Figure 23 above. NE Yilgarn Gruyere – Tropicana Radiometric targeting.
This paper examines using radiometrics for targeting gold mineralisation. The above figure, from 2017, shows mineralisation targeting using radiometrics around the Plumridge ring structure in the NE Yilgarn, Gruyere – Tropicana area.
Gruyere – Tropicana are big deposits with possibly 20 million ounces gold between them. It would be good to find another couple! Where do you start?
Gruyere and Tropicana are the type deposits on which this exploration targeting exercise is based. The Gruyere and Tropicana gold mines are located on strong potassium (K) anomalies with minor uranium (U) content. I noticed that both Gruyere and Tropicana had a fluoro pink radiometric signature and so I searched around the giant ring structures for similar radiometric anomalies.
There are many areas that have a similar potassium/uranium radiometric signature to the Gruyere and Tropicana mines. There are many that need exploring! The majority of these areas lay within the Plumridge ring’s outer Gruyere ring but there are some around the median ring.
The hypothesis is that the original, now buried, Plumridge giant ring structure was the concentrator of mineralisation in the middle crust and then was the structural driver for remobilisation of this pre-existing Archaean mineralisation. Plumridge GRS provides an easy upward path for fluids which then pass through the overlying upper Archaean crust to form the Gruyere deposit and through the Proterozoic crust to form the Tropicana deposit.
It would be interesting to compare these exploration targeting areas with the 300 km depth seismic tomography target areas. Something else to do one day? Then, it might be worthwhile selecting some of these doubly selected targets, applying your local targeting criterion on them and see what transpires??
Geology note.
The Plumridge ring is unaffected by the regional geology and is considered deeply buried. The underlying geology is comprised of the NNW trending Archaean greenstone and granite Yamarna terrane which is separated (on the surface) from the Fraser Orogen by the Fraser mobile zone.
The Fraser Orogen is Proterozoic on the surface but the underlying relatively undeformed rings suggest that the lower crust is Archaean and has remained rigid throughout the development of the overlying younger crust from >2.9 Ga at Gruyere, through 2.5 Ga at Tropicana and 1.1 Ga in the east. The terrane-crossing structure of the giant ring structures suggests the Yilgarn Craton did not form as a series of accreting terranes as suggested in Blewett and Hitchman, 2006.
An interesting exercise for any area is, overlying the new exploration area over a similar area and note where the well explored area has found mineralisation where the new area hasn’t been explored yet.
So, as a targeting exercise, I overlaid the Plumridge ring over the similarly sized, well explored Watchorn ring located near Leonora to see how they compared.
The Exploration Targets form a similar pattern to the mines and mineralisation around the similarly sized Watchorn ring’s Leonora median, and Agnew outer rings. If the distribution of mineralisation on Plumridge giant ring structure is similar to that around Watchorn there are still millions of ounces of gold (and other minerals like Leinster and Laverton nickel and Mt Weld REE) awaiting discovery.
Note the relative abundance of targets on the east side of Plumridge accords with the relative abundance of mines on the east side of Watchorn Ring. This is similar to the occurrence of Nickel mines in the Yilgarn.
This is such good fun and you never know…. 🙂 !