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<p>Hydrogeochemical sampling during core drilling in the Bushveld Complex, South Africa, as part of the Bushveld Complex Drilling Project (BVDP) funded by the International Continental Scientific Drilling Program (ICDP), is challenging due to contamination risks associated with circulating fluids, which can lead to the dismissal of valuable data. This study investigated pragmatic procedures and integrated analytical methods (chemistry, stable isotopes, and end-member mixing analysis (EMMA)) to collect and interpret data from a deep exploration well in the Bushveld Complex despite potential contamination. Findings showed that shallower samples (&lt; 450&#xa0;m below ground level (mbgl)) captured the regional hydrogeochemical signature, with EMMA indicating these samples primarily consisted of background groundwater (e.g. up to 100% at 110 mbgl and 90% at 75.5 mbgl) indicating the effectiveness of the applied measures. Conversely, deeper samples (&gt; 450 mbgl) were more influenced by the drilling fluids, quantifiable through EMMA, showing a clear shift towards source water dominance (e.g. up to 100% source water at 935 mbgl) suggesting potential mixing or displacement effects at depth. Furthermore, a distinct calcium chloride (CaCl<sub>2</sub>) water type with a peak electrical conductivity (EC) of approximately 8000 µS/cm was identified at 450 mbgl, indicative of saline fracture flow. The study demonstrates that hydrogeochemical data can be obtained through the application of best practices and integrated analysis in challenging drilling environments. It highlights the critical need for consistent, validated, and standardised protocols for this process.</p>

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Hydrogeochemical characterisation of the Bushveld Complex (South Africa), through water sample analysis in a core-drilled well with circulating drilling fluid

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年4月29日

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  • Rolene Lubbe,
  • Amy Jane Allwright,
  • Stephanus Steyn de Lange

摘要

Hydrogeochemical sampling during core drilling in the Bushveld Complex, South Africa, as part of the Bushveld Complex Drilling Project (BVDP) funded by the International Continental Scientific Drilling Program (ICDP), is challenging due to contamination risks associated with circulating fluids, which can lead to the dismissal of valuable data. This study investigated pragmatic procedures and integrated analytical methods (chemistry, stable isotopes, and end-member mixing analysis (EMMA)) to collect and interpret data from a deep exploration well in the Bushveld Complex despite potential contamination. Findings showed that shallower samples (< 450 m below ground level (mbgl)) captured the regional hydrogeochemical signature, with EMMA indicating these samples primarily consisted of background groundwater (e.g. up to 100% at 110 mbgl and 90% at 75.5 mbgl) indicating the effectiveness of the applied measures. Conversely, deeper samples (> 450 mbgl) were more influenced by the drilling fluids, quantifiable through EMMA, showing a clear shift towards source water dominance (e.g. up to 100% source water at 935 mbgl) suggesting potential mixing or displacement effects at depth. Furthermore, a distinct calcium chloride (CaCl2) water type with a peak electrical conductivity (EC) of approximately 8000 µS/cm was identified at 450 mbgl, indicative of saline fracture flow. The study demonstrates that hydrogeochemical data can be obtained through the application of best practices and integrated analysis in challenging drilling environments. It highlights the critical need for consistent, validated, and standardised protocols for this process.