论地幔流体参与大水金矿成矿的可能性  

POSSIBILITY OF MANTLE FLUID EXISTING IN GOLD METALLOGENESIS IN DASHUI

作　　者：代文军 陈耀宇 

机构地区：[1]甘肃省地矿局第三地勘院,甘肃兰州730050

出　　处：《甘肃地质》2014年第4期13-22,共10页Gansu Geology

摘　　要：通过对大水金矿时空分布及元素地球化学特征的分析研究,探讨了地幔流体参与大水金矿床成矿的可能性。大水金矿属于川甘陕"金三角"矿集区的一个组成部分,在时空分布上受深大断裂、壳幔混合源岩浆岩的控制,是西秦岭地区勘查发现的大型金矿床之一。研究表明,矿石及贯穿于整个成矿过程中的方解石脉的稀土配分模式总体具相对富集轻稀土的特征。流体包裹体显微测温显示矿床的成矿温度范围为105℃~400℃。包裹体(方解石)气相成分主要为CO2和H2O,液相成分中阳离子以K+为主,Na+次之;阴离子以SO42-为主,Cl-次之。矿物黄铁矿的δ34 S为-1.8‰^+4.1‰,平均值+2.4‰,反映成矿流体中硫部分来源于地幔。热液方解石的碳、氢、氧同位素组成反映成矿流体既有来自地幔的流体,也有来自岩浆岩、地层的流体,还有明显大气降水的加入。硅化灰岩矿石及硅质岩矿石的硅同位素组成具深部或岩浆热液和热水来源的特点,其氧同位素组成具火成石英来源的特点。矿石铅与矿区岩石铅(灰岩和脉岩)的铅同位素组成比较相近,在铅同位素构造模式图及Δγ-Δβ成因分类图解中,铅属壳幔混合铅。综上可知,矿床在成矿作用过程中存在地幔流体活动。The paper studied elemental geochemistry and spatial distribution and metallogenic age of gold deposit in Dashui area, discussed the possibility of mantle fluid taking part in gold. The deposit is controlled by deep fault and crust-mantle mixing magmatic rock. REE partition pattern of ore and calcite vein in the whole gold metallogenic period is characterized by rich LREE relatively. Study of fluid inclusion show that metallogenic temperature is 105℃-400℃, the main composition is CO2 and H2O in gas phase, and the main kation is K^＋, second is Na^＋, in fluid phase, the main anion is SO4^2-, the second is Cl^-. The value of pyrite 83% is -1.8‰-＋4.1‰, average is ＋2.4‰. This reveal the S composition of fluid may come from the mantle material. The carbon, hydrogen and oxygen isotope of hydrothermal calcite may come from the mantle fluid, magmatic and formation fluid, as well as meteoric waters. In the ore samples of siliconizated limestone and siliceous rock, Si isotope is the feature of deep or magmatic water source, O isotope is characterized by igneous quartzite. Pb isotope of ore sample is similar with rock （limestone and vein rock）, it may be the crustal-mantle mixing production according to the tectonic model of Pb isotope and △γ-△β genetic classification. The conclusion is the mantle fluid activity occurred in the metallogenic process.

关 键 词：地幔流体 稀土元素地球化学 流体包裹体 硫、碳、氢、氧、硅、铅同位素 金矿床 甘肃大水 

分 类 号：P618.51[天文地球—矿床学]