Ann: New Drilling Results Confirm Succoth Potential, page-21

Not certain if the Ni/Cu separate out quite as clearly as you believe.  The massive sulphides which can contain both Ni and Cu do tend to gravity settle to the bottom of systems but something unusual seems to be going on at some deposits in the WMP.  

From a post of mine 18/12/18     A couple of weeks back I had a wide ranging geological discussion with Greg Miles.  If results were available then he wouldn't have told me but it takes a good poker player to keep excitement or the reverse out of view.  Take it how you will there wasn't any obvious excitement re West Arunta in my take.    Hope I am wrong.

Dealing with geological conundrums was more the nature of the discussion which touched on a blatant one at Nebo Babel.

It isn't highlighted in announcements but is the subject of ongoing studies of potentially significant importance.

Why are the massive sulphides on top and not the bottom??  That is a conundrum.

The top heavy sulphide occurrences at Yappsu and Nebo-Babel appear to contradict a gravity settling model for such deposits. ETC etc

Some ideas as to why but nothing definite yet.

Metal zonation - off hand I don't think it is common in Ni rich deposits I have experience with.  The Ni and Cu tend to be mixed in the sulphides albeit at different ratios in different deposits. 
Kambalda/Thomson Ni/Cu 10:1 ,
Sudbury 1:1
Generally there appears to be near 1:1 for the more disseminated sulphide sections at the WMP,   Massive sulphides tend to be Ni>Cu 1+-6:1 when magamatically separated (e.g discovery hole 26.55m @ 2.45% Ni, 1.78% Cu) and Yappsu massive sulphides

I have seen some tension fractures become near pure chalcopyrite at their ends as a result of ?remobilization.  They were minor local features.  

There will be many variations in deposits as large as Succouth and N-B.  Large Ni/Cu rich zones at Succouth will come as a real bonus. 

The metamorphic grade and strong structures reported today could be genetically related to the high Cu:Ni ratio (~~5(-10):1) seen so far in drilling at Succouth.  Such a scenario would beg the question; Where did the Ni go if the original host had N-B/Yappsu Ni:Cu ratios?? 

The thin zones in dolerites hint at more Ni at depth but it is going to be deep in areas already drilled.  
One possible target area could be fold noses.  These would be tricky targets until structure and metal vectors are sorted out by geophysics/drilling and a modicum of Luck.
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On a pedantic note: the WMP prospects known so far are NOT VMS systems - magmatic sulphide deposits would be better IMO.

True VMS deposits often have strong metal zonation.  Usually Cu at base and Zn at top with no Ni of economic significance.