| The Muluozhai deposit is located in the north of the western Sichuan metallogenic belt and is the only deposit in the west of the Yalongjiang fault.The main ore-producing area,the Zhengjialiangz,contains marble and epidiabase in the surrounding rocks,which is mainly different from other deposits in the ore belts.It is a torsion-type fault that control the the ore structure of this section,and the ore bodies are vein-like,stratoid-like or lenticular-shaped,with mostly arranged in parallel.The attitude of ore bodies is similar to that of the mining area,with an inclination angle of about 70° and tending towards NW.The ore body mainly develops in the crush zone of epidiabase,the contact zones of epidiabase and marble,the fracture and interlayer zones of marble,and few in the growing fractures of syenite.The boundary is clear between the ore body and the surrounding rock,indicating that the ore-forming process is dominated by filling with less replacement.The ore types include fluorite-carbonate veins,fluorite-calcite fine veins,rhombohedrite veins,calcite veins,altered carbonate rocks,and brown and yellow sand-like rare earths.The ore minerals are mainly bastnaesite with less parasite,while vein minerals includes fluorite,calcite,strontianite,dolomite,barite,gelenite,and pyrite.The secondary minerals are flogopite,rutile,magnetite,flogopite,anorthose,quartz and so on.There is still illite during the epigenetic process.From the SEM observation of the strontianite,phlogopite and montmorillonite are closely symbiotic.The Ar-Ar dating of the phlogopite shows an average age of 27.6 ±0.2 Ma,and a corresponding anti-isochronal age of 27.1 ± 0.53 Ma.The age coincides with the ore-forming age of the bastnasite.The trace elements and rare earth elements diagrams of ore and veins minerals show a large positive excursion of lithophile elements such as Sr,Ba,U,Th and Pb,while the high field strength elements,Zr and Ti,show negative excursions.In addition,the ore is enriched in light rare earths and heavy rare earths,while the values of La/Yb are high.The results indicate the Lighter Rare Earths are enriched.The results of carbon and oxygen isotopes in calcite and ordovicite in the ore show that the value of ?53CV-PDB is between-4.6‰ and-5.9‰,and the value of ?18Ov-sMOW is between 11.7‰ and 16.0‰,indicating the carbon in ore might be a source of mantle,and it was affected by low-temperature alterations and dissolution of marine carbonates during the evolution of the fluid.Sulfur isotope results of pyrite and galena in ores show that the ?34S of sulfides is negative(-7.2?-14.1 ‰).Based on the analysis above,magma-carbonatite magma evolved from the magmatic stage to the hydrothermal stage during the Cenozoic ascending emplacement process,forming fluid rich in K+,Na+,Ca2+?Sr2+?Ba2+?F-?CO32-and SO42-.The fluid,which rises along the tension fracture of the mining area,invades the fracture zone of the epidiabase,the contact zone of the epidiabase and the marble,and is accompanied by the decline of the temperature,alkalifeldspar,calcite,fluorite,barite,rhombohedrite,and chalconeite were successively precipitated,which eventually form a large amount of bastnasite. |
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