Study On Geological Characteristics And Genesis Of Akechukesai Copper-Nickel Deposit In East Kunlun,Qinghai Province

Numerous deposits(mineral occurrences)have been found in Eastern Kunlun orogenic belt,Qinghai province.In recent years,with the prospecting breakthrough of magmatic copper-nickel sulfide deposits in this area,the study of this type deposit gradually deepened.The discovery of Akechukesai copper-nickel deposit was another important breakthrough after Xiarihamu nickel deposit was found,providing reference to the exploration of magmatic copper-nickel sulfide deposits in this area.Akechukesai copper-nickel deposit is located in the Middle Eastern Kunlun basement uplifted and granitic belt,which is near to the north Eastern Kunlun fault.The outcrop of strata are Neoproterozoic Jinshuikou Group and Cambrian-Ordovician Tanjianshan Group.There are two main faults that are nearly NW faults(F5 and F6),which have big scale and far extension and compressive torsion properties.The main igneous rocks are late proterozoic biotite monzonitic gneiss?Mid-Late Silurian granodiorite and mafic-ultramafic rocks?Variscan-Indosinian granite porphyry,quartz diorite and granite.There are five mafic-ultramafic complexes in Akechukesai.We have found a lot of sulfide in the trench and drilling holes.Also we found annabergite and covellite.The grade of ores are high.No ??? and ? are founded recently.From the currently construction situation,there are many sulfide in them.It suggests that have good metallogenic potential.No ? mafic-ultramafic complex in Akechukesai is nearly SN distribution and dip E.Lots of marble xenoliths of Tanjianshan Group are found in pyroxenites.The long axis of rock mass is NNE,the shape is irregular,unstable extension and grade changes in a wide range.No II mafic-ultramafic complex has a serious covering of Quaternary.Its overall strike is NE,dip SE.The obvious trends of II ore body are swelling,thickening and higher grade with the increase of the depth.Almost all grade of the samples are higher than 0.1%with the good continuity.It has a high grade area.Some places are found with higher grade and ore rich that have sideronitic texture.The ore-bearing rock facies of I,II is pyroxenite phase.The contact relationship between pyroxenite and marble is invasive transitional.A multi-stage magmatic activities formed the mafic-ultramafic complex.Liquation processes happen to be in the deep magma chamber.Due to the strong dynamics background,the pulse invasive of sulphide magma to the crust from ore-free magma,ore-bearing to ore-rich magma/ore magma to form the complex.The process has formed disseminated and sideronitic ores.According to the results of electron microprobe,clinopyroxene is mainly endiopside,which En value from 61.64 to 65.6,Fs value from 7.74 to 10.74,Wo value from 22.96 to 26.01.It belongs to the sub-alkaline tholeiite series and formed in the tectonic setting related to the arc.?,? mafic-ultramafic complexes are ore bodies.They have similar metal minerals,gangue minerals and fabric.Nickel-bearing minerals are pentlandite and a small amount of violarite.Copper-bearing minerals are chalcopyrite and covellite.Iron-bearing minerals are pyrrhotite,occasional limonite,pyrite and marcasite.Cobalt-bearing minerals are unknown minerals that contain nickel and cobalt.It as isomorphism hosting in the petlandite.The ores present sideronitic textures,solid solution separation textures,idiomorphic or hypidiomorphic granular textures,xenomorphic granular textures,heterogranular textures,metasomatic textures.Structures are mainly disseminated,star-like,spotted,massive.Also has a small amount of block structure and fine vein structure.S topic and S/Se show that ?34S ranges from 6.7‰ to 11.5 ‰,which deviates from the mantle source of mantle sulfur 0±2;S/Se ratio ranges from 3738 to 15501,exceeding the average mantle value.The above indicate that during the process of mantle magma upwelling period,there are some earth's crust sulfur to join.LA-ICP-MS dating is applied to pyroxenite that the crystallization age is 422±10 Ma,which belongs to Middle Silurian.The Zr/Nb ratio of rock mass ranges from 16.75 to 30.93,which is close to the ratio of MORB(from 10 to 60);The Sm/Nd ratio of rock mass ranges from 0.18 to 0.25,which is similar to the range of MORB(average value is 0.32).These indicate that the magma originate from asthenosphere mantle.The analysis of the element correlation in Harker suggest that during the process of magma evolution,magma has experienced fractional crystallization of olivine(not foundin the field),orthopyroxene,clinopyroxene and plagioclase.Meanwhile surrounding rock carbonate contaminates the magma.The two together promote the sulfur saturation and liquation mineralization.By means of the characteristic of regional geological background,geological features of mafic-ultranafic complex,mining and ore deposit geology,?34S and S/Se,metallogenic epoch and dynamic analysis.We come to the conclusion that Akechukesai copper-nickel deposit formed in the Middle Silurian,and belong to deep magmatic liquation-pulse type injection type deposit.Its tectonic setting is that subduction plate stretched and broke off,forming slab window.Mantle magma liquated in the deep,upwelling and injecting upper rock in multi-stages,which formed Akechukesai copper-nickel deposit.