内蒙古高尔旗银铅锌矿区花岗岩的岩石成因:地球化学、锆石U-Pb年代学及Hf同位素约束

The Granite Petrogenesis in the Area of the Gaoerqi Lead-Zinc-Silver Deposit,Inner Mongolia: Constraints of Geochemistry,Zircon U-Pb Geochronology and Hf Isotope

高尔旗银铅锌矿床的发现不仅是二连—东乌旗多金属成矿带上重要的找矿成果,而且是寻找隐伏型矿床的重要突破。运用岩石地球化学、锆石U-Pb年代学和Lu-Hf同位素测试等方法,对该矿区含矿岩体的岩石成因、岩浆源区及构造环境等问题进行约束。含矿岩体主要为似斑状中粗粒二长花岗岩及中细粒正长花岗岩,它们具有较高的SiO_2（64.6%~79.12%）、Na_2O＋K_2O（5.59%~10.17%）及稀土元素含量,较低的P_2O_5、TiO_2、CaO和MgO含量,Eu具极大负异常特征;明显富集Rb、K等大离子亲石元素及Zr、Hf等高场强元素,强烈亏损Ba、Sr、P、Ti、Eu等元素,并且具有较高的εHf（t）值（4.4~14.0）和较年轻的地壳模式年龄t_（DM）~C（424~1 042 Ma）,揭示花岗岩主要来源于从亏损地幔中新增生的年轻地壳物质的部分熔融,具有A2型花岗岩的特征,形成于碰撞后的板块伸展阶段。获得的花岗岩LAICP-MS锆石U-Pb同位素年龄分别为（306.8±1.9）Ma和（310.4±2.3）Ma,属于晚石炭世岩浆-构造作用的产物,表明该时期华北板块和西伯利亚板块主碰撞结束,已经进入碰撞后伸展阶段。

The discovery of Gaoerqi lead-zinc-silver deposit is not only an important prospecting achievement in Erlian-Dongwuqi polymetallic metallogenic belt,but also a significant breakthrough for prospecting blind deposits. This paper,based on the study of geochemistry,zircon U-Pb geochronology and Lu-Hf isotopes of orebearing granites,has provided constraints on petrogenesis,magma source and rock-forming tectonic settings and other issues of the ore-bearing rocks. The ore-bearing rocks are mainly porphyritic-like medium-coarse grainedmonzogranite and medium-fine grained syenogranite. The contents of SiO_2,Na_2O ＋ K_2O and REEs are of higher values,but the contents of P_2O_5,TiO_2,CaO and MgO are of lower values in the ore-bearing rocks. The contents of SiO_2 and Na_2O ＋ K_2O are 64. 6%- 79. 12% and 5. 59%- 10. 17%,respectively. The Eu element has a characteristic of strong negative anomaly. The ore-bearing rocks are not only rich in Rb,K and other LILE,but also rich in Zr,Hf and other HFS. The ore-bearing rocks are with strong depletions in Ba,Sr,P,Ti,Eu,etc. The ore-bearing rocks are with higher values of εHf（ t） between 4. 4 and 14. 0,and have younger crust model ages with values of tDCcbetween 424 Ma and 1,042 Ma,which reveals that the granites mainly derive from the partial melting of young accreted crust which derives from depleted mantle. The granites are with characteritics of A2-type granites,and form in the plate extension phase after collision orogenesis. The LA-ICP-MS U-Pb isotope ages of zircons are（ 306. 8 ± 1. 9） Ma and（ 310. 4 ± 2. 3） Ma,respectively,which proves the zircons belong to the products of tectonic magmatism in Late Carboniferous. It reveals that the main collision between North China and Siberian plates has finished in this period,and has entered the post-collision extension phase.