黑龙江省嫩江县永新碲金矿床黄铁矿标型特征及稳定同位素研究

Typomorphic Characteristics and Stable Isotopes of Pyrite From the Yongxin Tellurium-Gold Deposit in Heilongjiang Province

为提取永新碲金矿床成因及找矿信息,对其载金矿物黄铁矿进行化学成分、稀土微量元素及S、Pb、Fe同位素等研究。结果显示,黄铁矿的S/Fe、Au/Ag、Co/Ni、Fe/（S＋As）和Co-Ni-As等成因标型显示该矿床属于中浅成火山热液型矿床,且所勘查的位置处于矿体中下部;具有轻稀土富集、重稀土亏损的＂右倾＂式稀土配分模式,较富集Th、U、Zr、Hf,亏损Ba、Sr和Nb等;Hf/Sm、Nb/La值表明成矿流体为含有部分F的弱还原性流体;Y/Ho、Zr/Hf和Nb/Ta值显示成矿过程稳定,没有外来物质混入,且成矿流体与地幔及地壳有密切关系。硫同位素分布具有明显的塔式效应（3.9‰~5.4‰）,表明成矿物质来源较深;其^206Pb/^204Pb=18.13~18.31,^207Pb/^204Pb=15.47~15.63,^208Pb/^204Pb=37.75~38.47,显示成矿物质为以地幔为主的壳幔混合来源;δ^57Fe集中在0.127‰~0.511‰,δ^56Fe集中在0.074‰~0.349‰,明显富集重同位素,也显示为壳幔混合来源。结合本区成岩时代、地球化学特征及区域典型矿床特征,认为该矿床应为早白垩世形成的中低温、中浅成的火山热液型碲金矿床,目前已剥蚀到中深部位置。

For the purposes of extracting genesis and prospecting information of the Yongxin tellurium gold deposit,a detailed investigation on chemical compositions,trace elements,rare earth element,as well as S-Pb-Fe isotopes of the Aubearing pyrite has been undertaken.Genetic typomorphic characteristics of the pyrite,such as S/Fe,Au/Ag,Co/Ni,Fe/（S＋As）,Co-Ni-As,etc.,suggest that this deposit belongs to the intermediate to epithermal volcanic hydrothermal gold deposit,with the pyrite from the middle-lower part of the prospecting orebody.The right-inclined REE distribution patterns,which are characterized with enriched LREE and depleted HREE,the enrichment of HFSE including Th,U,Zr and Hf,the deficiency of LILE including Ba,Sr,Nb,etc.,as well as ratios of Hf/Sm,Nb/La,etc.,of the pyrite indicate that the ore-forming fluid could be a weakly reductive fluid containing minor F.Ratios of Y/Ho,Zr/Hf,and Nb/Ta suggest that the pyrite was formed through a stable metallogenic process with no mixing of foreign materials,in the oreforming fluid closely related to the crust and mantle.Concentrative S isotopes（3.9%—5.4‰） with obvious ＂tower-like distribution＂reveal that the ore-forming materials were from a relative deep source.Ratios of ^206Pb/^204Pb（18.13—18.31）,^207Pb/^204Pb（15.47—15.63）,and ^208Pb/^204Pb（37.75—38.47） for the pyrites suggest that the ore-forming materials were sourced mainly from the mantle materials mixing with minor crustal materials.The δ^57Fe（0.127‰—0.511‰） and δ^56Fe（0.074‰—0.349‰） show that they are obviously rich in heavy iron isotopes with a feature of mixing source of crust and mantle.Combining with data of diagenetic ages,geochemical characteristics and characteristics oftypical ore deposits of this district,it is believed that the Yongxin tellurium-gold deposit is a medium-low temperature medium-epithermal volcanic deposit formed in the early Cretaceous.Furthermore,it is inferred that the surface of the current orebody could be the middle level of the original orebody due to the erosion caused by the regional uplift.