新城金矿蚀变带构造与地球化学特征

Structural and Geochemical Characteristics of Alteration Zone of Xincheng Gold Deposit

通过新城金矿的构造和蚀变岩剖面实测、构造测量和岩石地球化学分析,获得以下构造和岩石地球化学同步变化特点:(1)以焦家断裂为中心蚀变岩分带为断层泥-硅化带-黄铁绢英岩带-强钾化花岗岩带-弱钾化花岗岩带-未蚀变花岗岩带;(2)金矿化主要集中在硅化带及黄铁绢英岩带;(3)断裂下盘依次发育糜棱岩-碎裂岩-花岗质碎裂岩-碎裂花岗岩的构造岩分带;(4)构造测量显示,断裂下盘各蚀变带的构造主压应力依次显示东西向、北西向、北西向和北北西向,而蚀变岩石差应力分别为107.46MPa、135.58MPa、115.21MPa和86.75MPa,正常似斑状花岗岩仅71.56MPa的变化趋势;(5)蚀变带岩石常量元素分析揭示,Fe2O3、CaO、FeO、H2O、CO2的迁移量较大且与Au元素变化同步,明显在弱钾化花岗岩带向强钾化花岗岩带过渡地段变化量最大;微量矿化元素Au、Ag、Zn、As、Bi、Cu和Pb在蚀变过程中处于迁入状态,且在钾化和绢云母化强烈发育带迁入量最大。野外构造测量、室内岩石学观测和岩石化学测试结果充分说明,新城金矿的热液蚀变成矿过程与构造应力场的分布变化密切相关,揭示成矿元素富集强度与构造的强弱有一定相关性,在北西方向挤压且构造应力处于较高强度阶段,伴随强烈绢云母化和钾长石化蚀变而元素集中富集成矿。

By measuring section about structure and altered rocks in the Xincheng gold deposit, combining structural observation and geochemical analysis, the authors obtained that structure and geochemistry have synchronous variation characteristics： （1） altered rock zonation along the Jiaojia fault is fault gouge-silicified zone-beresitization zone-highly potassic granite-weakly potassic granite-unaltered granite; （2） gold mineralization mainly exists in the silicified zone and beresitization zone; （3） fault gouge-mylonite-fractured altered granitic rock-fractured granites successively developped in the down block of fault; （4） structural observation shows the orientation of principal compressive stress of alteration zones in the down block of fault changes by WE-NW-NW-NNW directions successively, while the stress values of the rocks are 107.46 MPa, 135.58 MPa, 115.21 MPa, 86.75 MPa, and 71.56 MPa of normal granites; （5） major element analysis for rocks of alteration zone reveals, the migration of Fe203, CaO, FeO, H2O CO2 is large, showing synchronous change of Au with the maximizes in the transition from highly potassic granite to weakly potassic granite; trace elements like Au, Ag, Zn, As, Bi, Cu and Pb keeps immigrating during alteration, and maximizes in the zone of potash feldspathization and sericitization. Field structural observation, petrology study and rock chemical analysis show clearly that hydrothermal alteration mineralization is closely associated with the distribution of tectonic stress field, which reveals the enrichment of minerogenetic elements has certain relationship with structure intensity, that is to say, during the process of NW compression and tectonic stress in the highest stage, elements enriched and mineralized.