Study On Geological Characteristics And Genesis Of Longshigeng Ferrum-Cobalt Deposit In Eastern Kunlun Orogenic Belt,Qinghai Province

Longshigeng Ferrum-Cobalt deposit is located in the southeast of Dulan County,Qinghai Province.The tectonic location is in the eastern section of East Kunlun Orogenic Belt and the Kunnan composite collage belt.The exposed strata are mainly gneiss and schist of Paleoproterozoic Jinshuikou Group and metamorphic basalt,limestone,phyllite and a small amount of black carbonite series of Meso-Neoproterozoic Wanbaogou Group.The structure are mainly EW-NWW trending and NW trending faults structures.The NW trending faults structure is the syngenetic fault determined in this study,which is the main ore-controlling structure in the mining area.It is not the post-metallogenic fault thought by predecessors,and the orebody is generally developed on the upper wall of the syngenetic fault.The magmatic rocks in the area are limited in distribution,mainly distributed in the north of the mining area,with Caledonian,Hercynian and Indosinian rocks developed.The lithology is dominated by quartz diorite,and gabbro,diabase,picrite and ophiolite are scattered.In this study,the zircon U-Pb age of ophiolites is 501.6±4.9Ma,which can be judged to be the product of backarc spreading environment according to the tectonic setting.At present,there are 6 ore-bearing belts(Fe Co??Cu??Ag Cu??Cu??Cu?and Fe?)in the mining area,among which 7 ferrum-cobalt orebodies and 5 cobalt orebodies are circled in the Fe Co?belt.The orebodies mainly occur in the contact zone between limestone and silkite phyllite,and a thin layer of black carbon-bearing rock series is developed above the orebodies.The ore bodies of sedimentary facies are mainly layered,lamellar and lenticular,which are consistent with the occurrence of surrounding rock,showing an integrated contact relationship and having obvious stratification control.The channel facies orebodies are distributed on the hanging wall of the syngenetic faults,with fine reticulate vein and disseminated vein mineralization,and the ore grade is not high.The ore type is mainly oxidized ore,and the ore minerals mainly include hematite,goethite,fibronite,cobaltite and hydrocobaltite.The ore structure is mainly composed of semi-idiomorphic grain structure,pseudomorphic structure and microsphere granular structure.The ore structure mainly includes honeycomb structure,porous structure,massive structure,layered structure,reticulated vein structure and colloidal structure.The orebody and surrounding rock have obvious vertical stratification in space,from bottom to top,carbonate,iron-cobalt orebody,hematite body,black carbonaceous rock series,which reflects that the mineralization underwent a reduction-oxidation-reduction process.The fluid inclusions in the channel facies are characterized by low temperature(123?167?),low salinity(1.5?13 wt.%Na Cl)and low density(0.93?0.95 g/cm~3)through the study of reticulation vein ore quartz vein and sedimentary siliceous rock.The sedimentary inclusions are characterized by low temperature(124?132?),low salinity(7.2?8.8 wt.%Na Cl)and low density(0.93-0.95 g/cm~3).The estimated ore-forming pressure is 15?22MPa and the ore-forming depth is 1.5?2.2km.The results of hydrogen and oxygen isotope analysis show that the ore-forming fluid of Longshigeng Ferrum-Cobalt deposit is mainly seawater mixed with a small amount of magmatic water.The results of carbon and oxygen isotope analysis show that the carbon of the deposit mainly comes from Marine carbonate of regional strata,and the ore-forming materials come from strata.Contemporaneous faults provide channels and favorable space for ore-bearing hydrothermal migration,and provide favorable conditions for mineralization.Analysis shows that several contemporaneous faults in the mining area indicate the location of the hot water activity center.In this study,1-2 layers of siliceous carbonate rocks were found near the orebody,which is closely related to the mineralization.The geochronology and petrogeochemistry of the rocks were studied.It is believed that the siliceous carbonate rocks are hydrothermal sedimentary rocks,and the sedimentary age of the siliceous carbonate rocks is determined to be later than 1032±19Ma,and the mineralization age of the deposit is determined to be the late Mesoproterozoic.The"hydrothermal sedimentary double formation"association related to mineralization is determined,which is composed of siliceous carbonate rock and black carbonaceous rock series.The siliceous carbonate rock reflects that the hydrothermal activity was weak at that time,resulting in lower grade and smaller size of the orebody.The black carbonaceous rock series reflects the reduction environment at that time,which represents the end of hot water activity.The orebody is generally produced in the lower part of the black carbonaceous rock series,which has certain control and indication significance to the orebody.In conclusion,it is considered that Longshigeng Ferrum-Cobalt deposit belongs to hydrothermal sedimentary deposit,which was formed under the background of regional tension.