青海省夏日哈木铜镍矿床岩石地球化学特征及其意义

张照伟，钱兵，王亚磊，李世金，刘长征

(1.国土资源部岩浆作用成矿与找矿重点实验室，西安地质矿产研究所，陕西 西安　710054；2.青海省地质调查局，青海 西宁　810001；3.青海省第五地质矿产勘查院，青海 西宁　810028)



青海省夏日哈木铜镍矿床岩石地球化学特征及其意义

张照伟1，钱兵1，王亚磊1，李世金2，刘长征3

(1.国土资源部岩浆作用成矿与找矿重点实验室，西安地质矿产研究所，陕西 西安710054；2.青海省地质调查局，青海 西宁810001；3.青海省第五地质矿产勘查院，青海 西宁810028)

摘要：新发现的青海省夏日哈木超大型镍矿床，在国内是仅次于金川岩浆铜镍矿床的第二大矿床。矿区发育5个镁铁-超镁铁岩体，目前仅Ⅰ号镁铁-超镁铁岩体内发现了具有经济价值的超大型矿体，其他4个岩体多为镁质橄榄岩及榴辉岩，是多种构造体制叠加岩浆活动的结果。分析发现Ⅰ号岩体所有岩石的SiO2含量为34.11%～54.28%，其m/f值为2.01～4.93，属铁质系列的镁铁-超镁铁岩石。通过对橄榄石Fo值与Ni含量研究表明，存在多期次的岩浆成矿作用，橄榄石Fo值与Ni含量正相关和负相关的协变关系，说明存在早期硫化物不混溶作用。结合区域年代学综合分析认为，夏日哈木超大型岩浆铜镍硫化物矿床的形成，是早泥盆世早期岩浆活动于柴达木盆地边缘东昆仑造山带夏日哈木地区具体的成矿表现。在其Ⅰ号和Ⅱ号岩体的深部，仍具有较大的找矿潜力，而其他3个镁铁-超镁铁质多以镁质橄榄岩为主，不具备镍矿成矿条件，可能没有发现铜镍矿的经济价值。

关键词：岩石地球化学特点，镁铁-超镁铁质岩体，铜镍矿床，找矿方向，夏日哈木，青海省

青海省夏日哈木岩浆铜镍硫化物矿床是近两年在东昆仑造山带发现的超大型矿床(李世金等，2012)，在国内是仅次于甘肃省金川岩浆铜镍(铂族)硫化物矿床的第二大镍矿床，也是继1996年加拿大沃尔斯贝(Voisey’s Bay)岩浆硫化物矿床发现以来近20年全球镍矿最重要的发现(LI et al., 2015)。夏日哈木地区发育5个镁铁-超镁铁岩体，110万t的镍金属量只赋存于其中的一个镁铁-超镁铁质岩体内，其余4个岩体的含矿性尚不清楚，这5个镁铁-超镁铁质侵入岩体之间的关系，无疑直接影响到进一步的含矿性评价和勘探找矿方向。通过详细的野外调查和钻孔岩心编录，发现夏日哈木岩浆铜镍硫化物矿床的含矿岩体是由橄榄岩、辉石岩及少量辉长岩组成，是多期次岩浆活动的结果。镍矿体的形成只与橄榄岩及辉石岩有关，辉长岩在含矿的超镁铁质岩之前之后均有发育。可见，夏日哈木岩浆铜镍硫化物矿床及其含矿岩体的地质特征有待进一步鉴别，其硫化物熔离机制与成矿过程、岩浆源区性质及构造背景也是制约深部找矿及含矿岩体形成过程的关键因素。本研究拟从夏日哈木镁铁-超镁铁质岩体的空间形态和岩相分异入手，结合岩体的岩石地球化学特点和含矿岩体的橄榄石成分，进一步探讨夏日哈木区域内镁铁-超镁铁质岩体的勘探找矿方向，初步总结可能产出的构造地质背景和成矿环境，对于深化岩浆铜镍硫化物矿床的形成机理认识、指导区域内类似岩体及矿床的发现与勘查，具有重要意义。

