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内蒙古白乃庙铜矿区含矿中酸性侵入岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及成矿时代

赵利刚, 李承东, 常青松, 高学生, 许雅雯, 樊建廷, 张阔

赵利刚, 李承东, 常青松, 高学生, 许雅雯, 樊建廷, 张阔. 2016: 内蒙古白乃庙铜矿区含矿中酸性侵入岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及成矿时代. 地质通报, 35(4): 542-552.
引用本文: 赵利刚, 李承东, 常青松, 高学生, 许雅雯, 樊建廷, 张阔. 2016: 内蒙古白乃庙铜矿区含矿中酸性侵入岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及成矿时代. 地质通报, 35(4): 542-552.
ZHAO Ligang, LI Chengdong, CHANG Qingsong, GAO Xuesheng, XU Yawen, FAN Jianting, ZHANG Kuo. 2016: A tentative discussion on zircon U-Pb geochronology and geochemistry of ore-bearing intermediate-acid intrusive rocks in the Bainaimiao copper ore district and the metallogenic epoch. Geological Bulletin of China, 35(4): 542-552.
Citation: ZHAO Ligang, LI Chengdong, CHANG Qingsong, GAO Xuesheng, XU Yawen, FAN Jianting, ZHANG Kuo. 2016: A tentative discussion on zircon U-Pb geochronology and geochemistry of ore-bearing intermediate-acid intrusive rocks in the Bainaimiao copper ore district and the metallogenic epoch. Geological Bulletin of China, 35(4): 542-552.

内蒙古白乃庙铜矿区含矿中酸性侵入岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及成矿时代

基金项目: 

国家自然科学基金项目 41272065

中国地质调查局项目 1212010811004

中国地质调查局项目 1212010561510

中国地质调查局项目 1212010811061

中国地质调查局项目 1212011120330

详细信息
    作者简介:

    赵利刚(1981-),男,硕士,助理研究员,从事区域成矿规律研究。E-mail:zhaoligang981@126.com

  • 中图分类号: P618.41;P597+.3

A tentative discussion on zircon U-Pb geochronology and geochemistry of ore-bearing intermediate-acid intrusive rocks in the Bainaimiao copper ore district and the metallogenic epoch

  • 摘要:

    为了限定白乃庙铜矿的成矿时代和成矿环境,对含矿中酸性岩类进行同位素年龄和岩石地球化学研究。获得的3个含矿花岗闪长岩样品的LA-MC-ICP-MS锆石U-Pb年龄分别为421.5±1.8Ma、438.6±3.4Ma和459.3±3.6Ma。含矿中酸性岩类属于过铝质钙碱性系列岩石,稀土元素曲线显示为轻稀土元素富集型,具有弱正Eu异常,微量元素曲线表现为明显的Ta、Nb亏损。综合含矿中酸性岩类时代、地球化学特征及区域构造背景,认为白乃庙铜矿总体形成于早古生代,具有多期成矿的特点,成矿作用与古蒙古洋早古生代俯冲消减事件有关。

    Abstract:

    In order to determine the metallogenic epoch and ore-forming environment of the Bainaimiao copper deposit, the au-thors carried out research on isotope geochronology and geochemistry of ore-bearing intermediate-acid rocks. LA-MC-ICPMS zir-con U-Pb dating shows that the ages of three ore-bearing granodiorites samples are 421.5±1.8Ma, 438.6±3.4Ma and 459.3±3.6Ma respectively. These rocks have peraluminous calc-lkaline characteristics, and are enriched in LREE. There is a weak positive anomaly of Eu. The trace elements are obviously depleted in Ta and Nb. According to comprehensive ages and geochemical characteristics of ore-bearing granodiorites and the regional tectonic background, the authors consider that the Bainaimiao copper deposit was on the whole formed in the early Paleozoic and characterized by multi-period mineralization. In addition, the metallogenesis was related to the subduction event of ancient Mongolia Ocean in the Early Paleozoic.

  • 白乃庙铜矿行政上属于乌兰察布盟四子王旗,是内蒙古中部为数不多的大型铜矿床。前人曾对白乃庙铜矿进行过大量研究[1-9],但在成因类型和成矿时代方面一直存在争议,主要包括:①南矿带最早期的成矿作用与海底幔源火山活动有关,时代与白乃庙群相当,为中元古代,北矿带为斑岩型矿床,与加里东期花岗闪长斑岩侵位和岩浆作用有关[2-3];②造山型铜(金)矿床总体形成于泥盆纪[8-9];③斑岩型或岩浆热液型矿床与加里东期花岗闪长斑岩密切相关[1,5,7,10-12],并获得了451.2±3.5Ma[10]和440.5±4.4Ma[12]的辉钼矿Re-Os等时线年龄,但二者相差近10Ma,说明白乃庙铜矿可能经历了不同期次的成矿作用。尽管大多数学者认为,中酸性侵入岩类与成矿密切相关,但含矿的中酸性侵入岩类缺乏精确的同位素年代学研究。为了限定白乃庙铜金矿床的成矿时代,笔者对北矿带含矿中酸性侵入岩进行了系统的取样,通过侵入岩的锆石U-Pb年龄限定矿床的成矿时代,并探讨矿床的形成环境。

