青海西部祁漫塔格地区主要矽卡岩铁多金属矿床成矿地质背景和矿化蚀变特征

青海西部祁漫塔格地区矽卡岩铁多金属矿床分布广泛,目前已成为中国西部最重要和最有找矿潜力的矽卡岩铁多金属成矿带.在大地构造上,该地区属东昆仑造山带；成矿主要与印支期(204～237Ma)闪长岩、花岗闪长岩和二长花岗岩有关；控矿地层包括蓟县系狼牙山组大理岩、硅质岩,奥陶系-志留系滩间山群大理岩、碎屑岩、硅质岩、中-基性火山岩和石炭系结晶灰岩、碎屑岩等.区内发育3类矽卡岩,即钙矽卡岩、镁矽卡岩和锰质矽卡岩,以前者为主.钙矽卡岩常伴生Fe、Cu、Mo(Pb,Zn)矿化,镁矽卡岩主要伴生Fe矿化,锰质矽卡岩则伴生Pb、Zn(Ag)矿化；矿石矿物组合多种多样,矿化具有一定的分带性.内接触带侵入岩广泛发育钾长石化,与矽卡岩类型一起构成该类矿床的重要找矿标志之一.

Metallogenic setting and mineralization-alteration characteristics of major skarn Fe-polymetallic deposits in Qimantag area, western Qinghai Province

Fe-polymetallic skarn deposits are widely distributed in the Qimantag area of western Qinghai Province. Recently, this area has become a major metallogenic belt with most promising ore potential. Geotectonically, it belongs to Eastern Kulun orogenic belt. Mineralization is related to Indosinian (204~237 Ma) diorite, granodiorite and mozonitic granite. Ore-controlling strata are composed of marble and silicalite of middle Proterozoic Langyashan Formation, marble, clasolite, silicalite and andesite-basaltic volcanic rocks of Ordovician-Silurian Tanjianshan Group, and crystalline limestone and clasolite of Carboniferous period. In the ore deposits, three types of skarns are developed, i.e. calcic, magnesian and manganoan types, with the first type being dominant. Calcic skarn is commonly associated with Fe, Cu, Mo, (Pb, Zn) mineralization, magnesian skarn is mainly associated with Fe mineralization, and manganoan skarn is always associated with Pb, Zn (Ag) mineralization. Mineral assemblage of the ores is extremely varied and has certain zonation. Potassic metasomatic phenomena are very entensive in the endo-contact zones of the deposits. In addition to different types of skarns, potassic metasomatism also constitutes one of the important ore-searching indicators.