1区域地质构造背景

青海省夏日哈木镁铁-超镁铁质侵入岩体及岩浆铜镍硫化物矿床位于柴达木地块南缘东昆仑造山带中(图1a)。东昆仑造山带以昆中区域性大断裂为界又可进一步分为昆北和昆南造山带。昆北造山带中发育有大量的391～410 Ma的花岗岩，这些花岗岩侵入到前寒武纪变质基底及古生代火山沉积地层中，零星可见三叠纪沉积地层(图1b)。在昆北造山带的东部，发现有～428 Ma的榴辉岩(MENG et al., 2013)。其他几处蛇绿混杂岩的年龄变化在467～518 Ma，并且这些蛇绿混杂岩的玄武质岩石表现出了典型的MORB 特征(BIAN et al., 2004；宋谢炎等，2009；杨合群等，2010；MENG et al., 2013；校培喜等，2014)。祁漫塔格早古生代岩浆弧以昆北断裂带为界与柴达木盆地接壤，昆南增生楔杂岩带则以昆南断裂带为界与巴颜喀拉造山带毗邻。青海省夏日哈木超大型岩浆铜镍硫化物矿床产出于祁漫塔格早古生代岩浆弧内，临近黑山-那陵格勒断裂(图1c)。矿区出露地层主要为古元古代白沙河岩群，岩石类型为黑云斜长片麻岩、眼球状混合片麻岩、大理岩、二云石英片岩等，原岩恢复为碎屑岩-碳酸盐岩-火山岩建造，经历了角闪岩相区域变质作用(张雪亭等，2007；耿林等，2007；李荣社等，2008；范丽琨等，2009；校培喜等，2014)。几个不同时代不同规模的岩浆铜镍硫化物矿床发育于柴达木地块的北缘及其附近，如牛鼻子梁(柴达木西北缘402 Ma)(钱兵等，2015)、亚曲(东南祁连441 Ma)、裕龙沟(东南祁连443 Ma)(ZHANG et al., 2014)。但牛鼻子梁、亚曲及裕龙沟等由于岩体规模较小至今尚未发现具有较大经济价值的矿体。

图1　青海省夏日哈木铜镍矿区域构造及地质略图(LI et al., 2015)Fig.1　The schematic tectonic and geological map of Xiarihamu in Qinghai Province

2夏日哈木岩(矿)体地质特点

夏日哈木岩浆铜镍硫化物矿床所在区域目前已发现5个镁铁-超镁铁质岩体，对应的岩体编号分别为Ⅰ号、Ⅱ号、Ⅲ号、Ⅳ号和Ⅴ号(图2)。夏日哈木铜镍矿体基本都产在Ⅰ号岩体内，笔者所研究及讨论的也主要是Ⅰ号岩体(图3)。矿区北部的正长花岗岩基形成于(391.1±1.4) Ma(王冠等，2013)。断裂构造以近东西向和北西西向为主，形成时代早。北东向和南北向断裂规模相对较小，形成时代晚，经常错断近东西向和北西西向断层(图2)。Ⅱ号岩体地表露头主要是辉石岩，发现少量硫化物，在其旁边发育榴辉岩。Ⅲ号岩体主要是镁质橄榄岩，同样发现有榴辉岩和榴闪岩。Ⅳ号和Ⅴ号岩体基本都是镁质橄榄岩。

夏日哈木矿区Ⅰ号岩体长约1.5 km，宽约0.8 km，长轴方向近东西向，西段略向南偏转。将所有施工钻孔投影到平面图上，主要是12号勘探线以西，以0.5%的Ni品位划分为见矿钻孔及未见矿钻孔，从而初步确定了矿体及岩体的边界(图3a)。岩体顶界面东高西低，东段出露于地表，西段隐伏于地下，且越向西埋深越深(图3b、图3e)，总体形态为向西倾伏的岩床(图3)。夏日哈木矿区Ⅰ号岩体在地表有氧化蚀变带及铁帽出露(图4b)，主要集中在0号勘探线东西两侧，1号勘探线与4号勘探线之间的区域(图3a)。从3条勘探线(2号、9号和17号勘探线)钻孔纵剖面图(图3c、图3d、图3e)来看，岩体岩性主要是辉石岩、橄榄岩、辉长岩，含少量的花岗岩脉(图4a)，并且橄榄岩相越向西橄榄石含量逐渐增多，同时埋深加大，围岩地层厚度增厚。在钻孔横剖面图上，上述情况则更加明显直观(图3f、图3g、图3h)，沿着NM线248°方向，岩石基性程度变高，岩体埋深增大，橄榄石含量增多，矿体增厚变富，并且向南向北边部岩体和矿体变薄甚至尖灭(图3f)。

