Tin transport and cassiterite precipitation from hydrothermal fluids  

作　　者：Xiangchong Liu Pingping Yu Changhao Xiao 

机构地区：[1]Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China [2]Key Laboratory of Paleomagnetism and Tectonic Reconstruction,Ministry of Natural Resources,Beijing 100081,China [3]The Laboratory of Dynamic Diagenesis and Metallogenesis,Institute of Geomechanics,CAGS,Beijing 100081,China

出　　处：《Geoscience Frontiers》2023年第6期49-69,共21页地学前缘（英文版）

基　　金：The work was financially funded by CGS Research Fund(DZLXJK202103,DZLXJK202206,DZLXJK202203);China Geologi-cal Survey project(DD20230344);Guizhou Provincial Science and Technology Project(Qiankehezhicheng[2021]408);major project of Guizhou Bureau of Geology and Mineral Resources Exploration and Development(Qiandikuangkehe[2021]1).

摘　　要：Cassiterite(SnO_(2))is the main ore mineral of tin in magmatic-hydrothermal tin deposits,but tin transport and precipitation mechanisms from hydrothermal fluids remain poorly understood.We critically evalu-ated aqueous tin speciation in hydrothermal fluids from extensive experimental data and thermody-namic modeling.Sn(II)chloride complexes in hydrothermal fluids exist mainly as SnCl^(+),SnCl_(2)(aq),and SnCl_(3).The revised Helgeson-Kirkham-Flowers model parameters of these three tin species and two tin ions(Sn^(4+) and Sn^(2+))were derived from the correlation algorithms among these parameters,and the standard molar properties of cassiterite were optimized to be internally consistent with the available thermodynamic dataset.These thermodynamic parameters,together with the available equilibrium con-stant equation of Sn(IV)chloride complexes,could reproduce the available solubility data of cassiterite in acidic solutions at 400-700℃under oxygen fugacity(f_(o2))levels buffered by hematite-magnetite(HM)or nickel-nickel oxide(NNO).These comparisons allow modeling chemical systems of SnO_(2)-NaCl-HCI-H_(2)O(liquid phase)to examine tin transport and cassiterite precipitation mechanisms under tin-mineralizing conditions:300--500℃,50-150 MPa,2 molal NaCI,and fo。levels from QFM(quartz-fayalite-magnetite)to HM.Sn(I)chloride complexes are commonly interpreted to dominate in aqueous tin speciation under f_(o2)=NNO,but our modeling results indicate that considerable contents of Sn(IV)chloride complexes also exist in those reduced fluids with high HCI contents,consistent with recent in situ high-temperature experiments and molecular dynamic simulations.The Sn(I)/Sn(IV)ratios in fluids depends onfo,temperature,and HCl contents.A considerable amount of Sn(IV)possibly exist in an early mineralization stage even under f_(o2)=NNO;if so,redox reactions are unnecessary to precipitate cassiterite from these mineralizing fluids.We find that even if the f_(o2) levels are constant,simple cooling can alter mineralizing fluids to be

关 键 词：CASSITERITE Aqueous tin species Precipitation mechanisms Tin deposits Thermodynamic modeling 

分 类 号：P618.41[天文地球—矿床学] P597.3[天文地球—地质学]