榍石U⁃Pb年代学与微量元素对山西刁泉斑岩-矽卡岩多金属矿床成矿的指示

U⁃Pb Geochronology and Trace Element Analysis of Titanite from the Diaoquan Porphyry⁃Skarn Polymetallic Deposit,North China:Implication for Cu⁃Ag⁃Mo Mineralization

山西刁泉矿床是五台山−恒山矿集区内最为典型的斑岩‒矽卡岩型多金属矿床,然而人们对该矿床斑岩和矽卡岩型矿化之间的成因联系及其成矿流体演化的认识还存在较大的争论.利用LA⁃ICPMS原位微区分析技术开展了对花岗斑岩和含矿矽卡岩中榍石的U⁃Pb同位素和微量元素分析,并测定了矿区侵入岩中锆石的U⁃Pb年龄.黑云母石英二长岩和花岗斑岩的锆石U⁃Pb定年结果表明其侵位时间分别为137.3±1.2 Ma和133.5±2.0 Ma,其中花岗斑岩的年龄与热液榍石的U⁃Pb年龄(133.6±2.2 Ma和132.8±2.5 Ma)在误差范围内完全一致,表明花岗斑岩与矽卡岩型铜银矿化关系密切.榍石中Sn元素的含量变化表明刁泉铜银多金属矿床成矿过程中氧逸度经历了一个升高的过程,然后又逐渐下降.

The Diaoquan deposit is a typical porphyry⁃skarn polymetallic deposit in the Wutaishan⁃Hengshan metallogenic district,North China.However,the relationship between porphyry and skarn mineralization processes have been the subject of intense debate.In this paper,in⁃situ laser ablation inductively coupled plasma mass spectrometry(LA⁃ICP⁃MS)has been applied to U⁃Pb isotope and trace elements analysis of the zircon and titanite from granitic porphyry,biotite⁃quartz monzonite,and mineralized skarn.Zircons from biotite⁃quartz monzonite and granitic porphyry have weighted mean U⁃Pb ages of 137.3±1.2 Ma and 133.5±2.0 Ma,respectively.The age of granitic porphyry is consistent with the hydrothermal titanite U⁃Pb ages(133.6±2.2 Ma and 132.8±2.5 Ma)of the mineralized skarn,suggesting the Cu⁃Ag skarn mineralization at the Diaoquan deposit was caused by coeval magmatism that related to the emplacement of granitic porphyry.The variation of Sn contents in titanite from the Diaoquan deposit suggest the oxygen fugacity of hydrothermal mineralization fluids significantly increase at prograde skarn stage,and then slightly decreased at retrograde skarn stage.