The Study On Geological Characteristics And Mineralization Of Volcanic Massive Sulphide Deposit In Maikain, Kazakhstan

The Maikain deposit is located in the west of Maikain town in Ekibasto,northwestern Kazakhstan.It is a ultra large volcanic massive sulfide deposit on the Boshekul-ChengjisSulbuti metallogenic belt of the Balkhash-West Junggar mineralization province in Central Asian metallogenic region.On the basis of previous research,this article discusses the metallogenic tectonics background,ore-forming materials and fluisds sources of Maikain deposits and established metallogenic model through field investigation,observations of specimens,volcanic rocks geochemistry,fluid inclusions,sulfur isotopes and hydrogen and oxygen isotopes.The ore-bearing surrounding rocks of the Maikain deposit are andesite,basalt and intermediate subvolcanic rocks of the Late Ordovician Maikain Formation.Surrounding rocks develop quartz-sericitization,quartz-chlorite-sericification,chlorite and other alterations.The ore structures are mainly gas-hydrothermal structures,and it is mainly composed of filling ore structure.Filled ore is mainly divided into blocks,strips,fine veins and reticulate veins.Ore minerals are pyrite,chalcopyrite,pyrrhotite,sphalerite and a small amount of galena,arsenic,antimony copper and natural gold.Gangue minerals include quartz,barite,calcite,sericite,chlorite and epidote.Based on the analysis of the geological characteristics of the Maikain ore body and the observation of the mineral associations and their interpenetrating relationships under the microscope,the mineralization periods are divided into three stages: quartz-pyrite stage,barite-chalcopyrite stage and baritepolymetallic sulphide stage.The Y/Tb values of host andesite from Maikain deposits in Maikain mining area are between 20.5 ~ 27.2,and basalt Y/Tb values are between 38.8 ~ 39.1.Basalt Y/Tb value is significantly higher than 15,it shows the basalt magma mainly derived from the mantle,while andesite Y/Tb value is low,indicating that seafloor sediments and sedimentary rock composition added.The volcanic rocks from Maikain mining area are poor in Nb,Ta obviously,it suggests that the tectonic environment of volcanic rocks from Maikain mining area is island arc environment.From basalt to andesite,the composition of the aspergillus is continuously declining,while the composition of calcium and alkalinity continues to rise,the total amount of rare earths continues to rise and the differentiation of LREE and HREE is more pronounced,indicating that the tectonic environment in this region has undergone a transition from arc expansion to island arc maturation.Fluid inclusions in Maikain deposits are mainly distributed in quartz and barite in all mineralization stages,mainly for the gas liquid two phase and the pure liquid inclusions,and contains a small amount with crystal three-phase inclusions.Fluid inclusion studies have shown that the oreforming fluids of the Maikain deposits are low temperature(144.6 to 259.8°C),medium salinity(2.18 to 17.52%),and low density(0.841 to 0.967g/cm3).According to the data of fluid inclusions,the ore-forming pressure is 71.2 bar,corresponding to a metallogenic depth of 265.7 m.The sulfur isotope value in pyrite and barite are-2.2 ~-1.5‰ and 201.4 ~ 23.0‰.According to the proportion of mineral in the ore,it is estimated that the total sulfur isotope value of metallogenic system is 5‰,indicating that the source of sulfur in the ore-forming systems of the Maikain deposits is mainly a mixture of mantle source sulfur and seawater sulfur.The mantle source of sulfur is mainly through magmatic degassing or seawater leaching on surrounding rocks.The ?D and ?18O values in batite are-63~-13‰ and 10~13.6‰.The range of ?18OH2O in deposit ore-forming fluid is 2.48‰-6.06‰,indicating that the source of the fluid is mainly the mixing of seawater and the original magmatic hydrothermal fluid.Maikain deposits have typical mineral composition,wall rock alteration type and metallogenic tectonic environment of Kuroko type deposits,the main metallogenic stage characteristics of fluid inclusions,the composition of the sulfur isotopes and hydrogen and oxygen isotopes are also similar with foreign typical Kuroko type deposits,therefore Maikain deposits belong to Kuroko type deposits.