西藏拉抗俄斑岩Cu-Mo矿床含矿斑岩地球化学、锆石U-Pb年代学及Hf同位素组成

Geochronology,Geochemistry and Zircon Hf Isotopic Compositions of the Ore-Bearing Porphyry in the Lakang'e Porphyry Cu-Mo Deposit,Tibet

拉抗俄Cu-Mo矿床是冈底斯成矿带东段典型的斑岩型矿床,前人对该矿床进行了初步的矿床地球化学研究,但欠缺系统性.在系统的野外地质调查基础上,对拉抗俄斑岩Cu-Mo矿床的含矿斑岩开展了详细的地球化学和年代学研究,旨在精确确定矿床含矿斑岩的成岩年龄、岩石成因及源区特征.岩石地球化学特征显示,含矿花岗闪长斑岩富硅,相对贫镁和钙,SiO_2含量为62.51%~72.41%,MgO含量为0.59%~1.30%,CaO含量为0.95%~3.44%;碱含量高,Na_2O含量为3.51%~4.75%,K_2O含量为3.30%~4.97%;偏铝质或弱的过铝质,A/CNK比值为0.90~1.01;相对富集大离子亲石元素Rb、Ba、Th、U、Sr,明显亏损Nb、Ta、Ti、P、Zr等高场强元素.岩体稀土总量较低,为82.80×10-6~132.09×10^(-6);富集轻稀土,且轻重稀土分异明显;具有弱的Eu负异常和弱Ce负异常.采用LA-ICP-MS锆石U-Pb同位素测年技术对含矿花岗闪长斑岩进行定年,岩体成岩年龄为13.58±0.42Ma,系中新世岩浆活动的产物.锆石εHf(t)值为-3.99~4.49,Hf同位素两阶段模式年龄tDM2为808~1 349Ma.研究结果显示拉抗俄含矿花岗闪长斑岩具有埃达克岩地球化学特征,其岩浆源区主要来源于新生地壳部分熔融的组分,在岩浆侵位过程中遭受了古老地壳物质的混染,岩石形成于印度-亚洲大陆碰撞造山带的后碰撞伸展构造背景.

The Lakang＇e Cu-Mo deposit is a typical porphyry deposit in the eastern Gangdese metallogenic belt,on which previous geochemical studies are not adequate and systematic.In this paper,we present the results of the systematic logging of drillholes and provide new petrological zircon U-Pb age,and Hf isotope data for the deposit that allow the identification of the timing of formation and mineralization of the Lakang＇e porphyry Cu-Mo deposit and the relationship between this deposit and other porphyry-type deposits in the Gangdese belt.Chemical analyses show that the ore-bearing granodiorite-porphyry has high SiO_2,low Mg and Ca（SiO_2=62.51% to 72.41%,MgO=0.59% to 1.30%,CaO=0.95% to 3.44%）,highalkaline（Na_2O=3.51%to 4.75%,K_2O=3.30%to 4.97%）,metaluminous（A/CNK=0.90 to 1.01）,enriched in LILES such as Rb,Ba,Th,U,Sr,and depleted in HFSES such as Nb,Ta,Ti,P and Zr.The rocks also display low total REEcontents（∑REE=82.80×10^-6 to 132.09×10^-6）,enriched LREE and differentiate obviously,with weakly negative Eu and Ce anomalies.LAICP-MS zircon U-Pb dating indicates that the Lakang＇e ore-bearing granodiorite-porphyry emplaced at 13.58±0.42 Ma.εHf（t）values and two-stage model ages of zircons are-3.99 to 4.49 and 808to 1349 Ma respectively.The results indicate that the ore-bearing granodiorite-porphyry in the Lakang＇e deposit has adakitegeochemical characteristics,and the parental magmas were mainly derived from a juvenile crust and partly mixed with old continental crust rock during the evolution.The porphyry in Lakang＇edeposit was formed in post-collisional extension setting of India-Asia continental collision orogenic belt.