Predicting Archaean volcanogenic massive sulphide deposit potential from lithogeochemistry: application to the Abitibi Greenstone Belt

Archaean greenstone belts are prime exploration targets for volcanogenic massive sulphide deposits and the use of lithogeochemistry plays an important role in detecting and mapping hydrothermal alteration zones and in recognizing the massive sulphide potential of volcanic assemblages. This study reviews the state of existing lithogeochemical databases and the use of new geochemical analyses for the identification of alteration associated with massive sulphide deposits. This paper also provides a new methodology for the prediction of missing values in geochemical compositions. Through the application of statistical methods, combined sets of lithogeochemical data can be used to create predictive maps of prospective massive sulphide successions. Predictive maps are created through the use of multivariate statistical methods, lithogeochemical alteration indices and normative minerals from which areas of multi-element enrichment and depletion are defined. These indices, when combined in an exploration programme, are potentially useful for massive sulphide discovery. Additionally, the use of rare earth elements can be used to characterize differences in the various supracrustal assemblages and provide a better regional understanding of potential metal endowment.太古宙绿岩带（Archaean greenstone belts）是火山成因块状硫化物矿床（volcanogenic massive sulphide deposits）的首要勘查靶区。岩石地球化学（lithogeochemistry）在探测与填绘热液蚀变带（hydrothermal alteration zones）、识别火山岩组合（volcanic assemblages）的块状硫化物成矿潜力方面扮演着重要角色。本研究综述了现有岩石地球化学数据库（lithogeochemical databases）的发展现状，以及新型地球化学分析技术在识别块状硫化物矿床相关蚀变中的应用。本文还提出了一种用于预测地球化学组成中缺失值的新方法。通过统计方法的应用，整合后的岩石地球化学数据集可用于生成具有找矿远景的块状硫化物层序预测图件。预测图件的绘制依托多变量统计方法、岩石地球化学蚀变指数以及标准矿物（normative minerals），以此圈定多元素富集与贫化区域。上述指标在勘查项目中联合应用时，有望为块状硫化物矿床的发现提供有效助力。此外，稀土元素（rare earth elements）的应用可用于表征不同表壳岩组合（supracrustal assemblages）的差异，从而加深对区域潜在金属禀赋（metal endowment）的整体认知。