Geochemical Characteristics and Genesis of Crystalline Graphite Ore Bed Rocks in Northern Hebei Province
Crystalline graphite is an emerging strategic mineral.In recent years,several large-and medium-sized crystalline graphite deposits have been found in northern Hebei Province,with great mineralization potentiality in this area.The main ore-bearing horizons are Neoarchean Upper Chonglishang Group and Paleoproterozoic Hongqiyingzi Group.Through systematic field geological survey,sampling,analysis and testing,the petrography and geochemical characteristics of the ore-bearing horizon were studied in detail,and the carbon source was analyzed.The results showed that the main host rocks were graphite-bearing biotite plagioclase granulite,graphite-bearing biotite plagioclase gneiss,and graphite-bearing biotite plagioclase diopsides.The proto-rocks restoration are mainly argillaceous clastic and calcareous sedimentary rocks.The contents of main elements in graphite bearing strata vary greatly,with SiO2 content of 38.90%～80.42%,CaO+MgO of 2.05%～31.93%,and Al2O3 of 1.50%～15.34%.The content of rare earth elements is 79.1～321.4 μg/g.PAAS standardized distribution pattern generally has the characteristics of right leaning or relatively flat distribution.Some samples have slightly δCe negative anomaly and δEu anomaly.The characteristics of trace elements indicate that the sedimentary environment is a coastal and shallow sea environment,with oxygen rich conditions in some areas,reduction environment or hydrothermal addition in some areas.The carbon isotope value of graphite is-26.0‰ to-20.7‰,which mainly comes from biogenic organic carbon.The carbon isotope value of marble ranges from-3.8‰ to 1.1‰,mainly derived from inorganic carbon of carbonate origin.The crystalline graphite ore bed in the area is controlled by stratum,lithology and lithofacies.The favorable ore bearing horizon is sandy argillaceous clastic rock and calcareous sedimentary rock rich in organic matter in the coastal shallow sea facies of the ancient continental margin.The deposit is a sedimentary metamorphic deposit.
northern margin of North China Plategraphite oregeochemistrytrace elementisotope of carbon
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