内蒙古白乃庙铜钼矿区侵入岩LA-MC-ICP-MS锆石U-Pb定年及地质意义

冯晓曦,姚书振，王家松，魏佳林,李光耀,王佳营，冯旭彪

(1. 中国地质大学(武汉)资源学院，湖北武汉 430074； 2. 天津地质调查中心，天津 300170；3. 深圳市冠欣矿业集团，广东深圳 518048)

内蒙古白乃庙铜钼矿区侵入岩LA-MC-ICP-MS锆石U-Pb定年及地质意义

冯晓曦1,2,姚书振1，王家松2，魏佳林2,李光耀2,王佳营2，冯旭彪3

(1. 中国地质大学(武汉)资源学院，湖北武汉 430074； 2. 天津地质调查中心，天津 300170；3. 深圳市冠欣矿业集团，广东深圳 518048)

白乃庙铜钼矿是华北地块北缘最重要的大型铜钼矿，矿区中部花岗闪长斑岩与成矿关系密切。为探讨成岩成矿关系，笔者选取花岗闪长斑岩进行了LA-ICP-MS锆石U-Pb定年和岩石地球化学特征研究。花岗闪长斑岩测年分别为432.4±2.2 Ma、440.7±2.1Ma和443±1Ma，岩体侵位时代为早志留世，与铜矿石中辉钼矿Re-Os等时线年龄440.5±4.4Ma(待刊)基本一致。岩体属高钾钙碱性岩石组合系列，稀土曲线右倾，δEu 14.83～-19.54，弱亏损，富集Rb、Ba、Th、U、K，亏损Nb、Ta、Ti，具有岛弧花岗岩的地球化学性质。结合区域地质背景，认为白乃庙铜钼矿成矿与早志留世花岗闪长斑岩岩浆期后热液活动密切相关，成矿构造背景为早古生代古亚洲板块向华北板块俯冲形成的白乃庙古火山岛弧带。

LA-ICP-MS锆石U-Pb定年 花岗闪长岩 成岩成矿 白乃庙铜钼矿

Feng Xiao-xi，Yao Shu-zhen，Wang Jia-song，Wei Jia-lin，Li Guang-yao，Wang Jia-ying，Feng Xu-biao. LA-MC-ICP-MS zircon U-Pb dating of the pluton in the Bainaimiao Cu-Mo deposit of Inner Mongolia and its geological significance[J]. Geology and Exploration, 2014, 50(2):0369-0381.

1 引言

白乃庙铜(钼)矿位于内蒙古四子王旗白音朝克图苏木，矿区由南、北矿带，十三个矿段组成。2010年以后，深圳冠欣矿业在白乃庙铜(钼)矿Ⅱ、Ⅲ、Ⅳ矿段深部发现厚大铜矿体，找矿成果正逐步扩大。

白乃庙铜(钼)矿为华北地块北缘唯一的大型铜(钼)矿床，以其独特的成矿地质条件吸引许多专家学者从地质、地球化学、构造演化、成岩成矿时代等进行了许多研究。一些学者对矿区中部与成矿关系密切的花岗闪长斑岩进行了成岩时代的研究。王东方(1986)测得花岗闪长斑岩的Rb-Sr模式年龄为386Ma。花岗闪长斑岩呈岩床产于绿片岩中，认为是岛弧背景下中浅成岩浆分异产物。胡骁(1988)认为白乃庙岛弧岩系的深成岩花岗闪长岩、花岗闪长斑岩、石英闪长岩、英云闪长岩等岩石Rb-Sr模式年龄为400±30Ma(386、419、340Ma)，认为岩体属成弧期同熔型花岗岩。唐克东(1992)测得白乃庙含矿花岗闪长斑岩U-Pb年龄为466Ma(锆石)，花岗闪长斑岩K-Ar年龄为450Ma(角闪石)，白云母花岗岩K-Ar年龄为429.8Ma(白云母)，认为白乃庙铜矿是早古生代环大洋岛弧发育中晚期形成的斑岩型铜矿。聂凤军等(1995)测得花岗闪长斑岩岩体Sm-Nd同位素等时线年龄为440±40Ma(2δ)，εNd(t)=-3.2±1.7(2δ)，认为北矿带的形成过程与加里东期(440Ma)花岗闪长斑岩的侵位和结晶分异密切相关。陈衍景(2009)测得侵入白乃庙组的花岗闪长斑岩侵位年龄为430±6Ma(n=13，MSWD=1.1)，白乃庙北矿带容矿破碎斑岩年龄为445±6Ma(n=14，MSWD=2.4)，辉钼矿Re-Os等时线年龄为444±30Ma(MSWD=2.8)，认为矿区存在早古生代斑岩型铜矿化。由上述可见，矿区花岗闪长斑岩成岩时代的精确厘定是研究白乃庙铜(钼)矿床成矿机制的关键要素，但上述研究表明岩体侵位时代为386Ma～466Ma，时代跨度80Ma，不利于对矿床成矿的认识。

为了进一步精确厘定白乃庙铜钼矿成矿成岩关系，笔者选择矿区花岗闪长斑岩进行LA-ICP-MS锆石U-Pb定年和岩石化学特征研究(Hoskinetal,2003 ;Donaldetal,2003)，初步探讨研究白乃庙铜钼矿成岩成矿时代和地质构造背景。

