Hi Poodle,the significance of the Heavy Mineral Concentrate sample is not easy to determine. The sample is part of the Geoscience Australia’s Heavy Mineral Map of Australia (HMMA) project, a continental scale dataset that they made available to the public recently.
Very sparse samples, one per catchment or something, this was GA’s original aim, to give you an idea of what they wanted to use it for;
“We describe a vision for a national-scale heavy mineral (HM) map generated through automated mineralogical identification and quantification of HMs contained in floodplain sediments from large catchments covering most of Australia. The composition of the sediments reflects the dominant rock types in each catchment, with the generally resistant HMs largely preserving the mineralogical fingerprint of their host protoliths through the weathering-transport-deposition cycle. Heavy mineral presence/absence, absolute and relative abundance, and co-occurrence are metrics useful to map, discover and interpret catchment lithotype(s), geodynamic setting, magmatism, metamorphic grade, alteration and/or mineralization”
Re the samples, they are not like a rock-chip, or even a conventional soil sample, they are a heavy concentrate sample…more akin to a stream sediment sample than anything else. The samples start as a soil/sediment sample that is sieved to remove the fines, leaving only a coarse fraction. This goes through dense-media separation, to concentrate the particles/minerals with a high specific gravity (rutile, zircon, sulfides, phosphates etc). A portion of the ‘heavy concentration’ is then put in a scanning electron microscope that combines energy dispersive X-ray analysis and backscatter electron imaging to map out all the grains in the sample and determine what mineral they are. Back in the day you would stare down the microscope and do manual point/grain-counts and extrapolate to estimate the mineral proportions…now it’s all automated, the software spits out the mineral lists for each sample with mineral lists, grain counts, volume percentages etc
So, for the sample that S2 highlight at Warraweena, what they are saying is the automated mineralogy has identified 150 grains of pentlandite (Ni), 12 grains of chalcopyrite (Cu), and 9 grains of sphalerite (Zn)...and at least for the pentlandite that is an order of magnitude higher than the any other sample from the national dataset.
It then gets complicated looking at all the
ifs, buts and
maybes…with land-type, underlying rock type, sediment transport, weathering…where could it have come from. Honestly you could go round in circles….the key point for me is, it’s unusual to preserve sulfide under oxidizing conditions at surface and even less common to preserve fresh sulfide during surficial transport over long distances. So there is potential that the sulfide grains in that sample have come from nearby...how nearby? who knows.
How relevant is it...could dismiss it for a variety of reasons, but...its clearly a standout anomaly/sample within that particular dataset, so I agree its interesting, especially in the context of reginal position that has been picked up and the lack of exploration over the area.
From the quarterly; more ground and geophysics planned.
My outlook is the same as you really, I see the Warraweena project as another string to the bow.
