福建政和县东际金(银)矿床黄铁矿微量元素和硫-铅同位素及锆石年龄研究

Research on zircon U-Pb,S-Pb isotopes and trace elements of pyrite from the Dongji Au(Ag)deposit in Zhenghe County,Fujian Province

东际金(银)矿床赋存于燕山晚期南园组火山岩中,是东南沿海地区一个隐爆角砾岩型贵金属矿床,已探明金资源量达12.5 t,银资源量135.9 t。通过开展主要金属硫化物黄铁矿电子探针和硫-铅同位素分析,讨论了成矿作用和成矿物质来源等问题。研究表明,东际金(银)矿床黄铁矿Co/Ni值3~94(平均值23)且Co含量为500×10^-6~1070×10^-6(均值799×10^-6),Fe/(S+As)值0.827~0.871(均值0.860),Au/Ag值0.9~5.5(均值2.6),反映该矿床是与陆相火山作用有关的浅成中低温热液型矿床。黄铁矿δ34S在-6.6‰^-0.7‰,206Pb/204Pb为17.9801~18.4303,207Pb/204Pb为15.2689~15.9397,208Pb/204Pb为37.9052~38.7871,指示成矿物质主要来源于具有壳幔混源性质的花岗质岩浆,此外含矿热液也活化萃取了部分基底变质岩和火山岩围岩的金属元素。通过锆石U-Pb年代学研究和区域成矿资料对比,东际金(银)矿床成矿时代可被限定于早白垩世晚期。

The Dongji Au(Ag)deposit is a cryptoexplosive breccia deposit in the southeastern coastal area,with reserves of 12.5 tons Au and 135.9 tons Ag,and hosted in late Yanshanian Nanyuan Formation.To discuss metallogenic and metal material source of the Dongji deposit,the authors carried out multiple isotope(S-Pb)and electron microprobe analysis(EPMA).Pyrite Co/Ni ratio is 3-94(averaging 23),Co is 500×10^-6-1070×10^-6(averaging 799×10^-6),Fe/(S+As)is 0.827-0.871(averaging 0.860),Au/Ag is 0.9-5.5(averaging 2.6),which suggests that the Dongji Au(Ag)deposit is an epithermal deposit resulting from volcanism.δ34S of pyrite ranges from-0.7‰to-6.6‰,206Pb/204Pb is 17.9801-18.4303,207Pb/204Pb is 15.2689-15.9397,and 208Pb/204Pb is 37.9052-38.7871,which suggests that metal materials were mainly derived from crust-mantle granite magma and partly from metamorphic basement and volcanic wall rocks.Based on zircon U-Pb ages of crystal tuff and granite porphyry combined with regional mineralizaton in the Zhenghe-Jianou area,the authors hold that the metallogenic epoch of the Dongji deposit should be late early Cretaceous.