| Iron-oxide copper gold deposit(IOCG)is a new type of deposit worldwide currently.From the view of resource reserves,IOCG deposits are rich in a large number of economic elements,such as Fe,Cu,Au,U,Ag,REE,Co,Mo and other metal those can be comprehensive utilization.From the standpoint of the mineralization time,IOCG deposit are distributed from Archean and Phanerozoic.From the standpoint of special distribution,IOCG deposits are all over the world.The Lala IOCG deposit is turn out to be a typical Iron-Oxide-Copper-Gold(IOCG)deposit by recent research,which is located at the western margin of the Yangtze Block,Kangdian region in Sichuan.Lala IOCG deposit is one of the important copper and molybdenum production base of southwest China.The Lala IOCG deposit is hosted in the Luodang formation of Paleoproterozoic Hekou Group,which is a consequence of volcanic-sedimentary rocks.Metal reserves of Mo is more than 0.2Mt,average grade is w(Mo)=0.03%,copper and molybdenum mineralization are closely related.Therefore,this study focus on the molybdnite,combined with regional geology,mining area geology and ore deposit geology research,based on the geological survey,according to the mineragraphy,polytype,composition,Re-Os isotope,S isotope,trace elements,rare earth emelmets and H-O isotope of inclusions in fluorite which is intergrown with different stages of molybdenite in the lala IOCG deposit,conclusions are drawn as follows:1.There are two stages of molybdenite mineralization exist in the Lala IOCG deposit.Molybdenite(I)are regular plate column or bending plate column shaped,formed in the metamorphic hydrothermal stage,disseminated filled in the biotite schist,intergrown with fluorite,chalcopyrite,and magnetite.It is turn out that the Molybdenite(I)is 2H type by X-ray analysis,suggesting it was formed in a high temperature environment.The crystalline formula of Molybdenite(I)is:(Mo4+0.994612Se4+0.001434Te4+0.000632W4+0.000149Re4+0.000038Sn4+0.000045)S2+2.Molybdenite(II)are irregular thick and bulk shaped,formed in later overprinted hydrothermal mineralization,filled in the biotite schist,and intergrown with biotite,calcite,and chalcopyrite,formed in a relatively low temperature environment indicated by it 2H+3R polytype,The crystalline formula of Molybdenite(II)is:(Mo4+0.984358Se4+0.005304Te4+0.001385W4+0.000727Re4+0.000093Sn4+0.000339)S2+2.2.The Re-Os isotopic apparent age of Molybdenite(I)in Lala IOCG deposit is 1023~1042Ma.Ore-forming material of Molybdnite(I)are source from crust mantle mixed,the mineralization is mainly affected by the converge of Rodinia supercontinent.The Re-Os isotopic apparent age of Molybdenite(II)is 847 Ma and 852 Ma,which represents the late hydrothermal metallogenic time period of Molybdenite(II).Ore-forming material of Molybdenite(II)is crust or crust-mantle mixed source,the mineralization is mainly affected by the breakup of the Rodinia supercontinent,the intrusion of gabbro magma provided necessary space and heat of the location of molybdnite(II).3.S isotopic analysis suggests that:(1)δ34S∑S(‰)of Molybdnite(I)is 1.43‰,indicating that the S of Molybdnite(I)is sourced from the crust-mantle mixed source,the equilibrium temperature of S isotopic is 569.99℃;(2)δ34S∑S(‰)of Molybdnite(I)is-2.87‰,which demonstrated that the S of molybdenite(II)is mainly controlled by crust source and related to the crust-mantle source,equilibrium temperature of S isotopic is 304.48℃.4.H-O isotope analysis of inclusions in fluorites intergrown with two stages of molybdnite suggesting that:(1)δ18OH2O value of ore-forming fluid of Molybdnite(I)range between +4.70% and +13.50%,average at +9.10%,δ18DH2O values between-60.40% and-37.30%,Average at-31.85%,which suggesting the mineralization fluid is metamorphic water;(2)δ18OH2O value of ore-forming fluid of Molybdnite(II)range from-7.60% to-5.4%,average at-6.50%,δ18DH2O value is between-67.3% and-53.2%,average at-60.25%,indicate the ore-forming fluid of Molybdnite(II)is mainly controlled by meteoric water.5.Metal of molybdenite(I)is sourced from the country rocks,molybdenite(I)is characterized by high content of REE,LREE enrichment and negative Eu anomalies,which is mainly controlled by the fluid itself,or related to the biotite in the country rocks,suggesting the high formation temperature of ore-forming fluid.Ore-forming fluid of Molybdenite(II)may related to external fluid,and the formation temperature is relatively low,its positive Eu anomaly is controlled by the temperature,and the negative Ce anomaly is mainly controlled by the physical and chemical environment,indicating that the ore-forming fluid is characterized by high oxygen fugacity. |
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