图2　青海省夏日哈木岩浆铜镍硫化物矿区岩体地质分布略图(据张照伟等，2015b)Fig.2　Schematic geological map for mafic-ultramafic intrusions from Xiarihamu magmatic Ni-Cu deposit inQinghai Province (After ZHANG et al., 2015b)

夏日哈木矿区镍矿体主要赋存于辉石岩与橄榄岩中，且以二辉岩和二辉橄榄岩为主，不含矿的辉长岩与含矿的辉石岩及橄榄岩明显不是同期的产物。镍矿体主要赋存于夏日哈木矿区Ⅰ号岩体2号(AB线)勘探线以西地表以下的区域，在9号勘探线、11号勘探线的位置区域，镍矿体达到了最厚(超过300 m)，随着勘探线号的变大(向西)，岩体变薄，埋深增厚，橄榄石增多，镍矿体变富(图3c、图3d、图3e)。矿石矿物主要为镍黄铁矿、磁黄铁矿及少量的黄铜矿(图4f、图4g)，可见明显的橄榄石被辉石包裹的典型包橄结构(图4d、图4e)。

3岩石地球化学特点

3.1岩石地球化学特征

Ⅰ号岩体中各种岩石的主量元素分析数据见表1。所有岩石的SiO2含量为34.11%～54.28%，均属基性-超基性岩石。m/f值为2.01～4.93，属铁质系列。

图3　(a)青海省夏日哈木矿区Ⅰ号岩体纵投影、(b)平面及(c)、(d)、(e)、(f)、(g)、(h)剖面地质略图Fig.3　Schematic geological map for vertical projection (a)、plan (b) and profile (c)、(d)、(e)、(f)、(g)、(h) from Xiarihamu intrusion Ⅰ in Qinghai Province

各种岩石的稀土元素总量均较低，∑REE=7.62×10-6～51.23×10-6。橄榄岩相岩石的稀土元素丰度大多低于辉石岩相的相应丰度，而后两类岩石又低于辉长岩相的丰度。大多数超镁铁质岩石没有明显的Eu异常，少数样品有弱的负Eu异常。镁铁质岩石普遍有不同程度的正Eu异常。各种岩石均具有轻稀土元素富集型配分曲线(图5)。(La/Yb)N=1.74～10.66，平均值为3.69；(La/Sm)N=1.19～3.93，平均值为2.16；(Gd/Yb)N=1.03～2.41，平均值为1.57。显示了轻-重稀土元素之间、轻稀土元素之间分馏强，而重稀土元素之间分馏弱的特征。原始地幔标准化的微量元素配分曲线见图5。各种岩石具有相似的微量元素配分曲线，显著的Ba、Nb负异常。

3.2橄榄石成分特征

对钻孔岩心ZK602S和ZK1507系统采集样品进行矿物晶体化学成分分析，选择贫硫化物和无硫化物的二辉橄榄岩与二辉岩进行橄榄石Fo值与Ni含量的系统对比。从橄榄石Fo值与橄榄石Ni含量的协变图(图6)可以看出，随着钻孔深度的增加，橄榄石Fo值与Ni含量表现出了两种截然不同的相关关系，既有正相关也有负相关，一是说明岩浆演化的早期既有硫化物不混溶作用发生，从岩石学及显微照片也证实了这一点(图4c)，橄榄石晶体包裹了硫化物包体，而后又被较大的斜方辉石晶体所包裹。另一方面，说明成矿过程并非一次岩浆作用的结果，是多期次岩浆活动的产物。

Cp. 黄铜矿；Pl. 斜长石；Po. 磁黄铁矿；Pn. 镍黄铁矿；Ol. 橄榄石；Cpx. 单斜辉石；Opx. 斜方辉石;a.钻孔岩芯团块 　 　状矿石；b.地表露头辉石岩；c.橄榄石中的硫化物包体；d.含长二辉岩显微照片；e.包橄结构；f.黄铜矿、磁黄铁矿及镍黄铁矿共生；g.磁黄铁矿与黄铜矿共生图4　夏日哈木矿区岩矿石及显微照片Fig.4　Microphotographs of rocks and ore minerals in Xiarihamu magmatic Ni-Cu sulfide deposit

