太行山北段石湖金矿的成岩成矿机制:U-Pb年龄及地球化学证据

Petrogenetic and metallogenic machenism of Shihu gold deposit in northern Taihangshan:evidence from U-Pb geochronology and geochemistry

为讨论石湖金矿的形成与麻棚花岗岩体、石英闪长玢岩脉之间的联系,对花岗闪长岩、石英闪长玢岩进行了U--Pb年代学研究,并分别对花岗闪长岩、石英闪长玢岩、矿化蚀变岩和围岩的地球化学进行了系统测定。麻棚花岗岩体U--Pb年龄为(124.8±1.4)Ma(MSWD=0.74),石英闪长玢岩脉年龄为(127.3±1.1)Ma(MSWD=1.15),但二者地球化学特征表现不同,应有不同起源。地球化学特征表明,麻棚花岗岩与矿化蚀变岩具有较一致的稀土、微量元素配分型式,而与围岩差别大,说明金矿的成矿流体来源与麻棚花岗岩关系密切。此外,花岗闪长岩具高钾钙碱性,且重稀土亏损、轻稀土富集、弱Eu异常、高Sr--Ba和高Sr/Y、La/Yb比值,表明麻棚岩体的形成有幔源岩浆的混入。笔者认为成矿流体和成矿物质来源为幔源岩浆底侵和混合,并以花岗岩浆为载体而迁移上升。结合矿床地质特征,初次提出闪长玢岩脉与矿体时空关系密切,这应是闪长玢岩脉作为隔流体层对来自麻棚花岗岩体的成矿流体具有一定的封闭作用,使得矿化、蚀变富集产出,即岩脉封闭作用。石湖金矿的成岩成矿机制与中生代期间岩石圈减薄的地球动力学背景密切相关,应是一种非造山型金矿。

To discuss the connection of the formation of Shihu gold deposit with Mapeng granite rock mass and quartz-diorite porphyrite dike,the authors study the U-Pb chronology of granodiorites and quartz-diorite porphyrites,and analyze the geochemistry of granite diorites,quartz-diorite porphyrites,mineralized alteration rocks and wall rocks,respectively.The U--Pb zircon age of Mapeng granite is（124.8 ± 1.4） Ma（MSWD = 0.74） and the age of dioritic porphyrite dike is（127.3 ± 1.1） Ma（MSWD = 1.15）.But there are significant differences in their geochemical characteristics,which indicate different origins of them.Geochemical characteristics show that Mapeng granodiorites and mineralization-alteration rocks have a relatively concordant distribution pattern of rare earth and trace elements,but they are different in wall rocks.It is proved that the origin of ore-forming fluids of Shihu gold deposit is close to that of Mapeng granodiorites.Besides,Mapeng granodiorites have high potassium and calcalkaline,which is rich in LREE and deficient in HREE with weak Eu negative anomaly.The high Sr/Y and La/Yb ra-tios show that Mapeng intrusion is formed by mantle-derived magma mixed with granite magma.The mantle-derived magma invasion and mixed with granite magma that provides the ore-forming fluid and ore-forming materials.Mapeng intrusion is the carrier of ore-form fluids and materials.Combined with the features of the ore deposit geology,the study first proposed that dioritic porphyrite dikes are closely related to ore bodies in temporal and space,that should owe to the diorite porphyry dikes as impermeable layers,which have a certain sealing effect on the ore-forming fluids from the Mapeng intrusions and lead to the enrichment of mineralization and alteration near these dikes,that is,dike closure effect.Shihu gold deposit formed during lithospheric thinning and craton destruction of Mesozoic,and it should be a kind of an orogenic gold deposits.