胶东牟平金矿矿石、硫化物钕同位素组成及地质意义

Nd Isotopic Composition of Ores and Sulfides from the Mouping Gold Deposit, Eastern Jiaodong Peninsula: Constraints on the Origin of Mineralizing Materials and Metallogenesis

山东牟平金矿是胶东半岛东部近年来探明及开采的赋存于花岗岩岩体中的大型石英多金属硫化物脉状金矿床。含金多金属硫化物的钕同位素研究表明牟平金矿的成矿物质具有多源性 ,即来自成矿作用同期的镁铁质脉岩和控矿围岩昆嵛山花岗岩。结合前人对昆嵛山花岗岩、镁铁质脉岩、金矿床的成矿成岩时代及碳、氢、氧等同位素研究 ,得出成矿流体来源于脉岩岩浆水和广泛淋滤围岩的大气降水的混合。文章不仅阐明了幔源物质在金的成矿作用过程中起了重要的作用 。

Mouping is the second important large_size vein gold deposit in the eastern Jiaodong Peninsula (after the Jinqingding gold deposit, Rushan). This paper presents Sm_Nd isotope data of ores (quartz_sulfides) and sulfides from auriferous quartz_pyrite_pyrrhotite_chalcopyrite_galena veins in the Mouping deposit. Gold_bearing veins are hosted by the Mesozoic granitoids, which were intruded by quartz_sulfides veins and porphyry mafic dikes. Initial Nd isotope ratios of the ores and sulfides are ε Nd,T =-19.45～-20.71 and ε Nd,T =-15.49～ -20.55, respectively. Quartzs were in subsolid state and were isotopically exchanged with late hydrothermal fluids and wallrocks, and hence cannot be used to trace the source of mineralizing materials. Comparing with the Nd isotopic composition of dikes and granitoids, it is concluded that the mineralizing materials were derived from dikes and granitoids. The age difference between gold mineralization and granitoids exceeds 10 Ma, indicating that the mineralizing fluids were derived from meteoritic water instead of from granitic magma, for the duration of hydrothermal fluid activity associated with a single intrusion is shorter than 1 Ma. The same age for gold mineralization and dikes and the shift of O_H isotopic composition of ores indicate that the mineralizing fluids must have been derived from a mixture of dike_magmatic water and meteoric water. The mineralizing materials were derived from mantle_derived dike_magmas and wallrocks which were permeated by meteoric water. This study also shows that neodymium isotope is a good tracer for gold_mineralizing materials.