样品编号XH-8XH-10XH-58XH-91XH-2XH-13XH-15XH-24XH-28XH-56XH-83XH-b85岩性辉长岩辉石岩橄 榄 辉 石 岩SiO254.2847.2649.3647.7337.737.2738.1639.7739.1441.7139.6438.53Al2O319.413.762.673.672.291.402.254.621.541.673.332.33CaO7.118.641.144.582.151.521.802.260.821.271.901.27Fe2O31.911.902.921.643.185.234.381.924.652.713.294.84FeO5.0112.659.4212.0312.395.096.328.764.96.976.475.72K2O2.290.060.220.150.050.150.080.350.390.050.190.14MgO2.5220.7829.5423.5831.9537.0635.6632.5437.1236.3536.4235.03MnO0.120.170.140.150.130.130.130.120.110.100.140.11Na2O3.570.350.270.360.120.090.200.310.070.080.400.16P2O50.180.020.030.020.010.010.020.010.020.020.040.01TiO21.080.280.160.240.120.110.120.180.10.170.270.11LOI2.701.972.3747.5211.4510.587.4911.168.457.6610.64Total100.1897.8498.2498.1597.6199.5199.798.33100.0299.599.7598.89

续表1

样品编号XH-8XH-10XH-58XH-91XH-2XH-13XH-15XH-24XH-28XH-56XH-83XH-b85岩性辉长岩辉石岩橄 榄 辉 石 岩Mg#0.400.720.810.760.790.870.860.850.880.870.870.86Cr25.22570362129023171713750278338010681141258Co19.90382351394421142218173172212175169Ni43.5777514311756772452918416941993141576334634343Cu17.001818327916411127350577628145793307338Zn74.8074.588.593.810583.681.59490.256.784.577.5Rb117.005.3714.16.951.484.373.3618.223.71.9410.23.37Sr494.0024.426.629.810.118.64756.716.35.5581.132.9Cs6.532.095.384.181.250.60.6112.8120.661.360.91Ba501.0013.938176.0914.416.143.656.311.265.610.7Pb5.6910.513.65.155.798.95.196.011.293.5115.64.04Bi0.053.3611.20.992.991.531.377.011.492.870.934.02Th5.860.241.10.390.170.450.310.50.690.370.810.31U1.140.050.220.080.050.140.070.30.190.090.290.25Nb9.960.230.630.420.320.380.310.4710.371.160.46Ta0.500.050.050.110.050.050.050.060.060.050.070.05Zr202.0015.710.814.68.1710.18.8611.623.512.331.47.79Hf5.580.580.30.420.260.260.270.320.530.380.760.22Sb0.310.050.120.070.090.140.080.20.150.050.070.12Ti6510.001475827125868565467110806039591537677V158.0024678.418481.921.143.543.91752.649.722.6La22.101.132.041.20.611.10.821.441.250.963.460.86Ce46.703.353.762.921.542.571.973.273.032.387.282.1Pr6.030.550.420.410.230.330.280.410.420.360.890.27Nd24.902.911.51.981.121.441.271.811.771.673.71.37Sm6.761.050.420.620.380.40.40.540.530.561.020.35Eu2.030.310.120.210.120.110.160.20.150.140.370.11Gd5.661.110.340.630.420.460.410.650.420.530.940.42Tb0.940.250.060.140.090.070.070.10.070.120.170.07Dy5.511.50.440.890.60.440.530.640.430.81.090.4Ho1.060.330.090.20.120.080.110.140.080.160.220.1Er2.940.850.260.530.340.270.280.40.210.430.580.28Tm0.400.130.050.090.060.050.050.050.050.060.090.05Yb2.830.850.310.60.360.230.270.40.240.440.580.26Lu0.420.130.050.090.060.050.050.060.050.070.090.05Sc17.5041.6016.5030.0016.707.7411.608.865.9013.3010.607.52Y31.809.032.715.583.602.573.064.012.384.636.382.77

