Preliminary study on mineralization of metamorphic crystalline graphitite in Jiaobei area
This study involved field observations,petrographic analysis,major and trace element analysis,original rock restoration and graphite Raman spectroscopy on the graphite-bearing khondalite in the Pingdu Dajinbu,Pingdu Dongshiling,Laixi Nanshu mining area,as well as the Laixi Dongbaishi and Panggezhuang where is the adjacent area to the Nanshu,the studied areas are all within the Pingdu-Laixi crystalline graphite-forming belt of the Jiaobei massif.The protoliths of the studied graphite-bearing khondalite are all clay or shale rocks,and they exhibit the characteristics of a marine sedimentary environment.Graphite-bearing khondalite in the Nanshu graphite mining area formed in an island arc environment,whereas,those graphite-bearing khondalite from the Dajinbu,Dongshiling and Dongbaishi formed in the active continental margin,besides,the Pangezhuang graphite-bearing khondalite display geochemical characteristics of passive continental margin.As a result,these graphite-bearing khondalite are all sedimentary products which formed in different tectonic evolution stages of the Jiao-Liao-Ji orogenic belt.The crystallization degree of the flake graphite in graphite-bearing khondalite is high,and the Raman spectrum characteristics of the graphite are in accordance with the graphite formed under metamorphic conditions of the granulite facies rock.The petrographic and Raman spectrum analysises indicate that high-crystallinity graphite should be formed during the melt-cooling stage after the temperature peak stage of the metamorphism.Field outcrops and thin section characteristics of the graphite-bearing khondalite indicate that the universality of anatexis or migmatization,and the crystallization of high crystalline graphite is closely related to high temperature-ultra-high temperature metamorphism,and the studied graphite-bearing khondalite has recorded a kind major mineralization in flake graphite deposits,it is anatexis.The metamorphic age of about 1850～1830Ma not only represents the timing of anatexis or migmatization caused by decompression and exhumation in the Jiao-Liaoo-Ji Belt,but also the main period of high-crystallinity graphite crystallization,mineralization in the Pingdu-Laixi graphite metallogenic belt.
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