| Beiya Gold-Polymetailic Deposit is a typical representative of Himalayan porphyry-skarn type deposit on Sanjiang Tethyan metallogenic domain.On the basis of predecessors study and field geological investigation, this paper have a systematic study of magmatic rock sequence% magma evolution the source of iron and mineralization process, through the methods of element geochemistry、isotope geochemistry and fluid-inclusion geochemistry. Eventually, this paper have deepened predecessor’s metallogenic model. In this paper, the main achievements of understanding:(1)Systematic LA-MC-ICP-MS U-Pbzircondatingresults of intrusiverocks in Beiyadistrict show thatquartz monzonite porphyry on Wandong mountain section formed in38.82±0.28Ma,biotitesyenite porphyry on Tanyao village formed in37.87±0.38Ma, syenite porphyry on Tanyao village formed in38.4±1.3Ma,quartz syenite porphyry on Tanyao Guogai halls formed in38.6 ±1.6Ma, detrital zircon grainsformed in795.3±5.2 Ma.On the basis ofpredecessor’s dating and the relationship of intrusive bodies,the magmatic intrusion sequencesin sequence of quartz albitophyre (60-65Ma)% quartz-monzonite porphyry% syenite porphyry、biotitesyenite porphyry and lamprophyre (31～38Ma),they together construct the Beiya alkali porphyry.(2)Rock geochemistry data of quartz-monzonite porphyry and biotitesyenite porphyry shows that the Beiya alkali porphyry have high SiO2 and Al2O3,Sr/Y and (La/Yb)N,enrichSr and LREE,deplet HREE,with weak negative Eu abnormity.The geochemical characteristics shows it’s adakite.Overall,thesimilaritygeochemical compositions shows that quartz-monzonite porphyry and biotitesyenite porphyryhave the same magma source region.(3) Fe isotope composition data on basalt、quartz-monzonite porphyry、skarn type magnetite、porphyrytype pyrite shows that Fe origin fromalkali-rich porphyries and basalt during mineralization process.Fe heavy isotope is tended toenriched at basalt near porphyry than mining area periphery.Fe heavy isotope is tended to enriched at alkali porphyry than predecessors study.(4)Fluid inclusion microthermometry data of mineralized quartz veins in alkali-rich porphyry shows that the porphyry mineralization can be divided into two mineralization stages:(a)Molybdenite-chalcopyrite-pyritemineralization stages,the homogenization temperature from 286℃ to 527℃, average to 381℃, salinity from 0.9% to 28.4%;(b)Chalcopyrite-pyritemineralization stages,the homogenization temperature from 217℃ to 474℃, average to 316℃,salinity of mineralizing solutions manifests bimodal distribution pattern with two ranges from 2.4% to 22.2% and from 31.9% to 46.3%. Petrography feature and microthermometry dataoffluid inclusions shows that the upercritical fluidexsolution from alkali-rich porphyry separated into high salinityrich liquid inclusions and low-salinities rich gas inclusionsafter fluid boiling.(5)Rare earth element data of mainly rock and mineral in Wandongshan shows that porphyry copper-gold ore inheritance potassic porphyry REE characteristics and embodies the magma flow characteristics.Skarn Fe-Au ore formed in high temperature^ oxidizingand high water-rock ratio metallogenic environment.Iron enrichment under the long-term function of ore-forming fluid. Hydrothermal vein Fe-Au ore formed in an oxidizing environment. The mixed mereoric and magmatic fluid is the main mechanism of hydrothermal vein ore deposition. The variousREE patterns symbolize the multi-source of fluid and multi-phase metallization.(6) On the basisresearch of geological characteristics、fluid evolution、sources of ore-forming matters and metallization, it deepen the predecessor’s metallogenic model... |
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