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.

Issues on China Regional Metallogeny

According to geotectonic evolution and regional lithospheric features, the authors proposed six metallogenic domains in China: (1) Tianshan Xingmeng metallogenic domain, (2) Tarim North China metallogenic domain, (3) Qinling Qilian Kunlun metallogenic domain, (4) Yangtze metallogenic domain, (5) South China metallogenic domain and (6) Himalaya Sanjiang metallogenic domain. In this paper, the authors also discuss, on the bases of geotectonic background and metallogenic evolutionary history, some metallogenic features of China: (1) A large percentage of ore formation occurred in paleo continental margins, including continental marginal rift and continental marginal accretionary orogenic belt. The majority of main mineral deposits are discovered on continental margins. (2) Superimposition of mineralization, favored the building up of giant and large mineral deposits, but often made the mineral deposits more complex in composition (associated components), morphology and structure. (3) Mineralization of crust derived anatectic granite is intensive and especially concentrated in the South China metallogenic domain. Mineralizations, including W, Sn and REE, are the products of long and mature development of W Sn polymetal rich earth crust in the metamorphic basement of South China Caledonian fold belt. (4) Epithermal ore forming system is well developed in the southwest part of Yangtze continental block. Ore deposits of Hg, Sb, As, Au, Ag and U densely occur in sedimentary strata of the Late Paleozoic to Triassic. Ge, Tl, Te can also constitute independent ore deposits. (5) Ore formation caused by tectonic dynamic activities is distinctive. Small scale continental blocks of China display intensive activities, which played a widespread and diverse role in ore control. Junctions of faults, synchronous faults, shear zone structure and metamorphic core complex are main ore control structures. (6) The gold mineralization is complex and diversified. The greenstone type gold ores in China were emplaced in the Mesozoic Yanshanian epoch after repeated mineralization and enrichment. As a result, the co product gold constituted 32 % of the gold output of China. (7) The mineralization is characterized by multiple stages and heterogeneity. The metallogenic epoch of China almost covers all geological periods. The general trend, the increase in intensity with time, culminates in Mesozoic Cenozoic and so do the varieties of ores and types of mineral deposits. (8) Ore mineralization culminated on continental margin in the Mesozoic, especially in the Yanshanian orogeny of the east part of China, resulting in the diversity of ores and intensive mineralization. These metallogeny features of China can be generalized as “composite continental metallogenic system”.