摘要
中国地质工作者在20世纪80年代已发现南岭地区许多石英脉型钨矿床的蚀变晕宽度随深度递减, 然而这一蚀变特征的形成机制至今仍未得到较好的解释.通过模拟热液运移和硅从裂隙带向邻近围岩的扩散过程, 发现流体温度和围岩孔隙度是影响石英脉型钨矿床蚀变特征的重要变量.高温和高孔隙度会加速硅从裂隙向邻近围岩扩散, 形成较宽的蚀变.在围岩孔隙度呈均一分布的情况下, 由于深部温度高于浅部, 深部围岩蚀变宽于浅部蚀变.围岩孔隙度随深度递减会抵消温度对硅扩散速率的影响, 使深部围岩形成较窄的蚀变.围岩孔隙度随深度递减可能是形成石英脉型钨矿床蚀变宽度随深度减小的有效机制.前人将钨矿蚀变特征归因于岩浆热液过渡性流体, 该研究为这一科学问题提供了新的解释.
Geologists discovered in the 1980s that alteration halos decrease with increasing depth at many tungsten deposits in the Nanling Mountains. However, the mechanism for the formation of the alteration characteristics remains poorly understood. In this pa- per, the authors investigated hydrothermal flow and silica diffusion from fractures to adjacent wall rock at these tungsten deposits by using finite element based numerical experiments. The authors have found that fluid temperature and wall rock porosity exert a strong influence on silica diffusion from fractures to adjacent wall rock. Both high temperature and high porosity favor silica diffusion from fractures to adjacent wall rock and form wide alteration halos. Constant-porosity wall rock forms wider alteration halos at deeper lev- els, which is inconsistent with things at the tungsten deposits. Wall rock porosity that decreases with increasing depth forms alteration halos like those at the tungsten deposits. The wall rock lithology and fracture distribution at the tungsten deposits favor the formation of depth- dependent porosity and permeability. Evaluation of these two factors may help the exploration. Aqueous NaCl solutions were used in the numerical experiments. It is therefore concluded that inhomogeneous magmatic hydrothermal fluids are unnecessary in explaining the alteration characteristics at these tungsten deposits.
作者
刘向冲
张德会
邢会林
LIU Xiangchong;ZHANG Dehui;XING Huilin(Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China;The Laboratory of Dynamic Digenesis and Metallogenesis,Institute of Geomechanics,CAGS,Beijing 100081,China;The University of Queensland,Brisbane 4072,OLD,Australia;State Key Laboratory of Geological Processes and Mineral Resources,School of Earth Sciences and Resources,China University of Geo sciences（Beijing）,Beijing 100083,China）Geologists discovered in the 1980s that alteration halos decrease with increasing depth at many tungsten deposits in the Nanling Mountains.However,the mechanism for the formation of the alteration characteristics remains poorly understood.In this pa- per,the authors investigated hydrothermal flow and silica diffusion from fractures to adjacent wall rock at these tungsten deposits by using finite element based numerical experiments.The authors have found that fluid temperature and wall rock porosity exert a strong influence on silica diffusion from fractures to adjacent wall rock.Both high temperature and high porosity favor silica diffusion from fractures to adjacent wall rock and form wide alteration halos.Constant-porosity wall rock forms wider alteration halos at deeper lev- els,which is inconsistent with things at the tungsten deposits.Wall rock porosity that decreases with increasing depth forms alteration halos like those at the tungsten deposits.The wall rock lithology and fracture distribution at the tungsten deposits favor the formation of depth- dependent porosity and permeability.Evaluation of these two factors may help the exploration.Aqueous NaCl solutions were used in the numerical experiments.It is therefore concluded that inhomogeneous magmatic hydrothermal fluids are unnecessary in explaining the alteration characteristics at these tungsten deposits.)
出处
《地质通报》
CAS
CSCD
北大核心
2018年第7期1379-1384,共6页
Geological Bulletin of China
基金
国家自然科学基金项目《》（批准号：41373048、41602088）和国土资源部公益性行业科研专项经费（编号：201411024）
关键词
钨矿
蚀变晕
热液运移
孔隙度
扩散系数
南岭
tungsten deposits
alteration halos
find flow
diffusion coefficient
porosity
Nanling
