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Regional applications of low-density geochemical data to mineral exploration

Regional applications of low-density geochemical data to mineral exploration . The National Geochemical Survey of Australia. Andreas Scheib. GSWA Open Day 2014 . C ontent. Background Examples from the NGSA for Western Australia State-wide sediment composition Anomalous Pb and REE

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Regional applications of low-density geochemical data to mineral exploration

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  1. Regional applications of low-density geochemical data to mineral exploration The National Geochemical Survey of Australia Andreas Scheib GSWA Open Day 2014

  2. Content • Background • Examples from the NGSA for Western Australia • State-wide sediment composition • Anomalous Pb and REE • HFSE of the coastal areas • Terrane-scale characterization of the Yilgarn Craton • Conclusion Acknowledgments: Paul Morris, Ray Addenbrooke, Colin Strickland and Patrice DeCaritat (Geoscience Australia)

  3. Scales of geochemical sampling State and Federal surveys, and research institutions (often as collaborative projects, e.g. NGSA, GEMAS of Europe) State surveys (e.g. GSWA regional geochemical mapping projects) Mining industry or research groups

  4. Regional geochemical mapping at GSWA State-wide geochemical data available free for download at www.dmp.wa.gov.au Nova deposit

  5. Geochemical surveys encourage mineral exploration efforts State and Federal surveys, and research institutions (often as collaborative projects, e.g. NGSA, GEMAS of Europe) State surveys (e.g. GSWA regional geochemical mapping projects) This only happens, if the above are available, especially in greenfields areas!!!! Mining industry or research groups

  6. The National Geochemical Survey of Australia - NGSA For more information on the NGSA visit www.ga.gov.au

  7. The NGSA – sampling and data Bulk <2 mm <75 µm 0-10 cm (TOS) Sediment • XRF and ICP-MS (total digest) • Partial digestion using AR • MMITM (TOS <2 mm only) • Determination of grain size, pH and EC (bulk samples only) Bulk <2 mm <75 µm 60-80 cm (BOS)

  8. A sand-dominated sediment matrix Eucla Basin, exposed limestone Fine sediments (sand <50%) Alkaline (pH>8) Acidic (pH<6) Sand rich (>90%)

  9. Nickel • …a predictable distribution • Close spatial relationship of • elevated Ni concentrations in the fine fraction of NGSA samples, • known Ni prospects and • greenstone belts • within cratonic regions.

  10. HFSE of the coastal areas Elevated aqua regia Zr (>10 mg/kg) in the fine fraction scattered throughout the centre and reflect more intense weathering of bedrock Elevated total Zr (>1100 mg/kg) found in the fine fraction and relate to heavy mineral sands

  11. A surprise – Pb in the Wheatbelt 1:1 1:1 • No relationship with known Pb mineralization • Pb is highest in the fine fraction of the bottom sediment, regardless of digest. • Cluster of elevated Pb relate to samples from salt lakes in the central Wheatbelt • Pb associated with evaporates and clay minerals

  12. Another surprise – REE in the Wheatbelt • No relationship with known REE mineralization • REE are twice as high in the fine fraction • Cluster of elevated light and heavy REE found in salt lakes of the central Wheatbelt • Extractability indicates two controls Low extractability: relation to resistate mineral phase, e.g. garnets 1:1 High extractability: relation to evaporates and clay-minerals in salt lakes

  13. Terrane-scale characterization of the Yilgarn Craton The greenstone-dominated terranes reflect a strong chalcophile and ferro-alloy signature The gneiss-dominated South West Terrane is geochemically distinct reflecting strong signatures for REE, Pb, HFSE and major oxides Data of 96 NGSA samples achieved the same pattern as data of >2000 rock samples

  14. Low-density surveys are valid,… …because they • Help to define the regional to continental distribution of elements and their natural baseline. • can indicate regions of preferential accumulation of element associations • can point to surface expression of buried mineralization and • data can be applied in the wider research community

  15. Thank you A copy of this study is available for download at www.dmp.wa.gov.au

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