Genesis And Metallogenic Mechanism Of Vein Type Copper Deposit In The Northern Area Of Ningwu, Eastern China

There are many hydrotherm vein type copper deposits in the northern area of Ningwu,eastern China. However, the study on the genesis and metallogenic mechanism of thesedeposits was relative little. Based on the comparative researched on the geology、ore-forming fluids and geochemistry of the mineral from Nanmentou、Tongjing and GuliCu deposits, the genesis and metallogenic mechanism of these copper deposit arediscussed here.Firstly, there are distinguishing differences among these Cu (Au)deposits, especiallyin the host rock、ore structure、intrusive rock and mineral combination etc.Sencond, the inclusion geothermometry from Nanmentou Cu deposit show that thetemperature of the ore-forming fluid is middle-high to middle-low(166.7-355.4℃) withmiddle-low salinity(3.5-12.0%)and low density (0.75-1.01g/cm3). The inferred pressurewas relative low (12.8-35.1Ma)and the depth was shallow (0.43-1.17km). Thematerial precipitated of the ore-forming fluids mainly be controlled by thehomogenization temperature and the velocity of escape in the residual liquid forNanmentou deposit. The carbon and oxygen isotopic compositions of calcite indicate thatthe carbon was mainly derived from the magma, partial carbon from the carbonateformation added during the ore-forming stage.The sulfur isotope from Guli Cu deposit range0.62‰-1.93‰, which derivedfrom the mantle and related with the diorite porphyrite that was host rock. However, thesulfur isotope from Nanmentou show6.93‰～14.43‰and Tongjing with3.1‰～7.1‰,which indicated that the sulfur mainly be from the mantle-cruste mixture and be relatedwith granite and syenite. The magnitude mixed from layer are different betweenNanmentou and Tongjing. As well as the lead isotope also show that they are mixed leadfrom the mantle-cruste original source material in Nanmentou、Guli and Tongjing Cudeposits.Combined with geological and isotopic geochemistry characteristics, we tentativelyconclude that the genesis of the Nanmentou Cu deposit was possible related with twoperiod of magma intrusion activity, the later granite should provided the fluids、heat sourcesand parts material for ore-forming,the layer and early dioritic porphyrite were possibleprovid main ore-forming material and Sulfur；the genesis of the Guli Cu deposit was directly correlated with dioritic porphyrite and the Tongjing Cu-Au deposit associtive withthe orthophyre.The main and trace elements compositions of the ore-forming intrusive fromNanmentou、Guli and Tongjing show that there is a linear relationship between the cotent ofthe most of main elements and the content of silicon dioxide, and their REE patterns aresimilar,which suggest that they were possible derived from the same magma chamber andintruded at different stage.Finally, Base on the above comprehensive and comparative study, We speculate thatthere might be present two main Copper metallogenic periods in Northern Ningwu district:,one was relatived to early magmatic segregation with diorite porphyrite in Dawangshancycle,Guli copper deposit as the representative and the other was correlated with granite inlate Gushan cycle,the example of Nanmentou and Tongjing.