@CD1999 I had a quick look at Tatogga and it's even more unlikely Discuss is porphyry related, and why NWC changed their minds to VMS related IP anomaly. Tataooga comes to surface with the 0.2% Cu envelope outcropping in the NE. The detailed alteration mapping RHS below shows mineralised porphyry eroded to the surface within a host porphyry intrusion that has obviously eroded down the 'top of the porphyritic body' The IP anomaly at Tatogga comes to surface, though some of the IP anomalies are buried beneath shallow galcial till cover (eg Cebtral and South Tragets).
All porphyry's will have their own differences, but they all have a very similar and large alteration zonation from hydrothermal fluids emanating outwards and upwards form the porphyry intrusion. Most of the largest and most distal propylitic alteration zone often contains pyrite which will generate a IP chargeability anomaly. The high % Py moving down closer to the mineralised porphyry will usually generate a stronger anomaly.
Propylitic alteration at surface would be easily recognisable and probably generate a large coincident soil geochem anomaly, which is not present at Discuss. Without any evidence of porphyry alteration in the surface rocks of the Dick Rhyolite, the probability that the Discuss Ip anomaly is porphyry related is very small, and/or that the porphyry proper is very deep... so deep that none of the alteration has made it to surface and disseminated sulphide alteration responsible for the IP anomaly only reaches to ~350m below surface (excluding the small anomaly above the main system). Logic then says, if the outer alteration zone above the mineralised porphyry only makes it to ~350m below surface, then the higher-grade Cu-ore zone would probably be hundreds of meters below that level again...
Nothing about the geology says it's porphyry, NWC don;t want it to be porphyry, so I'm backing it to be primary volcanic formation alteration at the top of the Dick Rhyolite but extending deeper into the Dick Rhyolite footwall. If the small near surface IP anomaly hasn't come up with the goods (and they would have drilled that first for sure), then better hope downhole EM generates precise targets, because looking for a needle in an IP haystack at 400+ depth over 1km x 1km area is very difficult and expensive...
NWC Price at posting:
3.8¢ Sentiment: None Disclosure: Held
