Study On The Geological Characteristics And Ore Genesis Of The Oubulage Copper-gold Deposit In Wulatehouqi,Inner Mongolia

Oubulage copper-gold deposit,located in the western part of northern margin deformation zone of North China Plate,is a deposit with large-scale vision.The orebodies,which are related with the tectonic fissures near about and residual magma or lava,are mainly occur in the inside and outside contact zone of subvolcanic rock-quartz porphyry,diorite and dacitic welded volcanic breccias.There are many kinds of wall rocks and the main wall rocks comprise quartz porphyry,dioritic porphyrite,dacitic welded volcanic breccia,amphibolite dyke and so on.It is certain that the alteration levels of variant wall rocks are different,and among the alteration types,propylitization and silicification are the two ones that have a more intimate relationship with mineralizationOubulage deposit is divided into two mineralization periods and four mineralization stages according to the mineral assemblages and their contact relationships.The two mineralization periods include hydrothermal mineralization period and hypergene period.The hydrothermal mineralization period can be further divided into three stages including quartz-arsenopyrite-pyrite stage,chalcopyrite-polymetallic sulphide stage and carbonate stage.In addition,the hypergene period can also be described as the oxidation stageThe lead isotope ratios of ores are very stable and change in a small range.They have the same characteristics with normal lead isotope ratios.On the lead tectonic model diagram,the lead isotope of ore samples are located near upper crustal evolution line.The initial lead isotope ratios of rock samples would located closer to the lead isotope ratios of ore samples because of the accumulation of radiogenic 206Pb,207Pb and 208Pb following diagenesis.It proves that the lead isotope composition of ores and rocks is consistent and the lead of ores come from rocks.The lead source characteristics parameters of ores and diagram of ??-?? can also reflect the feature of leadThe sulfur isotopes have a uniform composition and a very small variation,which reflects the consistency of sulfur sources.The ?34S values fluctuate between 3.9‰and 5.2‰,and the average value is 4.38‰.The sulfur isotopic composition shows obvious tower distribution characteristics,which demonstrates that the sulfur of Oubulage copper-gold deposit is mainly from magma.Based on the study of the geological background,geological characteristics and the geochemical characteristics of the deposit,we deem that the mineral source of Oubulage deposit comes from volcanic eruption of Paleozoic.In late Hercynian,the copper,gold,silver and other elements are brought to the shallow place by multiperiodic volcanic and subvolcanic activities.Then the residual magma and lava promote the useful element enrich in the contact surface,pores and cracks of some certain rocks including quartz porphyry,dioritic porphyrite and volcanic layer.In the meantime,the useful elements react with wall rocks and form the medium-low temperature hydrothermal alteration with the precipitation of copper,gold and silver.For all the characteristics mentioned above,we can conclude that the Oubulage copper-gold deposit is a porphyry deposit associated with subvolcanic rocks.