西藏昂仁县多仁则—桑阿卡地区铜多金属矿点含矿岩体成因及成矿意义

冈底斯成矿带内的岩浆岩是印度板块与欧亚板块碰撞造山的产物，更是研究碰撞造山与成矿作用的理想对象。多仁则—桑阿卡地区位于冈底斯火山-岩浆弧中段中南部，区内含矿岩体为灰白色中细粒黑云母花岗闪长岩。LA-ICP-MS锆石U-Pb测年、岩石地球化学和Sr-Nd同位素研究表明：岩体就位年龄为（49.0±0.7）Ma，其形成时代为始新世；岩石具有高硅（w（SiO₂）为67.13%）、高钾（w（K₂O）为3.72%）、富碱（w（K₂O+Na₂O）为7.48%）、贫MgO（w（MgO）为1.34%，小于3%）的特征，为高钾钙碱性系列的高分异I型花岗岩；Eu负异常（δEu为0.70）和Sr的亏损暗示岩浆发生斜长石的分离结晶作用；岩石的微量元素表现出Th、U、K、Nd、Zr、Hf富集和Nb、Ta、Sr、Ti、P亏损的特征；全岩Sr-Nd同位素（（⁸⁷Sr/⁸⁶Sr）_i为0.705 280~0.705 530、ε_Nd（t）为-2.2~-1.6）、微量元素及元素比值揭示岩浆源区是壳幔混源，是在印度板块与欧亚板块俯冲-碰撞后板片断离构造背景下，热的软流圈地幔物质通过板片断离窗上涌，并诱发下地壳部分熔融，形成该地区壳幔混源岩浆-热液成矿作用。综合研究认为，多仁则—桑阿卡地区斑岩型-热液型铜多金属成矿作用是早始新世岩浆活动大爆发滞后的成矿响应，是与冈底斯成矿带内的壳幔花岗岩有关的Cu-Au-Mo-Fe-Pb-Zn成矿系统（52~47 Ma）的重要组成部分。

Petrogenesis and Metallogenic Implication of Ore-Bearing Rock Mass of Copper Polymetallic Ore Occurrence in Duorenze-Sangaka Area,Angren County,Tibet

The magmatic rocks in Gangdise metallogenic belt are the products of collision orogeny between Indian and Eurasian plates, and are of great significance to the study of collision orogeny and mineralization. Duorenze-Sangaka area is located in the south-central part of Gangdise volcano-magmatic arc, where ore-bearing gray white medium- to fine-grained biotite granodiorite is developed. The study of petro-geochemistry, Sr-Nd isotope, and LA-ICP-MS zircon U-Pb dating of the biotite granodiorite show that its emplacement age is (49.0±0.7) Ma, in Eocene period. The biotite granodiorites are featured by high silicon (w(SiO₂)=67.13%), potassium (w(K₂O)=3.72%), alkali-rich (w(K₂O+Na₂O) =7.48%), and low MgO (1.34%, less than 3%), which belong to high potassium calc-alkaline and highly differentiated I-type granite. The Eu negative anomaly (δEu=0.70) and Sr depletion suggest plagioclase crystallization during magmatic evolution. These samples are rich in Th, U, K, Nd, Zr, Hf, and poor in Nb, Ta, Sr, Ti, P. Their whole-rock Sr-Nd isotopes ((⁸⁷Sr/⁸⁶Sr)_i=0.705 280-0.705 530, ε_Nd(t)=-2.2-1.6), trace elements, and element ratios reveal that they were derived from mixed crust-mantle sources. The magmatic-hydrothermal mineralization was likely caused by partial melting of lower crust, which was triggered by asthenospheric mantle upwelling through the plate break-out window during the plate fragmental subduction-post-collision of Indian and Eurasian plates. The comprehensive study shows that the porphyry-hydrothermal vein-type copper polymetallic mineralization in Duorenze-Sangaka area was resulted from the eruption of Early Eocene magmatism, which is an important part of the Cu-Au-Mo-Fe-Pb-Zn metallogenic system (52-47 Ma) related to crust-mantle granitic magmatism in Gangdise metallogenic belt.