Study On Geochemical Characteristics And The Function In Iron-Copper Mineralization Of Alkali-rich Porphyry In The Dahongshan Area, Yunnan Province,China

The Dahongshan region in Yunnan is the enrichment region of "Dahongshan type" iron and copper ore, the ore rock of iron and copper deposit belong to lower Proterozoic Dahongshan formation Hongshan group and Manganghe group, that is a set of volcanic-sedimentary metamorphic facies of paleo-marine facies of low horblende facies. As the iron and copper ore exposes and the cognition improves, the geologic feature of the ore deposit, the ore-bearing lithology, and the occurrence regularity are more and more complex, ore-controlling condition and ore-controlling factors are more and more diversified.This paper is based on systematically collecting and analyzing the pre-existing data of geology, geophysical exploration, geochemical exploration, mineral deposit(site) and mine production in the study area by comprehensive research on the relationship between alkali-rich porphyry sample test and iron, copper mineralization. And the following results were achieved:1、. The alkali-rich porphyry in the Dahongshan region is mainly Brigitte-keratophyre volcanic rocks and Albite porphyry intrusive rocks, there are four kinds of Brigitte-keratophyre volcanic rocks:baschtaunite, metamorphous sodic lava, metamorphous sodic tuff and amphibolite metamorphous sodic lava.2、By analyzing the macroelement in the alkali-rich porphyry, the mean value of ω(SiO2)>61.04%, in ω(K2O)-ω(SiO2) diagram, it concentrates on low potassium series. The mean values of ω(Na2O+K2O) are60.57,33.73. Na2O/K2O is more than1, it belongs to rich alkali-sodic rock. The alkali-rich porphyry is mainly belongs to calc alkali basalt series, because of rich Na, low K in the rocks, it belongs to geosynclines-island arc type marine eruption spillite-keratophyre composition.3、The geochemical characteristic of the trace element in the alkali-rich porphyry shows that, the mean value of Nb/Ta is0.3,which is similar to the characteristic of mantle source,Ta is usually gathering at the late stage of magmatic evolution, it shows that the degree of the alkali-rich porphyry in this area is not strong. The concentration coefficient of the incompatible element Th in the alkali-rich porphyry is2.5, the correlation of Ba and Rb is very high. It can be concluded that the ore-forming element in the Dahonshan area is Ba, V, K, Na, Rb, Ni, Mo by factor analysis. 4、The alkali-rich porphyry rare earth element geochemical characteristic shows that, the mean value of∑REE is80.99x10-6.∑LREE/∑HREE is4.19,(La/Yb)N=4.15, that is light REE enrichment characteristic. There is a positive anomaly of Eu showing a certain epoch evolution characteristic.5、The formation of alkali-rich porphyry in the Dahongshan region is the result that under the influence of Ailaoshan-Jinsha River discordogenic fault belt, the deep crust source rock turns to magma because of fractional melting and then invades upward during the Longchuan tectonic motion. The spilite-keratophyre sequence is the ore-bearing lithology, providing the material source for iron and copper mineralization. The occurrence form of spilite-keratophyre controls the spatial position and and expanding range of the ore body, the quartz albite porphyry has a intrusive contact relationship to the surrounding rock, with no mineralization, it has a function of ore body dilution and enrichment. By studying the spatial distribution of alkali-rich porphyry, analyzing the majorelements, microelement and rare earth element of the rocks, the relationship between the alkali-rich porphyry and iron/copper mineralization in the Dahongshan region was discovered, the vision and mentality on the prospecting is expanded, which has a certain guiding significance of prospecting in the interior,edge and periphery of the Dahongshan iron and copper mining area.