Fengjun Nie

The Bairendaba and Weilasituo Polymetallic Sulfide Ore System of Inner Mongolia, China: the Role of Metal Fractionation in the Genesis of Zonation

deposits are located in south Great Xing’an Range, Inner Mongolia, China. They occur as zoned veins within fractures cutting the older Xilinhot metamorphic complex. Weilasituo lies on the west sector. Bairendaba lies 4 kmto the east of Weilasituo. The main alteration assemblage in both deposits is quartz-sericite-fluorite, and this is controlled by fractures in the vicinity of sulfides veins. The sulfides ores in these two deposits are massive, and consists mainly of pyrrhotite and dark Fe-rich sphalerite, with an assemblage comprising variable proportions of chalcopyrite, galena, and minor Agbearing minerals. Two predominant sulfides mineralization stages are recognized. During the early stage, sub-economic intermediate-sulfidation state euhedral pyrite and arsenopyrite were deposited. This was followed by the main stage of ore genesis which was characterized by low-sulfidation state fluids depositing pyrrhotite, Fe-rich sphalerite, chalcopyrite, galena and minor Ag-bearing minerals. The Weilasituo and Bairendaba deposits have metal zonation which follows the strike of the veins. The western part of the Weilasituo deposit is more copper-rich and the eastern part is more zinc-rich. The central zone of the Bairendaba deposit comprises Cu-bearing zinc sulfide and this deposit is zoned outwards to Zn-rich ores which are devoid of Cu, and then into zinc-lead-silver ores which dominate the outer part. There are three major veins in the Weilasituo and Bairendaba deposits, namely the #1 Zn-Cu vein at Weilasituo, the #3 Zn-Pb-Ag vein at west Bairendadba and the #1 Zn-Pb-Ag vein at east Bairendadba; together, these veins contain more than 50 wt.% of the metals contained in these two deposits. The metal tonnage, metal grade and metal ratios of these three major veins display systematic and gradual metal zonation pattern from west of Weilasituo to east Bairendaba. The metal zonation data indicates that these two deposits were formed from the same hydrothermal ore forming system, and represent two upstream and downstream end-numbers respectively, where the oreforming fluid laterally flowed from west to east. The quantitative metal zonation patterns are consistent with metal-bearing fluid entering the system to precipitate chalcopyrite in proximal setting and sphalerite and Agbearing minerals in more distal settings. There is no evidence to suggest that the metal zonation pattern of the two deposits resulted from superimposition of different hydrothermal activities; rather, the zonation results from metal deposition accompanying the evolution of a metalbearing fluid along the strike of the vein. The temperature gradient between the inflow zone and the outflow zone may be a key factor controlling this process. LIU Yifei, NIE Fengjun, JIANG Sihong, 2014. The Bairendaba and Weilasituo Polymetallic Sulfide Ore System of Inner Mongolia, China: the Role of Metal Fractionation in the Genesis of Zonation. Acta Geologica Sinica (English Edition), 88(supp. 2): 101.

Geological Features and Ore Genesis of the Ag‐Pb‐Zn Deposits Occurring in Tsav‐Jiawula Region along the Sino‐Mongolian Border

The Tsav-Jiawula region lies along the southeastern part of the central Mongolia-Argon Pre-Meso zoic metamorphic massif, which is located at northeastern part of the northern China-Mongolia block (NCMB) (Hu et al., 1998; Nie et al., 2011). Ag and Ag-Pb-Zn deposits are widely distributed both in Pre-Mesozoic metamorphic rocks and Mesozoic volcano-sedimentary rocks, but all of them are spatially and temporally associated with Mesozoic felsic intrusive dykes and stocks. At present, twenty-three deposits have been identified. Amongst them, the Tsav, Erentaoregai Tsagenbulagen and Jiawula deposits are well known for their large-tonnage, high ore grade and unique geological features (Hu et al., 1998; Nie et al., 2011). Three geological units were recognized in the region. (1) The Argon Group is the oldest units in the region, and constitutes a major part of the Mongolia-Argon massif (MIT, 2002). (2) The Cambrian-Ordovician strata mainly crop out in the Erentaoregai district. Permian basalt, andesite, rhyolite, tuff, slate and sandstone are distributed in the Jiawula and Tsagenbulagen districts. (3) Jurassic volcano-sedimentary rocks occur as a widely spread “blanket” covering the whole Tsav-Jiawula region. The region has experienced multiple phases of deformations since the Early Paleozoic (Nie et al., 2011). The ArgonHulun deep-seated fault and the subsidiary Muhaer fault zone transect the region. Faults and fractures strike nearly NE, NNE, SN and NNW. Of the fracture zones, the NNEtrending faults and associated fractures are the most spectacular features (Hu et al., 1998). During the Yanshanian orogeny, the large-scale fault zones were reactivated, accompanied by the emplacement of the granitoid magma that resulted in the formation of these Ag and Ag-Pb-Zn deposits and prospects. It has been noted that some of the Yanshanian granitoid dykes and stocks have intimate spatial and temporal relations with the Ag and Ag-Pb-Zn mineralization (Hu et al., 1998; Nie et al.,2011).

Geological Characteristics and Origin of the Hashitu Molybdenum Deposit, Inner Mongolia, China

The Hashitu molybdenum deposit is one of many large sized porphyry molybdenum deposits in Inner Mongolia, and the molybdenum grade of its ores is in a range of 0.08-0.36%, averaging 0.129%. It is located in Xinlin Town of Linxi County, Chifeng City, Inner Mongolia. its geographic coordinates are as follows: 44°03′30′′-44°05′ 30′′N and 117°58′00′′-118°05′00′′E. From the view point of tectonics, it is within a Late Paleozoic accretion orogenic belt between the West Lamulun River fault and the Hegenshan fault (suture) in the central-southern Da Hinggan Mountains(Nie et al., 2007; Ma et al., 2009). Intrusions, especially Middle Hercynian to Late Yanshanian intrusions, are widespread in the ore district. And the Hercynian-Indosinian intrusive rocks are mainly a series of granodiorite that intruded into the Carboniferous strata. The Yanshanian intrusive rocks mainly include medium-fine grained porphyritic biotite granite, graniteporphyry, medium-grained moyite, and quartz monzonite porphyry, of which the medium-fine grained porphyritic biotite granite and granite-porphyry are the main host rocks of the Hashitu molybdenum deposit(Zhang et al. 2012).