    研究区大地构造位置属华北陆块北缘温都尔庙早古生代增生带的包尔汗图-白乃庙岛弧带(图 1-a),南部为华北陆块北缘的中元古代基底,北部为温都尔庙俯冲增生杂岩带。

    图  1  内蒙古中部地区早古生代构造格局图(a)及白乃庙铜矿地质简图(b)(a据参考文献①修改,b据参考文献[7-8,12]修改)
    Figure  1.  The Early Paleozoic tectonic framework of the central part of Inner Mongolia (a) and geological sketch map of the Bainaimiao copper deposit (b)

    区内出露地层有寒武系白乃庙群、中志留统徐尼乌苏组、下二叠统三面井组、上侏罗统大青山组等。白乃庙群分布于矿区中部,为一套不整合在徐尼乌苏组之下的绿片岩和长英质浅变质岩系[13],可分为5个岩性段(图 1-b)。绿片岩系岩性组合为斜长角闪片岩、阳起斜长片岩、绿泥斜长片岩、绿泥阳起片岩、变质安山岩和变质玄武岩,局部见变安山质凝灰岩、钠长绿泥片岩,为一套中基性火山熔岩和火山碎屑岩建造,是铜矿的主要赋存岩段;长英质浅变质岩系岩性组合为长英质片岩、绢云绿泥钠长片岩夹薄层大理岩。

    侵入岩分布于研究区中部及东北部,包括大面积分布的晚奥陶世石英闪长岩和志留纪花岗闪长岩。晚奥陶世石英闪长岩分布于矿区东北部,地表未见矿化,但矿区西北部钻孔中发现了含矿的中晚奥陶世花岗闪长岩。志留纪花岗闪长岩分布于矿区中部,空间上与北矿带矿体关系极其密切,呈岩株或岩脉状侵入白乃庙群。在南矿带⑹、⑺矿段深部亦见有与矿化关系密切的花岗闪长斑岩岩枝。

    白乃庙铜矿矿体总体呈带状近EW向展布,根据矿体产出部位和围岩特征不同,分为南、北2个矿带。南矿带矿体主要分布于白乃庙群绿片岩系地层中,由⑵、⑶、⑸、⑹、⑺、⑽和⑾矿段组成;北矿带矿体产于花岗闪长(斑)岩脉及其接触带中(图 1-b),由⑺、⑼、⑿、⒀4个矿段组成。

    3个样品均采于北矿带,岩石本身都具有黄铜矿化或孔雀石化。

    变质中细粒花岗闪长岩(08MD101)位于矿区中部,⑼矿段西部边缘,地理坐标为N42°13′5.4″、E112°30′4.4″,其中见白乃庙群绿片岩捕虏体(图 2-a),蚀变强烈,其中可见浸染状黄铜矿化、黄铁矿化。岩性为变质中细粒花岗闪长岩,变质中细粒花岗结构,块状构造,主要矿物包括斜长石(60%)、石英(20%~25%)、微斜长石(5%~10%±)、黑云母(10%±)。

    图  2  白乃庙铜矿含矿中酸性侵入岩岩石特征
    a—花岗闪长岩中的白乃庙群绿片岩捕虏体;b—片理化孔雀石化花岗闪长岩;c、d—正交偏光。Pl—斜长石;Mc—微斜长石;Q—石英;Ms—黑云母
    Figure  2.  Petrology features of intermediate-acid rocks in Bainaimiao copper deposit

    变质花岗闪长岩(09NM401):采于矿区北部,⑿矿段采坑附近,地理坐标为N42°14′16.4″、E112°28′20.2″。岩体呈脉状侵入白乃庙群,岩石比较破碎,表面发育强烈的孔雀石化,并同白乃庙群一起变形(图 2-b)。岩性为变质花岗闪长岩、变质花岗结构,总体为块状构造,局部片理化强烈。岩石由斜长石(55%)、石英(20%)、白云母(5%~10%)、 黑云母(10%±)、 微斜长石(5%~10%)组成。少见被绿帘石、孔雀石、不透明矿物等充填的微裂隙(图 2-c、d)。

    中细粒花岗闪长岩(09NM411)采于矿区西北部ZK133302钻孔147~462m,钻孔地理坐标为N42°35′01.5″、E113°03′53.4″。岩心岩性以中细粒花岗闪长岩和白乃庙群绿泥斜长片岩为主,前者为块状构造,后者为定向片状构造,二者多次相间出现,中细粒花岗闪长岩侵入白乃庙群绿泥斜长片岩。黄铜矿呈细脉状分布于中细粒花岗闪长岩或白乃庙群绿泥斜长片岩中。中细粒花岗闪长岩为中细粒花岗结构,块状构造,由斜长石(60%)、微斜长石(15%)、石英(20%)和黑云母(5%~10%)组成,黑云母多已绿泥石化。

    测年样品前处理过程包括样品粉碎、锆石分选、样靶制作等环节。先将样品粉碎到80目,之后在显微镜下挑选锆石,然后挑选裂纹少、透明度好、干净的锆石制靶,拍摄锆石透射光、反射光照片、阴极发光(CL)图像(图 3),以便做锆石成因分析。

