早期，成矿与矿区深部或外围的燕山早期侵入体有关。因此，天宝山矿集区至少发生过海西期和燕山期两期大规模岩浆成矿事件。不同期次构造-岩浆-成矿作用的叠加应是该矿床矿化类型复杂、矿种多和规模大的主因。
关键词： 锆石U-Pb法测年     辉钼矿Re-Os测年     矽卡岩型多金属矿化     热液脉型钼矿化     叠加成矿     天宝山矿集区     延边    
Superimposed mineralization of the Tianbaoshan metallogenic region in Yanbian area (eastern Jilin Province), northeastern China：Indicated by the isotopic dating
SUN ZhenMing1, REN YunSheng1 , JU Nan2, ZHAO HuaLei1, CHEN Cong1, SUN YuChao3    
1. College of Earth Sciences, Jilin University, Changchun 130061, China;
2. Shenyang Institute of Geology and Mineral Resources, Shenyang 110034, China;
3. Hanfeng Mining Co. Ltd, Longjing 133400, China
Abstract: The large-scale Tianbaoshan metallogenic region, with over one hundred years of mining history, is located in eastern Yanbian area, northeastern China. Thanks to abundant nonferrous metal resources and diverse deposit types, metallogenic theory and ore-prospecting in the Tianbaoshan region have been paid attention to both at home and abroad for a long time. According to the recent research data, the Yanbian area in NE China belonged to the Paleo-Asian Ocean tectonic region during the Paleozoic Era and to the Paleo-Pacific Ocean tectonic region since the Jurassic period. Evolution and superimposition of the two tectonic regions resulted in multi-cyclic tectonic-magmatic activities and provided a beneficial ore-forming geological condition to the intensive nonferrous and precious metal mineralization in this area. Up to now, at least four types of deposits have been discovered, including skarn lead-zinc deposit (e.g. Lishan deposit and Xuanchanghoushan deposit), crypto-explosive breccia lead-zinc-silver deposit (e.g. Xinxing deposit), sedimentary metamorphic-hydrothermal copper-lead-zinc deposit (e.g. Dongfengnanshan deposit) and lode (-porphyry) molybdenum deposit (e.g. Dondfengbeishan deposit). Among these deposit, the Lishan and Dongfengbeishan are more valuable than others. The Lishan deposit occurs in the contact belt between the Late Paleozoic diorite and the Permian marble, the major ore body is controlled by the contact belt and fractures, metal minerals include pyrite, galena, sphalerite, chalcopyrite, pyrrhotite and minor magnetite. The Dongfengbeishan deposit is characterized by veinlet and stockwork molybdenum mineralization in the Late Paleozoic biotite quartz diorite, there are a small amount of such metal minerals as molybdenite, pyrite, chalcopyrite, pyrrhotite and minor arsenopyrite. Due to few accurate geochronology data, it's still uncertain that the two deposits are derived from either the same or different tectonic-magmatic events. Moreover, their tectonic setting is still in controversy. To determine the geochronology framework of the polymetallic mineralization and associated magmatic events in the this region, isotopic dating has been completed, including LA-ICP-MS U-Pb dating of zircons from the metallogenic diorite in Lishan skarn deposit and the ore-hosting biotite quartz diorite of lode molybdenum mineralization in Dongfengbeishan deposit, as well as the molybdenite Re-Os dating in Dongfengbeishan deposit. Isotopic ages of fifteen zircon grains from the Lishan diorite change from 277±2Ma to 254±3Ma, with the weight average age of 266.2±3.9Ma (MSWD=14). U-Pb isotopic ages of nineteen zircon grains from Dongfengbeishan biotite quartz diorite vary from 283±3Ma to 271±3Ma, and the weight average age is 278.4±1.8Ma (MSWD=2.9). These isotopic dating results indicate that both plutons emplaced in the Late Hercynian period. The REE composition and chondrite-normalized REE patterns of the zircon from the Lishan diorite and Dongfengbeishan biotite quartz diorite, together their similar isotopic age, imply that both plutons were derived from the contemporaneous co-magmatism. The Re-Os isochron age of six molybdenite samples from the Dongfengbeishan deposit is 192±3.1Ma, and model ages change from 190.3±3.1Ma to 194.6±2.8Ma, which suggests that the molybdenum mineralization took place in the Early Yanshian period. Because the Lishan lead-zinc deposit belongs to the skarn type, the age of the ore-forming diorite, 266.2±3.9Ma, can be regarded as the metallogenic age. Although the ore-hosting biotite quartz diorite in the Dongfengbeishan deposit emplaced in the Hercynian period, the molybdenum mineralization took place in Early Yanshanian period, which indicates that there should occur the Early Yanshanian intrusion closely related to molybdenum mineralization. Moreover, it can be concluded that the Tianbaoshan polymetallic metallogenic region underwent at least two large magmatic and metallogenic events, the Late Hercynian and the Early Yanshanian, respectively. The study area is located in the east edge of the Xing'an-Mongolian Orogenic Belt (Central Asian Orogenic Belt), and the northeastern part of the intersection region of the Xilamulun-Changchun and the Dunhua-Mishan faults. According to the popular tectonics views on NE China, this district belonged to the Paleo-Asian Ocean tectonic region in Permian period. There are more and more evidence support that the final closure of the Paleo-Asian Ocean from the latest Permian to the Early Triassic period resulted from the matching between the Xing'an-Mongolian Orogenic Belt and the North China Craton. Since the Jurassic period, intensive tectonic-magmatic actives in the east portion of the Xing'an-Mongolian Orogenic Belt were probably controlled by the subduction of the Paleo-Pacific plate. Based on previous research and data in this paper, it can be conclude that the Lishan diorite and associated skarn lead-zinc mineralization as well as ore-hosting biotite quartz diorite in Dongfengbeishan deposit were formed under the background of the Paleo-Asian ocean tectonic region, and the molybdenum mineralization in Dongfengbeishan deposit can be classified into the Paleo-Pacific tectonic-magmatic-metallogenic event. In addition, the superimposition of different period of tectonic-magmatic-mineralization may result in such especial characteristics as large-scale, complex types as well as paragenesis of several beneficial elements in Tianbaoshan region.
Key words: Zircon U-Pb dating     Molybdenite Re-Os dating     Skarn polymetallic mineralization     Lode molybdenum mineralization     Superimposed mineralization     Tianbaoshan metallogenic region     Yanbian area    

