Abstract:

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 high temperature 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 the ore-forming fluids. Bairendaba Pb-Zn-Ag ore deposit, together with Weilasituo Zn-Cu-(W) ore deposit, makes up a zoned vein metallogenic system of low sulphidation.

Key words: vein type deposit, element zonation, ore genesis, Bairendaba, Central-East Inner Mongolia, ore deposit