    图  3  白乃庙铜矿含矿中酸性侵入岩代表性锆石CL图像及测点位置
    Figure  3.  Representative CL images and dating spots of zircons from intermediate-acid rocks in the Bainaimiao copper deposit

    在天津地质矿产研究所同位素实验室,利用激光烧蚀多接收器等离子体质谱仪(LA-MC-ICPMS)对样品锆石进行微区原位U-Th-Pb同位素测定。仪器配置和测试流程参见参考文献[14-15]。采用标准锆石GJ-1作为外部年龄标准进行U、Pb同位素分馏校正[16],用中国地质大学刘勇胜博士研发的ICPMSDataCal程序[17]和Ludwig的Isoplot程序[18]进行数据处理,以208Pb校正法对普通铅进行校正[19]。利用NIST612玻璃标样作为外标计算锆石样品的Pb、U、Th含量。

    3个样品LA-MC-ICP-MS锆石U-Pb同位素测年结果见表 1图 3为3个样品代表性锆石CL(阴极发光)图像特征。图 4为样品分析的锆石UPb谐和曲线图。

    图  4  白乃庙铜矿含矿中酸性侵入岩锆石U-Pb谐和图
    Figure  4.  U-Pb concordant curves of zircons from intermediateacid rocks in the Bainaimiao copper deposit
    表  1  白乃庙铜矿中酸性岩类LA-MC-ICP-MS锆石U-Th-Pb同位素分析结果
    Table  1.  LA-MC-ICP-MS zircon U-Th-Pb dating results of intermediate-acid rocks in the Bainaimiao copper deposit
    点号同位素含量/10-6232Th/238U同位素比值年龄/Ma
    PbU207Pb/206Pb207Pb/235U206Pb/238U207Pb/206Pb207Pb/235U206Pb/238U
    测值测值测值测值测值测值
    09NM401
    1222200.460.05530.00180.5240.0170.06870.000442673428144283
    2383330.320.05450.00160.5030.0140.06690.000539464414124173
    3403900.420.05490.00150.5100.0140.06730.000440860418114203
    4424240.440.05330.00140.4960.0130.06740.000434359409114213
    5423800.340.05520.00150.5120.0140.06730.000442159420114203
    6333340.440.05330.00150.4870.0140.06630.000434063403114142
    7484850.460.05520.00140.5070.0130.06670.000441957416114162
    8393590.370.05500.00150.5160.0140.06800.000441361422124242
    9363260.350.05520.00150.5080.0140.06680.000441862417124172
    10363430.410.05460.00140.5050.0130.06710.000439459415114192
    11403840.410.05500.00150.5100.0140.06730.000441359419114203
    12484110.330.05480.00170.5160.0160.06830.000440369423134262
    13293110.530.05530.00180.5140.0170.06730.000542671421144213
    14393660.400.05540.00150.5200.0140.06810.000442861425124253
    15343560.510.05410.00160.5090.0150.06830.000437466418124263
    16353360.430.05540.00160.5220.0150.06840.000542763427124273
    17393380.340.05530.00170.5230.0160.06850.000442668427134273
    18494020.300.05540.00150.5240.0150.06860.000442961428124283
    19353830.530.05530.00140.5180.0140.06800.000442358424114242
    20433630.320.05340.00150.5020.0150.06820.000434565413124252
    21353180.370.05460.00170.5040.0160.06690.000539668414134183
    22404000.420.05340.00140.4920.0140.06690.000434560406114172
    23631830.060.05540.00220.5220.0210.06830.000542888426174263
    24393980.460.05460.00140.5030.0130.06680.000439858414114172
    25302660.370.05430.00160.5040.0160.06730.000438567415134203
    09NM401
    1365030.650.05370.00100.4940.0100.06610.00083594140884135
    2273650.500.05560.00130.5510.0130.07120.000743551446114444
    3212880.390.05560.00170.5510.0180.07110.000843769446144435
    4273540.640.05560.00140.5420.0140.07000.000443857440124363
    51549630.120.07550.00051.7750.0160.16880.001410821410361010068
    6415621.490.05670.00300.5060.0270.06400.0012481115416224007
    7141860.470.05580.00220.5520.0230.07100.000844590446184425
    8314030.590.05530.00110.5450.0120.07080.00064254544294414
    9324280.610.05540.00110.5430.0120.07030.000743046440104384
    10222810.610.05490.00150.5480.0150.07170.000840759444124465
    11273690.630.05590.00130.5350.0120.06870.000444851435104282
    12273720.630.05680.00140.5310.0140.06720.000848454433114195
    13385000.700.05550.00080.5500.0110.07110.00124333444594438
    14202600.520.05530.00180.5490.0180.07120.000842672444154445
    09NM401
    15293860.550.05420.00110.5390.0120.07130.00073814543894445
    16324150.630.05510.00100.5440.0100.07090.00064164144184424
    17212730.520.05660.00160.5650.0170.07180.000847462455134475
    18233040.630.05600.00140.5590.0150.07160.000745356451124464
    19222880.620.05460.00140.5510.0160.07240.001239657445134517
    20182330.560.05490.00210.5470.0210.07150.001140984443174457
    21374751.180.05470.00080.5420.0130.07110.0018401344401044311
    22273410.640.05440.00120.5530.0140.07300.001438848447114549
    23192500.660.05330.00240.5360.0260.07210.00163431034362144910
    24263370.530.05440.00150.5500.0190.07270.0021388634451545213
    25263350.670.05500.00190.5500.0200.07190.001241078445164477
    26334360.790.05720.00190.5510.0160.06920.0034499734461343121
    27455951.210.06040.00090.5350.0080.06350.00036193143563972
    28243110.580.05460.00140.5500.0160.07240.001439457445134519
    29354690.720.05900.00110.5600.0110.06820.00065664145294254
    30404990.890.05540.00100.5550.0110.07190.00104294044894486
    09NM41
    1212750.580.05380.00180.5440.0200.07330.001036275441164566
    2263330.520.05460.00110.5650.0140.07510.000939547455114675
    3303610.730.05710.00090.6040.0120.07660.00094963448094765
    4293460.820.05710.00140.5850.0160.07430.001049453468134626
    5354210.730.05750.00090.6050.0120.07630.00095093548094745
    6121490.520.05860.00220.6170.0260.07640.000855082488214745
    7415290.600.05620.00070.5800.0090.07480.00064612946474654
    8131670.590.05430.00210.5630.0230.07510.000738688453184674
    9455620.850.05640.00060.5720.0080.07350.00074702345964574
    10384790.700.05510.00080.5630.0080.07420.00074153245464614
    11293690.730.05690.00100.5720.0100.07290.00074893745984534
    12334160.810.05650.00080.5660.0080.07260.00074733145574524
    13384930.630.05620.00070.5640.0070.07280.00064582745464534
    14405180.620.05630.00070.5670.0070.07300.00074642945664544
    15405280.700.05680.00070.5540.0070.07070.00074842844764404
    16465800.760.05730.00060.5690.0060.07200.00075042345754484
    17384670.780.05580.00080.5730.0100.07450.00074443146084634
    18222710.740.05490.00130.5570.0140.07350.000641052450114574
    19323700.970.05550.00090.5780.0100.07550.00064343546384694
    20374790.640.05540.00070.5650.0090.07400.00084272745574605
    21394880.820.05720.00080.5760.0130.07300.001349931462104548
    22425480.590.05590.00060.5680.0080.07380.00074462245764594
    23425640.580.05600.00050.5520.0080.07150.00084532144674455
    24243120.640.05570.00120.5660.0140.07360.000844147455114585
    25151940.540.05660.00200.5860.0220.07500.000947778468174666
    26586800.900.05590.00060.5820.0100.07540.00104502246684696
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    变质中细粒花岗闪长岩(样品08MD101)代表性锆石CL图像显示,多数锆石形态完整,呈自形结构,具典型的振荡环带,为岩浆成因锆石。样品共测定了25个锆石U-Pb同位素数据点(图 3表 1),数据点均分布于一致曲线之上,25个数据点的206Pb/238U年龄加权平均值为421.5±1.8Ma(MSWD=2.8),代表了该变质中细粒花岗闪长岩的侵位结晶年龄。

