Protolith reconstruction and its significance in the search for the ore-hosting metamorphic rock series in Hekou Group, the Lala copper orefield, Sichuan Province
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摘要:
四川拉拉铜矿是中国著名的大型富铜矿床，其矿体均赋存于河口群变质岩系中，具有典型的层控特征，因此对这套变质岩开展原岩恢复工作能更好地限定其矿床成因，也可对区域下一步的深边部找矿提供指示。通过对赋矿变质岩开展了系统的岩相学和岩石地球化学研究，结果显示其原岩为一套泥质粉砂岩-细碧岩的岩石组合。其中，黑云石英片岩、二云石英片岩及白云石英片岩的原岩可能为泥质粉砂岩，而石英钠长岩、变火山角砾岩及变火山凝灰岩的原岩可能为细碧岩。河口群形成的构造环境可能为裂谷环境。结合矿体似层状、透镜状的层控特征及已有的成岩成矿年龄数据，认为该矿床存在早期VMS（火山成因块状硫化物矿床）型铜矿化，根据其围岩类型，可能属于"别子型"成矿亚类。本区此类矿床下一步找矿工作的方向为铁镁质火山岩与硅质碎屑岩的界面。
Abstract:The Lala copper deposit in Sichuan is one of the large copper-rich deposits in China.The ore bodies occur in the metamorphic rock series of the Hekou Group, and have typical stratabound characteristics.Therefore, the protolith reconstruction of this metamorphic rock can better define the genesis of the deposit and also provide directions for the next ore prospecting in this area.A series of geological and geochemical studies of its ore-bearing metamorphic rocks indicate that the original rocks are a set of argillaceous siltstone-spilite rock associations which were formed in an intracontinental rift of passive continental margin.The protoliths of biotite quartz schist, muscovite quartz schist and two-mica quartz schist are pelitic siltstone, while the original rocks of quartz albite, metavolcanic breccia and metavolcanic tuff are spilite.Based on the stratabound characteristics of stratiform as well as lenticular orebodies and diagenetic-metallogenic ages available, it is concluded that the deposit exhibits early VMS copper mineralization.Compared with the rock types of host rocks of different types of VMS deposits, Besshi type is considered to be of the early copper mineralization type.At last, the interface between mafic volcanic rocks and siliceous clastics in this region should be the direction of further prospecting work.
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Keywords:
- Lala copper orefield /
- protolith reconstruction /
- tectonic setting /
- VMS deposits
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致谢: 野外工作中承蒙四川省地质矿产勘查开发局四○三地质队和凉山矿业公司的帮助；论文在审稿过程中两位审稿专家提出了宝贵的意见，在此一并致谢。
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图 1 康滇裂谷系大地构造位置(a)及拉拉铜矿田矿区地质简图(b)
Figure 1. Geotectonic map of Kangdian rift(a)and geological sketch map of the Lala copper orefield(b)
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图版Ⅰ
a、b.黑云石英片岩；c、d.二云石英片岩；e、f.白云石英片岩；g、h.石英钠长岩；i、j.变火山角砾岩；k、l.变火山凝灰岩。Ab—钠长石；Ms—白云母；Bi—黑云母；Qz—石英；Dol—白云石
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表 1 主量元素分析结果及特征参数
Table 1 Major elements analytical results and characteristic parameters
% 样号 LD001 LD017 LD076 LD098 LD036 LD037 LD035 LD088 LD081 LD089 LD140 LD141 岩性 黑云石
英片岩黑云石
英片岩二云石
英片岩二云石
片岩白云石
英片岩白云石
英片岩石英
钠长岩石英
钠长岩石英
钠长岩石英
钠长岩变火山
角砾岩变火山
