Study On Geological Characteristics And Genesis Of Aikengdelesite Molybdenum (Copper) Deposit, Eastern Kuniun, Qinghai Province

The Eastern Kunlun is one of the most important polymetallic mineralization belt inChina and the Aikengdelesite molybden (copper) deposit is located in southern compositeaccretion belt, between middle and south Kunlun fault. The stratum outcropped in the miningarea is simple, just the Triassic, Jurassic-Cretaceous stratum only, and the TriassicHongshuichuan group is the main ore hosted stratum. Fault structure, mainly in NW andnearly SN terding, is the main structure in the mining area and fold structure is less developed.The magmatic activity is frequent in this aera. Intrusive rocks are widely distributed, andmainly for the Indosinian-Hercynian monzonitic granite, granite porphyry, medium-finegranite, diorite, dioritic porphyrite etc. which outputted in the form of batholith, stock anddike.The granite porphyry is the main host rock of Aikengdelesite Mo (Cu) deposit.Accordingto the results of petrogeochemical study, this granite porphyry belongs to peraluminouscalc-alkaline suite of granitoids, and has high content of SiO2and comparatively rich in Naand poor in K, Ca, Mg. The granite porphyry comes from Andeans-type active continentalmargin. Plate subduction leads to lowering melting point of the fluid in subducting slab andthe mantle happens metasomatism, and then the partical melting mantle become basic magma.The underplating of mantle-derived magma provides heat and makes the basic lower crustpartical melting material to be porphyry magma.The result of granite porphyry zinconLA-ICP-MS U-Pb dating shows that the intrusions mainly come from early Indosinian periodbut not late Indosinian period with the206Pb/238U average weighted age of248.3±1.5Ma(MSWD=0.13) and concordant age of248.4±0.83Ma (MSWD=2.3).The ore bodies are distributed mainly over Xiadeboli, north Aikengdelesite,southAikengdelesite anomaly areas,while the north Aikengdelesite can be seen many minerals withhigh engineering controlling. Ore minerals of Aikengdelesite molybdenum (copper) deposit are molybdenite, chalcopyrite, pyrite and a small amount of galena, sphalerite etc. Gangueminerals are quartz, sericite, feldspar, biotite etc.Major ore textures are anhedral granulartexture, euhedral-subhedral granular crystal texture, cataclastic texture and metasomatictexture etc. and ore structures are mainly disseminated structure, massive structure, veinstructure and net-vein structuren etc.The Fe content（0.73%）in sphalerite and Cd content(0.07%~1.13%) in gelenite are low.,and the primary halos show a mesotherma ore-forming element.These assume that main metalsulfides of Aikengdelesite Mo (Cu) deposit formed in middle temperature, that is obviouslydifferent from ordinary hydrothermal molybdenites which formed in high temperature.Theaverage Co content(0.08%) in pyrite implies that pyrites formed in deep-focus.S/Fe（average1.144）,less than1.148,shows it formed in high temperature.Pyrites are widely distributed inthe whole process of ore-forming. In the early metallogenic stage, temperature in deep heatsource and Co content in hydrothermal fluid are quite high, a small amount of Fe is replacedby Co when pyrite crystallized.The wall-rock alteration, consists of silicification, potassic feldspar, sericitization,kaolinization, gypsification etc.,shows planar-type distribution. Mineralization can be dividedinto4ore-forming stages： oxide stage （Ⅰ）, pyrite-pyrrhotite-quartz stage （Ⅱ）,molybdenite-polymetallic sulfide stage（Ⅲ） and carbonatite stage（Ⅳ）, among them,molybdenite-polymetallic sulfide stage（Ⅲ） is important metallogenetic stage.Through microthermometry, the type of fluid inclusions in mineral-bearing quartz veinsmainly includes gas-liquid two phase inclusions and halite-bearing three phase inclusions.The ore-forming fluid is belogs to H2O-NaCl system and the range of homogeneoustemperature （150~280℃）,salinity （2~30wt%NaCl） and density(0.76~1.16g/cm3) ofore-forming fluid is large.The homogeneous temperature in halite-bearing three phaseinclusions is low but the salinity is high, it mainly because of the fluid absorbed salinity inshallow saline formation.Limited by the conditions of laboratory,the early upper limitmetallogenic temperature is not measured.Howerve,the temperature about200℃is maintemperature of metallogenic stage-temperature of metallogenic stage Ⅲ.Rock and mineral formation and metamorphism of Aikengdelesite molybden (copper)deposit are homologous.That is to say, the oceanic crust subduction leads to deeper mantlematerial happen to partly melting,and then the partial melting of mantle materials upwellthrough fractures of the wall rocks and mix with crust materials.The mixed magma becomesporphyry magma at last. Ore-forming fluid mainly comes from magmatic water at early stage,mixture water of meteoric and magmatic at main mineralization stage and meteoric water atthe late mineralization stage. Through research of areal geology, ore geology, metallogenic physic-chemical conditionsetc. the Aikengdelesite Mo (Cu) deposit can be regarded as porphyry molybdenum (copper)deposit,and its minerogenetic geotectonic background is Andeans-type active continentalmargin and mineralization period is later than porphyry emplacement time.