    变质花岗闪长岩(样品09NM401)与08MD101样品具有相同的晶形和相似的CL图像特征(图 2),但颗粒较大,振荡环带清晰可见,也属于岩浆成因锆石。样品测定了30个同位素数据点(图 3表 1),除3个点略微偏离谐和线外,其他点都位于谐和线上。其中26个数据点的206Pb/238U年龄加权平均值为438.6±3.4Ma,代表了该变质花岗闪长岩的侵位结晶年龄。1、6两个分析点的206Pb/238U年龄值分别为413Ma和403Ma,由于数据点较少,不具有代表性;27号点偏离谐和线较远且不具代表性,计算时剔除;5号点207Pb/206Pb年龄为1082Ma,可能为捕获锆石。

    中细粒花岗闪长岩(样品09NM411)锆石颗粒较大,有些不完整,CL图像显示(图 2),锆石大都具有清晰的振荡环带,为岩浆成因锆石。样品共测定了30个同位素数据点(图 3表 1),且大多分布于谐和线上,只有1和8号点稍有偏离。26个数据点的206Pb/238U年龄加权平均值为459.3±3.6Ma,代表了该中细粒花岗闪长岩的侵入结晶年龄。

    样品(08MD101、09NM401)化学分析在中国地质科学院地球物理地球化学勘查研究所完成。主量元素除Fe2O3、FeO由容量法(VOL)测试外,其他均由X-射线荧光光谱法测定,重复样合格率100%。微量元素用等离子体质谱法(ICP-MS)测试。分析结果列于表 2表 3

