Petrological Characteristics Of The Lidongshan PDI Profile In Huangbi Mine District, Yanshan County, Jiangxi Province

Lizikeng volcanic basin is one of the most important polymetallic ore zones in the northeastern Jiangxi Province, where distributing several small size Pb-Zn polymetallic ore deposit with good prospecting.The study area is located in the north margin of Wuyi uplift of South China orogenic belt to the south of Pingxiang- Guangfeng deep faults, which is the junction belt of Yangtze plate and South China plate. The lamprophyre can indicate Cu and Au. That we know less about the age and origin of the lamprophyre and the granite porphyry restricts the development of prospecting. So we did research in the lamprophyre and the granite porphyry in Zhoujia Mine Area.Using methods including petrology, lithogeochemistry and chronology, we had a discussion on the characteristic of petrology, structure and alteration and importance of prospecting based on the former research.We named the lamprophyre olive lamprophyre because the phenocryst of the sample mainly consists of pyroxene and amphibole, without feldspar or quartz. The limited variation of content of main oxide and its stable M value (78.68～82.63) indicates a good differentiation degree. We analyzed the characteristic of mineralogy and petrology of the lamprophyre to find it belongs to potassic rock, for its chemical composition is limited in the area of alkaline rock (Macdonald, 1964) and calc-alkalic lamprophyre (Rock, 1987). Calculating content of aluminium of the amphibole from the sample, we estimated the range of crystallizing pressure is 0.8～1.23GPa, concentrated primarily between 0.8Gpa and 0.97GPa, which indicates crystallizing depth is between 29.45km and 45.41km. The REE gentle distribution curves of lamprophyre are of right inclinnation, which indicates they enrich LREE and deplete HREE. The MORB-normalized trace element spider diagrams shows they are relatively enriched in large ion lithophile elements (LILE), such as Cs, Ba, Pb, but are intensively depleted in Rb and depleted in high strength field elements(HFSE), such as P, Nb, Ta, Zr, Hf, Ti. Depletion in Nb and P may reflect the source characters. Negative Nb anomaly is characteristic of volcanic rocks in subduction zones. It can also be interpreted that the rock formed with great mass of material from continental crust (Jahn et al, 1999).Granite porphyry in this area has a higher content of SiO2 with 78.51% to 81.78%, Al2O3 with 10.81% to 12.41%, K2O with 0.17% to 0.42%, Na2O with 5.38% to 6.86%. Higher content of Na2O than K2O indicates calc-alkalic rocks. The chondrite-normalized REE gentle distribution curves of granite porphyry are of right inclination. Strong negative Nb anomaly indicates residual plagioclase in the source. Incompatible elements(Rb, Th, U, Pb)show distinct positive anomaly, while Ba, Nb, Ta, Sr, Ti show distinct negative anomaly, which indicates it originated from crust rocks. Enriching more Rb than Ba indicates residual potash feldspar in the source. Depletion in Sr indicates residual plagioclase in the source, which shows the granite mainly derived from partial melting of crust. Depletion in Eu and Ti may have relationship with fractional crystallization between plagioclase and ilmenite. Ta and Nb anomaly is not distinct. Characteristic of trace element in granite porphyry indicates it derived from the crust.Zircon U-Pb dating of the granite porphyry from ZK5 gives an age of about 164 Ma. The plots of tectonic discrimination indicates Zhoujia Mine Area was affected by extension in inside flat bar. There may be ocean sediments from the subduction and residual crust. Relatively enriching more Nb and Ta than Sr and Zr also reflect flat bar subduction. It has more relation to flat bar subduction than to partial melting of crust.