续表1

样品编号XH-87XH-52XH-41XH-43XH-46XH-48XH-b51XH-54XH-104XH-124XH-128HM-1岩性橄榄辉石岩辉 石 橄 榄 岩SiO241.5442.4241.2336.5137.0035.0038.9337.3937.8234.8434.1136.35Al2O31.217.053.531.810.991.341.911.833.381.571.180.75CaO0.945.672.271.180.511.421.710.871.981.250.231.02Fe2O34.872.832.205.495.673.662.426.633.535.234.814.77FeO6.256.416.937.738.6711.359.905.579.7711.028.426.97K2O0.100.340.810.170.090.100.080.330.150.070.130.13MgO36.429.1932.7535.2535.9336.0335.2634.8533.2034.2836.1236.98MnO0.110.130.140.150.140.140.140.120.140.140.100.13Na2O0.090.800.140.180.070.180.200.100.350.180.050.05P2O50.020.010.030.050.030.020.020.010.050.040.040.02TiO20.100.350.140.270.100.080.120.130.220.080.060.06LOI8.075.088.5510.709.568.437.3111.307.709.3012.9611.07Total99.70100.2898.7299.4998.7697.7598.0099.1398.2998.0098.2198.3Mg#0.860.850.870.830.820.810.840.840.820.800.830.85Cr592.00555.00592.00680.00258.00713.00818.00231.00962.00476.001625.00512.00Co175.0090.70172.00277.00332.00405.00299.00158.00310.00287.00350.00192.00Ni3354.001337.002708.008970.0011067.007308.005167.002094.0011512.009782.0015210.004694.00Cu84.5070.30335.001253.001968.001226.00620.00222.001753.001173.001351.00568.00Zn79.0069.4076.1087.40102.0081.4094.6072.90103.00174.0093.9070.90Rb4.6715.80102.008.824.602.323.0018.907.741.174.438.13Sr10.70166.0019.3024.109.4625.7023.0026.7055.5039.006.3312.40Cs1.473.3089.903.171.530.590.861.561.020.782.256.51Ba18.3028.4024.6029.6012.3022.8038.0055.6029.308.9311.3013.50Pb2.496.062.934.946.277.568.504.5111.00138.003.053.07Bi0.790.301.155.185.021.751.650.345.3911.1017.604.84Th0.441.860.540.760.640.190.290.650.820.200.710.32U0.131.010.140.170.180.050.060.220.150.280.210.06Nb0.511.471.301.120.460.240.300.880.730.170.970.26Ta0.050.150.060.080.050.050.050.090.050.050.060.05Zr10.2023.2015.6031.9015.207.7910.9016.5034.104.7812.003.56Hf0.260.730.380.810.360.230.300.410.770.140.230.10Sb0.070.250.090.130.110.050.050.210.140.490.220.20Ti543.002057.00832.001391.00549.00500.00755.00798.001202.00430.00319.00379.00V30.7082.3035.1042.6019.5024.8049.7015.2040.316.6018.719.80La0.833.001.562.280.930.930.821.892.080.491.400.62Ce1.926.973.515.192.042.091.914.414.601.232.671.40Pr0.250.830.470.710.260.290.280.530.610.150.310.18Nd1.113.742.153.171.151.221.272.382.650.601.140.76Sm0.331.150.630.940.290.370.450.580.730.210.250.23Eu0.100.330.200.260.080.120.160.100.240.070.080.06Gd0.311.240.560.830.280.320.420.500.720.260.240.26Tb0.060.210.110.170.050.070.090.080.140.050.050.05Dy0.371.360.671.000.350.410.560.450.870.250.250.26Ho0.080.280.130.200.070.080.120.090.170.050.050.06Er0.200.850.350.550.210.220.320.270.480.140.160.15Tm0.050.100.060.090.050.050.050.050.070.050.050.05Yb0.230.700.380.560.240.250.360.220.50.150.190.13Lu0.050.090.060.090.050.050.060.050.080.050.050.05Sc9.7018.5010.2011.006.037.9113.206.2010.205.865.938.12Y2.208.583.796.082.102.393.572.845.281.591.711.49

