内蒙古拜仁达坝铅-锌-银矿床:元素分带及其成因

Bairendaba Pb-Zn-Ag Polymetallic Deposit in Inner Mongolia: The Mineralization Zoning and Its Origin

内蒙中东部拜仁达坝矿床是一个以石炭纪石英闪长岩及锡林浩特杂岩为赋矿围岩的断裂充填型热液脉状铅-锌-银多金属矿床。矿床分东西两个矿段,拜东矿区1号矿体及拜西矿区3号矿体是矿床的主要矿体。矿体沿着走向方向具有明显的矿化分带特征,锌-铜矿石、锌矿石及铅-锌-银矿石依次从矿化中心向外侧产出。代表性矿体拜东矿区1号矿体的块段金属量、平均品位及元素比值由西向东沿着走向方向显示出明显而系统的变化规律。锌的块段金属量由西向东逐渐减少,铅和银的矿段金属量则先增加后下降;锌的块段平均品位由西向东逐渐降低,铅和银的块段平均品位则先上升随后下降;Ag/Pb值先上升随后下降,Ag/Zn和Pb/Zn值则逐渐上升。这种矿化的分带性可能是成矿热液在中偏高温向低温演化的过程中,沿着矿体的走向方向从矿化中心向外侧运移,在矿体不同位置有选择地将成矿物质卸载的结果。而成矿热液在断裂系统内与不同比例大气水的混合则可能是成矿系统内温度梯度形成的重要原因。矿床中不同位置的矿物组合记录了成矿热液中硫逸度由高向低,pH值由低向高的演化过程。拜仁达坝矿床与邻近的维拉斯托矿床组成了一个由温度场控制的具有明显矿化分带现象的低硫化热液脉状多金属成矿系统。

The Bairendaba ore deposit in central-east Inner Mongolia, China is a vein type deposit filled in faults of the Xinlinhot complex and Bairen quartz diorite. The deposit is divided into two parts. east Bairendaba and west Bairendaba. The No. 1 vein in east Bairenda and the No. 3 vein in west Bairenda are the main veins in which more than 77% ore of the deposit occurs. The ore bodies show obvious mineralization zonation, with Cu bearing ores in the central and Pb - Zn - Ag ores in the external parts. Metal tonnage, grade and ratio in varied ore blocks in No. 1 vein change systematically along the strike. The tonnage and grade of zinc in each ore block decrease from west to east, and the tonnage and grade of lead and silver of each ore block increase first and then decrease gradually. The Ag/Pb ratio of each block rises first and then increases gradually while the Ag/Zn and Pb/Zn ratios increase gradually. This regular and systematic variation is a reflection of cooling processes of the moderate to hightemperature ore-forming fluids from west to east. Such a temperature distribution along the ore- controlling faults is the products of imbalance mixing of medium to high temperature ore-forming fluids with cold meteoric water and the cooling process was accompanied by the selective deposition of metallogenic materials in the faults. The mineral assemblages observed in different ore blocks record decreasing logf（S2）, and increasing PH changes in deposit, together with Weilasituo Zn- Cu-（W） ore of low sulphidation. the ore-forming fluids. Bairendaba Pb - Zn - Ag ore deposit, makes up a zoned vein metallogenic system