2 地质背景及含矿岩体特征

2.1 地质背景

白乃庙铜(钼)矿床位于华北地台北缘中段，南邻华北地台北缘赤峰-白云鄂博深大断裂，北依温都尔庙俯冲-增生杂岩带(图1)。

矿区出露的地层有新元古代白云鄂博群，寒武系白乃庙组，中志留统徐尼乌苏组，二叠系下统三面井组，白垩系下统固阳组等。主要成矿围岩白乃庙组为一套中浅变质的绿片岩，其原岩为一套海底喷发的基性-中酸性火山熔岩、凝灰岩，夹少量正常沉积的碎屑岩和碳酸盐岩，为浅海火山沉积建造(图2)。

矿区构造复杂，主要以断裂构造为主。东西向构造是白乃庙矿区主要的控岩控矿构造，控制了早古生代基性-中酸性火山喷发及花岗闪长斑岩等中酸性岩浆活动。与成矿相关的花岗闪长斑岩呈岩株状东西向展布，侵入于白乃庙组(图2)。

北矿带矿体主要产在花岗闪长斑岩中，岩体受东西向构造控制，基本是顺层侵入于绿片岩中。矿体大部分产于岩体中，岩体控制明显，少数矿体受构造控制明显，矿体具有从岩体外延至围岩中的现象。南矿带矿体主要产于绿片岩中，矿体产状与围岩基本一致。矿体呈似层状、透镜体状、单层或者多层，平行或者斜列式产出。矿体具有膨大、收缩、分枝、尖灭等现象。围岩蚀变主要有：钾长石化、黑云母化、硅化、绢云母化、绿泥石化、绿帘石化、碳酸盐化，前三种蚀变与成矿关系最为密切。矿石类型有花岗闪长斑岩型和绿片岩型。

图1 内蒙古中部地区区域地质构造图(李文博等,2007,略改)Fig.1 Regional geological map of the central section of Inner Mongolia (after Li et al. ,2007 with slight modification) 1-南蒙古生代大陆边缘；2-南蒙古生代弧增生杂岩；3-索伦克尔缝合带晚古生代增生杂岩；4-华北早古生代大路边 缘；5-华北前寒武纪克拉通；6-蛇绿岩；7-高压变质岩1-Paleozoic continental margin of south Mongolia; 2-Paleozoic arc-accreted complex of south Mongolia; 3-late Paleozoic accretionary complex in the the Solonker suture zone; 4-early Paleozoic continental margin of North China; 5-North China Precambrian craton; 6-ophiolite; 7-high-pressure metamorphic rocks

图2 白乃庙铜钼矿地质构造略图(来自李进文2007，略改)Fig.2 Simplified geological map of the Bainaimiao copper-molybdenite deposit (modified from Li et al.,2007) 1-第四系；2-下白垩统固阳组砾岩；3-下二叠统三面井组砂岩；4-中志留统徐尼乌苏组细碎屑岩；5-白乃庙组第五岩段；6-白乃庙组第四岩段；7-白乃庙组第三岩段；8-白乃庙组第二岩段；9-白乃庙组第一岩段；10-中元古界白云鄂博群白音宝拉格组；11-志留世花岗闪长斑岩；12-二叠世石英闪长岩；13-二叠世白云母花岗岩;14-花岗斑岩脉;15-石英脉;16-矿化带、矿体及矿段编号;17-实测及性质不明断层;18-白乃庙断裂带;19-地质界线/不整合地质界线;20-岩石化学样品采集位置及编号; 21-测年样品采集位置及编号1-Quaternary; 2-low Cretaceous Guyang Fm. conglomerate; 3-low Permian Sanmianjing Fm. sandstone; 4-middle Silurian Sanmianjing Fm. fine-grained clastic rock; 5-fifth lithological member of Bainaimiao Fm.; 6-fourth lithological member of Bainaimiao Fm.; 7-third lithological member of Bainaimiao Fm.; 8-second member of Bainaimiao Fm.; 9-first member of Bainaimiao Fm. ;10-Mesoproterozoic Bayan Obo Group Baiyin Baolage Fm.; 11-top Silurian granodiorite;12-Permian quartz diorite; 13-Permian muscovite granite; 14-granite porphyry vein;15-quartz vein; 16-mineralization zone, orebody and number of ore section;17-measured and unknown fault; 18-Bainaimiao fracture zone;19-geological boundary / unconformity; 20-position and number of petrochemistry sample; 21-position and number of sam-ple for dating

2.2 岩体特征

花岗闪长斑岩主要出露于矿区中部、北部，南矿带绿片岩中也有零星出露。受区域变质作用，蚀变强烈。风化面多呈灰黄-褐黄色。花岗闪长斑岩体呈近东西向侵入白乃庙组，出露面积分别为0.5km2。岩石多为灰白-浅肉红色，似片麻状构造、班状构造。具花岗结构，花岗碎斑结构，交代残余。岩石由石英(35%)、碱性长石(20%)、斜长石(30%)和暗色矿物(角闪石、黑云母)的蚀变矿物组成。副矿物见有磁铁矿(<1%)、磷灰石(<1%)和金红石(<1%)，零星分布。蚀变矿物有绿泥石、绢云母、白云母、方解石及金属矿物黄铁矿、黄铜矿、辉钼矿等。

