Study On Multi-Period Superposed Mineralization Of The Kangkai Iron Deposit In Tiekelik Metallogenic Belt, West Kunlun

The Tiekelik tectonic belt is located in the northern margin of the West Kunlun,where the West Kunlun orogenic belt combines with the Tarim Basin.The Kangkai iron deposit is located in the margin of the middle section of the Tiekelik tectonic belt.On the basis of detailed recognization of the geological characteristics of the Kangkai deposit,the systematic studies of petrology,major-trace element geochemistry,stable isotope,fluid inclusion,and geochronoly been carried out to reveal geochemical characteristics,sources of metallogenic materials,ore-forming age,and metallogenic environment,and the metallogenic model has been established finally.The main achievements of this study are as followings.?1?There are two types of iron mineralization,the specularite and magnetite mineralization,developing within the metamorphic rocks of Palaeoproterozoic Kalakashi Group and Ailiantate Group.The specularite mineralization is controlled by fault and fracture structures,occurring as vein,stratoid,massive and veinlet types.The magnetite mineralization occurs both in the itabirite and the gabbro,the former is resulted from sedimentary-metamorphic process,and the latter is shown as disseminated magnetite and minor chalcopyrite within the gabbro.In terms of characteristics of mineral assemblage and paragenetic association,ore texture and structure,wall rock alteration,and crosscutting relationship of different types of mineralized body,the mineralization process of the Kangkai iron deposit is divided into sedimentary,metamorphic,magmatic,and tectonic hydrothermal periods.?2?The SiO₂/Al₂O₃;Sr/Ba,and Ni/Co ratios of itabirite ore show that the main material source is from marine sediments,and the terrigenous clastics account for a certain proportion.Also,Co/Zn,and Y/Ho ratios indicate that the material source of seafloor hydrothermal solution.Itabirite mineralization is the same as the sedimentary-metamorphism iron deposit.?3?The protolith of Kalakashi Group is composed of clasolite,carbonate,sandwiched with basic and intermediate-acidic volcanic rocks.The plagioamphibolite has high alkaline content of w?Na2O+K2O?ranging from 2.90%to 4.55%,and w?Na2O?/w?K20?ranging from 2.90 to 12.65,indicating the feature oftholeiite.Its value of ?REE between 40.84×10-6 and 91.04×10-6,having a nearly flat REE pattern,and enriched in LILE of Sr,K,Rb,Ba,Th.The geochemical characteristics are similar to that of island arc basalt.On the tectonic discrimination plots,all data of plagioamphibolite fall into the field of back arc basin.The depositional age of Kalakashi Group is Palaeoproterozoic,with underwent the regional metamorphism in Neoproterozoic??874Ma?.?4?The U-Pb dating of zircons from the gabbro yielded a isochron age of 462+3Ma,belonging to Middle Ordovician.Magnetite enrichment in the gabbro is the result of fractional crystallization.Its mineralization is samliar to magmatic differenttiation deposit.?5?The specularite ore body formed in the tectonic hydrothermal period.Hydrothermal fluids belong to NaCl+H2O system,which temperatures concentrate in 170?24?,and salinities in 19.45?23.44%NaCleq.The ?18O values of hydrothermal fluids rang from 1.2‰ to 8.7‰,with 5D values from-70.9‰ to-56.0%‰.All of these data indicate that the hydrothermal fluids are the mixed fluids of magmatic,metamorphic and meteoric water.The 556Fe values show the increasing pattern of specularite ore?-0.714?-0.447‰?<altered itabirite ore?-0.118‰?<quartz vein,altered wall rock?0.040?0.141‰?<unaltered itabirite ore?0.249?0.289‰?,gabbro ore?0.328?0.376‰?,unaltered wall rock?0.229?0.329‰?,which is the result of the iron remobilization and re-enrichment,indicating that the specularite formed during tectonic hydrothermal period is derived from the magnetite formed during sedimentary-metamorphic and magmatic periods.?6?On the basis of geological background and metallogenic characteristics,an ore model of multi-period of sedimentary,metamorphic,magmatic and tectonic hydrothermal superposed mineralizations has been established,and it is suggested that the specularite occurred in shallow ground can be used as a kind of prospecting criteria for the exploration of magnetite related to itabirite and gabbro at depth and surrounding area.