Mineral Chemistry And Their Implications For Petrogenesis And Mineralization Of The Ore-bearing Porphyry In Zhongdian Arc In Northwestern Yunnan,China

The Zhongdian arc is located at the southern margin of the Yidun island arc within the Sanjing-Tethyan tectono-magmatic belt in China.The Indosinian intrusive suites in this region,generated through the subduction of the Ganzi-Litang Ocean,are associated with a variety of mineralized plutons?eg.PL and LD?and also barren plutons?eg.SN?.Most of the previous studies were focused on the petrological,chronological and geological features of those plutons.In this paper,the major and trace element concentrations of minerals,such as plagioclase,biotite,amphibole,apatite and titanite,measured by EPMA and LA-ICP-MS techniques,are used to investigate the intensive variables of these magmatic intrusions with a view to constrain their petrogenesis and mineralization potential.Our EPMA data show that plagioclase,biotite and amphibole from east belt the mineralized PL and LD and barren SN quartz monzonite porphyries classify as andesine and oligoclase,hornblende species and “Mg biotites”,respectively.LA-ICP-MS data show that REE distribution patterns of plagioclase from PL,LD and SN are overall smooth and their fractionation between LREE and HREE is not obvious.?REE of plagioclases are significantly lower than the whole rock but Sr and Lu concentrations are higher in plagioclases.As compared to the whole rock in all three regions,?REE of amphibole is higher and has more obviously Eu negative anomaly.REE distribution patterns are the right type.Analyses of REE suggest that?REE of biotites are less than 5%?w/w?of the whole rock in all three regions.Trace elements analyses illustrate that biotite is an important carrier of Rb,Ba,K,Ti,Nb,Ta in comparison with host rocks.The mineral chemistry of biotites show that,All the representative biotites analyzed in this study are crust-mantle mixed source causes and fall in calc-alkaline orogenic fields.However,the quartz monzonite porphyry from PL formed under condition of higher temperature and oxygen fugacity,and it has a higher degree of differential evolution compared with porphyry copper deposit from LD and SN.The results also show that biotites from PL have higher XMg,SiO₂,TiO₂ and F content and lower FeO,Al₂O₃ and MnO content than those from LD or SN.?REE and Rb,Hf and Cr contents in biotites from PL are higher than those from LD and SN.Amphiboles from PL deposit have higher Al₂O₃,TiO₂,FeO,CaO,Na2 O and K2 O content but lower SiO₂ and MgO content.The apatite from PL deposit is characterized by relatively higher F and lower SO3 content and Ce₂O₃/ Y₂O₃ ratio than those from LD or SN.The halogen chemistry of biotite from PL is distinctly different from that those from LD or SN by its lower IV?F?and IV?Cl?but higher IV?F/Cl?.Moreover,Cu concentration is higher?>10×10-6?in mineralized plutons from PL or LD than in barren plutons from SN.And there is a remarkable negative linear relationship?|r|>0.8?between log?f HF/f HCl?and log?f H2O?/?f HF?ratios from the mineralized PL and LD plutons,which significantly differentiates them from barren SN intrusion.