豫西栾川中鱼库锌(铅)矿床闪锌矿Rb-Sr年龄及其地质意义

Rb-Sr dating and geological significance of sphalerites from the Zhongyuku Zn(Pb) deposit in Luanchuan,West Henan,China

中鱼库矽卡岩型锌(铅)矿床位于华北陆块南缘河南省西部栾川Mo-W-Pb-Zn-Ag多金属矿集区南部,矿体呈层状-似层状赋存于新元古界栾川群三川组碎屑岩、碳酸盐岩地层中。因缺乏精确的成矿年代学研究,对该矿床成因的争议较大。本文在矿床地质背景和岩石矿物学研究的基础上,对13件矿石样品中的闪锌矿进行Rb-Sr同位素年代学研究。闪锌矿87 Rb/^(86)Sr和^(87)Sr/^(86)Sr同位素比值分别集中在0.802~18.98和0.713 359~0.748 684,二者具有良好的线性关系;其等时线年龄为(136.4±0.8)Ma(2σ,MSWD=3.6),(^(87)Sr/^(86)Sr)t=0.711 913±0.000 074。Rb-Sr同位素年龄反映该矿床形成于早白垩世,稍晚于研究区内的斑岩-矽卡岩型Mo-W矿床(146±2 Ma B.P.),与区内最后一阶段花岗质岩浆活动(142~136Ma B.P.)有关,属于栾川Mo-W-Pb-Zn-Ag多金属成矿系统。结合区域资料,认为该矿床形成于中生代陆-陆碰撞过程中由挤压向伸展转变的阶段,或碰撞后造山的局部伸展背景。

Zhongyuku skarn type Zn （Pb） deposit is located in the southern part of Luanchuan Mo-W- Pb-Zn-Ag polymetallic ore district, southern margin of the North China Block. Bedded ore bodies occur in clastic and carbonate strata in the Sanchuan Formation of the Neoproterozoic Luanchuan Group. However, the genesis of this deposit is controversial, because of the lack of accurate metallogenic geochronology. Based on the study of geological setting, petrology and mineralogy of the deposit, the Rb-Sr isotopic compositions of sphalerite from 13 ore samples are analyzed. It shows that 87Rb/86Sr and STSrffSSr isotopic compositions have a linear correlation, ranging from 0. 802 to 18. 980 and 0. 713 359 to 0. 718 684 respectively, and it reveals that tile isochron age is （136. 1±0.8） Ma （2a, MSWI）=3. 6）, and （87Sr/86Sr）, is 0. 711 913 ±0. 000 071, indicating that the Zhongyuku deposit formed in early Cretaceous period, slightly later than porphyry-skarn type molybdenum-tungsten deposits in the I^uanchuan ore district. It is considered that the formation of the Zhongyuku det）osil associates with the last stage of granitic magma activilies （142- 136 Ma B. P. ） in the ore district. The porphyry skarn type Mo-W deposits and skarn-type Zn Pb deposit constitute a Mo-W-Pb-Zn Ag polyrnetallic metallogenic system. The study indicates that the Zhongyuku deposit possibly formed in a transition stage from compression to extension setting during continent continent collision process in Mesozoic, or locally extension setting of post-collision orogenic process.