An opinion? More a shotgun of ideas and words without any real conclusions - I doubt I could and might be difficult for all but real experts.
From my first post on DUN this paragraph was tucked away in a PDF.
Graphite tends to form in stratiform to linear zones rather than ‘blobs’ and salt water at hundreds of metres below the surface is unlikely. Not strong arguments but basically leaves massive/semi massive sulphides which may or may not contain economic mineralisation. Technical success if only pyrrhotite/pyrite, but without drilling there is no way to know at present.
Prophetic words (?) now the first diamond hole has come back with lots of sulphides but apparently only a trace of Cu bearing ones. The water bore had sulphides but expedited assays show negligible to low Au/Ni/Cu.
The first hole didn't really test the guts of the AMT anomaly in the way hole 2 hopefully will. So although the initial indications are for part of the system to be barren it does not mean there will not be economic zones elsewhere. Here writes an exploration geo with a perennial half full glass. Gets knocked over many times but comes up smiling.
The textures visible in core images and alteration reported have led some to consider a VMS style of mineralisation. If this is the case then it may be one of the largest VMS systems in the world based on the 10 Km size of AEM (and, to a much lesser extent, AMT) response.
Gravity and magnetics are generally weak or peripheral to the Central AEM anomalies something that may be reflected in the presence of pyrite dominance in the hole over magnetic pyrrhotite.
As @tarlinca says the textures are reminiscent of the footwall stringer sulphide zone below a VMS. The previous photos I posted were from a banded iron ridge with an associated structural controlled alteration and patchy sulphide zone. The PDF below comes from what would have been the discovery hole at Gossan Hill (Golden Grove) if the rig hadn't broken down 15m from hitting massive sphalerite at around 110m. These images are 100m beyond the economic sulphides in the stringer zone. The sulphides here are pyrrhotite dominant and, from memory, barren for all but traces of Cu or Zn. or Au/Ag.
The darker photos are wet core with the one on the left (tray 34) a dry tray.
bronze/brassy mineral pyrrhotite, green (black wet in upper image) chlorite, greys silicified sediments.
Not the most convincing of examples but gives an idea of why this is one possibility.
I say one possibility because of the potential size of the system. Just because it is probably big doesn't mean there HAS to be zones with economic mineralisation.
Using Golden Grove as an example for a VMS system.
The overall system has the scale but the main feeder zones tend to be restricted to the area of the pits and for a few hundred meters around the Scuddles undergound operation. In this case the surface expression is relatively short by comparison with the vertical to 1500m at Scuddles I believe and still going.
Kidd Creek, in Canada, is now down to 3Kms below surface.
Sudbury nickel mining goes to a similar depth.
VMS deposits tend to be zoned with Zn commonly on top of Cu on top of the stringer zone and associated alteration. Many are thought to have been deposited on ancient to more recent sea floors and then structurally moved, or not, into their current positions. Very simplistic statements so DYOR for more detail.
Size of the system is not necessarily a problem for this to be a VMS but IMO it would be unusual so I would suspect something else is afoot here. S32 and AQD are exploring some 50Kms to the NE of Central - for of all things VMS deposits plus Ni/Cu. Magnetic trends probably mean there is little to no connection to DUN ground.
The metamorphic grade and structural deformation will impact VMS or any other style of deposits formed early in the history of the area.
Lots of words and a few ideas but the nature of the sulphides and alteration is beyond me. Probably even if I could see the actual core. =============== Going back to Olympic Dam that I mentioned in another post. There is probably more consensus about its origins now after 50 years of mining, thousands of kilometers of drilling and many PhDs. One diamond hole and a few shallow water bores into what hopefully will turn into a new style of deposit are unlikely to solve what tends to be a perennial issue about deposits. How they were formed.
Hemlo in Canada needed 76 holes before they came up with a 10+Moz Au deposit! Kidd Creek had an interesting discovery history that showed persistence can be very worthwhile.
However, if there is nothing there it is not possible to do much more than try and then walk away.
DUN do have Matilda South which IMO is likely to be a different beast.
Gravity and Magnetics suggest it is likely to be mafic/ultramafic on a more extensive nature than Central. The AMT is OK but not as strong as Central.
