The Intermediate-Acid Magmatism And Polymetallic Mineralization In East Kunlun,Paleo-Tethys

The East Kunlun Ogogenic Belt?EKOB?is an extensive tectono-magmatic-metallogenic belt,which contains complex and abundant polymetallic mineralization.Many ore deposits are closely related to the Paleo-Tethys granitoids.This thesis,three typical deposits?Xiaowolong Sn deposit,Duolongqiarou Mo deposit,Nagengkangqie'er Ag deposit?in EKOB were selected as research objects.Here,we reported zircon and cassiterite U–Pb ages,molybdenite Re–Os age,and used these to constrain the timing of intrusion and mineralization in the Xiaowolong,Duolongqiarou and Nagengkangqie'er deposit.The whole-rock elemental,Sr–Nd and zircon Hf isotopic data for ore related granitoids in the deposit,to identify the petrogenesis and magmatic sources.Combining mineralogy,mineral geochemistry,and sulfide S-Pb isotopes to discuss the source of ore materials and their metallogenic mechanism,and to analyze the genesis of the deposit.Based on the regional deposits,the temporal and spatial distribution rules were summarized,and the relationship between ore-deposit and magma were discussed.We bulid the regional metallogenic model,and analyze the prospecting potential in the EKOB.The new obtained findings and conclusions can be summarized as follows:1.Age determinations by LA-ICP-MS U–Pb zircon dating indicated that the Xiaowolong porphyry monzogranite formed at 260.0±0.7 Ma.Cassiterite from the ore-bearing skarn yielded a Tera-Wasserburg U–Pb lower intercept age of 258.0±3.7Ma.These ages suggested that both granitic intrusion and related Sn mineralization in the Xiaowolong deposit were initiated during the Permian?ca.260 Ma?.The porphyry monzogranites had high Si O₂?71.26–73.13 wt%?and Al₂O₃?13.84–14.46 wt%?contents,were alkali-enriched?K₂O+Na₂O=7.08–7.69 wt%?,had A/CNK values that ranged from 1.01 to 1.05,were enriched in light REEs and large ion lithophile elements such as Rb,Th,U and K,were depleted in high field strength elements,and had relatively low Zr,Nb,Y and Ce contents.They thus exhibited the geochemical characteristics of I-type granite.The porphyry monzogranite had consistent negative whole rock?Nd?t??-6.8 to-7.1?and magmatic zircon?Hf?t?values ranging from-7.4to-1.6,detailed elemental and isotopic data demonstrated that the porphyry monzogranite were derived from partial melting of ancient crustal source.The magma fluid enriched in Si and Al metasomatized with the wall rocks enriched in Ca and Mg,formed skarn mineralization.When the oxygen fugacity of the system increased and temperature decreased,the cassiterite and magnetite crystallized from the enriched Sn fluid,and finally ore body was formed at a favorable structural site in the northeast.The Xiaowolong Sn deposit is a typical skarn deposit.2.The Duolongqiarou ore-bearing monzogranite and ore-barren granodiorite and have zircon U–Pb ages of 236.8±1.8 Ma and 237.6±1.5 Ma,respectively.Molybdenite Re–Os dating yielded a weighted mean model age of 235.9±1.4 Ma.These ages suggest that both the granitic intrusions and related Mo mineralization at Duolongqiarou were fromed during the Triassic?ca.236?Ma?.The ore-bearing monzogranite and ore-barren granodiorite belong to a high-K calc-alkaline I-type granite.The monzogranite and granodiorite have zircon?Hf?t?values varying from-3.0to 0 and from-4.6 to 0.5,with T_DM2 ages of 1271–1459 Ma and 1240–1558 Ma,and?