天宝山矿集区位于吉林省延边朝鲜族自治州龙井市境内，是一个具有百年开采历史的大型有色金属矿山。因矿集区及外围的矿床(点)数量多、资源量丰富、矿化类型复杂，其理论研究和地质找矿在延边乃至东北地区具有引领作用。长期以来，众多研究者在该区的成矿地质条件、矿床类型、矿床地质和地球化学特征、矿床成因以及成矿系列等方面开展了较为深入的研究。目前，该区矿床属“多类型、多成因和多来源的复式成因”观点为越来越多的学者所接受(李宝树和李鹤年，1991；孙钧，1994；孙景贵等，2006；张勇等， 2011，2012；鞠楠等，2011)，但仍存在“矿床数量多和类型复杂的根本原因何在？”以及“不同矿化类型是同期还是不同期次岩浆成矿事件的结果？”等科学问题。

上述问题的解决均需以精细的年代学资料为基础，而这恰是天宝山矿集区研究的薄弱环节。基于此，本文以立山矽卡岩型多金属矿床和新发现的东风北山热液脉型钼矿床为重点，在成矿地质条件和矿化特征研究基础上，采用锆石U-Pb法和辉钼矿Re-Os法进行了同位素测年，初步厘定天宝山矿集区内代表性矿床的成岩成矿时代，进而探讨矿集区内生金属矿床的成矿期次和叠加成矿。

1 矿集区地质概况

矿集区位于天山-兴蒙造山带东段，西拉木伦-长春断裂带与敦化-密山断裂(简称“敦密断裂”)交汇部位的北东侧(图 1)。古生代以来，该区经历了古亚洲构造域、环太平洋构造域以及两大构造域的叠加与转换等不同大地构造演化阶段(彭玉鲸等，2002；祁进平等，2005；陈衍景等，2009)，多期次构造-岩浆活动强烈，成矿地质条件优越。