石英碎斑呈它形粒状，具波状消光。碱性长石呈它形板状，微斜长石可见格子双晶，钠长石可见聚片双晶。斜长石呈它形-半自形板状，可见环带构造，颗粒中心较具较强的绢云母、帘石、碳酸盐化。碎基含量60%，粒径小于0.5mm，由石英、碱性长石碎粒和蚀变矿物组成。石英碎粒呈它形粒状集合体分布，长石呈它半条-粒状碎粒分布。蚀变矿物绿泥石、帘石、白云母、绢云母、方解石及铁质呈它形粒状、片状集合体、略具定向性分布(图3)。

图3 矿区中部D016点花岗闪长斑岩(4×10正交偏光)比例尺Fig.3 Granodiorite of D016 dot from the central deposit(4×10 orthogonal polarization)

3 岩石化学特征

对矿区中部花岗闪长斑岩采集4件样品进行岩石化学分析，分析结果列于表1。

表1 花岗闪长斑岩的主量元素氧化物(%)、微量元素和稀土元素(×10-6 )分析结果

续表1

Continued Table 1

样品号D016D017D016-1D010H2O-0.440.370.380.39CO21.740.0212.240.018Cu51.84200129975Pb5.908.825.948.68Cr8.4810.407.788.42Li15.48.6417.4021.10Rb81.69691.5122Cs4.121.344.483.34W7.641716.0312Sr436642493436Ba936322843472V140168140155Sc12.410.311.115Nb9.6210.69.6311Ta0.580.620.630.66Zr126125125127Hf3.713.753.783.84Be1.441.311.631.57Ga15.516.615.316.8U1.894.661.713.42Th13.89.4916.316.5La35.115.135.446Ce54.636.456.667Pr7.24.277.049.17Nd27.216.826.134.4Sm4.923.784.666.06Eu1.51.291.421.7Gd4.183.794.044.99Tb0.570.640.550.71Dy33.942.853.84Ho0.60.820.570.75Er1.622.41.612.11Tm0.260.390.260.34Yb1.82.821.862.36Lu0.280.430.270.35Y1521.114.619.3F7361470979985

注：天津地质矿产研究所测试，2013年。

本文所研究的4件样品的SiO2：60.09%～65.21% ；A12O3：15.40%～16.47%;MgO:1.58%～2.73%;K2O:2.52%～3.78%;Na2O:3.18%～4.00%；A/CNK为1.42～1.79。采用Geokit2012软件对数据进行处理(路远发，2004)。

在REE元素球粒陨石标准化分布型式图上显示平坦型，略右倾特征(图4)，∑REE值为113.97～199.08, LREE/HREE值为2.13～4.93，Eu弱亏损，δEu值为14.83～19.54，LaN/YbN=3.62～13.17，LaN/SmN=2.51～4.78，GdN/YbN=0.62～0.75，REE富集型，轻稀土分馏程度要高于重稀土，为典型的花岗岩浆岩的特征(李洪普等，2011)。

图4 白乃庙铜钼矿侵入岩球粒陨石标准化稀土配分模式图(C1球粒陨石据Sun and Mc Donough,1989)Fig.4 Chondrite-normalized REE patterns of granite in the Baibaimiao Cu-Mo deposit(chondrite from Sun and Mc Donough,1989)

在微量元素标准化模式图上, 元素含量均高于原始地幔岩，相对富集Rb、Th、K 和La、Sm,相对亏损Ba、Ta、Nb、Ti、P和Yb(图5)，Nb/Ta为15.28～17.10(正常花岗岩Nb/Ta约11)，Zr/Hf为33.1～33.9(正常花岗岩Zr/Hf约36～39)，Rb/Sr为0.15～0.28，具岛弧的钙碱性岩系的地球化学特征(赵振华，1997;梁亭等,2008;熊欣等,2011)。

图5 白乃庙铜钼矿侵入岩原始地幔标准化微量元素蛛网图(C1球粒陨石据Sun and Mc Donough,1989)Fig.5 Primitive-mantle normalized spidergram in the Baibaimiao Cu-Mo deposit(chondrite from Sun and Mc Donough,1989)

4 锆石样品测试

4.1 测试方法

锆石样品 Tj08采自Ⅻ矿段、Tj09采自Ⅸ矿段、Tj11采自Ⅷ矿段(图2)。

锆石样品靶的制作和锆石阴极发光照相在北京离子探针中心完成。LA-MC-ICP-MS锆石U-Pb定年在天津地质矿产研究所实验室完成。

4.2 测年结果

3件锆石样品在透射光下为无色，颗粒自形程度较好，多呈柱状，长轴变化于100～150μm，个别达300μm，长短轴之比在1∶1～1∶2之间。在阴极发光图像中，大多数锆石均发育较好的振荡环带，Th/U一般大于0.5,显示为岩浆锆石(图6、图7,表2～4)，该年龄代表了岩浆结晶年龄(余吉远等，2010)。测年结果分述如下：

Tj08样品测试了33粒锆石，锆石U的含量为204×10-6～1228×10-6，平均为546×10-6，Th/U为0.39～ 1.60 ,Th/U一般大于0.5。206Pb/238U年龄范围在314.4±2.91Ma～442.2±7.22Ma，加权平均年龄为432.4 ±2.2 Ma，MSWD =1.8, 拟合概率0.008(图6)。大部分锆石振荡环带清晰，为岩浆锆石，测年为418.3±3.71Ma～442.2±7.22Ma,在误差范围内与谐和年龄一致。此外还有3粒锆石206Pb/238U年龄为：Tj0801点314.4±2.91Ma、Tj0806点368.3±3.29Ma、Tj0818点372.7±3.58Ma，前两者具环带，但颗粒小，第三粒无环带，略具晶形，三者可能为热液锆石，与变质热液叠加有关。

