山东招远金翅岭金矿床H,O,He,Ar同位素组成及其对成矿流体示踪的研究

金翅岭金矿是位于胶东西北部招莱成矿带内的一个中型石英脉型金矿床,受招平断裂带下盘次级NE-NNE向密集构造裂隙带控制,成矿围岩为玲珑花岗岩和郭家岭花岗闪长岩。本文通过对成矿作用过程中的贯通性矿物石英H,O同位素及黄铁矿中流体包裹体He,Ar同位素进行研究,探讨了成矿流体的来源。研究表明:金翅岭金矿床成矿流体的氢、氧同位素组成存在明显的变化趋势,10件样品的氢氧同位素组成δD值变化于-74.80‰～-95.70‰之间,平均值-85.41‰;δ18 O值变化于+1.30‰～+11.12‰之间,平均值为+4.95‰。分析结果显示,成矿流体早期以岩浆水为主,晚期主要为岩浆水和大气降水的混合。黄铁矿流体包裹体3 He/4 He值为0.09R/Ra～1.51R/Ra,平均0.72R/Ra,位于地壳氦和地幔氦之间。根据成矿流体的壳幔二元混合模式进行计算:地幔流体参与成矿的比例为7.49%～11.85%,地壳流体占主导地位。40 Ar/36 Ar值为365.9～4 042.6,集中在地壳流体与地幔流体之间,大气饱和水的范围附近。结合H-O同位素的结果可知,金翅岭金矿床成矿流体是以地壳流体占主导地位的壳幔混合流体,而地壳流体端元又是岩浆水和大气降水的混合流体,并且大气降水参与成矿流体的比例随着成矿作用从早到晚,以及成矿流体由深到浅的运移而不断增多。

H-O,He-Ar ISOTOPIC COMPOSITIONS OF FLUID INCLUSIONS FOR TRACING THE SOURCE OF ORE-FORMING FLUIDS OF JINCHILING GOLD DEPOSIT, NORTHWEST JIAODONG AREA

Jinchiling gold deposit,controlled by NE-NNE trending structural fissures developed in the footwall of Zhaoping fault zone,is a medium-sized quartz vein type gold deposit located in the northwest of Jiaodong area,with Linglong granite and Guojialing granodiorite as its country rock.Ore-forming fluids and ore genesis are studied through analyses of He-Ar and H-O isotopic composition of fluid inclusions in pyrite and quartz.It is showed that the hydrogen and oxygen isotopes composition exist obvious evolving trend.The δD and δ18O ratios of fluid inclusions from 9 samples range from-74.80‰ to-95.70‰ and from +1.30‰ to +11.12‰,with an average of-85.41‰ and +4.95‰,respectively.The early stage ore-forming fluid is mainly magmatic water,while the late stage R/Ra ore-forming fluid is the mixture of meteoric water and magmatic water.3He/4He ratio of fluid inclusion in pyrite ranges 0.09 R/Ra to 1.51 R/Ra with an average of 0.72 R/Ra,plotted at the area between the earth′s crust Helium belt and mantle Helium belt on the diagram of He isotopic composition.According to the crust-mantle binary model and calculation of the ore-forming fluid,the mantle Helium involved in the ore-forming fluid is 7.49%～11.85%,remaining the earth′s crust fluid being dominant.40Ar/36Ar ratio is 365.9～4 042.6,concentrated between the earth′s crust fluid and mantle fluid,near the scope of meteoric saturated water.Combining the results of H-O isotopes,ore-forming fluid of the Jinchiling gold deposit is the earth′s crust-mantle mixed fluid,and the earth′s crust fluid is dominant.Meanwhile,the crustal fluid is magma-meteorite mixed fluid.The proportion of meteorite fluid in the ore-forming fluid grows more and more as the mineralization process from early stage to late stage,and the fluid migrates from deep to shallow.