东坪式与正长岩类有关的金矿床成矿机理的同位素地球化学制约

Isotopic geochemical constrains on metallogeny of the Dongping-type gold deposits associated with syenites.

东坪式金矿床产于华北地台北缘金矿成矿带的冀西北金矿集中区,构造上位于华北克拉通北缘深大断裂-尚义-赤城断裂的南侧。金矿床产于泥盆纪早期(386～410Ma)水泉沟正长岩杂岩体内及接触带附近,矿体分布受脆-韧性剪切断裂构造的制约。金矿成矿作用具有多期次的特点,成矿时代为燕山期(156～203Ma)。矿石类型主要为石英脉型、石英网脉+脉旁钾硅化蚀变岩型和钾硅化蚀变岩型,具有典型的碱性岩金矿的金-碲组合,(含)金矿物主要为自然金、碲金矿和碲金银矿。流体包裹体的 H、O 及 He 同位素研究表明,成矿流体为以大气降水主的混合热液流体并可能存在深源流体的参与。矿床的 S、Pb、Sr 和 Si 同位素组成表明,金矿成矿物质主要来源于正长岩杂岩体,部分源于太古宙桑干群变质岩和燕山期花岗岩。因此,东坪式金矿是由燕山期伸展构造环境下热液流体在上涌地幔及岩浆活动的热驱动下对泥盆纪早期形成的正长岩交代改造的产物。

The Dongping-type gold deposits occur along the northern margin of the North China Craton, south of the Shangyi- Chicheng fault. Ore bodies occur either inside of or in the contact zone of the Shuiquangou syenite complex that formed in early Devonian （386 -410Ma, SHRIMP zircon U-Pb）, which controlled by the brittle-ductile faults. The deposits were formed in Yanshannian （156 -203Ma, ^39Ar-^40Ar dating on hydrothermal K-feldspar, quartz and sericite） through multi-phase hydrothermal oreforming processes. The Dongping-type gold deposits consist of three kinds of ore bodies： auriferous quartz vein, quartz vein ＋ metasomatized rock, and silicified and potassium altered rocks. Gold bearing minerals include native gold, calaverite, and antamokite, the typical Au-Te element assemblage of the ores is similar to those of the gold deposits associated with alkali rocks. H, O, and He isotopic compositions of fluid inclusions suggest that the ore-forming fluid was of muhi-sources that dominated by meteoric water with possible contribution of mantle-derived fluids. S, Pb, Sr and Si isotopic characteristics of the Dongping-type gold deposits show that the ore-forming elements were derived mainly from the syenties, but the Archean metamorphic rocks and the Yanshannian granites might also have contributed to the ore-forming processes. Thus, the Dongping-type gold deposits were probably formed through the leaching and alteration of the early Devonian syenites by hydrothermal circulation intrigued by the upwelling mantle and magmatie activities in Yanshannian under extensional tectonic settings.