Genesis and Chromogenic Mechanism of Dushan Jade Ore of Nanyang in Eastern Section of East Qinling Mountions
Dushan jade is produced in a vein shape in the Dushan gabbro of Nanyang City.Taking dry white jade,green white jade,purple jade,black jade and polychromatic mixed jade as representative sam-ples,the mineral composition and microstructure of the samples are studied,and the genesis,chromogenic mechanism and geodynamic mechanism of Dushan jade are discussed.The results show that the subduction of Shangdan Ocean stretched the back arc and formed the Erlangping back arc ocean basin.Due to subduc-tion fluid replacement,the mantle wedge partially melted and formed the original mafic magma of Dushan gabbro.The stratified gabbro protolith was formed by the accumulation of magma crystals.Through the early dynamic metamorphism and the late hydrothermal metamorphism,the minerals in the protolith were altered and recrystallized to form Dushan jade.Its color is related to the mineral composition and the distribution of trace elements.Higher plagioclase content,smaller average particle size,lower phenocryst content,closer combination,and greater transparency result in lighter Dushan jade.Higher zoisite content leads to white Dushan jade,while elevated levels of dark minerals like amphibole,diopside,and tremolite produce black Dushan jade.Trace elements such as Cr3+,Fe3+,Fe2+,Ti4+and Mn3+impart green,purple,yellow and red hues to Dushan jade,respectively.
Dushan jadeDushan gabbrogenesis of depositchromogenic mechanism
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