GIS-based geospatial tools for estimating the magnetic anomaly depth of hydrothermal mineral deposits using inverse distance weights method

The data used in this study consist of high-resolution airborne magnetic datasets for solid mineral exploration acquired across the Nigerian nationwide Terrains by the two Canadian firms awarded the contracts (a.g., Fugro Airborne Survey Services, and Patterson Grant and Watson), by the Nigerian Geological Survey Agency (NGSA). The Canadian firms had obtained the airborne magnetic data between 2003 and 2009, approximately along the NW–SE flight lines that were positioned at 90 degrees to the most significant narrow geological strike in the areas covered. Aircraft was flown at typical spaced of about half kilometers intervals to acquire the data, with a 2 km tie-line spacing along the northeast-southwest (NE-SW) directions at 80 m nominal flight elevation. The magnetometer settings were set at 0.1 s intervals to record the data. The combination of the nominal flight height—that was set exceptionally close to the ground surface using narrow line spacing—and the extremely small recording time gaps, helped to achieved a higher resolution of the magnetic anomalies than the general high-altitude airborne magnetic surveys. Prior to the data distribution by the Nigerian Geological Survey Agency, (NGSA) to the interested users, Fugro Airborne Surveys Company preprocessed the essential magnetic data corrections: the geomagnetic gradient was removed from the data using the existing model with the International Geomagnetic Reference Field (IGRF), January 2005 version, as specified in the World Geodetic System 1984 ellipsoid. The Universal Transverse Mercator (UTM) coordinate system was used to project the airborne magnetic data. The airborne magnetic survey data presented in this study covered the Omu-Aran Schist belt zone in parts of the Nigerian South-western Precambrian basement complex (NSPBC), with moderately shallow overburden lithologies.本研究使用的数据集为两家中标加拿大企业（即福格罗航空测量服务公司（Fugro Airborne Survey Services）与帕特森·格兰特与沃森公司（Patterson Grant and Watson）），以及尼日利亚地质调查局（Nigerian Geological Survey Agency, NGSA）在尼日利亚全境地形区获取的、用于固体矿产勘探的高分辨率航空磁测数据集。上述加拿大企业于2003至2009年间完成航空磁测数据采集，飞行航线大致沿北西-南东（NW–SE）方向布设，与研究区内最显著的窄幅地质走向呈90°夹角。航测飞行以约500米的测线间距巡航，同时沿东北-西南（NE-SW）方向布设了间距为2千米的联络测线，标称飞行高度为80米。磁力仪以0.1秒的采样间隔记录观测数据。相较于常规高空航空磁测，本次航测通过极近地面的标称飞行高度、窄间距测线布设搭配极小的采样时间间隔，实现了更高分辨率的磁异常捕捉。在尼日利亚地质调查局（NGSA）向意向用户分发数据前，福格罗航空测量公司已完成必要的磁测数据预处理校正：基于1984世界大地测量系统（World Geodetic System 1984, WGS84）椭球，采用2005年1月版国际地磁参考场（International Geomagnetic Reference Field, IGRF）模型，从原始数据中移除地磁梯度干扰。该航空磁测数据采用通用横轴墨卡托（Universal Transverse Mercator, UTM）坐标系进行投影。本研究呈现的航空磁测数据覆盖尼日利亚西南前寒武纪基底杂岩（Nigerian South-western Precambrian basement complex, NSPBC）部分区域的奥穆-阿兰片岩带，该区发育中等厚度的浅覆盖层岩性。