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 coUisional 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 oreforming 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 ore- forming 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 metaliogenetic 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.

Zinc, copper, and strontium isotopic variability in the Baiyangping Cu–Pb–Zn–Ag polymetallic ore field, Lanping Basin, Southwest China

The Baiyangping Cu-Ag polymetallic ore district is located in the northern part of the Lanping-Simao foreland fold belt,between the Jinshajiang-Ailaoshan and Lancangjiang faults,and the deposit can be divided into eastern and western ore zones.Based upon microscope observation of ore minerals and analysis of zinc,copper,and strontium isotope composition,we conclude that:(1)the zinc isotopic compositions of sphalerite from the eastern and western ore belt of the Baiyangping polymetallic ore deposits are enriched in both the heavy(-0.09‰ to+0.15‰) and light(-0.19‰ to-0.01‰)zinc isotopes.Rayleigh fractionation is likely the additional factor controlling the observed temporal and spatial variations in zinc isotopes in the two studied ore zones.The zinc isotopic composition in the Baiyangping polymetallic Pb-Zn deposits may have the same fractionation as that of magmatic-hydrothermal,VHMS,SEDEX,and MVT deposits,as demonstrated by geological and other geochemical evidence;(2) the range of δ^(65)Cu in massive tetrahedrite is from-0.06‰ to+0.12 ‰ that relates to the early stages of ore-formation,which are higher than that of venial chalcopyrite(from-0.72‰ to-0.07‰)formed at a late ore-forming stage in the western ore belt.Different ore-forming stages and alteration or leaching processes are likely the main factors controlling the observed variations in copper isotopes in the western ore zone;(3) the ^(87)Sr/^(86)Sr value of hydrothermal calcite in eastern(0.7080-0.7093) and western(0.7085-0.7113) ore belt suggested that mineralization of early calcite,with^(87)Sr/^(86)Sr values much higher than in ancient Late Triassic seawater,may be related to recrystallization from a radiogenic Sr-rich or silicifying fluid,either from the strata that the ore-forming fluid flows through or from other fluids.

Geology and isotopic composition of helium,neon,xenon and metallogenic age of the Jinding and Baiyangping ore deposits,northwest Yunnan,China

Both the Jinding and Baiyangping ore deposits developed in the Lanping basin, which is a Mesozoic-Cenozoic terrestrial clastic sedimentary basin. Their occurrences can easily lead many people to compare them with the Pb-Zn deposit hosted in sedimentary rocks, such as Mississippian Valley-, Sedex- and sandstone-type Pb-Zn deposits. However, the Lanping basin developed in the settings of strong tectonic activity of the continental crust, which could cause an effective material exchange between the lower crust and the upper mantle. The orebodies are clearly tectonically controlled without syngenetic features, which probably represents a new type of the sedimentary rock-hosted Pb-Zn deposit. The isotopic compositions of noble gases in ore-forming fluids indicate that 2%32% of helium (3He/4He = 0.19 Ra1.97 Ra) is derived from the mantle, 50.1% of neon (20Ne/22Ne = 10.4510.83; 21Ne/22Ne = 0.03) from the mantle, and considerable amount of xenon (129Xe/130Xe = 5.846.86; 134Xe/130Xe = 2.262.71) from the mantle, which show that mantle fluids played an important role in the ore formation. The ore-forming age of 6760 Ma obtained by Re-Os and 40Ar-39Ar dating methods is later than the host rock, which is coeval with the Himalayan alkali magmatism of the mantle source and mantle-crust source. In this paper, the mineralization of the Jinding and Baiyangping ore deposits is considered to be related to the mantle fluids which move upward with the magma or along the deep faults, and mix with the meteoritic brine in the crust to result in large-scale deposition.

Giant Mineral Deposits and Their Geodynamic Setting in the Lanping Basin, Yunnan, China

There are giant mineral deposits, including the Jinding Zn-Pb and Baiyangping Ag-Co-Cu, and otherimportant mineral deposits (e.g., Baiyangchang Ag-Cu, Jinman Cu deposits, etc.) in the Lanping Mesozoic-Cenozoic Basin, Yunnan Province, China. The tabular ore-bodies and some veins hosted in terrestrial clastic rocks of the Mesozoic-Cenozoic age and no outcropping of igneous rocks in the giant deposits lead to the proposal of syngenetic origin, but the giant mineral deposits are not stratabound (e.g. MVT, sandstone- and Sedex-type). They formed in a continental red basin with intense crust movement. The mineralization is controlled by structures and lithology and occurs in different strata, and no sedimentary nature and no exhalative sediments are identified in the deposits. The deposits show some relations with organic matter (now asphalt and petroleum) and evaporates (gypsum). The middle-low-temperature (mainly 110℃ to 280℃) mineralization took place at a depth of about 0.9 km to 3.1 km during the early Himalayan (58 to 67 Ma). The salinity of ore-forming fluids is surprisingly low (1.6% to 18.0 wt% (NaCl)eq). Affected by the collision of the Indian and Eurasian plates, the mantle is disturbed under the Lanping Basin. The large-scale mineralization is closely linked with the geodynamics of the crust movement, the mantle and mantle-flux upwelling and igneous activity. Giant mineral deposits and their geodynamic setting are unique in the Lanping Basin.