Yingchao Liu

Rb-Sr and Sm-Nd Isochron Ages of the Dongmozhazhua and Mohailaheng Pb-Zn Ore Deposits in the Yushu area, southern Qinghai and Their Geological Implications

: Located on the northeast margin of the Qiangtang terrane between the Jinshajiang suture zone and Bangonghu-Nujiang suture zone, the Dongmozhazhua and Mohailaheng Pb-Zn deposits in the Yushu area of Qinghai Province are representative Pb-Zn deposits of the Pb-Zn-Cu polymetallic mineralization belt in the northern part of the Nujiang-Lancangjiang-Jinshajiang area, which are in the front belt of the Yushu thrust nappe system. The formed environments of these two deposits are different from those of sediment-hosted base metal deposits elsewhere in the world. The authors hold that they were formed during the Indian-Asian continental collision and developed within the fold-thrust belt combined with thrust and strike-slip-related Cenozoic basins in the interior of the collisional zone. Studying on the metallogenic epochs of these two deposits is helpful to the understanding of ore-forming regularity of the regional Pb-Zn-Cu mineralization belt and also to the search for new deposits in this region. The age of the Dongmozhazhua deposit has been determined by the Rb-Sr isochron method for sphalerite residues, whereas the age of the Mohailaheng deposit has been determined by the Rb-Sr isochron method for sphalerite residues and the Sm-Nd isochron method for fluorite. The age of the Dongmozhazhua deposit is 35.0±0.0 Ma ((87Sr/86Sr)0=0.708807) for sphalerite residues. The age of the Mohailaheng deposit is 32.2±0.4 Ma ((87Sr/86Sr)0=0.708514) for sphalerite residues and 31.8±0.3 Ma ((143Nd/144Nd)0=0.512362) for fluorite with an average of 32.0 Ma. Together with the regional geological setting during mineralization, a possible tectonic model for metallogeny of the Dongmozhazhua and Mohailaheng Pb-Zn deposits has been established. These two ages are close to the ages of the Pb-Zn deposits in the Lanping and Tuotuohe basins, indicating that it is possible that the narrow 1000-kilometer-long belt controlled by a thrust nappe system on the eastern and northern margins of the Tibetan plateau could be a giant Pb-Zn mineralized belt.

Metallogeny of the Baiyangping Lead-Zinc Polymetallic Ore Concentration Area, Northern Lanping Basin of Yunnan Province, China

The Lanping Basin in the Nujiang-Lancangjiang-Jinshajiang (the Sanjiang) area of northeastern margin of the Tibetan Plateau is an important part of eastern Tethyan metallogenic domain. This basin hosts a number of large unique sediment-hosted Pb-Zn polymetallic deposits or ore districts, such as the Baiyangping ore concentration area which is one of the representative ore district. The Baiyangping ore concentration area can be divided into the east and west ore belts, which were formed in a folded tectogene of the India-Asia continental collisional setting and was controlled by a large reverse fault. Field observations reveal that the Mesozoic and Cenozoic sedimentary strata were outcropped in the mining area, and that the orebodies are obviously controlled by faults and hosted in sandstone and carbonate rocks. However, the ore-forming elements in the east ore belt are mainly Pb-Zn -Sr-Ag, while Pb-Zn-Ag-Cu-Co elements are dominant in the west ore belt. Comparative analysis of the C-O-Sr-S-Pb isotopic compositions suggest that both ore belts had a homogeneous carbon source, and the carbon in hydrothermal calcite is derived from the dissolution of carbonate rock strata; the oreforming fluids were originated from formation water and precipitate water, which belonged to basin brine fluid system; sulfur was from organic thermal chemical sulfate reduction and biological sulfate reduction; the metal mineralization material was from sedimentary strata and basement, but the difference of the material source of the basement and the strata and the superimposed mineralization of the west ore belt resulted in the difference of metallogenic elements between the eastern and western metallogenic belts. The Pb-Zn mineralization age of both ore belts was contemporary and formed in the same metallogenetic event. Both thrust formed at the same time and occurred at the Early Oligocene, which is consistent with the age constrained by field geological relationship.

Building An Independent Pb-Zn Mineralization System Related to Magmatism: A Case Study of Narusongduo Pb-Zn Deposit in Tibet

Five Pb-Zn mineralization types can occur in the compression environment in the world, which include porphyry Pb-Zn mineralization(Zuo et al., 2008), crytoexplosive breccia-type Pb-Zn mineralization(Zhang et al., 2012), Skarn-type Pb-Zn mineralization(Meinert et al., 2005), Manto-type Pb-Zn mineralization(Bonsall et al., 2011) and Vein-type Pb-Zn mineralization(Voudouris et al., 2008). However, nobody has done some research to judge whether these five types Pb-Zn mineralization can form in an independent Pb-Zn mineralization system. A Pb -Zn mineralization belt formed in the northern margin of the Gangdese metallogenic belt in the Tibet plateau(Tang et al., 2012). The Pb-Zn reserves are huge and there many types of Pb-Zn mineralization related to magmatism have been found, which make these Pb-Zn deposits be good examples to answer scientific question above. Narusongduo Pb-Zn deposit, located in the middle-west of the Pb-Zn mineralization belt in Gangdese, is a super large LIU Yingchao, YANG Zhusen, HOU Zengqian, JI Xianhua and MENG Xiangjin, 2014. Building an Independent Pb-Zn Mineralization System Related to Magmatism: A Case Study of Narusongduo Pb-Zn Deposit in Tibet. Acta Geologica Sinica (English Edition), 88(supp. 2): 916-918.