磷灰石主、微量元素的偏最小二乘判别分析在斑岩型矿床中的应用

Application of the Partial Least Squares Discriminant Analysis of major and trace elements of apatites in porphyry deposits

如何区分成矿和不成矿斑岩,以及斑岩型铜和钼矿床成矿岩浆存在何种差异一直是矿床学界关心的科学问题。本文选取不同类型(包括成矿斑岩、不成矿斑岩、含铜矿斑岩、含钼矿斑岩等)斑岩中的岩浆磷灰石作为研究对象,通过多元统计方法(PLS-DA)对其进行聚类分析,尝试通过磷灰石的元素特征区分出成矿与不成矿斑岩以及形成不同矿种的斑岩,进而为副矿物找矿提供理论依据与技术支撑。通过PLS-DA模型的建立与讨论分析,发现根据岩浆磷灰石的Cl、SO_(3)、La、Ce、Eu、Sr、Y、Yb、Th等元素含量的差异,指示成矿斑岩的岩浆相比于不成矿斑岩的岩浆具有较高的氧逸度和水含量,且斑岩铜矿相比于斑岩钼矿具有相对高的岩浆氧逸度和较低的岩浆演化程度。

How to distinguish the ore-forming porphyry from the ore-barren porphyry as well as the differences between the oreforming magma of porphyry Cu deposit and that of porphyry Mo deposit have always been scientific issues in the field of economic geology.In this paper,magmatic apatites in different types of porphyry rocks,including ore-forming porphyry,ore-barren porphyry,porphyries of porphyry Cu and Mo deposits,are selected as research objects to carry out the cluster analysis of element characteristics of apatites by using the multivariate statistical method(PLS-DA),aiming to distinguish the ore-forming porphyry from the ore-barren porphyry and to discriminate different metal-bearing porphyries.This could provide theoretical basis and technical pathfinder for mineral prospecting using relevant data of accessory minerals.Through the establishment and discussion of the PLS-DA model,it is concluded that there are differences of Cl,SO_(3),La,Ce,Eu,Sr,Y,Yb,Th and other elements in various magmatic apatites.It is indicated that the magma of ore-forming porphyry has higher oxygen fugacity and water content than that of ore-barren porphyry.Additionally,compared with the magma of porphyry of the porphyry Mo deposit,that of the porphyry Cu deposit had relatively high oxygen fugacity and relatively low evolution degree.