湖南柿竹园花岗岩体远接触带Pb-Zn-Ag矿床成矿机理及与近接触带W-Sn-Mo-Bi矿关系研究

Zonal arrangements of metallic minerals around magmas: proximal tungsten and tin and distal lead, zinc, and silver occur in many localities. At present, there is still considerable debate about the genesis of the distal Pb-Zn-Ag veins, also the knowledge about mineralization regularity of Pb-Zn-Cu-Fe-Au-Ag-As-Sb elements involved in magmatic hydrothermal metallogenic system is little, the researching on metallogenic processes of distal and proximal zonation failed to link up. Zonal occurence is significant in South China, especially in southern Hunan. This project focuses on the "metallogenic mechanism of distal Pb-Zn-Ag", furthermore, through researching on difference of nature of the ore-forming fluid and physical-chemical condition between distal and proximal zonation, and crystallization sequences of main sulfides, characteristics and significances of metallogenic elements and theirs precipitation mechanisms and laws of distal zonation, also studying the S isotopic composition gradients in different zonations and sphalerite Rb-Sr and Mica 40Ar-39Ar dating, establishing spatial and temporal relationship between distal Pb-Zn-Ag and proximal W-Sn-Mo-Bi deposits.Finally, we determine multi-element spatial zonal characteristics around magmatic hydrothermal center, and give deposit model on scale of ore district.

在世界各地的矽卡岩矿床中，成矿元素常呈显著的分带-近接触带矽卡岩型W-Sn矿和远接触带脉状Pb-Zn-Ag矿。目前，对于远接触带Pb-Zn-Ag矿成矿机理认识存在争论；较少讨论Pb-Zn-Cu-Fe-Au-Ag-As-Sb成矿元素在岩浆热液成矿系统中的成矿规律；远-近接触带成矿过程研究未能衔接。华南地区矽卡岩具有显著的成矿分带，特别是湘南地区。本项目围绕柿竹园矿田远接触带Pb-Zn-Ag矿床成矿机理，主要通过剖析远-近接触带的成矿流体性质与物理化学条件变化、远接触带金属矿物结晶次序和成矿元素组成特征及指示意义、沉淀机制和规律，结合S同位素组成在不同蚀变带梯度变化和闪锌矿Rb-Sr与云母40Ar-39Ar同位素年代学信息，建立远接触带Pb-Zn-Ag矿床与近接触带W-Sn-Mo-Bi矿之间时空与物质关系，厘定以花岗岩体为中心的热液矿床多元素空间分带特点, 建立矿集区尺度的矿床模型。

世界各地的W矽卡岩矿床常显示成矿分带现象—近接触带矽卡岩型W–Sn矿和远接触带脉状Pb–Zn–Ag矿。目前，对于远接触带Pb–Zn–Ag矿成矿机理认识存在差异。湘南地区矽卡岩型W矿床具有显著的成矿分带现象。我们开展了柿竹园矿田远–近接触带的巷道填图，理清了各蚀变成矿带的空间关系；剖析远接触带的成矿流体性质与物理化学条件变化；查明远接触带矿物结晶次序和成矿元素组成特征及沉淀机制和规律；并对各蚀变阶段矿物开展C–H–O–S–Pb同位素分析，获得了成矿流体来源、演化和成矿作用。远接触带脉状Pb–Zn–Ag矿体由硫化物和硫盐组成，包括三个成矿阶段：（1）早期黄铁矿和毒砂；（2）中期闪锌矿和黄铜矿；（3）晚期方铅矿、载Ag、Sn和Bi的硫盐和磁黄铁矿。流体包裹体和电子探针分析，表明远接触带脉状Pb–Zn–Ag矿床早阶段成矿在400°C条件下，流体在~200bar静岩压力发生沸腾作用，晚阶段降低到~200°C。早阶段成矿的硫逸度在10–8~10–6bars之间，而晚阶段在10–16~10–13bar之间。矽卡岩中方解石δ13C和δ18O值在-6.5~-3.6‰和4.8~8.4‰之间，而Pb–Zn–Ag矿脉中方解石它们的值分布在-3.5~-1.5‰和8.1~15.8‰之间，指明矽卡岩形成于岩浆流体的渗滤交代作用，而远接触带碳酸盐脉来自脉状充填过程中的水岩反应。块状云英岩中石英的δDH2O和δ18OH2O值分别为-77‰和5.1‰，矽卡岩中石榴石的它们的值分布为-97‰和9.2~9.4‰，远接触带石英脉中石英它们的值分别为-83‰和2.8‰，表明远–近接触带成矿流体为岩浆水。远–近接触带矿石中硫化物的δ34S值的范围在0.3~9.9‰，具有岩浆硫特征。远–近接触带中方铅矿的Pb同位素表明W多金属元素来源于上地壳岩石，少量地幔物质加入。远接触带Pb–Zn–Ag矿床的成矿过程为：在千里山岩体结晶的晚阶段，流体从熔体中出溶，并沿着裂隙上升，当它温度将到<400°C，在静岩压力~200bar条件下，流体发生了沸腾作用，在温度降低到200°C，硫逸度逐渐减少的过程中，硫化物和硫盐相续从热液流体发生沉淀。