The state of gold in phases of the Cu-Fe-S system:In situ X-ray absorption spectroscopy study  

作　　者：Boris R.Tagirov Olga N.Filimonova Alexander L.Trigub Ilya V.Vikentyev Elena V.Kovalchuk Maximilian S.Nickolsky Andrey A.Shiryaev Vladimir L.Reukov Dmitry A.Chareev 

机构地区：[1]Institute of Geology of Ore Deposits(IGEM RAS),35,Staromonetnyi per,119017 Moscow,Russia [2]National Research Centre‘Kurchatov Institute’,1,Akademika Kurchatova pl,123182 Moscow,Russia [3]Institute of Physical Chemistry and Electrochemistry(IPCE RAS),31,Leninsky Prospect,119071 Moscow,Russia [4]Institute of Experimental Mineralogy(IEM RAS),142432 Chernogolovka,Moscow Region,Russia

出　　处：《Geoscience Frontiers》2023年第3期103-116,共14页地学前缘（英文版）

基　　金：the ESRF for the beamtime allocation under proposals No.ES-184(ID26 beamline)and ES-703(BM20 beamline)study was supported by the Russian Science Foundation grant No.20-17-00184(XAS experiment,interpretation,geological application);Grant of the President of the Russian Federation for the state support of the leading scientific schools of the Russian Federation No.NSh-2394.2022.1.5(synthesis experiments,analysis of the synthesis products);support by the Russian Ministry of Science and Education under grant No 075-15-2022-1107(XAS experimental setup).

摘　　要：Chalcopyrite and bornite are the main Au-bearing minerals at Cu porphyry deposits,volcanogenic massive sulfide(VMS)deposits,Cu-Ni deposits of the mafic magmatic complexes,and ores of submarine sulfide edifices.Bornite and intermediate solid solutions with wide compositional variations(bnss and iss–high-temperature chalcopyrite,correspondingly),which can scavenge economic concentrations of Au,appear in the Cu-Fe-S system at ore-forming conditions.However,the state of Au in bnss and iss is yet unknown.To solve this conundrum,we synthesized samples with net chemical composition of bnss and iss,studied them by in situ X–ray absorption spectroscopy(XAS),and used the experimental data to explain the Au distribution among natural ore-forming minerals.The sulfide samples were obtained at 495–700℃ in Au-saturated system by means of salt flux method.The bnss contained1.2–1.6 log units more Au than iss:up to 18 wt.%Au in bnss vs 0.4 wt.%Au in iss at 700C.An increase of temperature resulted in the sharp increase of Au concentration in both phases,1 log unit per 100℃ at f(S2)close to S_((l)) saturation.Analysis of Au L_(3)-edge spectra recorded at 25–675℃ revealed that at 25℃ Au exists mainly in the metallic state.At t>500℃ the spectral features of Audisappear,and “chemically bound”Au predominates.The Au form of occurrence in the iss field is interpreted as Au-bearing clusters with a stromeyerite-like(CuAgS)structure.Digenite Cu_(2–x)S and bnss contain Au in a mixture of stromeyeritelike and petrovskaite-like(Au_(0.8)Ag_(1.2)S)clusters.The chemical composition of both forms is close to CuAuS,where the nearest Au neighbors are two S atoms at R_(Au-S)=2.34–2.36Å.Results of the present study allow to determine the state of Au and its concentration in the main Cu-bearing minerals of sulfide ores as a function of the T-f(S_(2))-compositional parameters.Due to the sharp increase of the CuAuS clusters stability with increasing temperature,in high-temperature ores formed at t>350℃ Au enriches Cubearing

关 键 词：“Invisible”gold Bornite solid solution Intermediate solid solution DIGENITE CHALCOPYRITE X-ray absorption spectroscopy 

分 类 号：P618.51[天文地球—矿床学] P597.3[天文地球—地质学]