激光剥蚀电感耦合等离子体质谱-电子探针分析白山堂铜矿中的黄铁矿成分

Determination of Composition of Pyrite in the Baishantang Copper Deposit by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry and Electron Microprobe

通过激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)获得被测物相中痕量元素的丰度值是目前原位分析矿物物相的技术之一。黄铁矿作为斑岩铜矿中的重要矿物,其主量、微量元素的特征能为成矿过程提供重要信息。本文建立了应用LA-ICP-MS测定黄铁矿微区微量元素组成、电子探针(EMPA)测定主量元素的方法,并将该方法应用到白山堂斑岩铜矿区。LA-ICP-MS实验采用60μm的激光束对分析样品进行斑点式剥蚀,以氦气作载气,重复频率5 Hz,激光能量约6 J/cm^2;单点分析时间60 s,分析数据以Fe作内标,用MASS-1黄铁矿标样进行校正,多数元素分析精度好于10%。针对黄铁矿与毒砂光学性质相似,容易混淆的问题,可以利用二者物理性质的差异进行区分。测试结果显示:矿区黄铁矿的主量元素呈亏硫高铁的特征,指示其为热液成因;微量元素特征表明其形成深度为中部,属与火山作用有关的中低温热液型黄铁矿。此结论对白山堂铜矿的成因类型、成矿流体来源等提供了相应的证据,对矿区的勘查具有理论指导意义。

Determination of trace elements in analyzed mineral phase by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry（ LA-ICP-MS） is a new in situ technique for mineral phase analyses. As an important mineral in porphyry copper deposits, the major and trace elements of pyrite can provide important information for the ore-forming process. A method for determination of the trace elements in pyrite by LA-ICP-MS and major elements by Electron Microprobe was developed and has been applied to the Baishantang porphyry copper ore district. For the LA-ICP-MS experiment,the laser beam is 60 μm,the carrier gas is helium,the repetition frequency is 5 Hz, the laser energy is6 J / cm^2,and the analysis time of single point is 60 s. Iron was used as an internal standard and MASS- 1 was used to calibrate the data. Analysis precision of most elements is better than 10%. For the similar optical properties of pyrite and arsenopyrite, the differences of physical properties can be used to distinguish them.Pyrite in the Baishantang porphyry copper deposit is depleted in sulfur but rich in iron,indicating a hydrothermal origin. The trace element composition of pyrite indicates that pyrite was formed at a medium depth and belongs to the medium-low temperature hydrothermal type related to volcanism. This conclusion has provided important evidence for the ore genesis and the source of ore-forming fluids of the Baishantang porphyry copper deposit,which can also guide the next-step exploration.