Chronology,Geochemical Characteristics And Genesis Of The Xiaodouling Graphite Deposit In Xichuan County,Henan Province

Xiaodouling graphite deposit in Xichuan county Henan province locates in South Qinling tectonic zone,which at the south side of Shangnan and Danfeng fracture belt.It’s one of the important tectonic units in boundary block between north China and Yangtze plate,belongs to the crystalline basement margin type in Xixia-Tanghe-Pohe early proterozoic metamorphic belt.Deposit has the characteristics of mobile belt type,distributes in line. Graphite flake is tiny as medium temperature and pressure regional heat flow metamorphism type.Graphite plagioclase gneiss, containing graphite plagioclase gneiss and graphite(plagioclase) schist are natural types of graphite ore.According to si-(al+fm)-(c+alk) and Zr/Ti O2- Ni graphical points of geochemical protolith restoration,obtains gneiss protolith is a set of argillaceous and silty sedimentary formation containing carbon and rich aluminium, and the sedimentary differentiation is distinct.Summarize geochemistry analysis of major elements, trace elements and rare earth elements,deformation and metamorphism at active continental margin as arc type in Neoproterozoic is related to arc hyperplasia orogenic event in northern Yangtze plate.The evidences as follows:For major elements, the plagiogranite sample point falls into I granite area on magmatite origin type discrimination diagram,shows as earthcrust remelted granite.It falls into VAG(volcanic arc granite) or IAG(island arc granite) on the granite tectonic environment discrimination diagram.Above 2 suggests that it formed in the active continental margin tectonic environment.For trace elements, the plagiogranite sample shows rich on K, Rb, Ba, Th such LIL(large ion lithophile elements), loss on Nb, Ta, Ti, P such HFS(high field strength elements), low Y and Yb on the primitive mantle standardization spider diagram.This indicates that it has typical characteristics of island arc formation.We infer that it should be formed in the active continental margin environment as island arc type.For rare earth elements geochemical characteristics,gneisses have characteristicsof depositional greywacke which takes dissected magmatic arc as source area.This reflects that it takes continental island arc as the depositional environment.The gneiss sample points fall into island arc area on tectonic environment discrimination diagram can prove it.According to the zircon U-Pb dating and geochemical analysis, Early proterozoic amphibolite facies graphite deposit metallogenic mechanism can be summarized as follows:the palaeocontinent lifted the dissociated in 2248±23 Ma(206 Pb / 238 U age)ago,generated shallow sea and semi-closed bay,then craton basin accepted deposits,sand-mud and carbonate rocks began to deposit in rift environment,the original rocks of khondalites were formed.2.0?1.8Ga ago,Continent and continent collided, the basin closed.Khondalites involved in the lower crust, then amphibolite facies medium pressure regional heat flow metamorphism happened, metamorphic and deformation of sedimentary clastic rocks appeared on more stable archicontinent margin and trough belt in silicon and aluminum crust, Eventually formed Xiaodouling graphite deposit.Deposits exist in the Khondalites and the similar metamorphic sedimentary rock series, so the genetic type of Xiaodouling graphite deposit belongs to sedimentary metamorphic ore deposit.