The Geochemical Characteristics And Its’ Ore-forming Signitlcance Of The Pluton In The Haoyaoerhudong Gold Deposit Of Inner Mongolia

The Haoyaoerhudong gold deposit, which is attached to Xinhure town in UradMiddle Banner of Inner Mongolia, locates in the west of the Mesoproterozoic Bayan Oborift on the west section of the northern margin of the North China plate. As a gold ore ofbig reserves and low grade, the Haoyaoerhudong ore deposit reach to213t in provedreserve, while its grade only is0.82g/t. The orebody occurs in the greyish blackmetamorphic fine sandstone and siltstone. There is large area of hercynian graniticplutones in the orefield, which is deemed to have a close relationship with the formationof ore deposit. On the basis of petrography, the article takes the granitic plutones as theobject of study, emphasizes to analyse its geochemistry characteristics in order to remodethe tectonic setting in the processing of invasion, and discusses its ore-formingsignificance combining the research achievements of predecessors.By the CIPW standard mineral calculating and the QAP chart, the Haoyaoerhudongplutone can be divided into three types: the monzonitic granite, the quartz monzobioriteand the alkali feldspar granite. Among them, the monzonitic granite mainly exposes ineastern part of the orefield in the form of dykes; the quartz monzobiorite appears inmiddle and east part of the orefield as small laccoliths; while the alkali feldspar granite,whose area is the largest, mainly as batholith distributes in north and northest part oforefield.By analyzing the geochemistry datum of the three types plutones, we can concludethat all of them have the property of high potassium calcium alkaline and thecharacteristic of enrichment of large-ion lithophile elements like Rb、K and the deficit ofHSFE elements such as Nb、Ta、Ti、P. What’s more, the isoplot of Sr and Nd both indicatethat their’s lithogenous material contaminated by the mantle material in different degreesmainly derived from lower crust and the invasion of the plutones have intimate relationswith collision orogenesis between North China plate and Siberia plate. Nevertheless, thequartz monzobiorite has lower content on SiO₂, while higher on Fe₂O₃^T、MgO and TiO₂,especially higher on Sr; the monzonitic granite, whose fractionation degree of LREE andHREE is the highest, is characterized by high SiO2and low Al₂O₃; while alkali feldspar granite has the most alkali content and obvious negative anomaly of Eu elememt so as toexpress the characters of A-type granite.Combining with the discrimination diagrams of structural environment, theHaoyaoerhudong plutone is thought to be formed in syn-collision—post-collisionenvironment between the North China plate and the Siberia plate. Among them, themonzonitic granite formed in syn-collisional environment, and possibly be influenced bythe heat of melting of the underthrust plate and the mantle wedge in the process ofsubduction, of which the parental magma derived from partial melting of lower crust; thequartz monzobiorite formed in the uplift environment of post-collisional, resulting fromthe melt of the thickening lower crust; while the alkali feldspar granite formed in thelateorogenic era while the mantle basaltic magma underplated leading to the lower crustmelting and being mixed.According to the mineralization ages, the ore-forming fluid properties and thecharacteristics of geochemistry of host rocks, combining with the theory achievements ofthe relation between the granitic plutones and gold ore-informing, the invasion of theHaoyaoerhudong plutone, as a essential factor of ore-forming, is considered to offerenough heat and a part of ore-forming fluid sources.