内蒙古巴彦都兰铜矿地质特征及矿床成因——岩石地球化学、锆石U-Pb年代学及Hf同位素证据

U-Pb Zircon,Geochemical and Hf Isotopic Constraints on Origin of the Bayandulan Copper Deposit,Inner Mongolia,China

巴彦都兰铜矿是内蒙古二连浩特—东乌旗成矿带近年来新发现的一处中—高温热液脉型铜多金属矿床。通过对矿区内与成矿关系密切的花岗岩岩体开展同位素年代学、岩石地球化学和Hf同位素测试,据此探讨了该矿床的成因机制。分析结果显示,黑云母二长花岗岩LA-ICP-MS锆石U-Pb年龄为(300.2±2.2)Ma和(300.0±2.0)Ma;具有富硅、高钾钙碱性、弱过铝质,富集轻稀土元素及Rb、K等大离子亲石元素,亏损Sr、Nb、Ta等高场强元素的特征;锆石Hf同位素εHf(t)=6.1~10.7,TDM2=632~924 Ma,表现出洋壳俯冲形成的新生下地壳部分熔融的特征。综合研究认为,巴彦都兰铜矿形成的大地构造背景处于晚石炭世—早二叠世二连—贺根山洋盆闭合、区域构造环境逐渐由挤压转为后碰撞的伸展环境,在此期间碰撞后的岩石圈拆沉作用以及拉张机制下上涌的地幔物质使得新生下地壳得到再活化,产生的混合有基性幔源物质的酸性岩浆体系为成矿系统提供了主要成矿物质与流体。

The Bayandulan high-mesothermal vein-type copper deposit is a newly discovered deposit in the Er- enhot-East Ujimqin Banner metallogenic belt. In this paper, the authors present the new results of zircon laser ablation-inductively coupled plasma-mass spectrometry （LA-ICP-MS） U-Pb dating, rock geochemistry and in- situ Hf isotopic analyses of biotite monzogranite from the deposit. These data provide insights into the timing as well as the mineralization of the Bayandulan deposit. The LA-ICP-MS U-Pb dating of （300. 2 ± 2. 2） Ma and （300. 0 ± 2.0） Ma for biotite monzogranite. The rock yields the crystallization ages geochemistry of the granite is rich in Si, high potassium calc-alkali, weakly peraluminous, together with highly enriched the light rare earth element （LREE）, Rb, K and other large-ion lithophile element （LILE）, depleted Sr, Nb, Ta and other high field-strength element （HFSE）. The granite has high positive ~sf（t） values of 6. 1 -10. 7 and two-stage model ages （ TDM2 ） of 632 -- 924 Ma, which reveals that granites are mainly derived from the partial melting of young accreted lower crust converted from the subduction of oceanic crust. Based on these analytical results, we in- ferred that the tectonic setting of the Bayandulan deposit has been entered into the post-orogenic stage and grad- ually turned to widely extension setting, since the Hegenshan back-arc basin closed between Late Carboniferous and Early Permian. During this period, the lithosphere delamination effect after collision and the upwelling of the mantle material under tension mechanism made young accreted lower crust reactivation, then acidic magma mixed with mantle source material, the emplacement of the magma brought sufficient metal elements and hydro- thermal fluids, which in the end formed the Bayandulan copper deposit.