东秦岭祁雨沟金矿床189号矿体黄铁矿标型特征及其地质意义

Typomorphic Characteristics and Geological Significance of Pyrite in No.189 Orebody of Qiyugou Gold Deposit,East Qinling

祁雨沟金矿床位于东秦岭熊耳山多金属矿集区中部,近年来在深部400 m水平以下新发现了189号斑岩型金矿体,其深部成矿与找矿潜力有待厘定。以祁雨沟金矿床220 m与280 m标高的189号矿体为研究对象,基于野外地质调查、矿相学、载金黄铁矿的成分标型和热电性标型特征的系统研究发现:①祁雨沟189号矿体成矿过程可划分为3个阶段,第Ⅰ阶段为钾长石+石英+黄铁矿±磁铁矿,第Ⅱ阶段为石英+辉钼矿+黄铁矿+黄铜矿,第Ⅲ阶段为石英+黄铁矿+黄铜矿±自然金±银金矿±碲化物;②黄铁矿可划分为两个主要类型,其一为浸染状分布于花岗斑岩中的黄铁矿,含矿性良好;其二为赋存于石英-黄铁矿脉中的黄铁矿,部分呈脉状、团块状产出;③280~220 m标高黄铁矿呈富铁贫硫趋势,w(Fe)/w(S+As)和w(Au)/w(Ag)值指示其岩浆热液成因且形成于中—浅成环境,微量元素变化与深度变化呈正相关;④黄铁矿形成温度范围集中于277.5~332.5℃,指示中低温热液成因,220 m与280 m标高黄铁矿基本以N型为主(97%以上),剥蚀率为75.5%~85.5%,为矿体中下部特征。综合上述分析,认为189号矿体向下仍有一定的延伸空间和深部找矿前景,且祁雨沟金矿外围具有较大的砂金找矿潜力。

Qiyugou Gold Deposit is located at the central segment of the Xiong′ershan polymetallic district in Eastern Qinling.In recent years,the No.189 porphyry gold orebody has been recently discovered below the level of 400 m,the mineralization and prospecting potentials in deep remain unsolved.In this paper,taking the No.189 orebody with elevations of 220 m and 280 m of Qiyugou Gold Deposit as the study example,the integrated study,including detailed geological investigation,mineralogy,compositional typomorphic characteristics and thermoelectricity typomorphic characteristics of gold bearing pyrite is conducted.The study results show that:①The ore-forming process of Qiyugou No.189 orebody can be divided into three stages,including stage I k-feldspar+quartz+pyrite±magnetite,stage II quartz+molybdenite+pyrite+chalcopyrite vein and stage III quartz+pyrite+chalcopyrite±gold±electrum±telluride vein.②Pyrite can be divided into two main generations,one is disseminated pyrite in granite porphyry,which has good ore-bearing property;the second type occurs in quartz-pyrite veins,presenting as veins and lumps.③From the elevations from 280 m to 220 m,pyrites show an increasing trend of iron and decreasing trend of sulfur,w(Fe)/w(S+As)and w(Au)/w(Ag)ratios indicate magmatic-hydrothermal origin and they are formed in a shallow to medium depth environment.The trace element concentrations are positively correlated with the depth.④The formation temperatures of pyrites are mainly concentrated at 277.5~332.5℃,indicating hydrothermal origin with low to medium temperature.The pyrites at 220 m and 280 m elevations are basically N-type(more than 97%)and the range of denudation rate is 75.5%~85.5%,which is the feature of mid-lower part of orebody.In conclusion,it is believed that the deeper level of the No.189 orebody still has potential for Au mineralization,and the periphery of Qiyugou Gold Deposit has prospecting potential for placer gold.