浙西开化石龙头金矿含金黄铁矿的成分标型及硫同位素特征研究

Composition and sulfur isotope characteristics of auriferous pyrite from the Shilongtou gold deposit in Kaihua, western Zhejiang Province

浙西开化石龙头金矿位于皖浙赣断褶带中,矿体明显受断裂控制.为了解含金黄铁矿的矿物学特征及其对金矿化作用的指示,对矿床中黄铁矿进行了X射线衍射、电子探针及其硫同位素分析.结果显示,矿石中主要金属矿物为黄铁矿和毒砂,含少量褐铁矿和磁黄铁矿,脉石矿物有石英、绢云母、伊利石和白云石等.黄铁矿的Fe/（S＋As）值在0.777～0.886之间,平均为0.828,说明其在中深部环境生成;Co含量（64×10^-6～111×10^-6）及Au/Ag值（3.6～17.8）指示其形成于中低温环境;Co/Ni值为1.95～4.47,平均为3.59,指示其为热液成因;较高的As含量和As-Co Ni相对含量三角图显示成矿流体与岩浆热液有关,具有地下热卤水的特征;硫同位素值介于6.14‰～8.27‰之间,偏离陨石硫的范围,而与超镁铁质岩的硫同位素值相近,表明成矿流体来自深部,后期受壳源物质影响.

The Shilongtou gold deposit in Kaihua of western Zhejiang lies in the Anhui-Zhejiang-Jiangxi faultfold belt,with its orebodies obviously controlled by regional faults.In order to understand the mineralogy of pyrite and the indicator of gold mineralization,the authors studied the pyrite by using X-ray diffraction （XRD）analysis,electron microprobe analysis and sulfur isotopic composition analysis.The results show that major metal minerals are pyrite and arsenopyrite,with minor limonite and pyrrhotite,whereas gangue minerals are dominated by quartz,sericite,illite and dolomite.Electron microprobe analyses of auriferous pyrite show that the （Fe）/（S ＋ As） ratios are between 0.777 and 0.886,indicating that it formed at the middle to shallow depth.Co content is relatively low （64 × 10^- 6～ 111 × 10^-6）,and Au/Ag ratios vary from 3.6 to 17.8,suggesting that it formed in a low temperature environment.Co/Ni ratios are between 1.95 and 4.47,with an average of 3.59,indicating its hydrothermal genesis.The high As content and the As-Co-Ni ternary diagram show that the hydrothermal fluid was related to primary magmatic activity,with a nature of underground thermal brine.Sulfur isotope values vary from 6.14‰ to 8.27‰,similar to those of ultrarnafic rocks from deep crust,with the values affected by crustal sulfur at the later stage.