图 1 天宝山矿集区大地构造位置(据陈衍景等，2012修改)与矿区地质略图

1-第四系；2-下侏罗统明月沟组；3-二叠系庙岭组；4-石炭系天宝山群；5-志留系青龙村群；6-海西期侵入岩；7-印支期侵入岩；8-燕山期侵入岩；9-花岗岩；10-黑云母花岗岩；11-碱长花岗岩；12-花岗闪长岩；13-石英闪长斑岩；14-闪长岩；15-石英斑岩；16-次安山岩；17-矿床；18-压扭性断裂；19-张扭性断裂；20-推测压扭性断裂；21-推测张扭性断裂

Fig. 1 Tectonic location(modified after Chen et al., 2012) and geological sketch map of the Tianbaoshan metallogenic region

1-Quaternary; 2-Lower Jurassic Mingyuegou Formation; 3-Permian Miaoling Formation; 4-Carboniferous Tianbaoshan Group; 5-Silurian Qinglongcun Group; 6-Hercynian intrusive rocks; 7-Indosinian intrusive rocks; 8-Yanshanian intrusive rocks; 9-granite; 10-biotite granite; 11-alkali-feldspar granite; 12-granite diorite; 13-quartz diorite porphyry; 14-diorite; 15-quartz porphyry; 16-sub and esite; 17-deposit; 18-compresso-shear fault; 19-transtensional fault; 20-inferred compresso-shear fault; 21-inferred transtensional fault

区内主要发育志留系青龙村群和石炭系天宝山群变质岩系，二叠系庙岭组中性火山岩及其碎屑岩、角岩、板岩夹灰岩，以及侏罗系明月沟组中酸性火山岩、火山碎屑岩。侵入岩主要包括海西期黑云母花岗岩、花岗闪长岩、石英闪长斑岩、黑云母石英闪长岩，印支期花岗岩、碱长花岗岩、花岗闪长岩、石英斑岩、闪长岩，以及燕山期次安山岩(岩株或岩脉)(图 1)。区内近EW向区域性断裂形成较早，控制了古生代地层和侵入岩的空间展布方向；NW向和NE向断裂是主要的控矿构造，多控制矿体的形态、产状和规模；近SN向断裂形成最晚，多为成矿后断裂。

2 主要矿床类型及地质特征

20世纪70年代以前，立山和选厂后山矽卡岩型铅锌银矿床一直作为主要开采对象；1976年，在头道沟发现了隐爆角砾岩筒中的铅锌银矿体，之后在东风南山发现了火山沉积-热液改造型多金属矿床；1984年又在东风北山发现了细脉型钼矿体(陈冬，2009)(图 1)。上述四种矿化类型中，立山矽卡岩型铅锌银矿和东风北山热液脉型钼矿工业意义最大，矿化特征最具代表性。

2.1 立山矽卡岩型铅锌矿

矿体主要赋存于闪长岩与石炭系天宝山群大理岩的侵入接触带及其附近(图 2a)。目前已发现矿体600余条(包延辉等，2012)，所组成的矿带延长700m，宽500m，延深800m，走向310°~340°，倾向南西，倾角40°~70°，上部矿体以脉状为主，中部以透镜状和板状为主，下部似层状为主，矿石中Pb的平均品位为1.15%，Zn的平均品位为1.94%，总金属量为38.17万吨(徐仁杰等，2010)。矿石具有块状、条带状、角砾状和斑杂状构造(图 3a，b)。矿石中主要金属矿物为闪锌矿、方铅矿、黄铜矿和黄铁矿，含少量磁黄铁矿和磁铁矿(图 3c，d)；非金属矿物为石英、方解石、绿泥石、绿帘石、透辉石、绢云母和符山石等。矿石中金属矿物常表现为交代残余结构、骸晶结构和固溶体分离结构。

图 2 立山矿床剖面示意图(a，据汪志刚，2012修改)和东风北山矿床29线剖面图(b，据高岫生等，2010修改)

图(a):1-大理岩；2-板岩；3-角岩；4-英安质凝灰岩；5-闪长岩；6-英安斑岩；7-天宝山群；8-次安山岩；9-矽卡岩；10-矿体.图(b): 1-安山质凝灰岩；2-斑状二长花岗岩；3-石英闪长斑岩；4-黑云母石英闪长岩；5-闪长岩；6-地质界线；7-断层；8-矿体及编号

