东秦岭东沟矿集区斑岩型钼矿-脉状铅锌矿成矿机制研究

In recent years, the giant Donggou porphyry molybdenum deposits and many vein-type lead-zinc deposits have been found in the Dounggou ore concentrated area, East Qinling, but there are many controversies remaining, such as whether the spatial distribution of those deposits occurred by happenstance, or they resulted from the same ore-forming process. Based on systematic research of Economic Geology, our project chose the Donggou porphyry molybdenum deposits and the Laodaigou, the Xizaogou lead-zinc deposits, focusing on the porphyry granites, intrusion types, mineralization type, mineral assemblages, alteration, concentration regularity of elements, and by analyzing geochemistry of rocks, fluid inclusions, geochemistry of isotopes and chronology as well, to identify the relationships of (porphyry) granite, porphyry molybdenum deposits and vein-type lead-zinc deposits; the source of ore-forming elements, fluids; and the evolution and geochronology of ore-forming and rock-forming process; the enrichment mechanism of Mo, Pb, Zn; and establish suitable models of mineral deposits. Our project will be helpful to advance the understanding of ore-forming mechanism of porphyry molybdenum deposits and vein-type lead-zinc deposits, which occurred in inter-plate extensional environment; to enrich the Mo-Ph-Zn metallogeny of Qinling-Dabie district; and to summary the regularity and signs of ore deposits, ore-forming factors; to enlarge the exploration area; and to provide the theory basis for further exploration and evaluation activities.

东秦岭东沟矿集区发育东沟超大型斑岩型钼矿床和一些大-中型脉状铅锌矿床，但两者之间究竟是不同时代不同成矿作用在同一空间上的叠加，还是同一成矿作用下的必然结果，长期存在争议。本项目以东沟钼矿床和老代沟和西灶沟铅锌矿为重点解剖对象，以系统的矿床地质学研究为基础，重点对斑岩及其它侵入体，矿化类型、矿物组合、围岩蚀变，成矿元素富集规律进行研究，通过岩石地球化学、流体包裹体、同位素地球化学和年代学研究，查明花岗（斑）岩、斑岩型钼矿、脉状铅锌矿之间的关系，成矿物质、成矿流体来源及成矿演化，成岩和成矿时代，解析Mo、Pb、Zn等硫化物的聚集过程，探讨成矿机制，建立合理的成矿模型。本项目有助于认识产于早白垩世中晚期板内伸展环境斑岩型钼矿-脉状铅锌矿成因类型及成矿机制，丰富东秦岭-大别地区钼铅锌成矿理论；总结成矿规律、控矿因素和找矿标志，扩大找矿的时空域，为进一步找矿勘查工作提供理论基础。

对东沟钼矿床及其外围的铅锌矿床开展了系统研究。获得东沟花岗斑岩、太山庙花岗岩基第3阶段花岗斑岩的锆石U-Pb年龄分别为116.18±0.49Ma、117.33±0.93Ma；东沟钼矿辉钼矿Re-Os年龄为116.81±0.83Ma；三元沟铅锌矿绢云母39Ar-40Ar坪年龄为110.1±9.0Ma。东沟钼矿赋存于东沟花岗斑岩体外接触带中元古界熊耳群火山岩中,围岩蚀变为硅化、钾长石化，次为绢云母化、青盘岩化、碳酸盐化等，呈面型分布。钼矿化经历石英-钾长石阶段（Ⅰ）、石英-辉钼矿阶段（Ⅱ）、石英-碳酸盐化阶段（Ⅲ）。Ⅰ阶段成矿温度集中在250～440℃；盐度变化于7.17～15.07wt%和31.87～49.68wt%；Ⅱ阶段成矿温度集中在280～410℃；盐度变化于0.88～15.76wt%和31.87～54.518wt%；Ⅲ阶段成矿温度集中在146～268℃；盐度变化于1.4～11.93wt%。硫化物的δ34S集中于7.5‰～9.4‰，表明硫来自深源岩浆。石英δ18OH2O值为-2.6‰～6.28‰，δD介于-92‰～-69‰，表明主成矿阶段成矿流体以高温、高盐度、含CO2和富金属元素的CO2-NaCl-H2O型的岩浆流体为主，混有大气降水；晚成矿阶段流体以大气降水为主，流体沸腾，水-岩反应等是钼矿沉淀的主要控制因素。铅锌矿床呈脉状、透镜状产于断裂带中，围岩蚀变有硅化、绢云母化、黄铁矿化、黄铁绢英岩化、绿泥石化、绿帘石化、方解石化等。铅锌矿化经历了黄铁矿-石英阶段（Ⅰ）、石英-多金属硫化物阶段（Ⅱ）、石英-碳酸盐化阶段（Ⅲ）。Ⅰ阶段成矿温度集中在254～386℃；盐度变化于1.05～10.36wt%；Ⅱ阶段成矿温度集中在150～380℃；盐度变化于2.07～15.30wt%；Ⅲ阶段成矿温度集中在132～210℃；盐度变化于3.05～14.04wt%。硫化物δ34S集中于2.89‰～12.9‰，表明硫来自深源岩浆。石英δ18OH2O值为-3.4‰～9.3‰，δD介于-88‰～-78‰，表明主成矿阶段成矿流体为中温、中低盐度、含CO2的岩浆流体和大气降水混合；晚成矿阶段流体以大气降水为主。温度和压力降低，流体混合、水-岩反应是铅锌矿沉淀的主要控制因素。这些矿床构成早白垩世中晚期板内伸展环境与铝质A型花岗岩有关的钼铅锌成矿系统。