东秦岭杨斜金矿区石英闪长玢岩锆石U-Pb年代学、地球化学特征及地质意义

杨斜中型金矿床是东秦岭杨斜-丰北河地区典型的石英脉型金矿床，成矿与区内石英闪长玢岩密切相关，具中高温蚀变特征及矿物组成。LA-ICP-MS锆石U-Pb测年结果表明，石英闪长玢岩锆石²⁰⁶Pb/²³⁸U加权平均年龄为149.5±2.7 Ma，谐和年龄为149.5±2.1 Ma，属晚侏罗世。岩石地球化学研究显示，石英闪长玢岩具有高SiO₂(65.53%~65.76%)、高Al₂O₃(15.65%~15.87%)、富碱(N₂O+K₂O=8.07%~8.30%)及贫MgO(1.37%~1.40%)特征，属于高钾钙碱性准铝质系列岩石；相对富集Rb、Ba、K、Pb、Sr等大离子亲石元素和LREE，亏损Nb、Ta、Ti等高场强元素和HREE；其高Sr、高Sr/Y、低Y和低Yb值及正Eu异常等特征参数，与典型埃达克质岩一致，岩浆应起源于加厚下地壳的部分熔融。综合研究认为，杨斜金矿属岩浆期后热液型金矿床，成岩成矿时代一致，形成于秦岭造山带晚侏罗世-早白垩世陆内俯冲向伸展转换的构造环境。

Zircon U-Pb isotopic geochronology, geochemistry and geological significance of the quartz diorite porphyrite in Yangxie gold ore district, East Qinling

The middle-sized Yangxie gold deposit is a typical quartz-vein type gold deposit in Yangxie-Fengbeihe area, East Qinling. Its mineralization is closely related to quartz diorite porphyrite, which has the characteristics of medium-high temperature alteration and mineral composition. LA-ICP-MS zircon U-Pb dating indicates that the weighted average ²⁰⁶Pb/²³⁸U age and concordance age of zircons from the quartz diorite porphyrite are 149.5±2.7 Ma and 149.5±2.1 Ma respectively, suggesting the Late Jurassic. Petrogeochemical studies show that the quartz diorite porphyrite belongs to high K calc-alkaline metaluminous rocks which are characterized by high contents of SiO₂(65.53%~65.76%), Al₂O₃(15.65%~15.87%) and alkali (Na₂O+K₂O=8.07%~8.30%) but low MgO content (1.37%~1.40%). These rocks are relatively enriched in LILE (Rb, Ba, K, Pb, Sr) and LREE, and depleted in HFSE (Nb, Ta, Ti) and HREE. Meanwhile, their characteristic parameters of high Sr values, high Sr/Y rations, low Y and Yb values as well as positive Eu anomalies are consistent with those of typical adakitic rocks, indicating that the parental magma was probably derived from partial melting of the thickened lower crust. The comprehensive studies suggest that the Yangxie gold deposit is a magmatic-hydrothermal gold deposit, which was formed in the transitional environment of intracontinental subduction to extension of the Qinling orogenic belt from Late Jurassic to Early Cretaceous.