凝灰岩SiO2 46.22 47.60 46.90 51.30 50.71 42.37 48.76 44.14 41.34 40.67 50.18 50.69 TiO2 0.48 0.56 1.46 3.02 2.26 0.62 0.74 2.10 0.61 0.51 0.52 1.48 Al2O3 10.35 12.73 13.21 16.85 13.92 7.93 13.34 12.54 8.84 8.96 10.87 13.49 TFe2O3 17.52 21.36 24.75 11.91 18.28 12.07 4.50 13.03 4.49 9.60 4.90 8.30 MnO 0.36 0.51 0.16 0.15 0.61 1.29 0.30 0.42 0.47 0.71 0.19 0.19 MgO 2.51 1.82 2.86 1.48 1.10 4.42 1.06 1.55 1.41 4.58 2.50 2.41 CaO 5.40 1.38 1.88 3.09 1.23 12.26 13.37 8.24 21.35 12.71 13.27 7.06 Na2O 0.35 0.57 0.09 0.25 0.23 0.04 7.63 7.59 4.87 5.19 5.98 8.16 K2O 6.71 4.33 2.83 6.00 4.22 2.78 0.11 0.27 0.12 0.34 0.46 0.07 P2O5 0.12 0.13 1.16 1.15 1.00 0.15 0.17 1.12 0.16 0.17 0.32 0.82 烧失量 9.16 8.53 3.13 3.91 6.16 15.86 9.82 7.91 16.12 16.39 10.59 7.06 总计 99.17 99.52 98.44 99.11 99.72 99.81 99.82 98.90 99.79 99.84 99.77 99.73 FeO 13.39 14.16 17.08 8.27 11.38 7.17 1.51 6.69 2.62 6.40 2.47 2.47 KMg-K 0.93 0.83 0.95 0.94 0.92 0.98 0.01 0.02 0.02 0.04 0.05 0.01 MgMg-K 0.22 0.14 0.19 0.20 0.10 0.39 0.30 0.18 0.36 0.47 0.49 0.36 AA-C-FM 21.18 27.01 23.81 40.68 32.92 13.96 28.96 26.09 15.53 16.03 22.85 31.36 CA-C-FM 20.08 5.31 6.16 13.56 5.28 39.25 52.77 31.15 68.16 41.33 50.72 29.84 FMA-C-FM 58.74 67.67 70.03 45.76 61.80 46.79 18.28 42.76 16.31 42.65 26.43 38.80 KK-A 92.65 83.35 95.36 94.13 92.39 97.63 0.98 2.27 1.58 4.19 4.80 0.53 AK-A 45.39 66.98 73.34 64.34 71.04 34.45 38.72 43.78 25.14 32.93 35.54 46.89 DF3 5.62 -0.79 -4.92 5.00 -0.18 4.18 9.37 4.51 13.49 4.64 7.09 3.16 
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表 2 微量和稀土元素分析结果及特征参数
Table 2 Trace and rare earth elements analytical results and characteristic parameters
10-6 样号 LD001 LD017 LD076 LD098 LD036 LD037 LD035 LD088 LD081 LD089 LD140 LD141 a b 岩性 黑云石
英片岩黑云石
英片岩二云石
英片岩二云石
片岩白云石
英片岩白云石
英片岩石英
钠长岩石英
钠长岩石英
钠长岩石英
钠长岩变火山
角砾岩变火山
凝灰岩球粒
陨石[21]上
地壳[22]Rb 157.11 130.97 64.87 199.37 165.83 122.24 2.25 5.38 1.63 6.33 22.83 1.05 2.32 82 Ba 1343.12 1468.95 351.85 464.07 517.03 315.44 16.07 25.59 20.05 51.73 54.25 9.02 2.41 628 Th 9.99 11.99 10.54 5.58 5.95 7.40 1.16 9.37 1.38 0.90 0.86 2.99 0.029 10.5 U 3.04 2.83 14.31 7.71 1.62 0.97 1.01 26.55 1.70 0.70 1.08 3.20 0.008 2.7 K 55682.91 35936.19 23512.66 49838.53 35017.50 23089.48 953.03 2226.96 989.08 2863.30 3810.10 544.51 545 23244 Nb 9.60 9.96 75.93 84.63 67.24 9.44 10.29 64.38 6.62 14.74 37.08 38.22 0.246 12 Ta 0.68 0.75 4.28 6.00 4.59 0.62 0.76 3.87 0.47 0.52 1.54 3.08 0.014 0.9 Sr 73.76 20.41 34.43 31.65 17.22 82.44 57.69 89.59 149.92 100.03 42.77 54.45 7.26 320 Pb 1.51 0.99 1.24 0.53 1.05 1.61 1.45 0.85 0.24 0.07 0.09 0.45 2.47 17 P 543.40 578.74 5084.51 5025.71 4367.06 658.04 762.89 4888.67 712.95 720.29 1395.85 3590.48 1220 655 Zr 98.28 139.70 543.06 558.62 465.05 136.07 140.78 446.41 145.97 115.88 218.07 614.18 3.87 193 Hf 2.58 3.65 12.69 13.41 10.58 3.51 3.64 10.09 3.86 3.11 5.89 15.19 0.1066 5.3 Y 37.68 19.99 95.34 76.04 55.21 22.97 41.16 73.49 147.02 15.55 69.49 61.01 1.57 21 Ti 2887.21 3364.66 8780.51 18122.41 13571.17 3746.59 4411.11 12559.66 3672.91 3056.41 3096.32 8844.30 445 3836 Cr 80.09 85.69 3.49 51.42 17.42 42.92 74.60 22.79 31.79 30.53 46.44 18.75 - 35 Co 22.92 43.26 