续表1

样品编号HM-5HM-8HM-9HM-29HM-33HM-36HM-39HM-69HM-73HM-74HM-77HM-81岩性辉 石 橄 榄 岩SiO240.6438.4836.3338.6438.0138.4536.9540.9837.3936.5437.3836.48Al2O33.022.163.240.881.092.963.763.831.231.020.571.44CaO3.762.382.140.681.271.692.202.190.750.740.821.04Fe2O33.823.562.244.023.484.664.423.524.184.506.085.22FeO5.858.6911.216.327.834.359.456.505.325.606.395.41K2O0.180.150.160.060.200.210.100.170.120.080.050.15MgO34.0234.5533.3938.7638.0936.1832.1134.2138.5138.8137.2037.09MnO0.140.140.120.120.160.110.140.150.120.120.130.13Na2O0.300.310.330.080.160.230.450.490.070.060.050.07P2O50.010.010.010.040.020.010.010.020.010.010.010.01TiO20.240.160.200.100.090.130.140.370.120.080.050.11LOI7.508.519.139.048.1110.858.706.4810.8211.0310.2411.62Total99.4899.1098.598.7498.5199.8398.4398.9198.6498.5998.9798.77Mg#0.870.840.820.870.860.880.810.860.880.880.850.87Cr1026.00515.00303.0087.40260.00381.00279.00837.00446.00397.00469.00397.00Co122.00199.00264.00184.00176.00123.00244.00121.00141.00150.00171.00147.00Ni1941.003256.004401.002663.004029.002564.006917.001885.003365.003931.002016.003369.00Cu162.00371.001010.0097.00556.00153.001777.0079.60347.00394.00290.00329.00Zn68.5065.8066.7095.3083.8065.9089.1071.5060.8064.4094.0073.70Rb8.164.743.991.537.948.102.646.416.872.380.058.37Sr65.9034.1082.7020.9024.8096.6096.6074.4017.3014.906.5918.60Cs1.351.090.740.801.522.910.390.444.301.560.246.33Ba31.3020.1024.9010.8029.1036.820.1030.608.148.563.2810.60Pb4.697.8517.407.125.213.6317.503.005.206.822.533.60Bi0.511.351.281.072.260.342.180.122.242.090.442.00Th0.930.690.460.380.490.660.320.810.300.260.110.27U0.210.320.160.120.180.170.090.170.100.100.050.09Nb0.510.470.620.650.520.520.330.770.280.200.090.25Ta0.060.060.070.140.050.050.050.060.050.050.050.05Zr18.4014.8013.807.0010.7012.2010.1032.607.737.173.158.10Hf0.570.400.430.220.290.340.280.770.220.210.100.23Sb0.060.100.070.140.170.060.170.160.120.100.140.12Ti1543.00889.001226.00623.00527.00768.00815.002298.00700.00503.00300.00663.00V70.4048.4036.2012.6011.9019.0024.5056.5018.0015.3015.2021.30La1.711.561.471.091.162.631.042.220.690.580.300.73Ce4.173.693.922.682.734.752.485.591.651.480.741.74Pr0.550.470.540.330.320.520.320.760.240.180.100.22Nd2.702.152.691.351.542.141.513.601.020.840.461.12Sm0.820.550.670.340.350.480.421.010.300.220.120.28Eu0.230.150.200.090.090.150.170.290.090.06<0.050.11Gd0.940.560.760.300.390.470.471.060.350.290.120.40Tb0.160.090.120.050.060.070.070.190.060.050.050.06Dy0.950.590.790.350.360.430.471.140.370.290.140.38Ho0.210.130.140.060.060.090.100.230.080.060.050.08Er0.600.390.490.220.200.300.310.710.210.180.120.24Tm0.080.050.070.050.050.050.050.090.050.050.050.05Yb0.520.340.440.200.220.250.290.630.200.160.120.23Lu0.080.060.050.050.050.050.050.100.050.050.050.05Sc18.5012.809.325.015.246.347.7813.606.656.135.687.72Y5.723.864.482.052.082.772.867.332.271.721.022.33

图5　球粒陨石标准化稀土元素分布模式和原始地幔标准化多元素蛛网图(据SUN et al., 1989)Fig.5　Chondrite-normalized REE patterns and PM-normalized trace elements spider diagrams(After SUN et al. 1989)

4讨论

4.1成岩成矿构造背景认识

夏日哈木Ⅰ号岩体表现了轻稀土元素相对重稀土元素富集，亏损高场强元素，具有普遍负Nb异常，推测岩浆作用伴有弧物质的卷入(LI et al., 2015；ZHANG et al., 2016)。在钻孔岩心二辉岩和二辉橄榄岩中，橄榄石Fo值和Ni含量表现了正负相关性的两个特点，进一步表明非一次岩浆成矿作用的结果。并且橄榄石Fo值在岩体自西向东的剖面中表现了逐渐减小的特点，可能是岩浆流动过程中橄榄岩相结晶的响应，与岩浆流动方向一致。

