Ann: Mineralised Carbonatites Discovered at C3 and C4 - Mangaroon, page-50

Thanks for the writeup @salpetie, was a good read!

I can’t be certain, but my guess is the 100m exclusion zone is the standard compliance with the conditions/endorsements listed against the EL.
The project is within the Gascoyne River and Tributaries surface water proclamation area, and Gascoyne Groundwater proclamation area under Rights in Water and Irrigation Act, 1914. The tenement(s) are also subject to the provisions of the Waterways Conservation Act, 1976.

And so one of the standard conditions listed against EL's:
All activities to be undertaken so as to avoid or minimise damage, disturbance or contamination of waterways, including their beds and banks, and riparian and other water dependent vegetation.
DRE will likely have lodged an Environmental Management Plan with EARS, to specify all the measures that they will be following to manage the environmental impact associated with the exploration activities.

My guess would be that it does not preclude drilling under the exclusion zone, provided the holes are collared outside the exclusion zone and there is no issues with groundwater etc. So purely from an exploration perspective it may be just to avoid surface disturbance and so not too much of an encumbrance. As you say though, would pay to get clarification.

Goes without saying that there will be many hurdles to cross on the long pathway towards any kind of development (down the track), and EIA process is one of them. But, the good thing is there are numerous mining operations operating successfully within 100m of major waterways (and most of them responsibly) throughout WA (and the rest of AUS).