Fig. 2 Geological profile maps in Lishan deposit(a，modified after Wang，2012) and of 29# exploration line in Dongfengbeishan deposit(b，modified after Gao et al., 2010)

In Fig. 2a: 1-marble; 2-slate; 3-hornstone; 4-dacitic tuff; 5-diorite; 6-dacitic porphyry; 7-Tianbaoshan group; 8-sub- and esite; 9-skarn; 10-ore body. In Fig. 2b: 1-dacitic tuff; 2-porphyritic monzonitic granite; 3-quartz diorite porphyry; 4-biotite quartz diorite; 5-diorite; 6-geological boundary; 7-fault; 8-ore body


图 3 立山矿床与东风北山矿床岩石和矿石特征照片

(a)-立山矿区块状矽卡岩矿石；(b)-立山矿区角砾状矽卡岩矿石；(c、d)-立山矿石中的交代结构；(e)-东风北山脉状辉钼矿化；(f)-东风北山矿石中的叶片状辉钼矿；(g)-立山矿区的绿泥石化、绿帘石化闪长岩；(h)-东风北山黑云母石英闪长岩.矿物代号：Ccp-黄铜矿；Gn-方铅矿；Py-黄铁矿；Pl-斜长石；Chl-绿泥石；Ep-绿帘石；Qtz-石英；Bt-黑云母；Sp-闪锌矿；Po-磁黄铁矿；Mlb-辉钼矿

Fig. 3 Photographs of the intrusive rock and polymetallic ore in Lishan and Dongfengbeishan deposits

(a)-massive skarn ore in Lishan deposit;(b)-brecciated skarn ore in Lishan deposit;(c，d)-metasomatic texture in the ore from Lishan deposit;(e)-vein molybdenum mineralization in Dongfengbeishan deposit;(f)-foliated molybdenite in Dongfengbeishan deposit;(g)-chloritization and epidotization in Lishan diorite;(h)-biotite quartz diorite in the Dongfengbeishan deposit. Ccp-chalcopyrite; Gn-galena; Py-pyrite; Pl-plagioclase; Chl-chlorite; Ep-epidote; Qtz-quartz; Bt-biotite; Sp-sphalerite; Po-pyrrhotite; Mlb-molybdenite

主要蚀变类型有矽卡岩化、钾长石化、石英化、绿泥石化、绿帘石化、绢云母化和方解石化。其中，矽卡岩化主要发育在天宝山群大理岩与闪长岩的接触带及其附近，与银多金属矿化具有密切的空间和成因关系。 2.2 东风北山热液脉型钼矿

已探明矿体近百个，绝大多数为盲矿体，主要受东风南山NW向断裂及其次级构造裂隙控制，呈细脉状或网脉状，少数为扁豆状。单矿体一般长50~100m，厚1~3m，最厚12.84m，走向325°~350°，倾向南西，倾角50°~65°。矿化主要表现为黑云母石英闪长岩体中的含辉钼矿石英细脉或网脉(图 2b)。围岩蚀变主要有钾长石化、石英化、绿泥石化、绿帘石化、绢云母化、方解石化和高岭土化等。矿石中金属矿物主要为辉钼矿(图 3e，f)，偶见黄铁矿、黄铜矿、磁黄铁矿和毒砂等；非金属矿物主要有石英、透辉石、绿泥石、绿帘石、沸石和方解石等。矿石中金属矿物主要为半自形-他形粒状结构，少数呈自形鳞片状结构；矿石主要呈细脉状和网脉状构造，局部见细脉浸染状构造。

3 样品描述与测试方法 3.1 锆石U-Pb法测年

立山矿床用于锆石U-Pb法测年的样品(编号TBS5-6)取自立山竖井(井口坐标：E128°57.811′，N42°56.753′)21中段矽卡岩型铅锌矿体附近的强蚀变闪长岩体。具有中细粒半自形结晶结构，块状构造；主要组成矿物为斜长石(40%)，绿帘石(25%)，黝帘石(10%)，阳起石(20%)以及极少量钾长石。其中，斜长石为原生矿物，局部有黝帘石化，部分可能全部蚀变呈黝帘石；绿帘石和阳起石多为角闪石等暗色矿物蚀变而成(图 3g)。

