Study On Metallogenesis Of Nickel And Copper Deposits In Kaerqueka-Akechukesai Area,Western Segment Of The East Kunlun Orogenic Belt,Qinghai Province

The Kaerqueka-Akechukesai area of Qinghai Province is located at the junction of Qinghai Province and Xinjiang Province.The tectonic location belongs to the southern margin of Qaidam massif,the western segment of East Kunlun orogenic belt.This area has undergone the formation of the Eoarchean-Paleoproterozoic crystalline basement,the Meso-Neoproterozoic plates converge,the evolution of the Pre-Proto-Tethys Ocean basin and the formation of the Oceanic Basalt Plateau,the evolution of the Proto-Tethys tectonic domain during the Caledonian to early Hercynian periodand the Paleo-Tethys Ocean Tectonic Domain from Late Hercynian to Early Indosinian,lithospheric delamination caused by intracontinental orogeny from Late Indosinian to Early Yanshanian and the regional uplift from Late Yanshanian to Himalayan.The long and complex tectonic evolution leads to the development of multi-stage and multi-type mineral resources in the area.However,limited by objective conditions and some scientific problems in recent years.For example,the degree of geological research is low,some basic geological information is fuzzy,the tectonic evolution in the area is controversial,and the deposit type and mineralization need to be further studied.This paper studies various types of rocks and typical mineral deposits in the area,improves basic geological information,discusses the kinetic model of mineralization,and summarizes the laws of mineralization,so as to further summarize the regional mineralization theory and assist the mineral exploration work in the region.Through the study of the geochronology and geochemistry of the biotite two-feldspar gneiss,quartz diorite,granodiorite and monzonitic granite porphyry in the study area,it is concluded that:“Paleoproterozoic Jinshuikou Group gneiss”in Akechukesai area is actually an early Neoproterozoic(?946Ma)intrusive rock,and the rock mass has the characteristics of syn-collision S-type granite.Combined with regional studies,it is found that magmatic activities developed extensively in this period in the region.It is believed that strong tectonic-magmatic events developed in the Meso-Neoproterozoic in the East Kunlun area,which may respond to the global convergence of the Rodinia supercontinent.Akechukesaihigh-Mg diorite was formed in the late Caledonian period(?426Ma),and the rock has the geochemical characteristics of sanukitoids.Affected by the evolution of the Proto-Tethys Ocean in the late Caledonian period,the Wanbaogou oceanic basalt plateau collided above the southern margin of the northern Qaidam block.The deep oceanic crust continued to subduct and broke off,and the asthenosphere surges up to the shallow part of the crust to form mafic-ultramafic intrusive rocks along the slab windows formed by the slab fragmentation.During the upwelling process,it mixes with the Mg-rich broken slabs to form high-Mg diorites in this area.Kaerqueka granodiorite was formed in the early Indosinian period(?242Ma).The rock is formed by mixing new basalt crust and ancient silico-aluminum crust,which is consistent with the characteristics of subduction zone magmatic rocks.It shows that the magma intrusion related to the subduction of the Paleo-Tethys Ocean was strong in the early Indochina.Akechukesai monzonitic granite porphyry was formed in the late Indosinian period(?221Ma).The rock is highly differentiated I-type granite,and the magma is mainly derived from partial melting of the lower crust,and with the addition of mantle-derived materials,it is formed under a strong extension of the tectonic background.The Paleo-Tethys Ocean in the East Kunlun area subducted northward in the late Hercynian period,and the Middle Triassic ocean basin closed,forming crust-derived magma related to the subduction.In the Late Triassic,the East Kunlun area entered the post-collision extension stage.The delamination and thinning of the lithosphere led to large-scale extension,and the mantle-derived magma surged and directly emplaced to form basic-ultrabasic rocks.In the process of upward invasion,it may be mixed with crustal materials to form crust-mantle mixed-source magma,or the crust may be heated to form crust-sourced magma.The Indosinian magmatic activity was the strongest,and it was the most important magmatic-hydrothermal deposit mineralization period in the East Kunlun area.Conduct research on four typical mineral depositsin the study area,the intrusions originally classified as Devonian diorite in Akechukesai area are actually mafic-ultramafic complexes formed by pyroxene and gabbro through auto-metamorphism.The formation age includes Gary Two phases of diagenesis in the late Eastern and Late Indosinian.The U-Pb age of the zircon of ore-bearing pyroxene is 416±3Ma,and the U-Pb age of the zircon of metamorphic gabbro is 424±3Ma.The deposit type is a magmatic copper-nickel sulfide deposit.The ore-bearing magma originated from partial melting of the depleted mantle and was added by subduction components.At the same time,the Ordovician-Silurian Tanjianshan Group marble strata were mantle-derived magma during the emplacement process.The mineralization of magma provides exogenous sulfur.The addition of Ca²⁺and Mg²⁺plasma leads to a decrease in the crystallization temperature of magma,which makes the sulfide in the magma supersaturate and dissociates from the magma to form minerals.Late Triassic(?220Ma)gabbro intrusions are newly discovered in the area.The intrusions were formed under the tectonic background of the delamination and thinning of the lithosphere after the orogenic and the undercutting of mantle-derived materials.The magma source area is the rich lithospheric mantle,with poor magma crystallization differentiation,single lithofacies,low sulfide fusion,and weak alteration and mineralization.In summary,the prospecting potential of the late Caledonian copper-nickel sulfide deposit in the western section of East Kunlun in Qinghai is huge,while the prospecting potential of the late Indosinian