Worth their weight. Image: Artemis Resources
An old-school gold rush kicked off in the Pilbara goldfields last year, following the discovery of hundreds of gold nuggets uniquely shaped like watermelon seeds.
Sole prospectors and exploration companies alike flocked to the area in search for these nuggets hosted as conglomerates (groups in rocks), on or near to the Earth’s surface.
One company, Artemis Resources, recovered 547g of nuggets from prospecting the area in just four days. While the nuggets are valuable in their own right (their bounty was roughly worth $25,000) the hype since has focused on what they might mean for bigger gold discoveries in the area.
What’s the hype?
Could these nuggets be a fruitful sign of a profitable gold deposit hiding below the surface? Is there potential for a whole series of new discoveries of similar mineral rocks across the region?
Speculation has drawn similarities to the host rocks around Witwatersrand (aka Wits) gold deposit in South Africa, arguably the largest gold deposit in the world.
Right now, we don’t have any scientific evidence to back this claim. What we do know is that these nuggets are different from most of the known gold reserves in Western Australia, such as around Kalgoorlie.
Until we look into the geology of the rocks and how they formed – in other words, the origin of the mineralisation – more questions than answers will remain.
Key is understanding how the nuggets formed
We’re working with Artemis Resources to get to the bottom of how these unusual gold nuggets formed and why they exist.
Our research will investigate different possibilities of how the nuggets formed, such as whether the gold was laid down as part of the sedimentary rock or introduced by hydrothermal fluid flow underground.
We’ll also be looking beyond the host rocks themselves at the broader area, as understanding this bigger picture is key to accurately predicting what’s underground. The aim is to test the models, as well as to come up with new tools, which can be applied to understand the area’s prospectivity and help Artemis better target their exploration program.
The project brings together a team of experts in both gold deposits and sedimentary rocks who will use advanced analytical techniques to understand the characteristics of the gold and their host rocks. And, we could have the answers in as little as a year – so stay tuned.
We’re a trusted advisor to the Australian exploration industry, focused on research and innovation to enable the next wave of mineral resource discoveries. We work with more than 50 exploration companies each year from juniors to the major miners.
5th August 2018 at 5:58 pm
If the gold nuggets are supergene, might their hypogene source be fine-grained gold?
5th August 2018 at 5:51 pm
Doesn’t the gold composition suggest supergene (high purity) rather than hypogene gold, in which case are they initially deposited where found or is it supergene re-deposition in cavity textures in the sediment (eg after diagenetic sulphates)?
10th July 2018 at 7:11 am
Wikipedia: Bacteria biooxidation is an oxidation process caused by microbes where the valuable metal remains (but becomes enriched) in the solid phase.
6th July 2018 at 3:26 am
Some nuggets are formed by overlapping oxygen bubbles.
27th June 2018 at 5:15 am
My theory of how the nuggets formed – with some scientific background:
In the beginning of planet earth there were indescribable quantities of oxygen fixed to carbon CO2 in the sea water and atmosphere. And first photosynthetically active cyanobacteria were able to multiply unchecked exponentially over millions of years. These bacterias were the very first creatures without any predators – there was no strong limiting factor like nowaday. It was an overall living ur soup to water and on the first emerging land. By photosynthesis of the carbon they released infinitive quantities of oxygen as unusable waste product into the water and atmosphere. These force of nature was so powerful to create the gigantic banded iron formation (iron + oxygen = rust) all over the Pilbara and the complete atmosphere with oxygen we are living in. And the same mighty effect let to the gold fall out from sea water by oxygen – the great gold deposit from 3 to 2.7 Ba ago. There must have been an even gold distribution in sea water cause it was permanent mixed up by giant tide waves rolling over the sea and the little first land of Ur powered by the moon, still very very close to the earth at these times.
The bacteria are forming so called stromatolites next to a shore – nowaday and in those archean times. I think the oxygen producing stromatolites are the root cause for the seed size and shape of the nuggets. You need oxygen for the chemical reaction and fall out of gold. The oxygen forms small bubbles at the surface of the stromatolites. First very small, then slowly more and more increasing. With some mm the bubble detaches from the surface and rises to the water surface and the next bubble is formed at the same position. Gold deposit happens only at the edge of the bubble where gold containing seawater and oxyde bubble are in contact along the surface of the stromatolite for a longer period. So the size of the nuggets are the size of the oxygen bubble before it detaches from the stromatolite. Every new growing bubble deposits a new very thin layer of gold atoms at the same position growing to the watermelon seed size after millions of cycles. Attached you will find a YouTube link showing the formation of an growing and detaching oxygen bubble. Please switch the video to loop. On a stromat it would take a very long time to cycle from one bubble to the next and the bubbles are on top, at the side, underneath or inside of the fissured structure of a stromat. The bubble will even enclose first little deposits of the next layer of the growing stromat, building a gold halo until its completely covered by the next layer.
Imagine the oxygen bubble on the surface of a stromatolite inside gold containing sea water. Gold formation will happen as thin atom layers at the edge of the very slowly growing bubble again and again. This explains the high gold purity of the nuggets too.