东风北山矿床用于锆石U-Pb法测年的样品(编号YB096)取自东风北山井下(井口坐标：E129°0.590′，N42°56.935′)9至12中段内的含矿岩体，岩石类型为黑云母石英闪长岩。岩石具有中细粒半自形结晶结构，块状构造；主要组成矿物为石英(15%)、斜长石(55%)、黑云母(15%)、钾长石(5%)以及角闪石(5%)(图 3h)。

锆石分选由河北省廊坊诚信地质服务有限公司完成；锆石制靶、CL图像采集、U-Pb测年以及锆石微量元素分析等均在西北大学大陆动力学国家重点实验室完成。锆石数据分析使用193nm的ComPex102型ArF准分子激光器和Agilent7500a型ICP-MS仪器，采用高纯He气作为剥蚀物质的载气，使用美国国家标准技术研究院的人工合成硅酸盐玻璃标准物质NIST610进行仪 器最佳化，使用哈佛大学国际标准锆石91500作为外标，对剥蚀和传输以及离子化过程中的质量歧视效应和同位素分馏进行校正。本文锆石测定过程中激光束斑直径为30μm，所测单点的同位素比值及元素含量采用GLITTER4.0软件进行处理，普通Pb校正按照Andersen(2002)的方法用ComPbCorr3.15软件进行，最后使用Isoplot3.0软件进行锆石U-Pb谐和图的绘制和年龄计算。详细的实验分析步骤和数据处理方法参见Yuan et al.(2004)。 3.2 辉钼矿Re-Os法测年

东风北山矿床用于Re-Os法测年的6件含辉钼矿石英脉矿石样品，3件取自坑口的矿石堆，3件取自井下9至12中段(样品坐标与YB096的坐标相同)。矿石中主要金属矿物以辉钼矿为主，偶见微量的黄铁矿、黄铜矿、磁黄铁矿等。矿石结构主要为半自形-它形粒状结构，少数自形鳞片状结构；矿石构造主要有细脉-网脉状构造和浸染状构造。

将挑选出的6件纯辉钼矿样品，研磨至200目以下，用于Re-Os同位素测定。同位素测试工作在国家地质实验测试中心进行，样品中的Re和Os含量测定均采用同位素稀释法完成。具体流程详见参考文献(杜安道等，1994；屈文俊和杜安道， 2003，2004)。

4 同位素测年结果 4.1 立山成矿岩体的锆石U-Pb测年

立山蚀变闪长岩中的锆石多呈无色透明四方柱和四方双锥的聚形体，粒径一般在135~200μm之间，长宽比1.61~2.21。CL图像显示(图 4a)，晶体生长环带清晰，少数颗粒具有规则的环带结构，多数颗粒环带宽窄不一，或者呈平行晶体长轴方向的条带状，Th/U比值为0.45~0.83，均大于0.1，平均值为0.61，为典型的岩浆成因。

图 4 立山(a)与东风北山(b)岩体中锆石阴极发光图

Fig. 4 Cathodoluminescence images of zircons from the Lishan(a) and Dongfengbeishan(b)plutons

锆石U-Pb法定年测试结果见表 1。根据测试数据所做的锆石U-Pb年龄谐和图(图 5a)显示，所测岩石形成于晚古生代，测年结果以206Pb/238U年龄计算，单个数据点的年龄误差均为2σ。所测15个测点的206Pb/238U年龄介于277±2Ma和254±3Ma之间，在206Pb/238U-207Pb/235U谐和图上，所有数据均位于谐和线上或分布在谐和线附近。对15个测点的206Pb/238U值加权平均，在MSWD=14、可信度95%条件下，得到206Pb/238U平均年龄为266.2±3.9Ma。

表 1 立山蚀变闪长岩与东风北山黑云母石英闪长岩中锆石U-Pb同位素数据

Table 1 U-Pb compositions in zircons from Lishan diorite and Dongfengbeishan biotite quartz diorite


图 5 立山蚀变闪长岩(a)与东风北山黑云母石英闪长岩(b)LA-ICP-MS锆石U-Pb年龄谐和图

Fig. 5 Concordia diagrams of zircon U-Pb ages for Lishan diorite(a) and Dongfengbeishan biotite quartz diorite(b)

