Research On The Geological Characteristics And Its Genesis Of The Tongkuangyu Cu-po丨ymetalic Deposit In The Zhongtiao Mountains

The Zhongtiao mountains copper deposits locate in the southern margin of the NorthChina Craton and the northern part of Qinling mountains orogenic belt. Stronglytectonic movement and many magma activity episodes happened in this area which alsoeasy for Cu-polymetalic deposit formation.This article focus on the studies of the regionalgeological features, geological characteristics, Isotope geochemical characteristics and thechronology of Tongkuangyu Cu-polymetalic deposit, accompanied with a comparativeanalysis with other typical porphyry copper deposits, in order to discuss the depositmetallogenic tectonic background, source of ore-forming materials, deposit genesis ofTongkuangyu Cu-polymetalic deposit.Faults and folds developed well in this area in facour of mineralization. Ore bodiesmainly occurred in the Tongkuangyu subgroups, Paleoproterozoic Jiangxian formation.From bottom to up, it can be divided into: Luotuo Feng group, Xijing Gou group, ShujingGou group. Among these, Luotuo Feng group is the most important ore bearing stratum.The surrounding rocks of ore body were composed of Luotuo Feng group and Xijing Gougroup, the most common lithology is biotite schist, which is a set of Metamorphic basicvolcanic rocks.So far, it has been proved339ore bodies in the Tongkuangyu Cu-polymetalic deposit with two main ore bodies (4,5#ore body), account for85%of total reserves in this area.These two bodies have the same lenticular shape, in addition,4#ore body was mounted onthe top of5#ore body. The major metallic minerals in the ores are pyrite and chalcopyrite,also with small amount of associated magnetite, bornite, molybdenite. Main gangueminerals are quartz, biotite, calcite, sericite, chlorite and so on. Copper mineralizationoccurs as hypidiomorphic-xenomorphic granular and metasomatic dissolution textures,disseminated and veinlets filling structures. Wall rocks alteration consists of red sodiumfeldspathization, biotitization, sericitization, silicification, carbonation, chloritization andso on.Analysis of major elements shows that the rocks should be alkaline or tholeiite series.Among them,the ore-bearing porphyries and sericite quartz had high-K,-Al characters,biotite-schist had high-K,-Al,-Mg, low-Si,-Ca characters. The spider diagram of traceelement ratio is right tilting. Trace element analysis shows that the enrichment of large ionlithophile elements(LITE) such as K， Rb， Ba, depleted in high field strengthelements(HFSE) such as P，Y，Ti，Nb，Ta, which has the geochemistry characteristics ofisland arc basalts, inferring the enrichment of garnet and plagioclase in magma source.The chondrite standard curve of rare earth elements reveals a deficit of light rare earth andenrichment of heavy one.H, O isotope compositions shows that ore stage solution is of a mixed origin ofmagmatic water and meteoric water. Pb isotope compositions shows that mother rock wasmetamorphic granodiorite-porphyry. Pb isotope compositions suggest that multiplesources mainly come from the orogen and upper crust.The granite samples are located at volcanic arc granite area(VAG) in the tectonicdiscriminal diagram for granite, and have the transition to syn-collision granitesfield(Syn-COLG). In the Th-Hf/3-Nb/16tectonic discriminal diagram, the samples areplotted in the island-arc environment. Zr/Nb-Nb/Th，Nb/Y-Zr/Y tectonic discriminaldiagram shows the subduction metasomatism environment.According to the Zircon U-Pb ages, the formation epoch of Tongkuangyu deposit was 2.1~2.2Ga. This deposit was formed in the conversional tectonic setting with themagmatic activities. After that, Tongkuangyu Cu-polymetalic deposit has been sufferedfrom the Zhongtiao Stage Ⅰmetamorphism and deformation activities.