Ar-Ar chronology of the brittle deformation age for the ore-controlling shear zones in the Jiaodong Peninsula and it's constrains on gold mineralization

Abstract

胶东地区是典型的剪切带型金矿集中区，精确厘定该地区控矿剪切带的活动时代，可为探讨剪切带与金矿成因关系提供关键的时限约束，并且对矿床成矿模式的建立具有至关重要的意义。大量矿床地质证据显示胶东地区控矿剪切带中脆性变形活动对金矿体的形成具有直接影响，但其脆性变形时代尚不十分清楚。据此，本文在详细研究金矿体赋存特征的基础上，系统选取胶东焦家、玲珑、邓格庄、乳山这四个金矿区控矿剪切带断层泥中白云母进行⁴⁰Ar-³⁹Ar年代学研究。定年结果显示，胶东地区焦家剪切带、招平剪切带以及牟乳剪切带的脆性变形时代分别为110.3±1.5Ma、122.8±1.7Ma、119.6±1.2Ma~115.8±1.4Ma。其中焦家剪切带的脆性变形时代明显晚于招平和牟乳剪切带，可能代表了焦家蚀变岩型矿化形成后易遭受后期的构造叠加。综合胶东各金矿区控矿剪切带变形时代、岩体侵位时代、成矿时代及剪切带活动特征和矿体产出特征，本文认为在多期岩体侵位以及控矿剪切带递进变形过程中，剪切带韧性变形区中由高压流体作用产生的同期脆性破裂可形成脉型矿化，如乳山金矿；而在脆-韧性和脆性变形区中发生的大规模脆性变形可导致脉型和蚀变岩型矿化的形成，如玲珑、邓格庄和焦家金矿。但随着剪切带的递进变形和隆升剥蚀，后期多期次的脆性构造变形叠加，可导致多种矿化类型出现在同一构造部位，如焦家金矿中石英脉型和蚀变岩型矿化。;Jiaodong Peninsula is a typical concentration area for shear zone type gold deposits. Accurate determination of the deformation age of ore-controlling shear zones in this area can provide a key time limit for exploring the relationship between shear zones and the genesis of gold deposits, and is of vital significance to the establishment of metallogenic mechanism. A large number of geological evidences show that the formation of gold orebodies is directly controlled by brittle deformation activities of ore-controlling shear zones in Jiaodong Peninsula, but this deformation age is still unclear. Based on detailed study of the occurrence characteristics of orebodies, we systematically selected muscovite samples from fault gouge in Jiaojia, Linglong, Denggezhuang and Rushan gold mining areas for the Ar-Ar chronology study. ⁴⁰Ar/³⁹Ar dating results show that the brittle deformation ages of Jiaojia, Zhaoping and Muru shear zones in Jiaodong Peninsula are 110.3±1.5Ma, 122.8±1.7Ma and 119.6±1.2Ma~115.8±1.4Ma, respectively. Among them, the brittle deformation age of Jiaojia shear zone is obviously later than those of Zhaopin and Muru shear zones, which may represent that the altered rock type mineralization in Jiaojia deposit is susceptible to structural superposition in the later period. Comprehensively comparing shear zone deformation ages, pluton emplacement ages, metallogenic ages, shear zone activities and orebody occurrence characteristics in Jiaodong gold deposits, it is suggested that: (1) The contemporaneous brittle fractures caused by high-pressure fluids in ductile deformation region of shear zones can lead to the formation of vein type mineralization, e.g. Rushan gold deposits; (2) Large-scale brittle deformation in brittle-ductile and brittle region can lead to the formation of vein type and altered rock type mineralization, e.g. Linglong, Denggezhuang and Jiaojia gold deposits. Both stages take place during the process of multi-stage emplacement and progressive deformation of ore-controlling shear zones. However, with the progressive deformation and uplift denudation of shear zones, the superposition of brittle deformation in the late stage may lead to the occurrence of multiple mineralization types in the same structural site, e.g. quartz vein type and altered rock type mineralization in Jiaojia gold deposit.