Genesis and prospecting potential of Yangchang phosphorus deposit in north-eastern Yunnan Province
The Yangchang phosphate deposit in Zhenxiong County has been confirmed as a super-large hidden phos-phate deposit,and the explored resource is exceeding 2.7 billion tons and potential resource exceeding 10 billion tons.The phosphate orebodies occur in a set of phosphorous-bearing in the middle part of a carbate-argillaceous clastic sedimentary Formation of the Cambrian Newfoundland System Meishucun Formation.The lithology is dominated by phosphorous rock and phosphate rock,with a small amount of phosphorous-bearing dolomite and siliceous dolomite.The occurrence of the orebodies are consistent with that of the stratum,and it is distributed in layered and/or quasi layered that occurred in two sides of the Yangchang broad anticline with nearly East-West ex-tension.The drilling data indicate that the average thickness of the orebodies is 34 m,the average grade of phos-phorus w(P2O5)is 24.3％,and the buried depths are 450～1500 m.The dominant mineral phase,fluorapatite(collo-phanite),is formed in a closed or semi-closed sea and precipitates near the REDOX interface of seawater.The metallogenic process includes three stages:biochemical deposition,diagenesis and physical enrichment.Previous studies have shown that the phosphate deposit formed in a semi-enclosed shallow platform facies of the Zhaotong shelf in a passive continental margin of eastern Yunnan,which is controlled by paleostructure,sedimentary pa-leoenvironment,and lithofacies or paleogeographic conditions.Stratigraphic and structural ore control effects are obvious.Comprehensive study of metallogenic geological background,ore genesis,ore control factors and region-al metallogenic geological conditions,the authors views that the Zhenxiong-Weixin region where Yangchang phosphate deposit is located has great prospects and resource potential based on the similar sedimentary facies and stratigraphic sequence.This study provides theoretical basis and comparative clues for prospecting for phos-phate deposits in the Early Cambrian marine sedimentary facies in this region.
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