冀东太古宙末期基底构造约束下的金成矿作用及演化

Gold Mineralization and Evolution Under Structural Constraints of the Basement in the Jidong Area, North China Craton

冀东地区是华北克拉通具有代表性的金矿成矿带之一,分布众多金矿床,大部分矿体产在前寒武系基底岩系内,矿体形态和相关岩体侵位受到基底构造的影响和制约。本文在前人工作的基础上,将冀东太古宙结晶基底划分为金厂峪-遵化-马兰峪紧密褶皱绿岩带和都山-太平寨-迁安片麻岩穹状隆起区,并在此基础上开展了金厂峪、华尖、峪耳崖等典型金矿床大中比例尺构造背景研究,总结了矿田构造特征。对围绕在片麻岩隆起区的混合花岗岩开展了LA-ICP-MS锆石U-Pb测年,结果显示2514.7±8.7 Ma存在一次与克拉通化有关的构造岩浆事件,并使金初步富集。峪耳崖金矿床两件辉钼矿Re-Os模式年龄分别为168.4±2.7 Ma和167.2±2.4 Ma,表明成矿作用发生于燕山中期。结合前人已获得的年代学数据,认为冀东地区金矿形成于印支期-燕山中期,并且可能存在20 Ma左右为间隔的岩浆活动强烈期,成矿具有阶段性特征。根据大地构造特征建立了冀东三阶段的金矿成矿演化模型。

Being rich in gold deposits, the Jidong area is considered one of the most representative gold metallogenic belts in the North China Craton. Most ore bodies are hosted in the Precambrian basement rock series. The morphology of ore bodies and related rock mass emplacement are restricted by the basement structure. On the basis of previous studies, we divided the Jidong Archaean basement into the Jinchangyu-Zhunhua-Malanyu compact greenstone belt and the Dushan-Taipingzai-Qianan gneiss quaquaversal upheaval area. The purpose of such separation was to study the large-and medium-scale constructive background of typical gold deposits in Jinchangyu, Huajian, and Yuerya, among others. The study was also intended to summarize the tectonic characteristics of the ore field. We obtained LA-ICP-MS zircon U-Pb dates for mixed granites surrounding the gneiss upheaval area. The results reveal that the occurrence of atectonic magma event was related to cratonization in 2514.7±8.7 Ma, which caused preliminary gathering of gold. The model ages of two Re-Os molybdenites from gold ores in the Yuerya are 168.4±2.7 and 167.2±2.4 Ma, respectively. The ages indicate that mineralization occurred in the Yanshanian. Combined with the chronological data obtained in previous studies, our findings suggest that the gold ores in Jidong were formed in the middle of Indochina- Yanshanian. A period of intense magmatic activities took place roughly every 20 Ma, and the mineralization exhibited stage characteristics. We established a gold metallogenic evolution model based on tectonic characteristics： during the period of micro-continental collision and Amalgamation （4500 Ma to 1850 Ma）, metallogenic materials were preliminarily enriched; during the Yan-Liao chasmic period in the Mesoproterozoic-Neoproterozoic era （1850 Ma to 600 Ma）, the NE-trending ore-controlling structural framework was established; during the intraplate orogenic metallogenic period （242 Ma to 165 Ma）, the most advantageous metallogenic location was formed by tectonic activation and fracture in the zone of extrusion schistosity. Gold deposits were formed through magmatic activities in various stages.