东昆仑夏日哈木铜镍矿床Ⅱ号岩体年代学、地球化学及其意义

Zircon SHRIMP U-Pb geochronology,geochemistry and implications of No.Ⅱ intrusion in Xiarihamu Cu-Ni deposit,East Kunlun Mountains

夏日哈木超大型镍矿床位于东昆仑造山带昆中岛弧带内,其Ⅱ号岩体主要由辉长岩和少量辉石岩组成,局部可见孔雀石、镍华、褐铁矿、磁黄铁矿、镍黄铁矿、黄铜矿等矿化。岩石主量元素化学特征具低硅(w(Si O2)=48.12%~50.18%)、低钛(w(Ti O2)=0.47%~0.73%)、高镁(w(Mg O)=13.15%~19.59%)的特征,属亚碱性系列岩石,m/f值为3.14~3.88,属铁质超基性岩类。岩石稀土、微量元素标准化配分模式具一致性,表现为轻稀土元素弱富集的右倾型,并具有富集大离子亲石元素,亏损高场强元素Nb、Ta、Ti的特征。辉长岩的锆石SHRIMP U-Pb年代学研究表明,岩体形成年龄为(424.1±4.6)Ma,属志留纪。笔者对夏日哈木Ⅰ号、Ⅱ号岩体的主要地质特征作了对比,认为二者同源,结合区域构造及Ⅰ号岩体形成的构造背景,认为Ⅱ号岩体形成于岛弧环境。

The Xiarihamu super large nickel deposit is located in the island arc zone in the middle part of the western segment of the East Kunlun orogenic belt. The No. Ⅱ intrusion is mainly composed of gabbro and pyroxenite with mineralization such as limonite, pyrrhotite, pentlandite and chalcopyrite. Major element values of Xiarihamu No. Ⅱ intrusion show sub-alkalic series and are characterized by low SiO2 content（ 48. 12% ~ 50. 18%） and low Ti O2 content（ 0. 47% ~ 0. 73%）, but high Mg O content（ 13. 15% ~ 19. 59%）. The m/f ratios of the rocks range from3. 14 to 3. 88, falling into the range of ferrous-ultramafic rocks. LREE-rich trace elements patterns are enriched in LILE and relatively depleted in HFSE（ Nb, Ta, Ti）. Zircon SHRIMP U-Pb dating of gabbro yielded（ 424. 1 ±4. 6） Ma, suggesting it formed in Silurian. In this paper, the geological characteristics between Xiarihamu No. Ⅰand No. Ⅱ intrusions were compared, which shows the same comagmatic evolution for No. Ⅰ and No. Ⅱ intrusions. Combined with regional tectonic evolution and structural setting of No. Ⅰ intrusion, the authors conclude that No. Ⅱ intrusion was formed in an island arc setting.