#somepapers No. 1: Secondary Au in the Australian Outback

The Paper

Anand, R., et al., 2017, The dynamics of gold in regolith change with differing environmental conditions over time. Geology, v. 45, p. 127-130.

What it says

Gold in the Moolart Well secondary Au deposit, out in the Yilgarn Craton of Western Australia is one of several small (<10 Mt) low grade (1-5 g/t) deposits that are hosted in weathered regolith. At Moolart Well, most of the gold is in pisoliths ("rounded bodies, commonly composed of an Fe-rich nucleus surrounded by a number of Fe-Al-Si-rich laminations") in a paleochannels that were formed in the mid- to late Eocene (~40 Ma?). This study found that most of the secondary Au was in carbon rich laminations/zones surrounding the Fe-oxide cores of the pisoliths. This makes sense but apparently this is the first documented case of small clusters of Au nanoparticles found in an organic carbon matrix surrounding pisoliths. The formation of the saprolite, the formation of the paleochannel that hosts the deposit, and the remobilization/deposition of the Au were all related to the changing environmental conditions from the Eocene through the Miocene.

An interesting, if minor, result of this paper is that the Au iddn't travel far from its primary source. This can be important for vectoring; you're (apparently) unlikely to have a halo of pointing you to the main orebody.

Why it matters

Most of the Au deposits that will be discoverd in the future will be under post-mineral cover. Understanding how those deposits form, and how the metals they contain are transported by groundwtaer helps geologists find new deposits.

Why I read it

One reason is that it's short! There are some 20+ page papers that I really want to read, but this four pager will get me started!

Besides being short, it is relevant to my current job. I work at a gold mine. The mine I work at is in a very different geologic setting, but understanding how other deposits are formed can be helpful, if for no other reason than to get me thinking a little outside the box. We're not going to be looking for pisoliths and secondary Au in saprolites here in northern Nevada, but we might want to think about Au mobility or maybe sampling vegetation for anomalous Au (a minor part of this paper).

Odds and ends

I'm trying to get back into a habit of writing about science. Pardon the stumbles while I find my voice.