镁铁-超镁铁质侵入岩及其所含铜镍硫化物矿床的构造背景认识对于进一步指导区域找矿具有重要意义(LI et al., 2009；高辉等，2009；张照伟等，2011，2012，2014)。对夏日哈木岩浆铜镍硫化物矿床矿体上下盘不含矿的钻孔岩心进行锆石挑选，具体位置是钻孔ZK5E07S 340～350 m处和钻孔ZK1501S 330～340 m处的岩心，岩性为非矿化橄辉岩，获得(412.9±1.8) Ma(MSWD=1.2)和(410.9±1.6) Ma(MSWD=3.1)的谐和年龄，比较一致的年龄信息可代表夏日哈木岩浆铜镍硫化物矿床含矿岩性的形成时代(张照伟等，2015b)。宋谢炎等也获得了夏日哈木岩浆铜镍硫化物矿床410 Ma锆石SHRIMP年龄(宋谢炎等，2014)，进一步表明青海省东昆仑夏日哈木铜镍矿床形成于早泥盆世。综合区域早泥盆世火山岩组合(玄武安山岩-安山岩-英安岩-流纹岩)，以及广泛出露的同时代的花岗岩基，多数学者认为该地区的早泥盆世处于碰撞后伸展阶段(宋谢炎等，2014)。已有研究认为，东昆仑岩浆弧大约形成于450～430 Ma，在昆北造山带的东部，发现有形成于428 Ma榴辉岩(MENG et al., 2013；杜玮等，2015)，其他几处蛇绿混杂岩的年龄变化为467～518 Ma，并且这些蛇绿混杂岩的玄武质岩石具有典型的MORB 特征(牛晓露等，2013，2015；秦克章等，2014)。夏日哈木超镁铁岩母岩浆表现了富集轻稀土 、明显的负Nb 异常，橄榄石中Ca亏损和高的SiO2含量，表现出了弧岩浆岩的特点(NALDRETT ,2009；MAIER et al., 2010；谢燮等，2014；LI et al., 2015)。混有弧岩浆物质的原生岩浆，在上升过程中遭受地壳硫的混染(LI et al., 2015)，导致岩浆中的硫化物达到饱和，上升的岩浆中充满了不混溶的硫化物小液滴。尽管表现出了岛弧环境的地球化学信息，但并非一定就是岛弧背景，深部岩浆在上升过程中混染一些其他属性的地球化学信息不难理解。夏日哈木镁铁-超镁铁质侵入岩及铜镍硫化物矿床的形成，可能与柴达木盆地边缘裂解岩浆作用关系密切，是稳定陆块边缘活动的产物。

图6　夏日哈木超镁铁质岩体橄榄石Fo值与Ni含量关系图Fig.6　Covariation graph of Fo value vs. Ni content from olivine in Xiarihamu ultramafic intrusion

4.2进一步找矿方向

夏日哈木矿区已发现5个镁铁-超镁铁岩体，但仅Ⅰ号岩体发育了具有经济价值的超大型矿体，其他4个岩体目前尚未发现有价值的矿化线索。究其原因，这5个镁铁-超镁铁岩体并非同期同构造背景的产物，夏日哈木狭小区域内除含矿的镁铁-超镁铁岩之外，既有镁质橄榄岩，又有与深俯冲密切相关的榴辉岩(祁生胜等，2014)，足见该区域地质构造背景的复杂性。夏日哈木Ⅰ号岩体表现了多期次的成矿作用，是深部熔离-多期贯入成矿作用的具体表现，在其深部主要是岩浆来源的方向，存在进一步找矿空间与潜力。夏日哈木Ⅱ号岩体，尽管已发现了少量的硫化物矿化，但岩体主体与旁边的榴辉岩是何关系尚不清楚，这也影响了对进一步找矿方向的判断。夏日哈木Ⅲ号岩体、Ⅳ号岩体及Ⅴ号岩体，发育了镁质橄榄岩，对成铜镍矿不利。除夏日哈木之外，在柴达木盆地西北缘发现了402 Ma牛鼻子梁含矿镁铁-超镁铁质侵入岩体(凌锦兰等，2014；钱兵等，2015；张照伟等，2015a)，在柴北缘也有类似侵入岩体的发现，并且伴有较好的镍矿化，只是成岩成矿时代尚未确定。这些岩体或者矿床的产出特点就是围绕柴达木克拉通周缘的造山带中，是稳定克拉通边缘的产物。围绕柴达木盆地周缘，成岩时代在412 Ma左右，岩相分异良好的铁质系列镁铁-超镁铁质侵入岩体是下一步重要的勘查对象。

