| Xiao chagou graphite ore in Zhenping county of henan province is located in Zhu yangguan-Liu quanpu metallogenic belt, the ore-bearing strata is crystalline schist. Ore type is simple and the basic ore is calcareoussparrygrapholite, graphite is sparryscalelike. Granite of mining area with high silicon and potassium is a kind of peraluminous rock,and it is I-type granite. Chondrite standardized rare earth element distribution curve shows the "V" shaped rightist trend.The light rare earth element distribution curve is steep and the slope is bigger, the heavy one is slower and the slope is smaller. The magma derives from the continental crust remelting. The metamorphic rocks’ Si O2 content is not very high and its Ca O content and loss on ignition(LOI) value is high,which shows the original rocks may be calcareous sedimentary rocks that has the characteristics of carbonate rocks. The ratio of Rb/Sr is low and it has a loss of Ba phenomenon,whichindicates that the sample may be from the marine sediments. Fractionation between light and heavy rare earths is obvious and the phenomenon of negative Eu anomaly happens. Graphite ore zircon SHRIMP U-Pb test results show that 206Pb/238 U age is between 440.0±4.9-2147±21Ma and age span is large, reflecting the formation of metamorphic rocks zircon is a long geological evolution.Thus it shows that graphite mine is not formed in a short term and it has undergone a lengthy process of forming. According to the occurrence of the strata in the mining area, the characteristics of rocks and mineral assemblages,chemical characteristics and the related graphic,mining area metamorphic rocks may be from the sedimentary clay sand, clay, calcium carbonate sediment with the carbon sandwich,which is likely to be in frequent oscillation sea water environment, the original rocks are formed in the environment of passive continental margin. The δ13C value of graphite ore samples is ranged from-17.3x10-3 to-18.1x10-3, and looks similar to theδ13C value of organic carbon and different from the inorganic carbon, which indicates that graphite carbon is mainly from organic carbon deposition.The mineralization mechanism of the Xiao chagou graphite ore is: in the process of regional metamorphism, under the action of temperature, pressure and metamorphic solution, carbon formation change original organic carbon gradually to the graphite formation. With the increase of regional metamorphism and late granite intrusion, which makes the carbonate produce some carbon.The dioxide from granite also provides new carbon graphite formation. The above several kinds of carbon underthe action of migration, relatively concentrated, recrystallization forms crystalline graphite deposit today. In a word, the causes of formation of Xiao chagou graphite ore is mainly under the action of diagenismand the late overlay of granite. Xiao chagou graphite ore is a polygenetic deposit that experienced the progress of sedimentation- metamorphism, magmatic hydrothermal. |
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