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    东昆仑西段晚志留世含绿柱石伟晶岩的发现和找矿意义

    Discovery and prospecting significance of Late Silurian beryl-bearing pegmatites in the western segment of East Kunlun Mountains

      摘要
    • 摘要:
      研究目的 青海省伟晶岩型锂铍矿床主要集中在宗务隆构造带和三江北段地区，东昆仑地区是否有形成硬岩型稀有金属矿床的潜力还不清楚。最近在东昆仑西段北祁漫塔格构造带阿达滩沟脑地区发现了铍矿化伟晶岩，暗示该区具有寻找铍稀有金属矿的潜力。
      研究方法 对阿达滩沟脑含绿柱石伟晶岩进行了磷灰石和锆石U−Pb定年、岩石学和地球化学研究，探讨含绿柱石伟晶岩的形成时代和构造背景。
      研究结果 铍矿化赋矿岩性主要为含绿柱石、电气石、石榴子石钠长石化白云母花岗伟晶岩，具有高SiO2（74.19%~79.46%）、Al2O3（12.45%~14.91%）和富Na2O（4.54%~6.35%）、K2O（1.15%~4.46%）特征，稀土元素总量很低(ΣREE=2.60×10−6~7.70×10−6)，轻稀土元素略富集（LREE/HREE=4.27~6.17，(La/Yb)N=9.37~12.07），Eu强负异常(δEu=0.29~0.57)，稀土元素曲线具略微右倾W型四分组效应。Nb/Ta平均值为4.81，Zr/Hf=9.36~20.55，Rb、Be元素富集明显，具有明显的高分异特征。锆石U−Pb年龄峰值为375 Ma，磷灰石U−Pb年龄为423.8±4.1 Ma。
      结论 综合研究认为，阿达滩沟脑含绿柱石伟晶岩形成时代为晚志留世，是东昆仑西段北祁漫塔格构造带在同碰撞挤压构造环境下局部伸展阶段的产物。东昆仑西段阿达滩沟脑晚志留世含矿（绿柱石）伟晶岩的发现，明确了青藏高原北部除中生代外，古生代也存在广阔的锂铍成矿潜力，为区域找矿工作部署提供了科学依据。

       

      Abstract:
      Objective The pegmatite−type Li−Be deposits in Qinghai Province are mainly concentrated in the Zongwulong tectonic belt and the northern segment of the Sanjiang region. Whether the East Kunlun region has the potential to form hard−rock type rare metal deposits remains unclear. Recently, beryllium−mineralized pegmatites have been discovered in the Adatan Gounao area of the North Qimantag tectonic belt in the western segment of the East Kunlun Mountains, suggesting that this area has the potential for prospecting beryllium rare metal deposits.
      Methods This paper carries out apatite and zircon U−Pb geochronological, petrological and geochemical studies on the beryl−bearing pegmatites in Adatan Gounao, and discusses the formation age and tectonic setting of the beryl−bearing pegmatites.
      Results The host lithology of beryllium mineralization is mainly beryl−, tourmaline−, and garnet−bearing albitized muscovite granite pegmatite, which is characterized by high SiO2 (74.19%~79.46%), Al2O3(12.45%~14.91%), enrichment in Na2O (4.54%~6.35%) and K2O (1.15%~4.46%), extremely low total rare earth elements (ΣREE=2.60×10−6~7.70×10−6), slight enrichment in light rare earth elements (LREE/HREE=4.27~6.17, (La/Yb)N=9.37~12.07), strong negative Eu anomaly (δEu=0.29~0.57), and the chondrite−normalized REE distribution patterns show a slightly right−inclined W−type tetrad effect. The average Nb/Ta ratio is 4.81, Zr/Hf=9.36~20.55, Rb and Be elements are obviously enriched, with distinct highly differentiated characteristics. The peak zircon U−Pb age is 375 Ma, and the apatite U−Pb age is 423.8±4.1 Ma.
      Conclusions Comprehensive studies suggest that the beryl−bearing pegmatites in Adatan Gounao formed in the Late Silurian and are products of the local extensional stage under the syn−collisional compressional tectonic setting in the North Qimantag tectonic belt of the western segment of the East Kunlun Mountains. The discovery of the Late Silurian ore−bearing (beryl−bearing) pegmatites in Adatan Gounao, western segment of the East Kunlun Mountains, clarifies that in addition to Mesozoic Era, Paleozoic Era also has broad Li−Be metallogenic potential in northern Qinghai−Xizang Plateau, providing a scientific basis for the deployment of regional prospecting work.

       

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