金矿成矿过程中构造应力场转变与热液浓缩-稀释作用

在大量野外地质观测和室内测试分析研究基础上 ,进一步证实热液金矿工业矿化富集大多数是在构造应力较为张弛的环境下形成的。构造变形岩相形迹的大比例尺填图及测量分析表明 ,热液金矿成矿早期的热液蚀变矿化作用是在压剪性构造背景之下进行的 ,而主要工业矿化与张剪破裂即引张构造有着密切的联系 ,两个阶段的构造应力场有近乎于正交的转化。岩石矿物及流体地球化学的系统分析发现 ,几乎所有的大中型热液矿床中都在热液蚀变基础上伴随强烈的成矿流体浓缩作用 ,初始浓度较稀薄的含矿流体 ,通过水岩反应生成富水矿物的交代带 ,使热液中的自由水大规模缩减 ,并且 ,其自由水通过与C、S等组分的反应也被大量地消耗 ,流体的减压沸腾也极大促进成矿热液中自由水的减少 ,从而使残余流体中金属浓度增高 ,水岩系统中流体的浓缩即时与构造应力场转化为引张作用耦合 ,引起新的流体加入 ,随后的稀释作用形成金属硫化物的沉淀。

TRANSITION OF STRUCTURAL STRESS FIELD AND INSPISSATION-DILUTION OF HYDROTHERMAL FLUID IN GOLD MINERALIZATION

Based on the study of field and indoor analysis, the authors further proved that many industrial hydrothermal gold orebodies were formed in tensile stress environment.Large\|scale geological mapping and measuring of tectonic deformation facies showed that the hydrothermal alteration in the early stage occurred in compressive shear structural belt, and the major industrial orebodies were formed in the later stage in tensile shear belt. The transition of the stress field in the two stages proceeded almost orthogonally.From the systematic analyses of rock, mineral and fluid geochemistry in Linglong,Sanshandao and other deposits, the authors found that almost in all mid\|to\|large type of hydrothermal deposits there have been intense inspissation of ore\|forming fluid based on the hydrothermal alteration. The initial low\|density ore\|bearing fluid turned into a replacement belt with water\|rich minerals by the water/rock reaction,which made the free\|water in the fluid inspissated heavily;additionally, through the reaction with C,S etc., more free\|water was consumed, and the boiling of fluid by the pressure relief further reduced the free\|water content.All these factors caused the metal density in the residual fluid increased. When the inspissation of water/rock system was coupled with the transition of the stress field from compressive into tensile and with the inflow of fresh fluid, the subsequent dilution of the fluid would cause the metal sulfide to be deposited.