5结论

(1)青海省夏日哈木镁铁-超镁铁质岩体产出构造背景复杂，岩体成群出现，Ⅰ号岩体表现出了多期次岩浆活动的特点，整体是一次大的岩浆成矿事件，是柴达木盆地边缘裂解岩浆活动与成矿作用的具体表现。

(2)夏日哈木Ⅰ号岩体和Ⅱ号岩体的深部具有较好找矿潜力。

(3)在柴达木盆地南缘东昆仑造山带内，形成时代约412 Ma，具有明显岩相分带铁质系列的镁铁-超镁铁质侵入岩体是下一步勘探寻找铜镍硫化物矿的重要对象。

致谢：野外地质工作得到青海省地质调查局、青海省地矿局、青海省第五地质矿产勘查院领导及野外一线工作同志的支持、关心与帮助；国土资源部岩浆作用成矿与找矿重点实验室的张江伟、李侃、张志炳、王博林共同参与野外工作及插图绘制；论文评审专家给予了很好的建议和具体修改意见，在此一致深表感谢。

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收稿日期：2015-06-30；修回日期： 2016-02-19

基金项目：国土资源部公益性行业科研专项“拉陵灶火镍成矿赋矿机理及勘查技术研究示范”(201511020)和中国地质调查局“东昆仑铜镍多金属资源基地调查”二级项目(DD20160013)共同资助

作者简介：张照伟(1976-)，男，副研究员，博士，主要从事岩浆铜镍硫化物矿床成矿理论研究与镍矿资源调查评价工作。E-mail: zhaoweiz@126.com

中图分类号：P618.41；P618.63

文献标志码：A

文章编号：1009-6248(2016)02-0045-14

Petrogeochemical Characteristics of the Xiarihamu Magmatic Ni-Cu Sulfide Deposit in Qinghai Province and Its Study for Olivine

ZHANG Zhaowei1, QIAN Bing1, WANG Yalei1, LI Shijin2,LIU Changzheng3

(1.Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits, MLR, Xi’an Institute of Geology and Mineral Resources, Xi’an 710054, Shaan Xi, China;2.Qinghai Bureau of Geological Survey, Xining 810028, Qinghai, China;3.No.5 Institute of Geology and Minerals Exploration of Qinghai Province, Xining 810028, Qinghai, China)

Abstract：Located in eastern Kunlun orogenic belt in Qinghai Province, the super-large Xiarihamu magmatic Ni-Cu sulfide deposit is the second ones after Jinchuan Ni-Cu sulfide deposit.Totally, 5 mafic-ultramafic intrusionswere developed 1n this mining area,in which some super-large economic ore-bodies have been found only in No.Ⅰintrusive rocks, but other 4 ones belong to basicto magnesium peridotite and eclogite, these maybe the results of at least two tectonic systems superimposed with magmatic activities. For the No.Ⅰintrusive rocks in the Xiarihamu deposit, their SiO2 contentsvary from 34.11% to 54.28%,and m/f ratios range from 2.01 to 4.93, belonging to ferruginous basic-ultrabasic rocks.The Fo and Ni valuesof olivine show that the Xiarihamu Ni-Cu deposit had experienced multiple stage of magmatic mineralization, the positive and negative correlations between Fo value and Ni content from olivine stand for the immiscibility of sulfide in the early mineralization stage. Combined with regional chronology and other geological information, it’s believed that the Xiarihamu super-large magmatic Ni-Cu sulfide deposit was the result of early lower Devonian magmatism and mineralization in the margin of Qaidam basin, eastern Kunlun orogenic belt. By the way, there maybe have better metallogenic conditions and prospecting potentiality in the depth of No.ⅠandⅡ intrusions, especially the place of magmatic origin or flowing direction, but the other three mafic-ultramafic intrusions that mainly belonged to magnesium peridotite have bad metallogenic condition on Ni-Cu sulfide deposit, and no economic value.

Keywords：petrogeochemical characteristics; mafic-ultramaficintrusions;magmatic Ni-Cu sulfide deposit; exploration direction; Xiarihamu; Qinghai Province