江西德兴地区中生代岩浆－热液矿床成矿机制对比研究

Two types of Mesozoic large magmatic-hydrothermal deposits occur in Dexing mineral district of Jiangxi Province, the porphyry Cu-Au-Mo type and the sub-volcanic Cu-Au-Pb-Zn-Ag type. How both types of deposits were produced in the same district at about the same time? Is there any metallogenitic relationship between both types of deposits? What were the controling factors on the production of both types of deposits? These are critial questions that need to be answered. In this proposal, we will target the Yinshan polymetallic deposit and the Dexing porphyry copper deposit, each representing one of the two types of deposits. Beginning with field investigation and systematic and detailed observation and mapping of representative mineral veins, and applying technologies of GIS data integration and spatial analysis and SEM-CL quatitative analysis, we shall establish magma intrusive sequence, understand hydrothermal fluid alteration, and reveal spatial and temporal associaton between different stages of mineralization. The EMPA and LA-ICP-MS analytical methods will be used to investigate trace elements of ore-forming minerals and fluid inclusion, in order to decipher evolution history of ore-forming elements and volatiles produced during magmatic-hydrothermal processes for different types of the deposits. The proposal also includes investiation of the constraints on formation of different types of deposits during the magmatic-hydrothermal processes, study of spatial-temporal association and transformation between differnet types of deposits and their physio-chemical constraints and conditions, and understanding of the tectonic and geologic settings of the magmatic-hydrothermal processes.

江西德兴地区主要发育了两套与中生代岩浆－热液作用有关的矿床，即斑岩型Cu-Au-Mo 矿床和次火山岩型Cu-Au-Pb-Zn-Ag 矿床。为什么能在该地形成几乎同时代、而类型不同的超大型矿床？这二者有何联系？其形成主要受哪些因素制约？是一个悬而未决的重要科学问题。本课题以银山多金属矿床和德兴斑岩铜矿为例，在系统野外地质调查和典型矿脉填图的基础上，利用宏观GIS集成与空间分析技术和微观SEM-CL定量分析技术，精细解析不同期次岩浆作用侵入序列、热液流体蚀变作用、不同矿种矿化作用的先后关系和内在联系；利用电子探针和LA-ICP-MS分析技术研究不同阶段、不同相矿物微量元素以及流体包裹体微量元素特征，构建不同类型矿床岩浆－热液过程中成矿元素和挥发份的演化历史；探讨岩浆－热液过程对不同类型矿床（种）形成的制约，揭示不同类型矿床（种）之间的时空转换关系及其物理化学条件制约因素，探讨其成矿地质背景。

德兴地区中生代主要发育了两套与岩浆-热液活动有关的大型金属矿床，即德兴斑岩Cu-Mo-Au矿床和银山与次火山有关的Cu-Au-Pb-Zn-Ag多金属矿床。为什么该地区能够几乎同时形成类型、成矿元素组合不同的两个大型的金属矿床？针对这一科学问题，项目组在详细野外地质工作的基础上，厘清了德兴斑岩铜矿和银山多金属矿床成矿的基本地质特征，从岩浆岩的演化序列、岩浆源区、成矿物质来源以及岩浆-热液精细演化历史及其氧逸度和挥发份的演化趋势等方面揭示了二者成矿的本质区别，厘定了二者的成矿地质背景，建立了德兴地区区域成矿模型。研究结果表明：（1）二者虽均均为高钾的钙碱性系列，但银山与成矿有关的岩石岩浆分异程度（Rb/Sr）、氧化程度（Fe2O3/FeO）均较德兴成矿斑岩花岗闪长斑岩高，二者差异这还表现在La/Sm、Sm/Yb、Co、V、Cr等地球化学参数上；（2）与成矿有关岩石的Sr-Nd-Pb同位素和矿石的Pb同位素表明，虽然二者Nd同位素组成差异不大，但其岩浆岩的源区差异明显，在成矿的过程中，成矿物质的来源明显不同，这些均体现在铀-铅和钍-铅上。（3）岩浆-热液演化过程的矿物学示踪表明：在岩浆早期结晶过程以及岩浆-热液演化过程中，二者在氧逸度以及挥发份的含量上均存在明显的不同，而且在演化过程中，氧逸度和挥发份的含量的变化趋势是不同的。由于氧逸度和挥发份的改变导致不同金属络合物的稳定性存在差异，从而导致成矿元素的组合差异。这些成果为正确认识斑岩型矿床成矿过程及其对成矿元素组合的制约提供了重要的科学依据。