| Irtysh metallogenic belt is located in northern Xinjiang, China, as the suture zone between Siberian plate and Kazakhstan-Junggar plate. This thesis makes detailed studies on the volcanic and intrusive rocks, typical deposits of Qiaoxiahala- Aketasi district in the eastern section of Irtysh metallogenic belt, including re-identifying geological background and evolution of the orogenic belt, dissecting systematically geological characteristics, fluid inclusions features, chronology of mineralization and stable isotope characteristics of Aketas gold deposit. On the basis study of multi-period of iron, copper and gold mineralization, this thesis discusses the genesis of deposits in this area and establishes a new metallogenic model; moreover, it summarizes a prospecting model and makes the evaluation of prospecting.Qiaoxiahala-Aketasi district developed middle Devonian Beitashan Group intermediate-mafic volcanic rocks with features of shoshonites. The volcanic rocks are overall low in ∑REE Contents(REE=14.09-122.52×10-6), enriched in LREE (LREE/HREE=2.43-6.41, (La/Yb)N=1.83-7.70) and Ba, Sr, depleted of Ti, Nb, Ta, and weak Eu(δEu=0.92-1.37) anomalies, indicating features of island arc volcanic rocks. There are large amounts of intermediate-acidic calc-alkaline I-type granites distributing in Qiaoxiahala-Aketas area:Kekekuduke monzonitic diorites are typical arc magmatic rocks; Aketas quartz monzonites (U-Pb age dating with LA-ICP-MS method yielded 309.0±4.7Ma)have the features of adakites that caused by plates subduction; Qiaoxiahala monzonitic granites are adakites formed by underplating of post-collision mantle magma, indicating the features of time and space evolution of island arc. Combined with previous findings, this thesis proposes that eastern section of the late Paleozoic Irtysh tectonic-metallogenic belt experienced four stages:subduction(D1-early C2),-collision orogeny(mid-late C2),-orogenic extension (P1-T2),-orogenic termination(T3)The Aketasi altered rock ore-body is mainly controlled by the NWW-striking fault fissures.Quartz vein type ore body is mainly controled by NEE-striking fault fissures. Mineralization stages can be divided into three stages:low (gold) grade pyrite-big pure white quartz veins stage(Ⅰ), Gold-pyrite-chalcopyrite-quartz veinlets stage(Ⅱ)and pyrite-quartz-carbonate stage(Ⅲ). The auriferous quartz veins and sericite of main mineralization stage Ar-Ar geochronology show that the crystallization ages are 240.38±4.89Ma、245.35±247.18Ma, gold mineralization is limited between 240.38-247.78Ma, that was Early Triassic of Mesozoic, which is also the result of sturcture-thermal events in the indosinian (260-245Ma).The main types of fluid inclusions in the Aketas gold deposit are W-type(NaCl-H2O inclusions), WC-type(CO2-H2O inclusions) and C-type(CO2-(CH4、N2)inclusions).The early stage of mineralization mainly contains WC-type and few W-type:the homogenization temperature varys from 229-356℃ and 161-276℃; salinity ranges from 4.8-10.3wt%NaCleqv and 6.0-12.3wt%NaCleqv; fluid density ranges from 0.79-0.99 g/cm3 and 0.84-0.95 g/cm3.The main metallogenic stage includes W-type,WC-type and a small amount of C-type:the homogenization temperatures of W-type is 200-350℃; WC-type is 235-320℃; the CO2 part of the homogenization temperature in C-type is 3.8-12.4℃; salinity ranges from 3.6-9.2wt%NaCleqv and 3.3-12.6wt%NaCleqv; ore fluid densities are 0.60-0.89 g/cm3,0.81-0.98 g/cm3 and 0.82-0.96 g/cm3. The late stage is mainly W-type:the homogenization temperature peak ranges from 176-262℃,salinities range from 6.0-7.1 wt%NaCleqv. The ore-forming fluids of Aketas gold deposit are characterized by a a H2O-CO2-NaCl system with low temperature, low salinity and low density. Hydrogen and oxygen isotope δ18O2O ranging from 6.6‰～11.2%o,5D rangeing from-97.3‰～-109.3‰, suggests that the ore fluid has a mixture sources of magmatic water and metamorphic water. The δ34S of sulfur isotope ranges from-3.1～-0.8‰, showing the characteristics of deep source magma sulfur.There is mutiperiodic mineralization of iron, copper and gold in Qiaoxiahala-Aketas belt:iron ore was formed by the submarine volcano in early-middle Devonian(-390Ma); copper ore was formed by the volcanic hypabyssal magmatic hydrothermalism in middle Devonian(390Ma-370Ma);gold ore was formed by the ductile-brittle tectonic deformation in the Permian-Triassic(290-240Ma). This thesis establishes the prospecting symbol, background model of geological prospecting, exploration technology method and geophysical and geochemical exploration methods combination process in Qiaoxiahala-Aketas belt, and puts forward two perspective areas with great potential for orogenic type gold deposit at Jieertai and Xile district. |
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