OK Tedi Mineral Deposit

SGC has produced a new and thought-provoking magnetic interpretation for porphyry exploration in mountainous terrain. Located in the highlands of PNG, the analysis of aeromagnetic data at the Ok Tedi Cu-Au deposit is an excellent example of integrated analysis for exploration in highly rugged environments.

Open-file aeromagnetic data over the Ok Tedi district was merged and reprocessed by SGC, then integrated with published geology maps to form a robust solid geology. The objective was to investigate, in some detail, the potential contribution of aeromagnetics to general geological mapping and exploration targeting. The work provides new and exciting insights into aspects of the geology which now require field investigation.

Key findings include:

  • Mio-Pleistocene intrusive bodies are strongly ‘extended’ EW /along strike, especially evident at depth. This is not a function of line direction or spacing, or any shortcoming in the RTP algorithm. It appears to be ‘real’. There is no clear indication of this in the outcrop mapping. In general, the extent of the intrusive complexes at depth is ‘revealed’ in the mag.. almost all have some magnetic character.
  • The (smaller, younger) intrusive bodies are strongly correlated with anticlines… this has been evident in the published outcrop & solid geology maps for some time.
  • NS to NE faults/contacts are clearly evident near-surface and at depth. These support the suggestion (from very coarse regional data sets) that there is an ‘Arc-normal’ fracture zone influencing the localisation of the intrusive activity at Ok Tedi. If known pre-discovery, this may have been an important factor in targeting- there are many intrusions evident- those in ‘Arc-Normal fault corridors’ would be prioritised.
  • The big mag anomaly (+1500nT) ‘in’ the Ok Tedi pit is not one intrusive lithology, but more likely an ‘alteration overprint’. It includes the (likely) thickest parts of the mineralised magnetite skarns, but does not appear to be exclusively due to these. ‘Circular’ zones of much lower magnetic intensity broadly coincide with the main and southern porphyries in the pit, but the 150m line spacing in the aeromagnetic data here does not show this association unequivocally. As always, much tighter data and ground sampling would be needed to elucidate this with confidence.
  • Two of the sedimentary units, the Cretaceous Ieru Fm and the Pliocene Birim Fm have sufficient magnetic character to assist with mapping. The Ieru appears to have at least one strong and semi-continuous ‘marker’ unit, while the Birim, near the top of the pile, has much magnetic volcaniclastic material, to the point where the mag signature may well be a definitive mapping characteristic.
  • In terms of topographic effects in the mag, they are there, but have very little impact on the interpretation. Having a good DEM and a radar altimeter image allows the right judgments to be made quite easily.

Solid geology interpretation integrating aeromagnetic data with published geological mapping.

Contact SGC to find out more.

Overall, the (relatively coarse) aeromagnetic data, when processed and presented well, and interpreted carefully in geological context, adds very significantly to both the general geology and the exploration ‘thinking’ in the area. If you would like more information about this case study, require the associated images and GIS products or need help with your own exploration project, please contact SGC.