    表  2  白乃庙铜矿中酸性岩类主量元素成分
    Table  2.  Major element composition of intermediateacid rocks in the Bainaimiao copper deposit
    %
    样品号
    岩性
    08MD10108MD10209NM401-109NM401-209NM401-3
    花岗闪长岩花岗闪长岩
    SiO266.9365.5663.9065.7063.70
    AI2O315.0315.1216.115.4516.1
    Fe2O32.592.823.082.453.82
    FeO1.091.392.382.681.78
    CaO2.943.613.351.943.28
    MgO1.521.621.981.941.94
    K2O3.693.562.784.223.34
    Na2O2.442.143.482.743.06
    TiO20.380.420.490.440.52
    P2O50.130.130.170.150.2
    MnO0.040.060.0460.0360.058
    烧失量2.983.001.761.841.91
    total99.7799.4399.5299.5999.71
    A/CNK1.121.081.081.221.10
    δ1.571.441.882.131.98
    下载: 导出CSV 
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    表  3  白乃庙铜矿中酸性岩类微量元素成分
    Table  3.  Trace element composition of intermediateacid rocks in the Bainaimiao copper deposit
    10-6
    样品号08MD
    101-1
    08MD
    101-2
    09NM
    401-1
    09NM
    401-2
    09NM
    401-3
    岩性花岗闪长岩花岗闪长岩
    La28.8221.7745.2038.8045.00
    Ce59.9339.2967.6068.0069.60
    Pr4.723.958.007.458.16
    Nd16.5813.8327.4026.4028.20
    Sm2.872.534.905.005.10
    Eu0.910.811.721.621.90
    Gd2.342.034.364.284.50
    Tb0.320.270.560.590.58
    Dy1.781.522.533.022.72
    Ho0.360.300.500.600.52
    Er1.040.921.381.631.46
    Tm0.170.170.220.270.24
    Yb1.311.231.561.921.67
    Lu0.210.190.260.310.26
    ZREE121.3688.80166.19159.89169.91
    LREE/HREE15.1312.3913.6211.6713.22
    (La/Sm)N6.485.555.965.015.70
    (La/Yb)N15.7512.6820.7814.5019.33
    δEu1.041.051.111.041.19
    Sr635.59547.04614.00473.00578.00
    Rb80.2856.1997.50114.50102.55
    Ba1053.45864.15684.501290.00953.00
    Th21.8314.7011.8013.2013.80
    U3.111.892.562.902.49
    Ta0.660.600.640.620.58
    Nb9.258.388.459.098.58
    Ta0.660.600.640.620.58
    Zr136.78116.72108.00122.00108.00
    Hf3.623.143.393.703.40
    Y10.308.1814.7016.6014.40
    Sr/Y61.7366.8841.7728.4940.14
    下载: 导出CSV 
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    样品08MD101烧失量较高,可能是该岩石矿化蚀变强烈,具有浸染状黄铜矿化和黄铁矿化造成的。总体看,白乃庙铜矿含矿中酸性岩类岩石化学成分变化范围较窄(表 2)。SiO2含量变化于63.70%~66.93%之间,属于中酸性岩类;Al2O3为15.03~16.1,A/CNK为1.08~1.22,属过铝质岩石(图 5-a)。在TAS分类图(图 5-b)上,样品点落于石英闪长岩和花岗闪长岩区域内,结合里特曼指数(δ=1.44~2.13),可以判定白乃庙中酸性岩类属于钙碱性系列岩石。

    图  5  白乃庙铜矿中酸性岩类A/CNK-A/NK判别图(a)和TAS分类图解(b)
    Figure  5.  A/CNK-A/NK discrimination diagram (a) and TAS diagram (b) of intermediate-acid rocks in the Bainaimiao copper deposit

    图 6表 3可以看出,岩石的稀土元素配分模式为轻稀土元素富集型,呈现右倾特点,具有较弱的正Eu异常(δEu=1.04~1.19)。含矿中酸性类各样品稀土元素配分曲线相互平行,反映其可能来自相同的源区(图 6-a)。稀土元素总量(∑REE)为88.80×10-6~169.91×10-6。(La/Sm)N值为5.01~6.48,(La/Yb)N值为12.68~20.78,LREE/HREE值为11.67~15.13。在中酸性侵入岩微量元素蛛网图(图 6-b)上,大离子亲石元素表现为明显的Rb、Ba和K富集,高场强元素富集Th、U,亏损Nb、Ta、Ti。

    图  6  白乃庙铜矿中酸性岩类稀土元素配分模式图(a)及微量元素蛛网图(b)(球粒陨石和原始地幔标准化值均据参考文献[20]
    Figure  6.  Chondrite-normalized REE patterns (a) and primitive mantle-normalized spidergrams (b) for intermediate-acid rocks in the Bainaimiao copper deposit

    本次对白乃庙铜矿区北矿带含矿中酸性侵入岩进行了LA-MC-ICP-MS锆石U-Pb定年,获得3个花岗闪长岩样品的年龄分别为459.3±3.6Ma、438.6±3.4Ma和421.5±1.8Ma,表明本区至少存在中奥陶世末期、早志留世和晚志留世晚期3期含矿侵入岩。