Tj09样品测试了31粒锆石，锆石U的含量为51×10-6～1706×10-6，平均为703×10-6，Th/U大多0.52～ 1.43，Tj0909点为0.2，为基底捕获锆石，Tj0919点为0.06，原因不明。206Pb/238U年龄范围在372.3±2.24Ma～1742.2±12.05Ma，加权平均年龄为440.7±2.1 Ma，MSWD = 3.1, 拟合概率0(图6)。大部分锆石振荡环带清晰，为岩浆锆石，测年为423.3±2.54Ma～450.5±3.08Ma。Tj0906、Tj0909点、Tj0910点均为捕获基底锆石。

Tj11样品测试了32粒锆石。锆石U的含量为454×10-6～4445×10-6，平均为715×10-6，Th/U大多为0.50～ 1.01。206Pb/238U年龄范围在383.0±2.43Ma～1487.8±10.17Ma，加权平均年龄为443±1 Ma，MSWD = 0.34, 拟合概率1。大部分锆石振荡环带清晰，为岩浆锆石，测年为440.1±2.69Ma～446.3±2.73Ma。Tj1110点与Tj1111点测年分别为1238.3±10.1Ma、1487.8±10.17Ma，Tj1128点测年为1288.3±11.94Ma，均为捕获基底锆石。

图6 白乃庙铜钼矿花岗闪长岩样品Tj08、Tj09、Tj11锆石阴极发光照片图像Fig.6 CL images of zircon grains for granodiorite sample Tj08, Tj09, and Tj11 from Bainaimiao Cu-Mo deposit

图7 白乃庙铜钼矿区Tj08、Tj09、Tj11花岗闪长岩锆石U-Pb谐和曲线图Fig.7 U-Pb concordia diagram of zircon in granodiorite from Tj08, Tj09 and Tj11 samples of Bianaimiao Cu-Mo deposit

分析号含量(×10-6)同位素比值年龄(Ma)Tj08PbU206Pb/238U1σ207Pb/235U1σ207Pb/206Pb1σ208Pb/232Th1σ232Th/238U1σ206Pb/238U1σ207Pb/235U1σ1406680.05000.00050.68870.01070.09990.00140.01670.00040.82940.0054314.42.91532.08.252283830.07020.00090.54560.00840.05640.00080.02800.00040.39000.0062437.45.56442.16.823445800.06880.00070.56720.00700.05980.00070.01980.00020.74320.0016428.74.38456.25.654435520.07010.00060.55750.01200.05770.00120.02710.00060.55580.0034436.73.89449.99.665354620.06810.00080.55130.00870.05870.00090.01900.00020.83160.0035424.95.25445.97.066558500.05880.00050.51970.00400.06410.00050.01110.00011.05500.0135368.33.29424.93.277506510.06920.00070.55920.00750.05860.00080.01740.00020.84170.0077431.24.19451.06.068364650.07000.00060.57550.00620.05960.00060.02240.00020.65490.0084436.43.90461.65.009577540.06800.00040.54060.00620.05760.00070.01490.00010.98660.0036424.22.43438.85.0610294010.06920.00110.53020.00730.05550.00070.01570.00040.68300.0162431.66.56432.05.9511415420.07030.00060.57720.00560.05950.00060.02210.00010.54420.0018438.03.88462.64.4812486360.07040.00080.54970.00470.05660.00040.01970.00020.66830.0045438.54.79444.83.8113273680.06780.00060.55200.01780.05910.00180.02180.00050.60340.0042422.84.01446.314.3714445810.06950.00070.54790.00680.05710.00080.02220.00020.61050.0021433.44.16443.65.5115253510.06960.00090.55830.00730.05820.00070.02150.00020.44250.0051433.55.76450.45.8916486000.07040.00100.56250.00590.05800.00050.02110.00020.80030.0019438.56.06453.24.7717425410.06970.00100.56820.00600.05910.00060.02020.00020.79520.0055434.46.43456.94.84189112280.05950.00060.59520.00510.07250.00060.01340.00011.60050.0063372.73.58474.24.0719192440.07030.00070.55390.01610.05710.00130.02020.00070.71000.0063438.24.34447.512.9820455610.07050.00100.55540.00560.05720.00060.02080.00010.82910.0046439.06.48448.54.5021354680.07010.00050.56150.00850.05810.00090.02530.00050.46810.0026436.73.10452.56.8622405030.06920.00060.53990.00830.05660.00090.02300.00020.76560.0042431.44.00438.36.7723425740.06700.00060.56460.00660.06110.00071.100.00040.77100.0147418.33.71454.55.2924162040.07010.00060.56680.02090.05860.00203.420.00070.39280.0017436.93.95456.016.8125536950.06850.00070.55500.00540.05870.00060.960.00020.80040.0077427.24.23448.34.3926516760.07020.00110.56360.00510.05820.00050.790.00020.63150.0052437.46.73453.84.1427465990.07050.00070.56700.00620.05830.00061.020.00020.58820.0029439.24.30456.15.0028344560.06750.00070.55850.00940.06000.00101.700.00020.94450.0043421.04.16450.67.5729344070.07000.00100.55980.00810.05800.00101.710.00010.99090.0247436.36.28451.46.5030385100.06920.00070.55870.00800.05860.00081.410.00020.62610.0044431.14.43450.76.4231415130.07100.00120.54520.00710.05570.00071.200.00020.66830.0040442.27.22441.95.7632496110.06890.00080.54800.00640.05770.00061.090.00020.83760.0085429.65.22443.75.1633283690.07030.00100.55370.00960.05710.00101.770.00040.56060.0038437.96.35447.47.76

