大兴安岭北东段森林覆盖区岔路口巨型斑岩钼多金属矿床的发现过程及意义

The discovery and exploration process of the Chalukou giant porphyry molybdenum polymetallic deposit in forest-covered area of northeastern Da Higgnan Mountains and its geological significance

岔路口巨型斑岩钼矿的发现是近年来大兴安岭北段森林覆盖区找矿的重大突破,其规模居中国北方钼矿之首。矿床位于伊勒呼里山南1 029高地火山机构旁侧,成矿与晚侏罗世—早白垩世以超浅成相侵入的石英斑岩、花岗斑岩及其相伴产生的隐爆作用有密切时空关系。矿体产于火山沉积岩和成矿斑岩体中,钼矿化以呈网脉状和细脉的裂隙充填形式为主,少量为大脉状和细脉浸染状;钼矿体呈隐伏穹隆状,延深巨大。热液蚀变发育、分带性明显,以硅化强烈、萤石化广泛为显著特征。矿区剥蚀程度甚低,地表大范围表现为泥化带,仅中心地带发育有弱石英绢云母化和低品位钼矿化;向深部蚀变矿化逐渐增强,矿化延深达千米。钼矿体上部共伴生有脉状铅锌银矿化。成矿同期火山岩碱质含量高,该矿床为碰撞拼接后陆内伸展构造环境中岩浆活动产物,成矿岩浆-热液体系具高氟富硫高氧化的特征,与美国的Climax钼矿较为相似。该矿床的发现和探明,为研究斑岩-脉状钼锌银成矿体系提供了范例,对区域构造-岩浆过程研究与区域找矿勘查均具有重要意义。

The discovery of the Chalukou giant porphyry molybdenum polymeatllic ore district,the largest molybdenum ore district in northern China,is a major breakthrough in the exploration work conducted in the forest-covered area within northeastern Da Higgnan Mountains in recent years.This ore deposit is controlled by No.1029 volcanic mechanism located in southern Yilehuli Mountain and its mineralization is spatially and temporally associated with Late Jurassic subvolcanic quartz porphyry,granite porphyry and cryptoexplosive breccias.The dome-shaped ore body,hosted by volcano-sedimentary rocks and mineralized porphyry stocks,is concealed in the depth and has a great deep extension.Stockworks and filling veinlets are main mineralization types in this ore deposit,together with a few lode and veinlet dissemination types.Hydrothermal alterations are developed widely and show obvious zoning,characterized by notable intense silicification and fluoritization.From the surface to the depth of more than 1 500 m,the extent of mineralization and alteration increases gradually from low-grade ores and weak quartz-sericite assemblage surrounded by large-size argillic zone to high-grade ores and intense silicification and potassic alteration assemblage.There are vein-type lead-zinc-silver ore bodies associated with the mineralization system in the upper part of the Mo ore body.Tectonically,this ore deposit was formed by magmatism that originated from an intra-plate extensional environment after collision-collage of plates.The magmatic-hydrothermal system is highly oxidized and remarkably enriched in F and S,which is similar to the feature of the Climax porphyry Mo deposit in the United States.The discovery and exploration of the Chalukou Mo deposit provide an example for research on the transition of porphyry Mo mineralization to vein-type Pb-Zn-Ag mineralization and has significance for the regional ore prospecting work and the study of tectonic-magmatic processes in northeastern Da Higgnan Mountains and adjacent areas.