Structural Framework and Ore-Controlling Structures of Jinding Superlarge Lead-Zinc Deposit
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    Abstract:

    Jinding Pb-Zn ore deposit is a superlarge deposit hosted by sedimentary rocks (limestone and sandstone). Based on studies of structures of the mining areas and characteristics of the deposit, this paper discusses emphatically the ores structure types, microstructures and textures of two types of ore bodies (sandstone type and limestone type). It is shown that well-developed fault systems are the basic structural characteristic of Lanping Basin. Along the boundaries and in the basin, pre-mineralization faults with characteristics combined of thin-skinned thrust and nappe structure are developed, which results in large scale reverse and stacking of the stratigraphic column. A syn-mineralization central axis fault zone in NE-NNE direction and with a width of near 3 km consists of zones of structural breccias and lensoids in the basin. It controls the emplacement and distribution of ore bodies or deposits. Post-mineralization normal faulting in NS direction results in the formation of Lanping graben that destroys the ore deposits and denudes them to the surface. Two types of deposits, tabular or layered sandstone type and brecciaed limestone type, are situated respectively in two thrust sheets which are made up of Cretaceous calc-feldspar-quartz sandstones and Triassic asphaltene limestones respectively. Exemplified by Fenghuangshan mining area, Jinding Pb-Zn deposit is of three layers: at the top the Triassic dolomitic limestone cover, at the bottom the limestone type ore body, and the sandstone type ore body between them. Those layers are separated and trapped by two major thrust faults. As the channels where ore fluid migrates upwards during mineralization, several breccia pipes connect ore bodies of the sandstone and limestone types. Fractures and microcracks, massive structure, syntaxial veins and pseudomorphic crystals are the most popular microstructures, which reveal that the processes of fracturing and fragmentation, open space filling and metasomatism play an important role in Pb-Zn mineralization. The formation and emplacement of Jinding Pb-Zn deposit are directly controlled by structural processes. Pre-mineralization thrusting leads to the formation of high pressure mineralizing fluids and gives rise to traps for mineralization. The activity of the central axis fault zone enhances the upward migration of ore fluid. The physical properties of limestone and sandstone (e.g. porosity, permeability and mechanical properties), however, contribute to the differences in mineralization in the two types of rocks and formation of two types of ore bodies. The low permeability and compact limestone is heated and softened by ore fluid. Meanwhile, the high pressure fluid with decreasing temperature results in the cracking of the wall rocks into fine breccia, coarse breccia and fractures. During cracking, mineralizing materials precipitate to cementing the breccias to form limestone type ore bodies. After migrating into the high porosity sandstone through fluid channels, the high pressure fluid disperses in the sandstone and fills the grain boundaries and cracks, and replaces the clastic K-feldspar and calcite cement, forming massive sandstone type ore bodies.

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LIU Junlai, Wang Anjian, Zhai Yunfeng, Xia Haoran, Cao Dianhua, Gao Lan, Xiu Qunye.2009. Structural Framework and Ore-Controlling Structures of Jinding Superlarge Lead-Zinc Deposit[J]. Acta Geologica Sinica,83(10):1376-1387

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History
  • Received:May 06,2009
  • Revised:August 06,2009
  • Adopted:August 06,2009
  • Online: October 19,2009
  • Published: