NPF stands for Ngwako Pan Formation. This is the rock shown as brownish in the diagram at the top of page 4. The contact (blue line, below) between this rock type and the green 'Target Sequence' seems to be where a lot of Cu has been concentrated in a homogeneous, contiguous, flat structure on a, potentially, regional scale.
I'm not a geologist, however. Perhaps if Dr Jonathan is reading these threads he could chip in and help.
Cheers
John
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