4.2 东风北山含矿岩体的锆石U-Pb测年

东风北山黑云母石英闪长岩中的锆石多呈无色透明的四方柱和四方双锥聚形体，粒径一般在65~200μm之间，长宽比1.21~3.81。CL图像显示(图 4b)，晶体生长环带清晰，少数颗粒具有规则的环带结构，多数颗粒环带宽窄不一，或者呈平行晶体长轴方向的条带状，Th/U比值介于0.46~0.78，平均值为0.57，均大于0.1，为典型的岩浆成因。

锆石U-Pb法定年测试结果见表 1和图 5b。所测岩石形成于海西晚期，测年结果以206Pb/238U年龄计算，单个数据点的年龄误差均为2σ。所测19个测点的206Pb/238U年龄介于283±3Ma和271±3Ma之间，在206Pb/238U-207Pb/235U谐和图上，所有数据均位于谐和线上或分布在谐和线附近。对19个测点的206Pb/238U值加权平均，在MSWD=2.9、可信度95%条件下，得到206Pb/238U平均年龄为278.4±1.8Ma。

4.3 辉钼矿Re-Os测年

对6件辉钼矿样品分别测定了Re和Os的含量以及187Re/188Os和187Os/188Os比值测定，具体结果如表 2所示。6件样品模式年龄范围190.3±3.1Ma~194.6±2.8Ma，加权平均年龄为192.2±1.2Ma；采用ISOPLOT软件对6件样品的结果进行等时线加权拟合，得到等时线年龄为192.0±3.1Ma(图 6)，初始187Os为(0.001±0.019)×10-9，MSWD值为4.5。等时线年龄与加权平均年龄在误差范围内一致，显示了数据的可靠性。

表 2 东风北山钼矿床中辉钼矿Re-Os同位素分析结果 Table 2 Re-Os isotopic data of the molybdenite from the Dongfengbeishan molybdenum deposit

图 6 东风北山辉钼矿Re-Os同位素等时线及模式年龄加权平均值

Fig. 6 Re-Os isochron age and weighted average ages of molybdenites in Dongfengbeishan deposit
5 讨论与认识 5.1 立山岩体与东风北山岩体的成因关系

岩相学研究和上述测年结果表明，立山闪长岩和东风北山黑云母石英闪长岩具有相似的矿物组成和结构构造，形成时代相近，因此应具有密切的成因联系。

2个岩体中锆石的Th为72.67×10-6~247.1×10-6，U为148.4×10-6~399.4×10-6，Th/U比值介于0.45~0.83之间(表 1)。锆石微区稀土元素测试结果(表 3)及球粒陨石标准化稀土配分曲线(图 7)表明，上述锆石的稀土元素具有明显的Ce正异常，Pr负异常和Eu的弱负异常，∑REE含量较高(∑REE=609.4×10-6~1120×10-6，平均805.2×10-6)，HREE富集，配分曲线与岩浆锆石稀土元素特征一致，表明其为典型的岩浆锆石(Hoskin and Irel and ，2000)。另外从表 3以及图 7中可以看出，立山闪长岩与东风北山黑云母石英闪长岩中的锆石稀土元素特征极其相似，因此二者可能为同期、同源岩浆作用的结果。

表 3 立山蚀变闪长岩与东风北山黑云母石英闪长岩的锆石中稀土元素分析结果(×10-6) Table 3 REE compositions of zircons from Lishan diorite and Dongfengbeishan biotite quartz diorite(×10-6)

图 7 立山闪长岩与东风北山黑云母石英闪长岩锆石稀土元素对球粒陨石标准配分曲线

Fig. 7 Chondrite normalized REE patterns of zircon grains in Lishan diorite and Dongfenbeishan biotite quartz diorite

5.2 立山矽卡岩型铅锌矿的成岩成矿时代

立山矿床的成矿闪长岩体LA-ICP-MS锆石U-Pb法测年结果表明，岩体结晶年龄为266.2±3.9Ma(二叠纪)，为海西晚期。由于矽卡岩型矿床的成矿岩体年龄可近似代表成矿年龄，因此认为，立山铅锌矿床的成矿时代为海西晚期。