    白乃庙铜矿成矿作用与中酸性侵入岩类关系密切,已得到众多学者的认可[1,5,7,10-12,21-22],本次采集的花岗闪长岩类样品也都含矿或发生了强烈的矿化蚀变。中奥陶世末期的中细粒花岗闪长岩(09NM411)黄铜矿呈细脉状,说明与之相关的成矿作用晚于岩体,而其459.3±3.6Ma的U-Pb同位素年龄也稍早于赵云等[10]获得的辉钼矿Re-Os等时线年龄(451.2±3.5Ma)。早志留世变质花岗闪长岩(09NM401)同白乃庙群一起变形,表面发育强烈的孔雀石化,内部见被不透明矿物充填的微裂隙,其U-Pb同位素年龄438.6±3.4Ma也与冯晓曦[12]获得的辉钼矿Re-Os等时线年龄(440.5±4.4Ma)基本吻合。晚志留世晚期变质中细粒花岗闪长岩为白乃庙铜矿出露面积最大的含矿岩体,甚至部分地段岩体即矿体,08MD101样品采于⑼矿段西端,是否能代表整个岩体的时代尚需讨论,但样品本身含矿至少说明有一期成矿作用与该岩体有关。因此,在中奥陶世末期—晚志留世晚期,白乃庙铜矿至少发生了3期与中酸性侵入岩有关的成矿作用。

    综上所述,白乃庙铜矿具有多期成矿的特点,且总体形成于早古生代。

    岩石地球化学特征显示,白乃庙含矿中酸性岩类属于过铝质钙碱性系列岩石,稀土元素球粒陨石模式图(图 6-a)显示,岩体属于轻稀土元素富集型,具有弱正Eu异常;微量元素(图 6-b)表现为明显的Ta、Nb亏损。运用Pearc等[23]的Y-Nb(图 7-a)、(Yb+Nb)-Rb(图 7-b)构造环境判别图解分析,样品点都落入火山弧花岗岩区,表明它们可能形成于岛弧环境。

    图  7  白乃庙铜矿中酸性岩类Y-Nb(a)及(Yb+Nb)-Rb(b)图解[23]
    WPG—板内花岗岩;ORG—洋脊花岗岩;VAG—火山弧花岗;syn-COLG—同碰撞花岗岩
    Figure  7.  Y-Nb (a) and (Yb+Nb)-Rb (b) diagrams for intermediateacid rocks in the Bainaimiao copper deposit

    花岗岩能否判断构造环境存在很大争议,需要通过区域岩浆-构造-沉积事件进行综合分析。研究区北部的温都尔庙俯冲增生杂岩带通常被认为是包尔汗图-白乃庙早古生代岛弧对应的俯冲带[24-25]。刘敦一等[26]对矿区东北部温都尔庙俯冲增生杂岩带图林凯蛇绿岩中的埃达克岩进行了锆石SHRIMP测年,获得石英闪长岩年龄为467±13Ma,英安岩年龄为459±8Ma,奥长花岗岩年龄为451±7Ma,斜长岩岩墙年龄为429±7Ma,认为温都尔庙-图林凯古洋壳在467~429Ma经历了逾38Ma的消减事件。白乃庙铜矿含矿花岗闪长岩侵位时间与该消减事件基本吻合,因此,认为它们形成于岛弧环境,且白乃庙铜矿的形成与古蒙古洋早古生代俯冲作用有关。

    (1)运用LA-MC-ICP-MS法对白乃庙矿区含矿中酸性侵入岩定年,获得的中细粒花岗闪长岩年龄为459.3±3.6Ma,变质花岗闪长岩年龄为438.6±3.4Ma,变质中细粒花岗闪长岩年龄为421.5±1.8Ma,表明本区至少存在中奥陶世末期、早志留世和晚志留世晚期3期含矿侵入岩。

    (2)白乃庙铜矿总体形成于早古生代,具有多期成矿的特点,中奥陶世—中志留世晚期,共有3期与中酸性侵入岩有关的成矿作用。

    (3)白乃庙铜矿形成于岛弧环境,与古蒙古洋早古生代俯冲作用有关。

    致谢: 成文过程中天津地质矿产研究所李俊建、周红英研究员提出了宝贵意见,耿建珍、张建工程师在实验测试方面给予了帮助,在此表示衷心感谢。
  • 图  1   内蒙古中部地区早古生代构造格局图(a)及白乃庙铜矿地质简图(b)(a据参考文献①修改,b据参考文献[7-8,12]修改)

    Figure  1.   The Early Paleozoic tectonic framework of the central part of Inner Mongolia (a) and geological sketch map of the Bainaimiao copper deposit (b)

    图  2   白乃庙铜矿含矿中酸性侵入岩岩石特征

    a—花岗闪长岩中的白乃庙群绿片岩捕虏体;b—片理化孔雀石化花岗闪长岩;c、d—正交偏光。Pl—斜长石;Mc—微斜长石;Q—石英;Ms—黑云母

    Figure  2.   Petrology features of intermediate-acid rocks in Bainaimiao copper deposit

    图  3   白乃庙铜矿含矿中酸性侵入岩代表性锆石CL图像及测点位置

    Figure  3.   Representative CL images and dating spots of zircons from intermediate-acid rocks in the Bainaimiao copper deposit

    图  4   白乃庙铜矿含矿中酸性侵入岩锆石U-Pb谐和图

    Figure  4.   U-Pb concordant curves of zircons from intermediateacid rocks in the Bainaimiao copper deposit

    图  5   白乃庙铜矿中酸性岩类A/CNK-A/NK判别图(a)和TAS分类图解(b)

