Hi @Black Cat - I'm still thinking we have a dual system here...

Hi @Black Cat - I'm still thinking we have a dual system here with two Goldilocks Zones, one in the south and the other starting from GRE rock chips and running up into ARV's north eastern unit. I just have to get to work on the Geology and see if I can get some sense into my rusty old head.
Anyway what we know is the fertile Black Hill Well granitic rock is younger and intrudes the Andover host rock - but what we dont know is whether the granite underlies the whole of the andover, (or a substantial part) or even under other host rocks to the north west.

So is there only one fertile granite, and one host sequence - or could this area have more of each.

I've been away in the other Black Hills the ones in South Dakota where there are pegs with single spod crystals to be carried away in a truck.
Here is a very interesting review of the mineralisation of those pegs - you may wish to jump to the mid point of the presentation and in particular to 'The Spodumene Problem' - many attempts to explain why those giant crystals seem to float in the pegmatite instead of sinking as would be normal ??
https://www.dakotamatrix.com/content/pegmatites-of-the-black-hills

Thanks for your charts.