is mediocre.Through field exploration,a new porphyry-type mineralization point was discovered in the Akechukesai area.The Early Triassic granite porphyry(?244Ma)has undergone strong alteration.The shallow part of the borehole can be seen with a blue rock formation zone,and the deep part of the borehole on the west side appears a mud zone,and developed disseminated pyrite,galena,Sphalerite etc.Lead and zinc are of low grade and good continuity,which is in line with the surface alteration and zoning characteristics of porphyry deposits.Limited to the late discovery of mineralization points and low work levels,the current research is still in the periphery of the alteration zone.However,the hydrothermal alteration of this mineralization point is intense,the alteration zone is large in scale and the degree of denudation is small,and there is a potential for further exploration in the deep part.The discovery of this mineralization point indicates that there is a possibility of prospecting Indosinian porphyry deposits in the northern part of the East Kunlun Central Belt.Kaerqueka A area can be divided into two mining sections,north and south.The mineralization and silicification of the south section are closely related.The ore body is strictly controlled by the fault structure.The ore develops a massive structure,and the copper ore grade is high and changes greatly.The Ar-Ar isochron age of the ore-bearing vein is 241±2Ma,which represents the mineralization age.The S-Pb isotopes show that the ore-forming materials have the characteristics of crust-mantle mixing,and the H-O isotopes show that the ore-forming fluids are dominated by magmatic water with the participation of atmospheric water.The fluid inclusions develop a three-phase rich liquid phase,daughter minerals and CO₂ inclusions.The homogenization temperature of the main mineralization stage is 293??360?.The minerals mainly migrate in the form of liquid phase.The fluids in the early stage of mineralization are not mixed.Soluble,fluid immiscibility and temperature reduction are the dominant factors for mineral precipitation.Comprehensive studies believe that the southern section of Kaerqueka A area is a mid-high temperature hydrothermal vein copper deposit controlled by fault structures.The ore body of the northern section is produced in the body of cryptoexplosive breccia.The thickness of mineralization is small,and the plane extension is much larger than the vertical extension.The breccia is not rounded and has no large displacement.The cryptoblast only occurs in the crust of the rock mass Different from the typical cryptoexplosive breccia tube deposit,this paper defines it as a cryptoexplosive breccia shell deposit produced on the top of the rock mass.The S isotope shows that the ore-forming fluid mainly comes from magma;the H-O isotope shows that the ore-forming fluid is a mixture of atmospheric precipitation and magmatic water.The fluid is rich in CO₂ and N₂,indicating that mantle-derived fluids may participate in the mineralization.The ore deposit has a large metallogenic depth,undeveloped faulted structures and no hydrothermal upward migration channel formed,which makes it difficult for the magma to reach the conditions of secondary boiling and sustained cryptoexplosion.Therefore,the deposits are mainly formed by the small-scale cryptoexplosion of the limited gas-water hydrothermal fluid gathered on the top of the rock mass and in the fissures.Although they can constitute mineralization,they do not have the potential to form large deposits.Kaerqueka B area is a typical skarn-type copper-molybdenum deposit.The surrounding rock is Marble of the Tanjianshan Group.The deposit is formed in the skarn formed in the contact zone between granodiorite and strata.The age of granodiorite(?242Ma)related to mineralization is consistent with the Re-Os isotope age of molybdenite ore(?242Ma),which represents the early Triassic.Comprehensive research suggests that the contact metasomatism of granodiorite intrusions in the Tanjianshan group formation produces skarn,the ore-bearing hydrothermal fluid formed by the evolution of the rock mass and the continuous extraction of useful components from the strata together form the ore-forming fluid,which is affected by the atmosphere.The mixed cooling of precipitation or other shallow ground waters further precipitates and enriches minerals in weak parts of the structure,forming a large-scale skarn-type copper-molybdenum deposit in this area.There are three main metallogenic periods in the western section of East Kunlun in Qinghai:Late Caledonian,Early Indosinian and Late Indosinian.In Late Caledonian,magmatic Cu-Ni sulfide deposits related to the slab fragmentation were mainly formed,mantle-derived magma originated from depleted mantle.Skarn or mid-high temperature hydrothermal vein-type Cu/Mo deposits were formed under the background of subduction in Early Indosinian,Cu is mainly derived from mantle-derived magma.;in the late Indosinian period,it entered the post-collision and extensional environment,lithospheric delamination and mantle-derived magma undercut,resulting in the development of basic to acid rocks,Mainly formed the porphyry-skarn type copper,iron,lead,zinc and other metal deposits related to the extensional background.The overall uplift and erosion of the western section of the eastern Kunlun area in Qinghai is greater than that of the eastern section,while the western section has the largest degree of denudation in the Kunzhong zone,bounded by the Heishan-Nalinggele River fault.The deposits are almost completely denuded,and the prospecting direction is mainly magmatic deposits and mid-deep high-temperature hydrothermal vein deposits.The uplift and denudation in the north are relatively weak.Indosinian porphyry,skarn,and mid-low temperature hydrothermal vein deposits have good metallogenic and preservation conditions.However,the magmatic copper-nickel sulfide deposits in this period have limited prospecting potential and should be targeted at porphyries.Rock type,skarn type and mid-low temperature hydrothermal vein type deposits.