华北板块北缘首例大型高品位隐伏斑岩型金矿床——内蒙古毕力赫金矿

摘要

The Bilihei gold deposit(No.II ore zone) in Inner Mongolia,found by Gold Geological Institute of CAPF in 2006-2008,is one of the fatal breakthrough deposits supported by the Project of Supersedable Resource Prospecting of Critical Mines in China.It is located in the Mesozoic(Jurassic) continental facies volcanic basin on the northern margin of North China plate.The main characteristics of the deposit are as follows:(1) the concealed ore body occurs in the contact zone(mainly in the inner-contact zone) between granodiorite porphyry and volcanic rocks;(2) a large ore body 500m long,300m wide and averagely 52.85m thick was identified,which contains 21916 kg Au at the average grade of 4.5×10~(-6)(the highest grade being 54.76×10~(-6));(3) ores can be classified into altered granodiorite porphyry type and andesite porphyrite type,with the former type having typical unidirectional solidification texture(UST).There are only small amounts(<1%) of metallic minerals,such as pyrite,chalcopyrite and molybdenite,in the ore;gold mainly occurs in lumpy or veinlet quartz formed during alteration;(4) just like gold-rich porphyry copper deposits,the alteration shows obvious ring-shaped zoning;the concentric alteration zones from the inner part outwards and from early to late stages are successively the K-silicate zone,the quartz-sericite zone,and the propylitic zone;the structure-controlled argillic alteration locally occurs as patches,superimposed by other alteration zones;(5) the early ore-forming stage has very high temperature(>550℃),and the temperature of the middle-late stage is 108～375℃,194℃ on average.It is concluded that this deposit is a large-sized and high-grade independent and concealed porphyry Au deposit and is the first deposit of this kind discovered on the northern margin of North China plate.%内蒙古毕力赫金矿床(Ⅱ号带)是全国危机矿山接替资源勘查获得重大突破的矿床之一,由武警黄金地质研究所勘查发现(2006-2008年).矿区位于华北板块北缘叠接俯冲带南部华北板块一侧的陆相火山岩盆地中.该矿床有如下主要特点:(1)矿体呈隐伏状态(距地表1～40 m)产出于隐伏的燕山期花岗闪长斑岩体接触带内.并以内接触带为主;(2)矿体规模大(目前控制长500 m,最宽处300 m,最窄处约40 m.最大厚度128.17 m,最小厚度10.53 m,平均厚度52.85 m),品位高(平均4.5×10~(-6),最高52.76×10~(-6)),单个矿体资源量达20 t以上;(3)矿石为蚀变的花岗闪长斑岩和火山岩型.前者具有典型的单向固结结构(UST).金属矿物以黄铁矿、黄铜矿、辉钼矿等为主,但含量低(小于1%),金主要赋存于蚀变形成的团块状或细脉状石英中;(4)围岩蚀变以钾化、硅化、绢云母化、高岭土化、青磐岩化等为主,具有富金斑岩型铜矿床的分带特征;(5)成矿温度明显分为两个区间.早期石英流体包裹体均一温度大于550℃,为含矿热液沸腾结果;中晚期温度变化在108～375℃,平均值为194℃.初步研究表明,该矿床应为独立的大型高品位斑岩型金矿床,在华北板块北缘地区为首次发现,具有典型性和代表性.对于区域相似地质环境内类似矿床的寻找和勘查具有重大示范意义.