Geochemistry of Platinum Group and Rare Earth Elements of the Polymetallic Layer in the Lower Cambri

来源 :Acta Geologica Sinica(English Edition) | 被引量 : 0次 | 上传用户:linyuan0213
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The black shales of the Lower Cambrian Niutitang Formation in Weng’an,on the Yangtze platform of south China,contain voluminous polymetallic sulfide deposits.A comprehensive geochemical investigation of trace,rare earth,and platinum group elements(PGE) has been undertaken in order to discuss its ore genesis and correlation with the tectono-depositional setting.The ore-bearing layers enrich molybdenum(Mo),nickel(Ni),vanadium(V),lead(Pb),strontium(Sr), barium(Ba),uranium(U),arsenic(As),and rare earth elements(REE) in abundance.High uranium/ thorium(U/Th) ratios(U/Th>l) indicated that mineralization was mainly influenced by the hydrothermal process.TheδU value was above 1.9,showing a reducing sedimentary condition.The REE patterns showed high enrichment in light rare earth elements(LREE)(heavy rare earth elements (HREE)(LREE/HREE=5-17),slightly negative europium(Eu) and cerium(Ce) anomalies(δEu=0.81- 0.93),and positive Ce anomalies(δCe=0.76-1.l2).PGE abundance was characterized by the PGE-type distribution patterns,enriching platinum(Pt),palladium(Pd),ruthenium(Ru) and osmium(Os).The Pt/Pd ratio was 0.8,which is close to the ratios of seawater and ultramafic rocks.All of these geochemical features suggest that the mineralization was triggered by hydrothermal activity in an extensional setting in the context of break-up of the Rodinian supercontinent. The black shales of the Lower Cambrian Niutitang Formation in Weng’an, on the Yangtze platform of south China, contain voluminous polymetallic sulfide deposits. A comprehensive geochemical investigation of trace, rare earth, and platinum group elements (PGE) has been undertaken in order To discuss its ore genesis and correlation with the tectono-depositional setting. The ore-bearing layers enrich molybdenum (Mo), nickel (Ni), vanadium (V), lead (Pb), strontium (Sr), barium uranium (U), arsenic (As), and rare earth elements (REE) in abundance. High uranium / thorium (U / Th) ratios (U / Th> 1) indicate that mineralization was primarily influenced by the hydrothermal process. was above 1.9, showing a reducing sedimentary condition. REE patterns showed high enrichment in light rare earth elements (LREE) (heavy rare earth elements (HREE) (LREE / HREE = 5-17), slightly negative europium (Eu) and cerium (Ce) anomalies (δEu = 0.81- 0.93), and positive Ce anomalies (δCe = 0.76-1.l2). PGE abundance was characterized by the PGE-type distribution patterns, enriching platinum (Pt), palladium (Pd), ruthenium (Ru) and osmium (Os). The Pt / Pd ratio was 0.8, which is close to the ratios of seawater and ultramafic rocks.All of these geochemical features suggest that the mineralization was triggered by hydrothermal activity in an extensional setting in the context of break-up of the Rodinian supercontinent.
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