注：天津地质矿产研究所，2013年4月测试。

表3 白乃庙花岗闪长斑岩LA-ICP-MS锆石U-Pb测试结果表Table 3 Zircon LA-ICP-MS U-Pb dating results of of granodiorite from Bainaimiao deposit

注：天津地质矿产研究所，2013年4月测试。

表4 白乃庙花岗闪长斑岩LA-ICP-MS锆石U-Pb测试结果表Table 4 Zircon LA-ICP-MS U-Pb dating results of of granodiorite from Bainaimiao deposit

注：天津地质矿产研究所，2013年4月测试。

图8 白乃庙铜钼矿花岗岩类(La/Yb)N-YbN图解(a,Martin,199)和Sr/Y-Y图解(b,Difant,1993)Fig.8 Diagrams of(La/Yb)N(a,Martin,1999)-YbN and Sr/Y-Y(b,Defant,1993)for granites in Bainaimiao Cu-Mo deposit

5 讨论

5.1 岩体的成岩时代

一般认为，岩浆锆石的封闭温度较高(>850℃)，其结晶年龄代表了岩体的侵入年龄。研究表明岩浆锆石环带清晰，Th/U值高，通常在0.5以上(Hoskinetal,2003; Donaldetal.,2003; Davisetal,2003)。花岗闪长斑岩Th/U 值绝大部分大于0.5，多具清晰振荡环带，并有少量锆石具有核幔结构,核部应为继承源岩的成分，锆石晶域的年龄可解释为该岩石的侵位年龄(李鹏等,2011;丛源等,2012)。

本文得到的花岗闪长斑岩LA-MC-ICP-MS锆石年龄加权平均值为435.5±1.9 Ma、439.8±2.5Ma、443.0±1.0Ma。与陈衍景(2009)测得的花岗闪长斑岩侵位年龄为430±6Ma～445±6Ma基本一致，晚于唐克东(1992)测得的含矿花岗闪长斑岩U-Pb年龄466Ma(锆石)约30Ma，早于胡骁(1988)测得的花岗闪长斑岩Rb-Sr年龄(400Ma)约30Ma。综合分析认为白乃庙矿区花岗闪长斑岩侵位时代435.4Ma～443.0Ma，为早志留世。

5.2 岩浆演化与大地构造环境探讨

图9 白乃庙铜矿花岗岩类(Y+Nd)-Rb 图解(a) 和Nb-Y 图解(b)(Pearce et al.,1984)Fig.9 Diagrams of (Y+Nd)-Rb and Nb-Y for granite in Bainaimiao Cu-Mo deposit(Pearce et al.,1984)

本次所研究的4 件花岗岩类岩石化学样品具有低场强元素Rb、K、Ba、Sr和高场强元素Sc、Y、Th、U元素正异常，Nb、P、Ti 、Ta高场强元素负异常，为俯冲环境下岩浆的典型特征(张建新等,2003;惠卫东等,2013, 姚志刚等，2010)，Eu亏损，推测为洋壳向陆壳俯冲到达一定深度时，洋壳中的角闪岩相会发生脱水，形成榴辉岩相，水就会携带角闪岩相中的Rb、Cs、Sr、Ba进入地慢楔，具有岛弧岩石的一般地球化学特征。

本文样品在LaN/YbN-YbN图解(图8a)和Sr/Y-Y图解(图8b)部分落入埃达克岩区与经典岛弧岩石区交叉区，主要落入经典岛弧岩石区，说明岩石具有岛弧成岩特征；在Rb-(Y+Nb)图解上(图9a)和Nb-Y花岗岩构造环境判别图解上(图9b)，主要落入火山岛弧花岗岩+同碰撞花岗岩区，说明岩石形成与弧陆碰撞有关；在K2O-SiO2分类图上(图10a)，投点主要落入高钾钙碱性系列区，个别点落入高钾钙碱性系列与钾玄岩系列、钙碱性系列过渡区，反映了岩浆来源环境变化大;在K2O-Na2O分类图上(图10b)，投点主要分布在I型花岗岩区，部分落入I型与A型花岗岩过渡区，反映了岩浆来源于与幔源混染的火成岩。综合分析认为岩石形成于与碰撞有关的火山岛弧构造环境。

图10 白乃庙铜矿花岗岩类SiO2-K2O图解(a)和K2O-Na2O图解(b)Fig.10 Diagrams of SiO2-K2O and K2O-Na2O for granite in Bainaimiao Cu-Mo deposit

白乃庙铜(钼)床矿中部花岗闪长斑岩的结晶年龄及岩石化学特征均说明了白乃庙地区早古生代中酸性岩浆形成演化和铜钼矿成矿具有密不可分的关系，这种关系和早古生代该区古亚洲洋板块向华北板块强烈俯冲相对应，可以认为白乃庙铜钼矿床的成矿主动力来自板块俯冲。

