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    青藏高原东北缘红岭北锂辉石花岗伟晶岩脉群的发现及找矿前景分析

    Discovery of spodumene granite−pegmatite dike group in Northern Hongling area, northeastern margin of Qinghai−Xizang Plateau and its prospecting prospect

      摘要
    • 摘要:
      研究目的 宗务隆构造带东段是近年来新发现的重要印支期Li−Be成矿带，已有的找矿发现与研究局限于茶卡北山地区。本研究在茶卡北山锂铍矿床东南方向30 km的红岭北地区发现了花岗伟晶岩脉52条，其中6条岩脉含矿性较好，岩性为含绿柱石锂辉石花岗伟晶岩和云英钠长石化锂辉石伟晶岩；Li2O品位最高达3.56%~3.71%、BeO品位在0.031%~0.048%，具有较好的成矿潜力。但是这些伟晶岩脉的时代、源区及成因尚不明确，制约了区域找矿潜力。
      研究方法 本文对红岭北新发现的含绿柱石锂辉石花岗伟晶岩开展了系统的岩石学、地球化学及年代学等方面的研究。
      研究结果 伟晶岩具高SiO2（75.4%~84.2%）、Al2O3（10.23%~16.15%）、K2O（0.32%~3.02%）和Na2O（0.99%~3.45%）的特点，为过铝质岩石；稀土元素总量非常低（∑REE=0.15×10−6~0.85×10−6），LREE略微富集（LREE/HREE =2.7~11.4，(La/Yb)N=3.9~24.7），δEu呈正异常；具有富集Rb、Ta、P、Cs、Pb等元素，亏损Ba、Th、La、Ce、Sr、Nd等元素的特征。伟晶岩锆石U−Pb年龄为(211.2±7) Ma，铌钽铁矿U−Pb年龄为(223±1) Ma，伟晶岩成岩年龄为223~211 Ma。其Hf同位素显示εHf(t)值介于−8.61~−9.43，对应的Hf同位素地壳模式年龄（tDM2）为1.801~1.843 Ga。
      结论 红岭北含绿柱石锂辉石花岗伟晶岩为LCT伟晶型岩，可能是古元古代变泥质岩部分熔融而成，Li−Be矿形成于印支期。红岭北含绿柱石锂辉石花岗伟晶岩的发现进一步指出了宗务隆构造带东段锂铍矿找矿方向，具有较好的成矿潜力，有望为青藏高原东北缘提供新的锂铍矿勘查基地。

       

      Abstract:
      This paper is the result of geological survey engineering.
      Objective The eastern part of Zongwulong tectonic belt is an important Indosinian Li−Be metallogenic belt newly discovered in recent years, and the existing prospecting discoveries and research are limited to the Chakabeishan area. In this study, 52 granite pegmatite dikes were found in Northern Hongling area, 30 km southeast of Li−Be deposit in Chakabeishan, among which 6 dikes have better ore-bearing property, and with lithology of beryl-bearing spodumene granite pegmatite and greisen albite spodumene pegmatite. The highest grade of Li2O is 3.56%−3.71%, and the grade of BeO is 0.031%−0.048%, which indicate good metallogenic potential. However, the age, source area and origin of these pegmatite veins are still unclear, which further restricts the regional prospecting potential.
      Methods The petrology, geochemistry and chronology of the newly discovered beryl−bearing spodumene granite pegmatite in the northern Hongling are systematically studied in this paper.
      Results The pegmatite is characterized by high SiO2(75.4%−84.2%), Al2O3(10.23%−16.15%), K2O (0.32%−3.02%) and Na2O (0.99%−3.45%),and is peraluminous rock; The total amount of rare earth elements in pegmatite is very low (∑REE=0.15×10−6−0.85×10−6), with slight enrichment of LREE (LREE/HREE=2.7−11.4, (La/Yb)N=3.9−24.7), and δEu is mainly positive anomaly. Characterized by enrichment of Rb, Ta, P, Cs, Pb and loss of Ba, Th, La, Ce, Sr, Nd and Ti. The zircon U−Pb age of pegmatite and columbite−tantalite is (211.2±7)Ma and (223±1)Ma, which indicate the diagenetic and metallogenic age is 223−211Ma. The Hf isotope shows that the εHf(t) value is between −8.61 and −9.43, and the corresponding crustal model age (tDM2) of Hf isotope is between 1.801 Ga and 1.843 Ga.
      Conclusions The beryllite−bearing spodumene granitic pegmatite in the northern Hongling area belongs to LCT pegmatite, which suggest that may be formed by partial melting of metamorphic argillaceous rocks of palaeoproterozoic era based on the geochemical data. The Li−Be deposit was formed in the Indosinian period. The discovery of beryllite−bearing spodumene granite−pegmatite in the northern Hongling area further points out the direction of lithium beryllium ore prospecting in the eastern part of the Zongwulong structural belt, which has good metallogenic potential and is expected to provide a new lithium beryllium ore exploration base for the northeastern edge of the Qinghai−Xizang Plateau.

       

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