_Nd?t?values range from-5.6 to-5.7 and from-5.5 to-5.7,respectively.These isotopic results indicate that the Duolongqiarou Mo-bearing and barren intrusions may have similar magma sources,and were formed by partial melting of Mesoproterozoic crustal components with an input of mantle-derived material.The temperature of amphibole show that the monzogranite and granodiorites range form 772?to 805?and from742?to 826?,the pressures are 109?145MPa,77?133MPa,and the oxygen fugacity?NNO is 0.2?0.9,0.6?1.5,respectively.The temperature and pressure of ore-bearing monzogranite are higher than ore-barren granodiorite,and monzogranites have characteristic of rich water.S-Pb isotopes indicate that ore-forming fluid is magmatic in origin.The monzogranites have a highly differentiated signature,which promotes Mo metal enrichment during magmatic evolution and subsequent formation of the magmatic-hydrothermal Duolongqiarou Mo deposit.The Duolongqiarou deposit is porphyry Mo deposit.3.The Nagengkangqie'er rhyolite porphyry has zircon U–Pb ages of 217.5±2.4Ma,indicating that the silver polymetallic mineralization age is similar or later than rhyolite porphyry.Geochemically,the rhyolite porphyry has the characteristics of high silicon,rich alumina and potassium,belonging to the high-K calc-alkaline series,with?Nd?t?value of-7.4 to-7.8,and zircon?Hf?t?value of-4.4 to-9.7,indicating that the rhyolite porphyry were produced during partial melting of a Neoproterozoic lower crust and input minor mantle materials.The S-Pb isotope indicates that the source of ore-forming materials mainly from magma,and mixed with sedimentary wall rock.The mechanism of the Nagengkangqie'er Ag deposit is mainly the fluid mixing.The Nagengkangqie'er Ag deposit is a epithermal deposit.4.The intermediate-acid magmatism of EKOB were analyzed and summarized,the granitoids related porphyry Mo deposit have characteristic of high Si O₂ and rich Al₂O₃,low Cr and Ni contents,and medium reduction.The granitoids related porphyry Cu deposit belong to a high-K calc-alkaline and metaluminous to peraluminous series and medium oxidation.With the increase of Si O₂,the granitoids associated with the skarn deposit have the trends of Fe-Cu,Fe-Sn,Pb-Zn.The Sr-Nd isotope indicated that the magma source were produced during partial melting of a lower crust,and had different contribution the mantle materials.The rocks have different degrees of anomalies Eu,Ti,and P,suggesting that magma experienced fractional crystallization.The oxygen fugacity of granitoids in different deposit have such trend:hydrothermal Cu deposits>epithermal Ag deposits>skarn Fe deposits>skarn Sn deposits>Porphyry Cu deposits>Porphyry Mo deposits>Orogenic Au deposit.5.The spatial and temporal distribution of different deposits in the EKOB were systematically summarized.The north Kunlun belt is mainly composed of skarn Fe-Cu-Pb-Zn-Sn polymetallic deposits and porphyry Cu-Mo deposits;the central Kunlun belt is mainly composed of porphyry Cu-Mo,porphyry Mo deposit,skarn Fe-Cu deposit,and orogenic Au deposit;the south Kunlun belt is mainly composed of hydrothermal Cu deposit,carlin-type Au deposit,and sedimentary superimposed hydrothermal and porphyry-skarn deposit.The mineralization of EKOB related granitoids are characterized by multiple stages,which concentrated in three peaks of245?238Ma,232?228Ma,and 225?218Ma.6.Based on sedimentary-tectonic-metamorphic-magmatic activity,three-stage dynamic evolution models are proposed,subduction stage,the slab break-off stage,and the asthenosphere underplating stage,corresponding tectonic setting is subduction,syn-collision,and post-collision,respectively.The Xiaowolong Sn deposit emplacement in a subduction tectonic setting,and the Duolongqiarou Mo deposit emplacement in syn-collision tectonic setting,and Nagenglangqie'er Ag deposit emplacement in post-collision setting.According to the magmatism and mineralization,we proposed a model of regional metallogenic model,Ag-Pb-Zn-Cu polymetallic deposit related low-temperature hydrothermal and epithermal deposit,and Fe-Cu-Pb-Zn-Sn polymetallic deposit related skarn deposits,and Cu-Mo-Au-Ag polymetallic deposit related porphyry deposits.