b'Minerals geophysics Minerals geophysicsA small local survey is clearly a job forby effects from widespread surficial ground geophysics; high mobilisationmaghaemite (see Figure 1b). Extensive costs and minimum line length andre-processing and low-pass filtering survey size limits will effectively negatewere required to deliver a more usable airborne options. There may also beproduct; detail was definitely superior to issues with resolution. On the otherthat provided by the regional airborne hand, a large sub-regional survey issurvey (see Figure 1c).clearly a job for airborne geophysics;Finally, the area of interest was long survey duration and the highopportunistically included in an cost will effectively negate the groundextensive detailed airborne magnetics option. Not unexpectedly, the greyprogramme flown over several areas in area for choice falls between these twothe general region. Survey parameters Terry Harveyextremes, as the magnetics explorationfor the area of interest comprised 50 m Associate Editor forhistory of a 3 x 7 km area of interestspaced lines flown at 38 m terrain Mineralsgeophysicsillustrates. clearance; average station spacing was terry.v.harvey@glencore.com.au Pre-existing coverage comprised regional3.5 m. By airborne standards this was airborne magnetics flown along 200 mquite small (490 line km extent, 1 days spaced lines at a nominal 60 m terrainduration). The survey results provided By land or air clearance; however, this was deemedexcellent detail (see Figure 1d).to provide insufficient detail. TheIn hindsight, the detailed airborne In mineral exploration, having settled on atotal magnetic intensity (TMI) image,survey provided the better product particular geophysical method, the choicewindowed for the area of interest, isand at a far cheaper cost. However, between using a ground-based or anillustrated in Figure 1a. for this area, the comparison between airborne approach is not necessarily clearA detailed ground magnetics surveyground and airborne is skewed cut. The paramount consideration will bewas commissioned, with readingsby the detrimental effects on the the capabilities of the survey techniquetaken along 50 m spaced lines at anground survey results of widespread (resolution, penetration, etc.) to achieve theaverage station spacing of 1.5 m. Bymaghaemite, and by the cost and exploration aims. But there are practicalitiesground survey standards this was quitelogistic benefits of opportunistically such as survey extent, duration, cost,substantial (380 line km extent, 17 daysincluding the airborne survey within access, ground conditions and systemduration). The survey provided far morea much larger programme. Things are availability that also need to be considered. detail but results were compromisedrarely straightforward! Figure 1.MI Comparisons left to right: (a) regional airborne, (b) ground, (c) filtered ground, (d) detailed airborne.OCTOBER 2021 PREVIEW 40'