Characteristics of Apatite from 160～140 Ma Cu (Mo) and Mo (W)Deposits in East Qinling
East Qinling hosts two types of mineralizaiton deposits: 160～140 Ma porphyry and porphyry-skarn Cu(Mo) deposits, and Mo(W) deposits.This study carried out composition analysis of the apatite collected from the ore-forming rocks.The results show that the apatites in these two deposits are magmatic in origin, although there are some differences between main compositions and volite matters.Apatites from the Mo(W) deposits have higher F/Cl values (81～262) and MnO contents (0.05％ ～0.91％, averaging0.25％) than that of the Cu(Mo) deposits (0.8～25;0.02％～0.18％, averaging0.07％), indicating that the magmatic source of the Mo (W) deposits is distinctly characterized by sedimentation provenance.With the change of geotectonic locations from the southern margin of the North China Plate to the North Qinling orogenic belt and the South Qinling orogenic belt, the F/Cl values and MnO contents of apatites from the metallogenic intrusive rocks decrease gradually, suggesting that the mantle material in magmatic source gradually increased.Meanwhile, mineralization types changed from Mo (W) type to Cu (Mo) type, and this change indicates that the characteristics of the magma source have certain restraints on the mineralization types.In addition, the apatites of ore-forming rocks in the Cu (Mo)and Mo(W) deposits contain various volatile contents, which have a certain selectivity for mineralization elements.Apatites of the Mo (W) deposits have higher F content (2.83％～5.81％, averaging 3.97％)than the Cu (Mo) deposits (0.69％ ～3.76％, averaging 2.78％).And higher F contents can not only improve hydroxyl content in the melt but also increase the partition coefficient of Mo, which then promotes Mo mineralization.Apatites of Cu (Mo) deposits have higher Cl content (0.13％ ～ 1.14％, averaging0.45％) than the Mo(W) deposits (0％～0.04％, averaging 0.03％), which may be related to the Cu occurrence as chloride compound in the fluid phase, and the coefficient distribution of Cu in the melt and fluid presents positively relationship with C1 content.Apatite contents in the Cu (Mo) and Mo (W)deposits are similar with an average SO3 content of 0.17％ , which is consistent with the SO3 content of apatite from the typical porphyry deposits.However, in comparison with typical large and super-large porphyry Cu deposits, ore-forming rocks of Late Jurassic-Early Cretaceous Cu (Mo) deposits in East Qinling have relatively lower SO3 content in apatite;correspondingly, ore-forming magma contains lower oxygen fugacity and S content.This may be one of the reasons resulting in small-scale Cu (Mo)mineralization in East Qinling.
volatile matterapatiteporphyry-skarn Cu (Mo) and Mo (W) depositEast Qinling
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