5.3 东风北山钼矿成岩成矿时代

利用LA-ICP-MS单颗粒锆石U-Pb法测得东风北山含矿黑云母石英闪长岩体的结晶年龄为278.4±1.8Ma，为海西晚期；辉钼矿Re-Os同位素等时线年龄为192.0±3.1Ma，为燕山早期。含矿岩体和钼矿化明显为不同时期构造岩浆活动的产物。

近年来的研究表明，除本文述及的东风北山钼矿床外，吉黑东部新发现的多个斑岩型(细网脉型)钼矿(鹿鸣、霍吉河、刘生店等)及辽西诸多矽卡岩型钼矿床均形成于燕山早期。例如，黑龙江东部的鹿鸣钼矿床中辉钼矿Re-Os等时线年龄为177.4±3.5Ma(谭红艳等，2012)； 霍吉河钼矿床中与成矿有关的黑云母二长花岗岩LA-ICP-MS锆石U-Pb年龄为186±1.7Ma(杨言辰等，2012)；延边地区刘生店、双山和汪清夹皮沟等钼矿床中的辉钼矿Re-Os等时线年龄分别为169.36±0.97Ma、174.5±2.0Ma和188.6±4.7Ma(王辉等， 2011，2013；王辉，2013)；辽西地区兰家沟、杨家杖子和肖家营子等钼矿床中辉钼矿Re-Os等时线年龄分别为186.5±0.7Ma、187~191Ma和177±5Ma(黄典豪等，1996)。陈衍景等(2012)指出，190~160Ma为中国东北钼矿形成的一个高峰期。可见，包括本文所述的东风北山钼矿床在内，吉黑东部和辽西地区的多个斑岩型(细网脉型)钼矿床均属东北地区燕山早期大规模岩浆成矿事件的结果。 5.4 构造叠合与叠加成矿

天宝山地区位于兴蒙造山带东缘，区域上处于古亚洲洋构造域与环太平洋构造域的叠加转换部位。古生代时期，该区处于多块体拼贴的古亚洲构造域发展阶段；从侏罗纪开始，随着太平洋板块向欧亚板块俯冲，研究区经历了两大构造域叠加转换，之后进入环太平洋构造域发展阶段，太平洋板块的俯冲作用对东北地区的构造、岩浆及成矿作用起着明显的控制作用(刘永江等，2010; Wu et al., 2011; Zeng et al., 2012; 2013)。

锆石U-Pb法定年结果显示，立山与东风北山含矿岩体均形成于二叠纪中晚期，此时区域处于古亚洲洋构造域发展阶段；而东风北山钼矿床形成于早侏罗世，此时古亚洲洋已闭合，区域上处于古亚洲洋构造域向环太平洋构造域的叠加转换期，构造岩浆活动频繁而强烈，钼矿成矿作用应该与太平洋板块的俯冲作用有关。换言之，天宝山矿集区的东风北山黑云母石英闪长岩、立山闪长岩及相关矽卡岩型多金属矿化形成于古亚洲(洋)构造域，而东风北山脉型钼矿属环太平洋构造成矿域的组成部分。

6 结论

(1)天宝山矿集区发育矽卡岩型、隐爆角砾岩型、沉积变质-热液改造型、热液脉型等四种矿化类型。

(2)天宝山矿集区至少经历了两期构造-岩浆-成矿作用的叠加：分别是海西晚期(266~278Ma)和燕山早期(~192Ma)。

(3)海西晚期，与古亚洲洋俯冲闭合有关的构造岩浆活动形成立山闪长岩体及相关的矽卡岩型铅锌矿化和东风北山黑云母石英闪长岩体；燕山早期，随着太平洋板块的俯冲，东北地区发生大规模内生金属成矿作用，在天宝山矿集区的东风北山海西期岩体内发生热液脉型钼矿化。

(4)两期成岩成矿事件的叠加应是该区矿化类型复杂、矿种多、矿床规模大的主因。

致谢 野外调研中得到了吉林省龙井市瀚丰矿业有限公司生产部张波、孙宇超、张博等同志的支持和协助;西北大学大陆动力学国家重点实验室和国家地质实验测试中心完成了样品测试工作;作者对上述单位和个人表示由衷感谢！

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