摘要
安徽马头钼矿床位于长江中下游成矿带的安庆-贵池矿集区内,矿体主要赋存在花岗闪长斑岩中,其矿化类型由浅部石英脉型和深部细脉浸染型矿体组成.其中,浅部蚀变以绢英岩化和青磐岩化为主,钾化和碳酸盐化相对较弱,深部蚀变主要为强钾化和少量硅化.成矿流体研究结果表明,该矿床浅部主要为Ⅰ型水溶液包裹体,而深部则包含Ⅰ型水溶液包裹体、Ⅱ型富CO_2包裹体和Ⅲ型含CO_2包裹体.浅部Ⅰ型包裹体均一温度集中在224℃~283℃,盐度在3.8wt.%~7.6wt.%NaCl之间;深部Ⅰ型和Ⅱ型包裹体均一到液相,其均一温度分别集中在263℃~316℃和311℃~331℃,盐度分别为5.1wt.%~10.3wt.%NaCl和0.6wt.%~2.0wt.%NaCl,Ⅲ型包裹体均一温度为335℃~362℃,盐度为2.7wt.%~6.7wt.%NaCl.深部大量Ⅰ型与Ⅱ型、Ⅲ型包裹体共生在同一石英颗粒中,均一温度相近,均一方式不同,表明深部细脉浸染型成矿作用过程中可能有流体不混溶作用发生,导致CO_2逃逸,流体性质改变致使Mo等成矿物质的沉淀.本研究发现NaCl-H_2O-CO_2体系流体不混溶为马头钼矿床属于斑岩型矿床提供了新的地质地球化学证据.
The Matou Mo deposit is located in the Anqing Guichi ore cluster area of the Middle-Lower Yangtze Valley metallogenic belt. The mineralization types are divided into shallow quartz vein type and deep veinlet disseminated type. The alteration types in shallow parts mainly include phyllie alteration, propylitization, with minor potassic alteration and carbonatation. The deep parts are mainly composed of intense potassic alteration and silicification. The ore minerals in the Matou Mo deposit are mainly molybdenite and chalcopyrite, with a small amount of scheelite, magnetite, pyrrhotite, sphalerite, and galena. Gangue minerals are mainly K-feldspar, quartz, sericite, and calcite. Three main types of inclusions can be identified in the hydrothermal veins：two-phase aqueous inclusions（type Ⅰ ）, two-phase CO2 rich inclusions （Type Ⅱ）and three-phase CO2-bearing inclusions （Type Ⅲ ）. The dominant fluid inclusions in the shallow part are type Ⅰ ,while deep quartz veins contain type Ⅰ , Ⅱ and Ⅲ inclusions. Type Ⅰ inclusions in the shallow quartz vein exhibit low to moderate salinities ranging from 3.8 wt.% to 7.6 wt.% NaCl equivalent,and homogenization temperatures from 224 ℃ to 283℃. Type I and coexisting type Ⅱ inclusions in deep veinlet disseminated mineralization show higher homogenization temperatures ranging from 263 ℃ to 316℃ and from 311℃ to 331 ℃,with salinities of 5.1 wt.% to 10.3 wt.% and 0.6 wt.% to 2.0 wt.% NaCl equivalent, respectively. Type m inclusions in deep veinlet disseminated mineralization yield homogenization temperatures of 335 ℃ to 362 ℃ ,with salinities 2.7 wt. % to 6.7 wt. % NaCl equivalent. The ore-forming fluid of shallow quartz vein orebody is NaCl-H2O system,while the ore-forming fluid in deep mineralization belongs to NaCl-H2O-CO2 system. A large number of type Ⅰ ,type Ⅱ and type Ⅲ inclusions coexist in the same quartz from the deep mineralization. Their similar homogenization temperature indicated that the fluid immiscibility may occurred in the deep part. The dramatic changes in chemical properties of fluids resulted from immiscibility lead to the decomposition of complex and molybdenite precipitation. The pressures of mineralization were 65 MPa-90 MPa, obtained from the microthermometric data of type Ⅰ and Ⅱ fluid inclusions from the deep part,which is corresponding to the depth of 2.4 km to 3.3 km. Alteration mineralogy research shows that the Matou Mo deposit exerts typical porphyry deposit alteration characteristics, with potassic alteration, silicified zone and serieitic zone. The identification of fluid immiscibility during mineralization provides new evidence for ore genesis and precipitation mechanism of Matou deposit.
作者
顾建峰
倪培
李文生
王国光
潘君屹
刘政
Gu Jianfeng1,2 ,Ni Pei1 ,Li Wensheng1 ,Wang Guoguang1 ,Pan Junyi1 ,Liu Zheng1(1.State Key Laboratory for Mineral Deposits Research, Institute of Geo-Fluids, School of Earth Sciences and Engineering, Nanjing University, Nanjing, 210023, China ;2.East China Geological Exploration Bureau of Nonferrous Metals in Jiangsu Province,Nanjing, 210007, Chin)
出处
《南京大学学报（自然科学版）》
CAS
CSCD
北大核心
2018年第2期351-365,共15页
Journal of Nanjing University（Natural Science）
基金
国家重点研发计划(2016YFC0600206)
关键词
马头钼矿床
斑岩型钼矿床
流体包裹体
流体不混溶
成矿机制
Matou Mo deposit, porphyry molybdenum deposit, fluid inclusion, fluid immiscibility, metallogenic mechanism
