Study On Geochemistry Of Weiruo Gold Deposit In Lannigou Gold Area

Weiruo gold deposit belongs to the northwest of nanpanjiang basin.It is a small gold deposit in the periphery of slug gold deposit.The ore-forming geological conditions are superior and the deposit has good prospecting potential.Although previous studies have done a lot of work on the sludgou gold deposit,the degree of study on the weiruo gold deposit is relatively low.On the basis of previous studies,the author systematically studied the successively interpenetrating relationship of various vein bodies,ore fabric characteristics,source of ore-forming fluid and the formation mechanism of sulfide in the weiruo gold deposit through detailed geological survey in the field and collection of typical representative samples.In this paper,H-O isotopes,EPMA and in-situ sulfur isotopes are used to determine Au occurrence and source of metallogenic materials in weiruo gold deposit.The main achievements are as follows:?1?According to the metasomatic and successively interspersed relationships between metal sulphides,pyrite is divided into two stages:the disseminated pyrite stage?S₁?and the veinlike quartz-pyrite stage?S₂?.?2?The occurrence state of sulfide gold and the in-situ sulfur isotope study indicate that arsenopyrite and arsenopyrite are the main gold carriers of weiruo gold deposit.Au mainly exists in the form of nanometer gold?Au⁰?,a small part of which occurs in arsenopyrite and arsenopyrite in the form of solid solution?Au⁺?.The in-situ sulfur isotope test results showed that the sulfides formed in the two stages had relatively similar sulfur isotope values,indicating that the two stages had the same sulfur sources,both from Marine sulfates,and TSR?thermo-chemical sulfate reduction?was the reduction mechanism of sulfate in weiruo gold deposit.?3?The fluid inclusions in weiruo gold deposit are simple and mainly gas-liquid inclusions.Fluid inclusion homogenization temperature between 110?³90?,216?,indicating the tail-in the gold deposit is a typical characteristics of the high temperature hydrothermal deposit;The gas phase composition of the fluid inclusion is mostly H₂O and CO₂,and a small amount of CH₄,N₂,H₂ and CO gases.The components of fluid encapsulation phase are Na⁺,K⁺,Ca²⁺,Cl^-and SO₄^2-.The measured salinity of the fluid inclusion is low,between 1%and 18%NaCl eqv.Therefore,it is considered that the weiruo gold deposit belongs to the medium-low salinity deposit,and the metallogenic pressure is high.The metallogenic condition is a weak acidic environment with low oxygen fugacity.?4?The metallogenic fluid?¹⁸O_H2Oranges from 11.7‰to 17.1‰,and the range of?D value is between-73.8‰to-65.4‰,suggesting that the metallogenic fluid may be from formation water.According to the H-O isotope test results,the range of the delta?¹⁸O_SMOWMOW value in the quartz vein is between+22.7‰and+26.1‰.This indicates that the oxygen in the hydrothermal solution is most likely from the same source.It is speculated that the ore-forming fluid of weiruo gold deposit comes from the mixed fluid of metamorphic fluid and formation water based on the comprehensive geological background of ore-forming and the isotope of mineral hydrogen and oxygen.