胶东蓬家夼金矿床地质与地球化学特征

蓬家夼金矿床是胶东地区新近发现的金矿床之一,矿体赋存在胶莱盆地东北缘层间滑动断层带中、莱阳组砾岩与荆山群地层的构造接触部位,为区内燕山期火山活动前期,在大气水和岩浆水的参与下形成的层间滑动角砾岩型金矿床。同位素研究表明,蓬家夼金矿的硫、碳来源于矿区围岩;部分铅则可能具有地幔成因。包裹体气相成分以H₂O、CO₂为主;液相成分中富Na⁺、Cl^-,贫K⁺、F^-。成矿流体δ¹⁸O_H2O为0.59‰～4.03‰,δD_H2O为-97.95‰～-89.5‰,反映了成矿流体由大气水和岩浆水混合组成的特点。成矿时代在100Ma。

GEOLOGICAL AND GEOCHEMICAL CHARACTERISTICS OF PENGJIAKUANG GOLD DEPOSIT, EAST SHANDONG

There are three types of gold deposits in west Shandong gold metallogenetic domain. The altered rock type (the Jiaojia type) and quartz vein type (the Linglong type) were discovered for several years. In recent years, a new type gold deposit, the interlayer sliding tectonic breccia type gold deposit, such as the Pengjiakuang and the Songjiagou gold deposits, has been discovered along the northeastern margin of Jiaolai Basin. The Pengjiakuang gold deposit occurs in a interlayer sliding fault zone between the conglomerate of Early Cretaceous Laiyang Formation and the metamorphic complex of Lower Proterozoic Jingshan Group along the margin of Jiaolai Basin, which was formed before Yanshanian volcanic period concerning with meteoric water and magmatic water. The minerogenetic epoch has been proposed about 100 Ma. The host rocks have been extensively subjected to pyritization, silicification, sericitization and carbonatization. Individual ore body has maximum length of 800 m, oblique extension of 500～700 m and gold grade of 1×10^-6～43×10^-6. Native gold is disseminated in silicified, phyllic or carbonatized tectonic breccia. A study on sulfur, carbon and lead isotope of gold ores and wall rocks shows that the sulfur may come from the metamorphic complex of Lower Proterozoic Jingshan Group, carbon from the marble of Jingshan Group, while a part of lead may come from the mantle. The mineralizing fluid is rich in Na⁺ and Cl^-, but relatively impoverished in K⁺ and F^-. According to the data from hydrogen and oxygen isotopic compositions (δ¹⁸O_H2O=0.59‰～4.03‰, δD_H2O=-97 5‰～-89.5‰), the conclusion can be reached that the mineralizing fluid of Pengjiakuang gold deposit was a kind of mixed hydrothermal solution which was mainly composed of meteoric water and magmatic water. A comparative study shows that the Pengjiakuang-type gold deposit, namely, the interlayer-sliding tectonic breccia type gold deposit, is different from the Jiaojia-type gold deposits and the Linglong-type gold deposits in the Jiaodong Block. It formed under an extensional tectonic background and located at interlayer-sliding fault zone along the margin of Mesozoic Jiaolai Basin. Also, the gold mineralization has closely genetic relationship with the alkaline magamtism.