An integrated geophysical approach using seismics and geoelectrical techniques was employed to investigate the architecture of historic narrow-reef workings and a proposed open-pit mine at Lancaster Gold Mine, near Krugersdorp, South Africa. The mining activities in the area were mainly carried out within the Kimberley Reef Package in the upper Central Rand Group of the Witwatersrand Supergroup, which hosts several gold-bearing conglomerates (locally known as reefs). The reefs are generally thin (≤ 2 m thick) and dip between 28° and 32° south. The low-velocity weathered layer introduces significant static shifts in the reflection seismic data. Moreover, environmental noise from drilling and trucking, and the prominent bedrock-overburden contact that produces various wave conversions (P-S conversion), caused undesirable noise that contaminates the shot gathers as high-amplitude, source-generated and monochromatic noise. The noise was removed from the shot gathers using frequency and velocity filtering techniques. The final depth-migrated sections are characterised by high-resolution images of the subsurface from ~10 to ~150 m depth, which are constrained by the borehole information. The reflection seismic data delineate the interfaces between different rock layers and the stopes. The refraction and resistivity tomograms, on the other hand, provide more detailed images of the top 20–50 m of the subsurface and depict the approximate shallow geometry of fluid migration paths, mined-out areas, and bedrock-overburden boundaries. The integrated results indicate that the study area is characterised by a weathered surface layer with variable low P-wave velocity (400–1200 m/s) and resistivity (150–800 Ωm). The deeper layer reveals an increase in resistivity and velocity, and it’s characterized by discontinuities, weak zones, cavities or water-bearing zones due to the mining activities. The combined borehole and geophysical data provide valuable information regarding the physical characteristics of the subsurface and can be helpful for future risk management decisions, environmental and engineering studies in the area.

中文翻译：

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南非克鲁格斯多普兰开斯特金矿的高分辨率综合地球物理调查

使用地震学和地电技术的综合地球物理方法被用于调查历史悠久的窄礁作业结构和南非克鲁格斯多普附近兰开斯特金矿的拟议露天矿。该地区的采矿活动主要在威特沃特斯兰德超级群的上中央兰德群的金伯利礁群内进行，该群拥有多个含金集团（当地称为珊瑚礁）。珊瑚礁一般较薄（≤ 2 m 厚），倾角在南纬 28° 至 32° 之间。低速风化层在反射地震数据中引入了显着的静态偏移。此外，钻井和卡车运输产生的环境噪声，以及产生各种波转换（PS 转换）的显着基岩-覆盖层接触，导致不希望有的噪声污染炮集，如高振幅、源生成和单色噪声。使用频率和速度过滤技术从炮点集中去除噪声。最终的深度偏移剖面的特征是地下从 ~10 到 ~150 m 深度的高分辨率图像，这些图像受到钻孔信息的限制。反射地震数据描绘了不同岩层和采场之间的界面。另一方面，折射和电阻率断层图提供了地下顶部 20-50 m 的更详细图像，并描绘了流体运移路径、采空区和基岩 - 覆盖层边界的近似浅层几何形状。综合结果表明，研究区的特征是风化表层，具有可变的低 P 波速度（400-1200 m/s）和电阻率（150-800 Ωm）。更深层显示电阻率和速度增加，其特征是由于采矿活动而产生的不连续性、弱区、空洞或含水区。钻孔和地球物理数据的结合提供了关于地下物理特征的宝贵信息，有助于该地区未来的风险管理决策、环境和工程研究。