Ore Genesis And Tectonic Settings Of Lishan Polymetallic Deposit In Tianbaoshan Metaltogenic Region, Yanbian Area

The Tianbaoshan polymetallic metallogenic region in Yanbian area is an old minewhich has a century of history. There mainly occur four mineralization types including thesedimentary-hydrothermal, contact metasomatism （skarn-type）, hydrothermal veins andporphyry type. Such polymetallic deposits have been discovered as Lishan, Xinxing,Xuanchanghoushan, Dongfengnanshan and Dongfengbeishan. The Lishan polymetallicdeposit is a typical skarn-type polymetallic deposit, and the ore-forming fluid isH₂O-CO₂-CH₄-NaCl system with low-medium temperature, low density, and mediumacidity. The polymetallic mineralization was controlled by the medium acidic,rich-siliceous and intensive reducing condition.The metallogenic diorite intrusion mainly consists of plagioclase, quartz, biotite andsmall amount of opaque minerals, with fine-grained hypidiomorphic texture and massivestructure. It belongs to the I-type granite series rich in sodic and calcium-alkaline.Moreover, they are rich in large ion lithophile elements （LILE） and Th, but depleted of thehigh field strength elements （HFSE） and Nb, Ta, reflecting that the metallogenic intrusionhas the similar geochemical characteristics with those in and the subduction zone, that is ina right tilt map’s form, enrichment in LREE, depletion of HREE, low in total REE andanomalies in positive Eu, indicating that the source of the rock body is the pluton in lowercrust or mantle. Generally speaking, we can conclude that the metallogenic intrusion wasresulted from the upper mantle contaminated by the crust.The zircon U-Pb dating results of the metallogenic diorite intrusion show that the emplacement age of the rock body is261.0±7.0Ma，which represents the age of Lishansharn-type deposit, which indicates that the mineralization occured in the mid-Permianperiod. Combined with diagenesis-mineralization age and geochemical characteristics, anconclusion can been drawn that the metallogenic rock body and associated mineralizationwere formed in the subduction tectonic settings of the northward subduction of the PaleoAsian Oceanic Plate. In other words, Lishan skarn-type polymetallic deposit was derivedfrom the magmatic activity that was resulted from the subduction of the Paleo Asian Oceanto continental crust.