    Figure  5.   A/CNK-A/NK discrimination diagram (a) and TAS diagram (b) of intermediate-acid rocks in the Bainaimiao copper deposit

    图  6   白乃庙铜矿中酸性岩类稀土元素配分模式图(a)及微量元素蛛网图(b)(球粒陨石和原始地幔标准化值均据参考文献[20]

    Figure  6.   Chondrite-normalized REE patterns (a) and primitive mantle-normalized spidergrams (b) for intermediate-acid rocks in the Bainaimiao copper deposit

    图  7   白乃庙铜矿中酸性岩类Y-Nb(a)及(Yb+Nb)-Rb(b)图解[23]

    WPG—板内花岗岩;ORG—洋脊花岗岩;VAG—火山弧花岗;syn-COLG—同碰撞花岗岩

    Figure  7.   Y-Nb (a) and (Yb+Nb)-Rb (b) diagrams for intermediateacid rocks in the Bainaimiao copper deposit

    表  1   白乃庙铜矿中酸性岩类LA-MC-ICP-MS锆石U-Th-Pb同位素分析结果

    Table  1   LA-MC-ICP-MS zircon U-Th-Pb dating results of intermediate-acid rocks in the Bainaimiao copper deposit

    点号同位素含量/10-6232Th/238U同位素比值年龄/Ma
    PbU207Pb/206Pb207Pb/235U206Pb/238U207Pb/206Pb207Pb/235U206Pb/238U
    测值测值测值测值测值测值
    09NM401
    1222200.460.05530.00180.5240.0170.06870.000442673428144283
    2383330.320.05450.00160.5030.0140.06690.000539464414124173
    3403900.420.05490.00150.5100.0140.06730.000440860418114203
    4424240.440.05330.00140.4960.0130.06740.000434359409114213
    5423800.340.05520.00150.5120.0140.06730.000442159420114203
    6333340.440.05330.00150.4870.0140.06630.000434063403114142
    7484850.460.05520.00140.5070.0130.06670.000441957416114162
    8393590.370.05500.00150.5160.0140.06800.000441361422124242
    9363260.350.05520.00150.5080.0140.06680.000441862417124172
    10363430.410.05460.00140.5050.0130.06710.000439459415114192
    11403840.410.05500.00150.5100.0140.06730.000441359419114203
    12484110.330.05480.00170.5160.0160.06830.000440369423134262
    13293110.530.05530.00180.5140.0170.06730.000542671421144213
    14393660.400.05540.00150.5200.0140.06810.000442861425124253
    15343560.510.05410.00160.5090.0150.06830.000437466418124263
    16353360.430.05540.00160.5220.0150.06840.000542763427124273
    17393380.340.05530.00170.5230.0160.06850.000442668427134273
    18494020.300.05540.00150.5240.0150.06860.000442961428124283
    19353830.530.05530.00140.5180.0140.06800.000442358424114242
    20433630.320.05340.00150.5020.0150.06820.000434565413124252
    21353180.370.05460.00170.5040.0160.06690.000539668414134183
    22404000.420.05340.00140.4920.0140.06690.000434560406114172
    23631830.060.05540.00220.5220.0210.06830.000542888426174263
    24393980.460.05460.00140.5030.0130.06680.000439858414114172
    25302660.370.05430.00160.5040.0160.06730.000438567415134203
    09NM401
    1365030.650.05370.00100.4940.0100.06610.00083594140884135
    2273650.500.05560.00130.5510.0130.07120.000743551446114444
    3212880.390.05560.00170.5510.0180.07110.000843769446144435
    4273540.640.05560.00140.5420.0140.07000.000443857440124363
    51549630.120.07550.00051.7750.0160.16880.001410821410361010068
    6415621.490.05670.00300.5060.0270.06400.0012481115416224007
    7141860.470.05580.00220.5520.0230.07100.000844590446184425
    8314030.590.05530.00110.5450.0120.07080.00064254544294414
    9324280.610.05540.00110.5430.0120.07030.000743046440104384
    10222810.610.05490.00150.5480.0150.07170.000840759444124465
    11273690.630.05590.00130.5350.0120.06870.000444851435104282
    12273720.630.05680.00140.5310.0140.06720.000848454433114195
    13385000.700.05550.00080.5500.0110.07110.00124333444594438
    14202600.520.05530.00180.5490.0180.07120.000842672444154445
    09NM401
    15293860.550.05420.00110.5390.0120.07130.00073814543894445
    16324150.630.05510.00100.5440.0100.07090.00064164144184424
    17212730.520.05660.00160.5650.0170.07180.000847462455134475
    18233040.630.05600.00140.5590.0150.07160.000745356451124464
    19222880.620.05460.00140.5510.0160.07240.001239657445134517
    20182330.560.05490.00210.5470.0210.07150.001140984443174457
    21374751.180.05470.00080.5420.0130.07110.0018401344401044311
    22273410.640.05440.00120.5530.0140.07300.001438848447114549
    23192500.660.05330.00240.5360.0260.07210.00163431034362144910
    24263370.530.05440.00150.5500.0190.07270.0021388634451545213
    25263350.670.05500.00190.5500.0200.07190.001241078445164477
    26334360.790.05720.00190.5510.0160.06920.0034499734461343121
    27455951.210.06040.00090.5350.0080.06350.00036193143563972
    28243110.580.05460.00140.5500.0160.07240.001439457445134519
    29354690.720.05900.00110.5600.0110.06820.00065664145294254
    30404990.890.05540.00100.5550.0110.07190.00104294044894486
    09NM41
    1212750.580.05380.00180.5440.0200.07330.001036275441164566
    2263330.520.05460.00110.5650.0140.07510.000939547455114675
    3303610.730.05710.00090.6040.0120.07660.00094963448094765
    4293460.820.05710.00140.5850.0160.07430.001049453468134626
    5354210.730.05750.00090.6050.0120.07630.00095093548094745
    6121490.520.05860.00220.6170.0260.07640.000855082488214745
    7415290.600.05620.00070.5800.0090.07480.00064612946474654
    8131670.590.05430.00210.5630.0230.07510.000738688453184674
    9455620.850.05640.00060.5720.0080.07350.00074702345964574
    10384790.700.05510.00080.5630.0080.07420.00074153245464614
    11293690.730.05690.00100.5720.0100.07290.00074893745984534
    12334160.810.05650.00080.5660.0080.07260.00074733145574524
    13384930.630.05620.00070.5640.0070.07280.00064582745464534
    14405180.620.05630.00070.5670.0070.07300.00074642945664544
    15405280.700.05680.00070.5540.0070.07070.00074842844764404
    16465800.760.05730.00060.5690.0060.07200.00075042345754484
    17384670.780.05580.00080.5730.0100.07450.00074443146084634
    18222710.740.05490.00130.5570.0140.07350.000641052450114574
    19323700.970.05550.00090.5780.0100.07550.00064343546384694
    20374790.640.05540.00070.5650.0090.07400.00084272745574605
    21394880.820.05720.00080.5760.0130.07300.001349931462104548
    22425480.590.05590.00060.5680.0080.07380.00074462245764594
    23425640.580.05600.00050.5520.0080.07150.00084532144674455
    24243120.640.05570.00120.5660.0140.07360.000844147455114585
    25151940.540.05660.00200.5860.0220.07500.000947778468174666
    26586800.900.05590.00060.5820.0100.07540.00104502246684696
    下载: 导出CSV