134.62 26.62 29.70 26.51 3.85 60.04 4.38 12.71 5.88 1.96 - 20 Ni 32.84 35.75 22.97 26.00 16.86 23.13 6.33 14.24 5.81 10.94 24.25 5.71 - 20 Ga 13.94 15.55 26.60 47.49 28.21 13.29 15.19 21.73 9.01 9.01 16.37 23.23 - 17 Li 19.36 8.90 21.34 52.59 8.09 7.18 1.36 0.85 1.63 1.01 5.07 1.23 1.57 24 Be 1.67 4.37 2.77 6.32 4.00 3.81 0.79 0.87 0.76 0.77 0.83 1.11 - - Sc 11.18 11.72 15.99 31.50 24.59 11.24 11.63 12.72 22.15 14.72 14.32 27.97 - 11 V 62.46 102.14 71.03 177.23 166.00 54.41 88.38 176.54 14.63 13.33 35.84 86.63 - 60 Sn 61.88 2.61 20.85 200.42 4.85 3.46 7.07 26.01 5.60 5.10 3.66 11.03 1.72 2.1 Cs 0.63 0.44 1.16 1.04 1.07 0.82 0.08 0.02 0.06 0.02 0.36 0.02 0.188 4.9 W 9.30 5.45 26.03 138.47 12.75 0.88 1.50 2.80 4.59 1.42 0.54 0.57 0.095 1.9 Th/Sc 0.89 1.02 0.66 0.18 0.24 0.66 0.10 0.74 0.06 0.06 0.06 0.11 Rb/Sr 0.81 0.61 0.01 0.09 0.04 0.32 0.53 0.05 0.22 0.26 0.21 0.03 - - Th/U 2.13 6.42 1.88 6.30 9.63 1.48 0.04 0.06 0.01 0.06 0.53 0.02 - - Ba/Rb 3.29 4.23 0.74 0.72 3.66 7.59 1.15 0.35 0.81 1.28 0.80 0.94 - - Zr/Hf 8.55 11.22 5.42 2.33 3.12 2.58 7.14 4.76 12.33 8.17 2.38 8.58 - - Sr/Ba 0.05 0.01 0.10 0.07 0.03 0.26 3.59 3.50 7.48 1.93 0.79 6.04 - - Cr/Zr 0.81 0.61 0.01 0.09 0.04 0.32 0.53 0.05 0.22 0.26 0.21 0.03 - - La 87.79 30.52 450.40 185.54 63.15 16.62 8.56 275.26 18.75 5.27 4.14 5.92 0.31 Ce 142.68 59.80 749.75 295.50 141.83 34.72 19.07 473.50 52.23 12.78 11.46 17.53 0.808 Pr 14.08 6.83 76.23 31.24 18.87 4.33 2.50 50.20 7.96 1.85 1.89 2.92 0.122 Nd 48.51 24.66 243.05 103.60 76.15 16.90 10.83 166.79 37.08 8.11 10.07 15.87 0.6 Sm 11.28 6.02 51.51 24.78 18.65 4.29 3.33 35.64 12.05 2.40 3.71 6.02 0.195 Eu 14.53 1.82 12.92 44.27 5.04 1.34 1.81 9.26 4.61 1.31 1.33 2.07 0.0735 Gd 9.11 4.62 31.98 21.35 14.79 4.42 4.74 25.45 16.56 2.80 6.93 9.77 0.259 Tb 1.32 0.67 4.26 3.09 2.17 0.72 0.99 3.39 3.33 0.48 1.45 1.75 0.0474 Dy 7.41 3.73 21.03 16.74 12.02 4.35 6.83 17.05 24.39 3.14 10.50 11.83 0.322 Ho 1.44 0.74 4.03 3.29 2.35 0.90 1.54 3.16 5.70 0.67 2.45 2.45 0.0718 Er 3.79 1.99 10.50 9.15 6.13 2.57 4.46 7.95 17.47 1.93 7.28 6.75 0.21 Tm 0.53 0.29 1.48 1.30 0.86 0.38 0.68 1.08 2.68 0.30 1.16 1.02 0.0324 Yb 3.12 1.78 8.60 8.61 5.21 2.48 4.38 6.13 17.94 1.98 7.69 6.51 0.209 Lu 0.43 0.26 1.12 1.19 0.77 0.37 0.65 0.81 2.57 0.32 1.20 0.90 0.0332 Sm/Nd 0.23 0.24 0.21 0.24 0.24 0.25 0.31 0.21 0.33 0.30 0.37 0.38 ∑REE 346.02 143.74 1666.89 749.64 367.97 94.41 70.36 1075.65 223.32 43.34 71.25 91.32 LREE 318.87 129.65 1583.87 684.92 323.68 78.22 46.10 1010.64 132.68 31.72 32.59 50.34 HREE 27.15 14.09 83.02 64.72 44.29 16.19 24.26 65.00 90.64 11.62 38.65 40.98 LREE/HREE 11.74 9.20 19.08 10.58 7.31 4.83 1.90 15.55 1.46 2.73 0.84 1.23 (La/Yb)N 18.98 11.58 35.30 14.53 8.18 4.52 1.32 30.28 0.70 1.79 0.36 0.61 (Dy/Y)N 1.54 1.36 1.59 1.26 1.50 1.14 1.01 1.81 0.88 1.03 0.89 1.18 δEu 2.62 0.62 0.54 3.58 0.55 0.60 0.94 0.54 0.67 1.01 0.56 0.57 δCe 0.57 0.18 0.59 0.54 0.79 0.67 0.10 0.64 0.95 0.64 0.56 1.14
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