早古生代古亚洲洋板块沿西拉木伦河-温都尔庙一线向华北地台俯冲(陈从云等，1987)，形成一带有洋壳的A型俯冲(芮宗瑶等，2007)，形成一条近东西向的大规模的铁、金、铜多金属矿带(王东方，1986)。寒武至奥陶系白乃庙组中基性海相火山作用在达茂旗北部-白乃庙-图林凯一带形成东西延长达300km的岛弧型基性火山熔岩喷发(许立权，2003;高计元等，2001;刘敦一，2003)，形成了黑矿型的白乃庙铜、钼矿床原始矿源层(文献①;李进文等，2007)，同时也形成了在白乃庙地区特有的”沟、弧、盆”构造体系(陈从云等，1987)。岩浆及期后含矿热液叠加改造原矿源层形成了具岛弧和斑岩型铜矿特点的白乃庙铜钼矿床(辛河斌，2006)。

6 结论

(1) 白乃庙铜钼矿床中具有古岛弧的地球化学性质的花岗闪长斑岩形成于(432.4±2.2)Ma-(443±1)Ma。早古生代古亚洲洋壳向华北板块消减、俯冲，早志留世洋壳熔融形成的岩浆侵入白乃庙组中基性岛弧火山岩形成花岗闪长斑岩，岩浆及期后热液形成白乃庙铜钼矿床。

(2) 花岗闪长斑岩侵位时代与主要成矿时代辉钼矿Re-Os基本一致，且北矿带矿体主要产于花岗闪长斑岩岩体中，成矿作用与早志留世花岗闪长斑岩侵位密切相关。

致谢 野外地质调查、采样和样品测试工作期间得到了天津地质调查中心司马献章院长的大力帮助，在此一并表示谢意。

[注释]

① 韩杰.1987.内蒙古自治区四子王旗白乃庙铜矿床地质特征及成矿规律研究[R].

Chen Cong-yun, Wang Dong-fang. 1987. The subduction and consumption of ancient Mongolian ocean plate and the upper Silurian-Devonian sedimentation in the flanke of the North China plate[J].Jilin Geology,2:54-60(in Chinese)

Chen Yan-jing, Zhai Ming-guo,Jiang Shao-yong.2009.Significant achievements and open issues in study of orogenesis and metallogenesis surrounding the North China continent[J].Acta Petrologia Sinica,25(11):2695-2726(in Chinese with English abstract)

Cong Yuan,Xiao Ke-yan,Dong Qing-ji,Mao Qi-gui.2012.Zircon U-Pb dating and geochemical characteristics of the gneissic granite in the Jinwozi gold deposit, Xinjiang and their geological implications[J]. Geology and Exploration, 48(4):790-798(in Chinese with English abstract)

Davis Donald W., Thomas E. Krogh, Ian S. Williams.2003.Historical development of zircon geochronology[J]. Mineralogy and Geochemistry,53: 145-181

Defant M J, Drummond M S. 1993. Mountst.Helens:Potential example of partial melting of subducted lithosphere in a volcanic arc[J]. Geology,21:547-550

Gao Ji-yuan,Wang Yi-xian ,Qiu Yu-zhuo ,Zhang Qian. 2001. Islands-ocean structural evolution of mid-western continent in inner Mongulia[J]. Geotectonica et Metallogenia,25(4):397-404(in Chinese with English abstract)

Hu Xiao.1988.On the tectonic evolution and the metallogenesis of the Palaeozoic continental margin in the north side of North China platform[J]. Journal of Hebei College of Geology,11(2):5(in Chinese)

Hui Wei-dong,Zhu jiang,Deng jie,Lv Xin-biao,Mo Ya-long,Li Chun-cheng.2013.U-Pb geochronology and geochemical characteristics of rhyolite porphyry in the Baishantang mine, Beishan,Gansu and their geological implication[J].Geology and Exploration,49(3):0484-0495(in Chinese with English abstract)

Hoskin Paul W. O, Urs Schaltegger.2003. The composition of zircon and igneous and metamorphic petrogenesis[J]. Mineralogy and Geochemistry,53: 27-62(in Chinese with English abstract)

Liang Ting,Chen Yu-chuang,Wang Deng-hong,Cai Ming-hai.2008. Geology and geochemistry of tin-polymetallic deposit in Guangxi dachang[M].Beijing:Geological Publishing House:1-340(in Chinese)

Li Hong-pu, Liu Ju-cang, Zhang Xi-quan, Cao Yong-liang, Lei Yan-zhi, Qu Jian-min.2011.Characteristics of magmatic rocks from the Sijiaoyang Fe-polymetallic ore district in the southern margin ofQaidam, Qinghai Province and their metallogenic significance[J]. Geology and Exploration,47(6):1009-1017(in Chinese with English abstract)

Li Jin-wen, Zhao Shi-bao, Huang Guang-jie. 2007. Origin of Bainaimiao copper deposit, Inner Mongolia [J]. Geology and Prospecting,43(5):1-5(in Chinese with English abstract)

Li Peng,Lv Xin-biao,Chen Chao,Cao Xiao-feng,Mayila,Su Yi-yun.2011. Geochronology and geochemical characteristics of the biotite-granite in the Xiaobaishitou Tungsten deposit, East Tian Shan Mountains of Xinjiang and their geological implications[J]. Geology and Exploration,47(4):543-554(in Chinese with English abstract)

