North Australian Craton iron oxide-copper-gold (IOCG) mineral potential assessment: geospatial data

Following the successful outcomes of the Tennant Creek-Mt Isa (TISA) mineral potential assessment (Murr et al., 2019; Skirrow et al., 2019), the methodology has been expanded to encompass the entire North Australian Craton (NAC). Like its predecessor, this assessment uses a knowledge-based, data-rich mineral systems approach to predict the potential for iron oxide-copper-gold (IOCG) mineralisation. With their high metal yield and large alteration footprint, IOCG mineral systems remain an attractive target in directing exploration efforts towards undercover regions.This mineral potential assessment uses a 2D GIS-based workflow to map four key mineral system components: (1) Sources of metals, fluids and ligands, (2) Energy to drive fluid flow, (3) Fluid flow pathways and architecture, and (4) Deposition mechanisms, such as redox or chemical gradients. For each of these key mineral system components, theoretical criteria representing important ore-forming processes were identified and translated into mappable proxies using a wide range of input datasets. Each of these criterion are weighted and combined using an established workflow to produce a models of IOCG potential. Metadata and selection rational are documented in the accompanying NAC IOCG Assessment Criteria Table.Two scenarios were modelled for this assessment. The first is a comprehensive assessment, targeting pre-Neoproterozoic mineral systems (>1500 Ma), using a combination of interpreted, geological and geophysical datasets. As geological interpretations are subjective to the geological knowledge of the interpreter, well-documented areas, such as shallow pre-Neoproterozoic basement, have a greater density of data. This increase in data density can create an inherent bias in the modelled result towards previously explored shallow terrains. The second assessment utilises only datasets which can be mapped consistently across the assessment area. As such, these are predominately based on geophysical data and are more consistent in assessing exposed and covered areas. However, far fewer criteria are included in this assessment, and observations are reflective of only the modern geological environment. Both assessments highlight existing mineral fields in WA, NT and QLD, and suggest that these regions extend under cover. Furthermore, regions not previously known for IOCG mineralisation display a high modelled potential, offering exploration prospects in previously unknown or discounted areas.

继滕南特克里克-芒特艾萨（Tennant Creek-Mt Isa，简称TISA）矿产潜力评价项目取得成功成果（Murr等，2019；Skirrow等，2019）后，该评价方法已被扩展至覆盖整个北澳大利亚克拉通（North Australian Craton，简称NAC）。与此前的评价项目一致，本次评价采用基于知识、依托海量数据的成矿系统方法，预测氧化铁-铜-金（iron oxide-copper-gold，简称IOCG）矿化潜力。鉴于其金属产出量高、蚀变分布范围广，IOCG成矿系统仍是引导勘探工作向隐伏区域拓展的极具吸引力的找矿靶区。本次矿产潜力评价采用基于二维地理信息系统（2D GIS）的工作流程，对四大核心成矿系统要素进行填图：(1) 金属、流体及配体来源；(2) 驱动流体运移的能量源；(3) 流体运移通道及构造格架；(4) 成矿沉淀机制（如氧化还原梯度或化学梯度）。针对上述每一项核心成矿系统要素，研究人员识别出代表关键成矿过程的理论判据，并依托多类输入数据集将其转化为可填图的替代指标。随后通过既定工作流程对各项判据赋予权重并进行综合，最终生成IOCG潜力预测模型。相关元数据及判据遴选依据已收录于随附的《NAC IOCG评价判据表》中。本次评价共构建了两类预测场景。第一类为全面评价场景，以新元古代前成矿系统（年龄大于1500 Ma）为目标对象，综合利用解译地质数据与地球物理数据集。由于地质解译结果受解译者的地质认知水平影响存在主观性，资料详实的区域（如浅部新元古代前基底）往往拥有更高的数据密度。这种数据密度差异会使预测模型结果产生固有偏差，更倾向于偏向此前已开展勘探的浅部地质体。第二类评价仅采用可在整个评价区内实现统一填图的数据集，因此此类数据主要基于地球物理资料，在评价裸露与覆盖地质体时一致性更强。但该场景纳入的判据数量大幅减少，且观测结果仅能反映现代地质环境特征。两类评价结果均凸显了西澳大利亚州（Western Australia，简称WA）、北领地（Northern Territory，简称NT）及昆士兰州（Queensland，简称QLD）已有的矿集区，并指出这些矿集区向覆盖层下方延伸。此外，此前未被发现存在IOCG矿化作用的区域也展现出较高的模型预测潜力，为此前未被关注或被低估的区域提供了新的勘探前景。