贵州锦丰(烂泥沟)金矿床含砷黄铁矿和脉石英及其包裹体的稀土元素特征

REE features of arseuian pyrite and vein quartz and their fluid inclusions in the Jinfeng(Lannigou)gold deposit,Guizhou province,China.

贵州锦丰(烂泥沟)金矿是滇黔桂"金三角"目前已探明的最大的卡林型金矿床。含砷黄铁矿是该矿床最主要的载金矿物,脉石英是最显著的热液蚀变作用产物。含砷黄铁矿、脉石英及其包裹体具有相同的稀土元素特征,表现为轻重稀土分馏明显(LREE/HREE:7.95～31.77,(La/Yb)_N:8.97～40.49);轻稀土有一定的分异((La/Sm)_N:3.20～5.29),曲线右倾程度大;重稀土分异不明显((Gd/Yb)_N:1.41～3.35),曲线平坦;负铕异常明显(δEu 0.59～0.71);微弱的铈负异常(δCe 0.97～0.98)。代表成矿流体特征的脉石英包裹体稀土配分型式及特征值与区域上不同时代的幔源基性-超基性岩差别较大,而与矿床围岩、矿石、含砷黄铁矿及其包裹体稀土配分型式及特征值十分相似,具上部地壳普通沉积岩的特点,反映成矿流体主要不是来源于地幔,而是以壳源为主。Eu负异常反映了偏酸性(富CO_2)、还原性的成矿环境;微弱的Ce负异常表明成矿流体来源于以沉积水和热脱水为主的盆地流体。

The Jinfeng,previously known as the Lannigou,is the largest known Carlin-type gold deposit in the Yunnan-Guizhou- Guangxi triangle area,southwestern China.Arsenian pyrite is the most important Au carrier mineral,and vein quartz is the product of the most marked hydrothermal alteration in the deposit.The two minerals and their fluid inclusions have the same REE features, showing a pronounced LREE/HREE fractionation with LREE/HREE=7.95～31.77 and(La/Yb)_N=8.97～40.49.The LREE shows a fairly pronounced fractionation with(La/Sm)_N=3.20～5.29 and has greatly right-inclined patterns;the HREE fractionation is not pronounced,with(Gd/Yb)_N=1.41～3.35,and the patterns are flat.The negative Eu anomaly is pronounced withδEu=0.59～0.71,and there is a weak negative Ce anomaly withδCe=0.97～0.98.The REE distribution patterns and characteristic values of inclusions in vein quartz,which represent the characteristics of ore-forming fluids,are quite different from those of mantle-derived basic-ultrabasic rocks of regionally different ages but similar to those of country rocks,ores and arsenian pyrite and its inclusions, showing the characteristics of ordinary sedimentary rocks of the upper crust.This indicates that the ore-forming fluids were mainly derived from the crust rather than from the mantle.The negative Eu anomaly suggests a sub-acid(CO_2-rich),reducing ore-forming environment.The weak Ce negative anomaly indicates that hydrothermal ore fluids may have stemmed from basin fluids dominated by sedimentary water and thermodehydration water.