The Magmatism Of Granitoid And Metallization Of Longtougang-Wangwu Copper Polymetallic Ore Field In North Wuyi Region

Longtougang copper polymetallic deposit and Wangwu Mo-Cu deposit have showed the potential of being a large scale deposit holding prospecting mineral reserves which have been verified in recent years in North Wuyi region. The study of petrologic feature in field and microscope illustrated that the igneous rocks are main consisted of granite porphyry, monzonitic granite porphyry and biotite monzonitic granite in Longtougang mining area. There is a close space relationship between granophyre vein of Wangwu mining and molybdenum ore body. The zircon LA-ICP-MS U-Pb dating results shows the weighted average ages of four types of granitoid, and they are 153.9±1.4 Ma(MSWD=4.1),151.3±1.4 Ma(MSWD=2.2)and 127.5±1.8 Ma(MSWD=1.4)respectively, which suggested that they formed in late Jurassic epoch and early Cretaceous epoch.The negative anomaly of Nb, Ta, Ti and the figure results of tectonic discrimination plots suggest that the tectonic setting of these granitoid are active continental margin, which is related to the subduction of paleo-pacific plate. The negative anomaly of Eu, Sr, Ba and positive Rb anomaly shows there is remnant of feldspar and plagioclase in source region. The high positive Pb anomaly illustrates arc magmas and magmas contaminated by the crust in the process of emplacement. In the classification map of Ab-An-Or, most of granite porphyry belongs to trondhjemite area and trends to evaluation of trondhjemite, with the ratio of Na2O/K2 O is 1.40-3.11(average is 2.24). The finding of middle potassic calc-alkaline series and albite in microscope prove that they are TTG rocks. Furthermost, low Al2O3 and Mg O content prove that they result from the partial melting of basaltic rocks at the bottom of the continental crust.The Longtougang copper polymetallic deposit is situated in the Outang Formation, and its ore body occurs as stratoid beds as a whole. The hornfels is found located mainly under the PD7 footrill for the first time. It is controlled by the PD9 footrill, and it has a length of ~400m and a width of 300-400 m along the N-W orientation, and towards to the deep, its width becomes larger. Considering the field occurrence and distinct features comparing with the carbon and oxygen isotopic characteristics of carbonatite in the South Africa, we suggest that the ―marble‖ in the ore district should belong to igneous carbonatite. The presence of melt inclusions of diopside and metal sulfide and oxide in the garnet and quartz in the skarn ore minerals indicates the existence of magmatic skarn and pulp. In addition, the biotite melt inclusions are found in quartz of hornfels, which suggesting that the hornfels results from a rapid cooling process of early melting of surrounding rocks due to the intrusion of metallogenic pluton. The presence of hornfels also indicates that the hidden porphyry rocks exist likely in the deep part of the ore district, suggesting that this area has potential of finding copper-molybdenum deposits. Therefore, the Longtougang deposit is a composite deposit, the skarn ore in the lower and the porphyry ore in the deep.The Wangwu copper-molybdenum deposit is situated in the Zhoutanyan Formation. The Re-Os analysis of molybdenite shows a isochron age of 153.7±3.2Ma(MSWD=3.9), indicating that the mineralization occurs in the late Jurassic epoch.The dating results of granophyresveins cutting across the molybdenum ore body suggest that they formed later than the mineralization, and thus have no genetic relationship with the deposit. By contrasting with the geologic features of adjacent deposits, we concluded that the mineralized igneous rock should be felsic granite porphyry or biotite granite porphyry, likely located in the deep of the southeastern area. It also has a good potential of finding the ore deposit.