Liu Dun-yi, Jian Ping,Zhang Qi, Zhang Fu-qin,Shi Yur-uo,Shi Guang-hai,Zhang Fu-qiao,Tao Hua.2003.SHRIMP dating of adakites in the Tulingkai ophiolite, Inner Mongolia: Evidence for the early Paleozoic subduction[J]. Acta Geologica Sinica,77(3):317-327(in Chinese with English abstract)

Li Wen-bo, Lai Yong, Sun Xi-wen. 2007.Fluid inclusion study of the Bainaimiao Cu-Au deposit in Inner Mongolia, China[J]. Acta Prtrologica Sinica, 23(9) :2165-2176(in Chinese with English abstract)

Lu Yuan-fa. 2004. GeoKit—A geochemical toolkit for Microsoft Excel[J].Geochimica. 33(5):459-464

Martin H.1999.Adakitic magmas modern analogues of Archean granitoids[J].Lithos.,46:411-429

Nie Feng-jun, Pei Rong-fu, Wu Liang-shi, Arne Bjorlykke. 1995.Nd-and Sr isotope study on greenschist and granodiorite of the Bainaimiao district, Inner Mongolia, China[J]. Acta Geoscientia Sinica,1(1)：36-43(in Chinese with English abstract)

Pearce JA，Harris BW and Tindle AG.1984.Trace element discrimination diagrams for the tectonic interpretations of granitic rocks[J].J.Petrol.,25:956-983

Rui Zong-yao,Hou Zeng-qian,Li Guang-ming ,Zhang Li-sheng ,Wang Long-sheng,Tang Suo-han.2006. Subduction,collision,deeperacture,adakite and porphyry cooper deposits[J]. Geology and Prospecting, 43(1):1-6(in Chinese with English abstract)

Sun SS and Mcdonough WF.1989.Chemical and isotopic systemic of oceanic basalts:Implications for mantle composition and processes.In:SanudersAD and Norry Mj(eds).Magmatism in the Ocean Basins[C]. Geol.Soc.London Spec.Publ.,42:313-345

Tang Ke-dong. 1992.Tectonic evolution and minerogenetic regularities of the fold belt along the northern margins of Sino-Korean plate[M].Beijing:Peking University Publishing House:1-265(in Chinese)

Wang Dong-fang. 1986.Mineraliation and preliminary division of metallogenic belts in a paleoplate convergence zone in the Wendurmiao-Bainaimiao area ,inner Mongolia[J]. Chinese Geology,525:70-80(in Chinese)

Wang Dong-fang. 1987. Minerametallogenic belt in the northern margin of North China platform[J]. Mineral Deposits,6(3): 1035-1043(in Chinese with English abstract)

Xin He-bin. 2006. Geological characteristics and Genesis of Bainaimiao copper plymetal deposit in inner Mongolia[J].Geology and Mineral Resource Research, 21(4):236, 241(in Chinese with English abstract)

Xiong Xin, Wang Cui-zhi,Wang Lin-gang, Li Jun.2011. Geochemical characteristics of Changan diorite in Minhou of Fuzhou and its geological significance[J]. Geology and exploration,47(6): 1035-1043(in Chinese with English abstract)

Yao Zhi-gang,Gao Shan,Wang Yong-dong,Yu Gang.2010. Geochemical Characteristics of the mid-acidity intrusive rocks in Nanhuashan and Xihuashan in the eastern segment of North Qilian Mountains,China. Journal of Xi an Shiyou University(Natural Science Edition [J].25(5)：37-41(in Chinese with English abstract)

Yu Ji-yuan,Li Xiang-min,Wang Guo-qiang,Wu Peng. 2010.A LA-ICP-MS U-Pb dating of zircons from Hamandaban granite body in the Honggou area,Qinghai Province:new evidence for metallogenic age and causes of the Honggou copper polymetallic deposit[J]. Geology and Exploration, 46(4):0592-0598(in Chinese with English abstract)

Zhang Jian-xin,Wan Yu-sheng,Meng Fan-cong,Yang Jing-sui,Xu Zhi-qin．2003．Geochimistry, Sm-Nd and U-Pb isotopic study of gneisses(schists) enclosing eclngites in the north Qaldam mountains-deeply subducted Precambrian metamorphic basement [J].Acta Ptrologica Sinica,19(3):443-451(in Chinese with English abstract)

[附中文参考文献]

陈从云,王东方.1987.华北古陆块北侧古蒙古洋板块俯冲、消亡及晚志留-泥盆系的沉积作用[J].吉林地质,2:54-60

陈衍景,翟明国,蒋少涌.2009.华北大陆边缘造山过程与成矿研究的重要进展和问题[J].岩石学报,25(11)：2695-2725

丛 源,肖克炎,董庆吉,毛启贵.2012. 新疆金窝子片麻状花岗岩锆石U-Pb 年代学、地球化学特征及其地质意义[J].地质与勘探,48(4)：790-798

高计元,王一先,裘愉卓,张乾.2001.内蒙古中西部多岛海构造演化[J].大地构造与成矿学,25(4)：397-404

胡骁. 1988.华北地台北侧古生代大陆边缘的构造演化及成矿作用[J].河北地质学院学报,11(2):5-25

惠卫东,朱江,邓杰,吕新彪,莫亚龙,李春诚.2013.甘肃北山白山堂矿区流纹斑岩的U-Pb年代学、地球化学特征及其地质意义[J].地质与勘探,49(3):0484-0495