    表  2   白乃庙铜矿中酸性岩类主量元素成分

    Table  2   Major element composition of intermediateacid rocks in the Bainaimiao copper deposit

    %
    样品号
    岩性
    08MD10108MD10209NM401-109NM401-209NM401-3
    花岗闪长岩花岗闪长岩
    SiO266.9365.5663.9065.7063.70
    AI2O315.0315.1216.115.4516.1
    Fe2O32.592.823.082.453.82
    FeO1.091.392.382.681.78
    CaO2.943.613.351.943.28
    MgO1.521.621.981.941.94
    K2O3.693.562.784.223.34
    Na2O2.442.143.482.743.06
    TiO20.380.420.490.440.52
    P2O50.130.130.170.150.2
    MnO0.040.060.0460.0360.058
    烧失量2.983.001.761.841.91
    total99.7799.4399.5299.5999.71
    A/CNK1.121.081.081.221.10
    δ1.571.441.882.131.98
    下载: 导出CSV

    表  3   白乃庙铜矿中酸性岩类微量元素成分

    Table  3   Trace element composition of intermediateacid rocks in the Bainaimiao copper deposit

    10-6
    样品号08MD
    101-1
    08MD
    101-2
    09NM
    401-1
    09NM
    401-2
    09NM
    401-3
    岩性花岗闪长岩花岗闪长岩
    La28.8221.7745.2038.8045.00
    Ce59.9339.2967.6068.0069.60
    Pr4.723.958.007.458.16
    Nd16.5813.8327.4026.4028.20
    Sm2.872.534.905.005.10
    Eu0.910.811.721.621.90
    Gd2.342.034.364.284.50
    Tb0.320.270.560.590.58
    Dy1.781.522.533.022.72
    Ho0.360.300.500.600.52
    Er1.040.921.381.631.46
    Tm0.170.170.220.270.24
    Yb1.311.231.561.921.67
    Lu0.210.190.260.310.26
    ZREE121.3688.80166.19159.89169.91
    LREE/HREE15.1312.3913.6211.6713.22
    (La/Sm)N6.485.555.965.015.70
    (La/Yb)N15.7512.6820.7814.5019.33
    δEu1.041.051.111.041.19
    Sr635.59547.04614.00473.00578.00
    Rb80.2856.1997.50114.50102.55
    Ba1053.45864.15684.501290.00953.00
    Th21.8314.7011.8013.2013.80
    U3.111.892.562.902.49
    Ta0.660.600.640.620.58
    Nb9.258.388.459.098.58
    Ta0.660.600.640.620.58
    Zr136.78116.72108.00122.00108.00
    Hf3.623.143.393.703.40
    Y10.308.1814.7016.6014.40
    Sr/Y61.7366.8841.7728.4940.14
    下载: 导出CSV
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  • 收稿日期:  2015-10-22
  • 修回日期:  2016-03-06
  • 网络出版日期:  2023-08-16
  • 刊出日期:  2016-03-31

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