| Luokuidong Mo ore deposit located in the Baoting county of Hainan Island,close to the south of the centre part of EW-trending Jiusuo-Lingshui fault zone and the south edge of the early cretaceous Tonganling continental volcanic petrofacies.It's a large-scale porphyry Mo deposit,having about 0.3 Mt Mo metal reserves with the average grade of 0.055%.In this paper,based on field geological investigation work and laboratory study,we first systematically summarized the characteristics of geology,focused research on geochronology,petrogenesis,the origin of ore-forming fluids and materials,and then preliminarily analysised the genesis of ore deposit,built up a metallogenic model.Some conclusions are made as following:1.Luokuidong mining area has many voluminous magmatic rocks.Thereinto,extrusive rocks are mainly of intermediate-acid volcanics and volcanoclastic rocks.Intrusive rocks include intermediate-coarse granular granite,porphyritic granite,granodiorite,adamellite,masanophyre and quartz syenite etc.Dyke rocks include diabase,andesitic porphyrite,dacite-porphyry and quartz vein etc.The main tectonics of diggings are liner structure and ring-shaped tectonic?crater tectonic?.Mo mineralization mainly occurred in the top of latent porphyritic granite,then in the peripheral volcanics,volcaniclastic rocks,adamellite and masanophyre.Orebody shape is mainly stratiform,stratiform-like.Ore textures are mainly hypidiomorphic foliated,flaky.Ore tectonics are mainly typical veinlet,stockwork,disseminated,star point and nodular.Metallic minerals mainly include molybdenite,secondly pyrite,chalcopyrite,slight sphalerite and scheelite.Gangue mineral compositions mainly include quartz and feldspar.The hydrothermal mineralisation period includes quartz-K-feldspar stage,quartz-sulfide stage and quartz-carbonate stage.Thereinto,molybdenite mainly appears in intermediate stage.Altered wall rock includes Mo-bearing high silicification,Mo-bearing silicon-potassium,Mo-bearing siliconization and epidotization-chloritization alteration zone from crater inside to outside.2.The LA-ICP-MS zircon U-Pb dating from Luokuidong Mo ore deposit,which include volcaniclastic rock?rhyolitic crystal pyroclast tufflava?,masanophyre,porphyritic granite and diabase,yielding their weighted mean ages are 104.1±0.7Ma,102.3±0.7 Ma/102.5±0.6 Ma,102.4±0.5 Ma and 97.2±1.0 Ma,respectively.Re-Os dating of seven molybdenite samples separated from the Luokuidong Mo ore deposit yielded an isochron age of 100.1±1.8 Ma.These ages indicate the mineralization is the product of ore-bearing hydrothermal activity after volcanism and emplacement of pluton in a relatively short time,and magmatic activity at least lasted ca.5 Ma.We hold the opinion that porphyritic granite is mother rock on the basis of geological characteristics of ore deposit.Combining with research on Mo metallogenic events in South China,the youngest ore-forming age of Mo mineralization occurs in Hainan Island and focus on the Cretaceous?ca.72112Ma?period,possibly corresponding to a large-scale stretching and thinning tectonic setting in Eastern China.3.Base on the major elements,trace elements,Sr-Nd isotopic compositions of whole rocks and zircons Hf isotope.We think that the origin of rhyolitic crystal pyroclast tufflava rock may derived from the lower crust rock remelting and erupting,which underwent the underplating of basaltic magma.The mother rock porphyritic granite,which geochemical characteristics are similar to the adakitic rock,may derived from incrassation lower crust rock?Mesoproterozoic?remelting after the underplating of basaltic magma.Meanwhile,their magma or magmatic hydrothermal system under a high oxygen,water-rich environment.Furthermore,abundant metallic elements of enriched mantle also provided the source of metallogenic elements.All these created advantaged geological condition for the forming of Luokuidong Mo ore deposit.Masanophyre and porphyritic granite have similar formation age,but they have higher?REE,obvious negative Eu and Sr anomaly,indicating they may derived from shallower lower crust rock?Mesoproterozoic?remelting.Diabase magma source once suffered from subduction zone fluid replacement transformation,and then caused mantle source region enrichment.4.H and O isotopic compositions of quartz from the main metallogenic stage of Luokuidong Mo ore deposit are?D=-70.8-59.7‰and?18O-water=-1.47.2‰.We infer the ore-forming fluid mainly formed from magmatic hydrothermal,but meteoric water cannot be excluded.5.The large range of molybdenite and pyrite?34S value from-4.7‰to 3.7‰,indicating that sulfur source may derived from magmatic source.Molybdenite and pyrite Pb isotopic characteristics indicate their ore-forming materials mainly originated from crust but mixed some contribution of mantle components.In addition,rhyolitic crystal pyroclast tufflava,porphyritic granite and masanophyre Pb isotopic characteristics are similar to these metal sulfides,indicating host-rocks also provided some ore-forming materials.Furthermore,Re content of molybdenite is 26.0450.39 ppm?average 33.65 ppm?,suggesting ore-forming materials may belong to crust-mantle mixed source type,and dominate of crust source.6.The genesis model of Luokuidong Mo ore deposit could use magma convection fluid enrichment mechanism to explain. |
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