辽东半岛内生金矿床基本特征、成矿作用与资源潜力
CHARACTERISTICS, MINERALIZATION AND RESOURCE POTENTIAL OF ENDOGENOUS GOLD DEPOSITS IN LIAODONG PENINSULA
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摘要: 辽东半岛是华北克拉通重要组成部分, 中生代发生强烈的构造、岩浆活动和金矿成矿作用, 其内部产有不同规模的金矿床, 并具有明显的地域特色. 通过系统总结辽东半岛金矿床的空间分布、赋矿围岩、控矿构造类型、矿化蚀变等基本特征和成矿作用, 分析金矿的资源潜力. 根据金矿床的空间分布, 划分4个金矿集区, 即: 猫岭、白云-青城子、五龙-四道沟和新房金矿集区. 猫岭和白云-青城子矿集区赋矿围岩为古元古代沉积变质岩系, 矿化类型分为蚀变岩型和石英脉型, 矿体主要受低角度层间断裂控制; 五龙-四道沟矿集区赋矿围岩分别为中侏罗世片麻状黑云母花岗岩和古元古代沉积变质岩系, 矿化类型以石英脉型为主, 蚀变岩型次之, 矿体受高角度断裂和低角度层间断裂控制; 新房矿集区赋矿围岩为太古宙片麻岩和新元古界青白口系变质砂岩、变粒岩和大理岩, 矿化类型为石英脉型和蚀变岩型, 矿体多呈脉状受变质核杂岩剥离断层下盘发育的韧-脆性次级断裂和上部新元古界青白口系盖层构造裂隙控制. 年代学研究表明, 金矿成矿时代可分为晚三叠世(约220 Ma)、早侏罗世(约190 Ma)和早白垩世(约120 Ma). 流体包裹体研究显示, 流体不混溶是金矿成矿的主要机制; 氢-氧同位素显示, 成矿流体主要来自岩浆水, 后期有大气降水加入; 氦-氩同位素数据揭示, 成矿流体主要来自壳源, 少量来自幔源; 硫-铅-锶同位素显示, 成矿物质主要来自中生代岩浆. 同时, 赋矿地层起到不可或缺的作用. 矿床地质特征及同位素数据显示, 辽东半岛金矿为与岩浆热液有关的金矿床. 结合区域构造大地构造演化, 认为, 辽东半岛晚三叠世金矿形成与扬子板块向华北板块深俯冲背景有关, 早侏罗世金矿形成与古太平洋板块向欧亚板块俯冲挤压构造背景有关, 早白垩世金矿形成于古太平洋板块向欧亚板块俯冲折返伸展环境. 结合典型矿床地质特征、区域地球化学和地球物理特征, 圈定找矿靶区23处, 预测3 000 m以浅金资源量2 414.56 t.Abstract: Liaodong Peninsula is an important part of North China Craton, where intense tectonic movement, magmatic activities and gold mineralization occurred in Mesozoic, and gold deposits of different scales are distributed with typical regional characteristics. Through the systematic summary of basic characteristics such as spatial distribution, ore-bearing wall rock, ore-controlling structures and mineralized alteration, as well as the metallogenesis of gold deposits, the paper analyzes the resources potential of gold deposits in Liaodong Peninsula. According to the spatial distribution of gold deposits, four gold deposit concentration areas are divided, including Maoling, Baiyun-Qingchengzi, Wulong-Sidaogou and Xinfang gold deposit concentration areas. The ore-bearing wall rocks of Maoling and Baiyun-Qingchengzi concentration areas are Paleoproterozoic sedimentary metamorphic rock series, with the mineralization of altered rock type and quartz vein type, and the orebodies mainly controlled by low-angle interlayer faults. The wall rocks of Wulong-Sidaogou concentration area are Middle Jurassic gneissic biotite granite and Paleoproterozoic sedimentary metamorphic rock series respectively, with the main mineralization of quartz vein type, followed by altered rock type, and the orebodies controlled by high-angle fault and low-angle interlayer fault. The wall rocks of Xinfang concentration area are Archean gneisses and Neoproterozoic Qingbaikouan metamorphic sandstone, granulite and marble, with the mineralization of quartz vein type and altered rock type. The orebodies are mostly in veins and controlled by the ductile-brittle secondary faults developed in the foot wall of metamorphic core complex detachment fault and by the structural fractures in the Neoproterozoic Qingbaikouou cap rock. The geochronological study shows that the gold mineralization epoch can be divided into Late Triassic (~220 Ma), Early Jurassic (~190 Ma) and Early Cretaceous (~120 Ma). The study on fluid inclusions indicates that fluid immiscibility is the main mechanism of gold mineralization. The H-O isotopes reveal the ore-forming fluid mainly comes from magmatic water, with atmospheric precipitation added in later period. The He-Ar isotopes show that the ore-forming fluid is mainly derived from crustal source and a little from mantle source. The S-Pb-Sr isotopes indicate that the metallogenic materials mainly come from the Mesozoic magma. Besides, the ore-bearing strata play an indispensable role. The geological characteristics and isotopic data show that the gold deposits in Liaodong Peninsula are of magmatic hydrothermal origin. Combined with regional tectonic evolution, it is believed that the Late Triassic gold deposits in the area are related to the deep subduction of Yangtze plate to North China plate, the Early Jurassic gold deposits related to the subduction and compression of Paleo-Pacific plate to Eurasian plate, and the Early Cretaceous gold deposits were formed in the subduction and exhumation extensional setting of Paleo-Pacific plate to Eurasian plate. According to the geological, regional geochemical and geophysical characteristics of typical deposits, 23 prospecting targets are delineated and 2 414.56 t of gold resources at 3 000 m below surface are predicted.