河北平泉下金宝金矿床载金矿物特征及其成矿指示意义

摘要

以位于河北永安—下营房—毛家沟金多金属成矿带的下金宝金矿床为研究对象,借助光学显微镜、电子探针点分析及面分析技术,对本区金的赋存状态以及主要载金矿物的形成环境和成因类型进行研究.研究结果表明:本区"可见金"的粒径集中在0.005~0.053 mm范围内,微细粒级金矿物质量分数占80%以上,主要以粒间金、包裹金及裂隙金的形式出现;载金矿物主要为银金矿、自然金、黄铁矿、闪锌矿;本区"不可见金"不仅以机械混入的"不可见"显微?超显微包体金存在,而且以晶格金的形式存在;本区黝铜矿As与As+Sb的物质的量比x(As)/(x(As)+x(Sb))高于0.25,银金矿中Au的质量分数w(Au)为73.512%~80.120%,闪锌矿的w(Zn)/w(Cd)为79.82~145.33,表明矿床形成于浅成—中低温环境中;黄铁矿、闪锌矿的主微量元素特征指示下金宝金矿床为与岩浆侵入活动有关的浅成中低温热液型金矿床.%Xiajinbao gold deposit is located in the Yong'an—Xiayingfang—Maojiagou poly-metallic belt, which has favorable metallogenic geological condition. According to systematic petrography observation and in situ elemental analysis by X-ray electron probe microanalyzer(EPMA), Xiajinbao gold deposit occurrence and the ore-forming environment and genesis of gold-bearing minerals were studied. The results show that the visible gold particle has a size of 0.005?0.053 mm in diameter. Fine grained gold composes more than 80% of the total minerals, which occur as mineral inclusions in the fractures or among the particles of the gold-bearing minerals. Major gold-bearing minerals include gold, electrum, pyrite and sphalerite. The "invisible gold" mainly exists in the form of mechanically-mixed "invisible" microscopic- ultramicroscopic gold inclusions, as well as solid solution(lattice gold).The molar ratio of x(As)/(x(As)+x(Sb)) of tetrahedrite is above 0.25. The mass fraction of gold of electrum ranges from 73.512% to 80.120%. The mass fraction ratio ofw(Zn)/w(Cd) of sphalerite ranges from 79.82 to 145.33, indicating that the deposit is formed in an epithermal moderate-low temperature environment. Major and trace element features of pyrite and sphalerite indicate that the Xiajinbao gold deposit is a moderate-low temperature hydrothermal gold deposit related to magmatic activities.