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Comparison on elemental and isotopic geochemistry of ore-bearing and barren porphyries from the Yulong porphyry Cu deposit,east Tibet.

JIANG YaoHui JIANG ShaoYong DAI BaoZhang LING HongFeiState Key Laboratory for Mineral Deposits Research,Department of Earth Sciences,Nanjing University,Nanjing 210093,China  
Geological and geochemical comparison studies indicate that the ore-bearing and barren porphyries in the Yulong porphyry Cu deposit were derived by different degree partial melting of the vein of phlogopite-garnet clinopyroxenite in an lherzolitic lithosphere. The ore-bearing porphyry represents the earliest melt derived by partial melting of accessory phases such as apatite and carbonate and hydrous mineral of phlogopite,and thus contains high contents of volatiles such as F,Cl and water,which is preferred for Cu to be extracted and enriched.The barren porphyry is the product at relatively high degree partial melting involving clinopyroxene and garnet, and thus depleted in volatiles,which makes it to be evolved as barren one.F and C1 contents (F1200 ppm,Cl150 ppm for ore- bearing porphyry and F1200 ppm,Cl150 ppm for barren porphyry) and K_2O/Na_2O (1.2 for ore-bearing porphyry and 1.2 for barren porphyry),Sm/Yb (6.5 for ore-bearing porphyry and 6.5 for barren porphyry) ratios of porphyries and Fe~(3+)/Fe~(2+) ratios (0.7 for ore-bearing porphyry and 0.7 for barren porphyry) of biotite are the important geochemical paralneter to discriminate ore-bearing and barren porphyries.The ore-bearing porphyries share similar Sr-Nd-Pb isotopic compositions as the barren porphyries,suggesting they have similar source regions.
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