与成矿相关的岩体成因:年代学,元素与Sr-Nd、Hf同位素地球化学特征——以江西九瑞矿集区宋家冲Au、Cu-Mo矿床为例

Petrogenesis of the Ore-Bearing Granitic Intrusion in the Songjiachong Au,Cu-Mo Deposit,Jiujiang-Ruichang Metallogenic District in Jiangxi Province:Constraints from Zircon U-Pb Age,Geochemistry and Sr-Nd,Hf Isotopes

宋家冲矿床是长江中下游成矿带九瑞矿集区西南部新发现的矽卡岩型Au、Cu-Mo矿床。矿区内与成矿关系密切的岩体为花岗闪长斑岩。LA-ICP-MS锆石U-Pb测年结果显示,该岩体形成于早白垩世早期((142.8±0.6)Ma)。主量元素组成上,宋家冲岩体属于准铝质岩石(A/CNK=0.80~1.03),具低镁(ω(MgO)=1.29%~2.58%)、富铝(ω(Al_2O_3)=15.52%~16.88%)、高碱(富钠)(K_2O/Na_2O=0.57~1.04)特征。微量元素方面,表现为富集Rb、Ba、Th和La等大离子亲石元素(LILE),相对亏损Nb、Ta和Zr等高场强元素(HFSE),ω(Sr)较高(>618×10^(-6))、ω(Y)较低(<17.1×10^(-6))、Sr/Y值大(39~61)、轻重稀土分馏强烈(ω(Yb)<1.45×10^(-6);(La/Yb)_N>30)等特点,类似于埃达克岩的地球化学特征。全岩Sr-Nd和锆石Hf同位素组成变化范围相对较小:(^(87)Sr/^(86)Sr)_i为0.705 8~0.706 7,ε_(Nd)(t)为-6.4^-4.9,ε_(Hr)(t)为-10.1^-5.1。结合区域地质研究成果认为:宋家冲岩体可能形成于陆内挤压-伸展的过渡环境下,为富集岩石圈地慢部分熔融的产物。

The Songjiachong skarn Au, Cu- Mo deposit is located in the southwestern part of Jiujiang- Ruichang metallogenic district in the Middle-Lower Reaches of the Yangtze River. The Songjiachong porphyritic granodiorite is the ore-related granitic intrusion. Zircon LA - ICP - MS dating of the intrusion suggests its emplacement age of （142. 8 ~ 0. 6） Ma. Whole-rock samples {rom the Songjiachong intrusion are metaluminous, low content of MgO（1.29O//oo-2. 580./00）, high content of A1203 （15.52O//oo-16.88%） and Na20（K20/Na20=0. 57 - 1. 04）. They are enriched in large ion lithophile elements （eg. Rb, Ba, Th and La） and depleted in high field strength elements （eg. Nb, Ta and Zr）. These rocks are of geochemical features of typical adakites, such as high content of Sr（〉618 × 10^-6）, low content of Y（〈17.1×10^-6）, highSr/Y（39-61）, and low content of Yb（%1. 45 ×10^-6） andLa/Yb（〉30）. They show a narrow range （87Sr/86Sr）j of 0.705 8-0.706 7, εNd（t） of -6.4-4.9 and εHf （t） of -10. 1 -5. 1. Based on integration of the geological characteristics of the studied area, we suggest that the Songjiachong granitic intrusion was derived from partial melting of an enriched mantle source. The petrogenetic--metallogenic event probably occurred in a transitional environment from an early compressional stage to the late intraplate extensional environment.