Airborne Gravity 2010 - Geoscience Australia

Airborne Gravity 2010
Even though weather was identified at the outset as the most significant risk factor, this factor only
affected production for 14% of the survey program. Analysis of the breakdown figures over time
revealed that the majority of the weather impacts on productivity occurred in the summer months,
when inclement weather related to storm activity was more prevalent. The weather downtime was
increased by the lack of weather radar and reliable forecasts in Botswana. The pilots had to err on the
side of caution at times and often didn’t fly due to the risk of a fast approaching storm. Mobile weather
stations that could transmit data via the mobile telephone network were deployed at high points
(telecommunications towers etc.) around the survey area to assist in the safety mitigation.
Even with the caution exercised during inclement weather, there was one serious incident where a
severe updraft was experienced which violently lifted the airship above its planned flight-path.
Although there were no injuries, the incident caused structural damage to the airship which in turn
caused several months of unexpected downtime before the repairs could be completed. In total, 16%
of the project duration was lost while waiting for hangar availability.
The statutory annual inspections consumed 8% of the available flying days, and the Bell instrument
was down 5% of the time.
Value-Add of Airship Data
The most important output that was sought from the airship gravity data was to identify the responses
of kimberlites with the targeted physical parameters. Upon conclusion of a drill program, a new
kimberlite had been discovered from the AGG response plotted in Figure 5. From constrained
modelling of ground geophysical data, this body was interpreted to have a surface area of 2.0 Ha. In
addition to the outcomes from orientation surveys over known kimberlites, this discovery demonstrated
that the airship could indeed detect bodies of the minimum target specifications.
Figure 5. Tzz vertical gravity gradient response of a kimberlite (star symbol) discovered from
airship data adjacent to a faulted boundary
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