内蒙古白乃庙地区铜（金）和金矿床钕、锶和铅同位素研究

Nd,Sr AND Pb ISOTOPIC STUDY OF COPPER(GOLD)AND GOLD DEPOSITS IN BAINAIMIAO AREA,INNER MONGOLIA

内自古白乃庙地区产出有白乃庙铜（金）矿床（南、北矿带）、白乃庙金矿床和徐尼乌苏金矿化带，是华北陆台北缘金属成矿带的重要组成部分。笔者测定和解释了上述三个矿床的钕、锶和铅同位素比值和变化特征。研究认为：白乃庙铜（金）矿床南、北矿带在成矿时代、成矿物质来源和形皮过程方面存在明显差异，南矿带条带状、块状硫化物矿石的形成作用始于１１３０×１０￣６ａ前的基性火山喷发活动。相比之下，北矿带细脉浸染状和脉状铜－钼－金矿石与加里东期（４４０×１０￣６ａ）花岗闪长斑岩的侵位和结晶分异密切相关。白乃庙金矿床和徐尼乌苏金矿化带是岩浆热液、大气降水混合，并且对基底岩层或绿片岩围岩进行淋滤、萃取的结果。白乃庙地区铜（金）矿床和金矿床（点）成矿物质来源和形成机制的厘定，对于了解华北地台北缘内蒙古中南段金属成矿带的形成与演化具有重要意义。

Sm-Nd,Rb-Sr and Pb isotopic data on ore samples from the Bainaimiao copper(gold)deposit(composed of SOuth ore zone and north ore zone),the Bainaimiao gold deposit and the Xuniwusu gold mineralized zone are prese-nted in this paper. ￣εNd(1130×10￣6)and ε_Sr,(1130×10￣6) values of seven whole ore samples from the south ore zone cons isting of mainly massive suifide copper(gold)ores raz3ge from 2.3 to 5.2 and from -67.8 to 70.5,respecti-vely. Pb isotope data show ￣(206)Pb/￣(204)Pb=17.929～18.321,￣(207)Pb/￣(204)Pb=15.496～15.579 and￣(208)Pb/￣(204)Pb=37.892～38.157.Copper (gold) mineralization of the north ore zone is spatially and temporally related to the granodiorite porp-hyry with Sm-Nd isochron age of 440×10￣6.Five disseminated-veinlet sulfide ore samples give eNd (440×10￣6)of-6.8～4.2 and ε_(Sr)(440×10￣6)of 40.9～97.6.The Pb isotopic ratios of five galena and pyrite are as follows:￣(206)Pb/￣(204)Pb=18.129～18.486;￣(207)Pb/￣(204) Pb=15.482～15.581 and ￣(208)Pb/￣(204)Pb=37.846～38.343.Pb isotope data show that salfide copper(gold)ore of the north ore zone contains higher ￣(206)Pb content than that of the south ore zone.The Bainaimiao gold deposit and the Xuniwusu gold mineralized zol1o have Similar ε_(Nd)(440×10￣6) values ranging from -4.6 to -6.5 and ε_(Sr)(440×10￣6)from 75.9 to 97.2.The Pb isotope analyses of 2 3 rulfide(pyrite and galena) and 1 native gold samples show’￣(206)Pb/￣(204)Pb= 17.854～18.914,￣(207)Pb/￣(204)Pb= 15.5l9～15.794 and ￣(208)Pb/￣(204)Pb = 38.155～39.063.Most of these Pb isotope data lie on or above the upper erust Pb isotope evolutionary curve,and show obvious increase in ￣(207)Pb and ￣(208)Pb content compared with the data from the Bainaimiao copper(gold)deposit.Sr isotopic feature suggests that the Rb-Sr isotopic system of copper(gold)and gold ores has been strongly disturbed,This is consistent with petrographic and tectonic studies, which indicate that all these ore deposits(or the ore zone)have undergone intense metamorphism and tectonism. Based on the Nd-Pb isotopic characteristics and available geochemical data,it is believed that ore fluid of the south ore zone was originally derived from a depleted mantle source,but slightly contaminated by crustal materials. In contrast,the north ore zone,the Bainaimiao gold deposit and the Xuniwusu gold mineralized zone were formed by a mixed ore fluid consisting mainly of magmatic water related to Caledonlan granodiorite porphyry,meteoric water and metamorphic fluid.