梁亭,陈毓川,王登红,蔡明海.2008.广西大厂锡多金属矿床地质与地球化学[M].北京：地质出版社：1-235

李洪普,刘具仓,张喜全,曹永亮,雷延智,曲建明.2011. 青海省柴南缘四角羊铁多金属矿区岩浆岩特征及其成矿意义[J].地质与勘探,47(6):1009-1017

李进文,赵士宝,黄光杰.2007.内蒙古白乃庙铜矿成因研究[J].地质与勘探,43(5)：1-5

李 鹏,吕新彪,陈超,曹晓峰,玛依拉,苏怡芸.2011. 新疆东天山小白石头黑云母花岗岩年代学、地球化学特征及其地质意义[J].地质与勘探,47(4)：543-554

刘敦一,简平,张旗,张福勤,石玉若,施光海,张履桥,陶华.2003.内蒙古图林凯蛇绿岩中埃达克岩SHRIMP测年:早古生代洋壳消减的证据[J].地质学报,77(3)：317-327

李文博,赖勇,孙希文,王保国. 2007.内蒙古白乃庙铜金矿床流体包裹体研究[J].岩石学报,23(9)：2165-2176.

路远发. 2004.GeoKit:一个用VBA构建的地球化学工具软件包[J].地球化学,33(5)：459-464

聂凤军,裴荣富,吴良士,Arne Bjorlykke.1995.内蒙古白乃庙地区绿片岩和花岗闪长斑岩的钕和锶同位素研究[J].地球学报,1(1)：36-43

芮宗瑶,侯增谦,李光明,张立生,王龙生,唐索寒. 2007.俯冲、碰撞、深断裂和埃达克岩与斑岩铜矿[J]. 地质与勘探,42(1)：1-6

唐克东.1992. 中朝板块北侧褶皱带构造演化及成矿规律[M]. 北京:北京大学出版社:1-265

王东方.1986.内蒙古温都尔庙-白乃庙地区古板块会聚带的成矿作用及金属带的初步划分[J].中国地质,525：70-80

王东方.1987.华北地台北缘地质构造演化及多金属成矿带的构造控制问题[J].矿床地质,6(3)：1-8

辛河斌. 2006.内蒙古白乃庙铜多金属矿床地质特征及成因讨论[J].地质找矿论丛,21(4):236-241

熊 欣,王翠芝,王林刚,李 骏.2011.福州闽侯长安闪长岩岩体的地球化学特征及其地质意义[J].地质与勘探,47(6):1035-1043

姚志刚,高珊,王永东,余刚.2010.北祁连东段西、南华山中酸性侵入岩地球化学特征[J].西安石油大学学报(自然科学版) ,25(5)：37-41

余吉远,李向民,王国强,武鹏.2010.青海红沟地区哈曼大阪花岗岩体锆石LA-ICP-MS 测年-对红沟铜矿床形成时代和成因的认识 [J].地质与勘探,45(4):592-598

赵振华. 1997. 微量元素地球化学原理[M] . 北京:科学出版社:1-238

LA-MC-ICP-MS Zircon U-Pb Dating of the Pluton in the Bainaimiao Cu-Mo deposit of Inner Mongolia and its Geological Significance

FENG Xiao-xi1,2,YAO Shu-zhen1,WANG Jia-song2,WEI Jia-lin2, LI Guang-yao2,WANG Jia-ying2,FENG Xu-biao3

(1.Institute of Earth Resources, China University of Geoscience, Wuhan, Hubei 430074; 2.Tianjin Center of China Geology Survey , Tianjin 300170; 3.Guanxin Mining Group of Shenzhen City, Shenzhen, Guangzhou 518048)

The Bainaimiao Cu-Mo deposit has become the foremost Cu-Mo deposit in the north margin of the North China plate, and its mineralization is closely related to the pluton. In order to study the relationship between diagenesis and mineralization, this work made zircon LA-MC-ICPMS dating of the granodiorite and study of its geochemistry. The dating yielded ages of 432.4±2.2 Ma, 440.7±2.1Ma and 443±1Ma for this rock.The emplacement age of the intrusion is the lower Silurian, which is accordant with the isochron age of the Re-Os isochron age 440.5±4.4Ma. Moreover, trace elements Rb, Ba, Th, U, and K are enriched , while the elements Cs, Nb, and Ti are depleted. The REE distribution pattern is of the right-dip type, δEu is in 14.83～-19.54, and there is a negative anomaly of Eu, which is similar to the geochemical characteristics of the island-arc granite and high-K calc-alkaline volcanic rock series. We suggest that this Cu(Mo) deposit formed in the early Silurian and was associated with magmatic activity in the early Silurian. Its tectonic setting was the Bainaimiao island arc zone that was produced by the Early Paleozoic underthrusting of the paleo-Asian oceanic plate beneath the northern margin of the North China craton.

LA-MC-ICP-MS zircon U-Pb dating，arc pluton，magmatism and mineralization， Bainaimiao Cu-Mo deposit

2013-06-21；

2014-01-13；[责任编辑]郝情情。

中国地质调查局项目(1212011085256)资助。

冯晓曦(1972年—)，男，1996年毕业于成都理工学院，获学士学位，在读博士生，高级工程师，长期从事地质调查和研究工作。E-mail：tjfengxiaoxi@163.com。

姚书振(1947年—)，学士，矿床学教授，博士生导师，长期从事矿床学、矿田构造学和区域成矿学的教学与研究工作。E-mail：szyao@cug.edu.cn。

P618.41

A

0495-5331(2014)02-0369-13