黑龙江东宁县金厂金矿围岩蚀变和成矿年代学特征

Wall rock alteration and metallogenic chronology of Jinchang gold deposit in Dongning County,Heilongjiang Province

金厂金矿床位于黑龙江省东宁县境内,构造上位于显生宙兴蒙造山带东端,隶属松辽地块。由于缺乏精确可靠的成矿时代和深入的热液蚀变研究,导致前人对该矿床的类型存在不同认识。为深入认识该矿床的类型和形成时代,文章对矿区18#矿体的7个钻孔岩心进行了详细的热液蚀变矿物组合分带和成矿时代研究。结果表明,该矿体在水平方向上和垂向上均存在较为明显的蚀变分带现象;从底部到顶部分别发育钾长石化带、绢英岩化带和青磐岩化带。该分带现象与典型的斑岩型矿床的垂向蚀变分带特征一致,暗示该矿床应为斑岩型;黄铁绢英岩化花岗岩和花岗斑岩脉中的绢云母单颗粒Rb-Sr同位素测年结果分别为(107±5)Ma和(110±3)Ma,表明成矿时代发生在110Ma左右。这与花岗斑岩脉中锆石获得的(113±2)Ma的U-Pb年龄一致,进一步支持该矿床类型为斑岩型金矿的结论。根据目前矿区矿体剥蚀情况来看,斑岩体尚未出露,深部仍有很大的找矿前景。

The Jinchang gold deposit, located geographically in eastern Heilongjiang Province and tectonically at the easternmost portion of the Central-Asian Orogenic Belt, is one of the important gold districts in eastern Jilin- Heilongjiang provinces. Mesozoic granitic intrusions and hydrothermal rocks related to gold mineralization are widespread in this region. Although numerous researches have been undertaken on this deposit, its genetic type, age and tectonic setting remain controversial, mainly because of the lack of precise and reliable geochronological data. Vertical and lateral hydrothermal alteration zoning of potassic, phyllic, propylitic and argillic minerals can be observed within and around the porphyry granite. These hydrothermal characteristics are similar to things of the typical porphyritic deposits. Sericites seperated from the pyrite-phyllic altered granite （with Early Mesozoic U-Pb ages） and porphyry granite yield Rb-Sr ages of ca. 110 Ma or so, and zircons from the porphyry granite yield a U-Pb age of （113 ± 2） Ma （2σ）. Therefore, the timing of the main gold mineralization in the Jinchang gold deposit is constrained around 110 Ma and the porphyry granite is spatially and temporally associated with gold mineralization. The denudation of the ore bodies indicates that the porphyry granite has not been exposed at the surface and the prospecting potential at depth is great.