Talk:Yilgarn Craton

Discussion

Since the zircon grains in the Jack Hills, Narryer Gneiss Terrane have now been dated at ~4.27 Ga, with one detrital zircon dated as old as 4.4 Ga., I think we have a geological dating conflict that needs to be cleared up concerning the accretion of the Yilgarn craton. After this statement of the zircons, the article states:

"The Yilgarn Craton appears to have been assembled between ~2.94 and 2.63 Ga by the accretion of a multitude of formerly present blocks or terranes of existing continental crust, most of which formed between 3.2Ga and 2.8 Ga. This accretion event is recorded by widespread granite and granodiorite intrusions."

I do not know enough about the 2.9-2.6 Ga assemblage to rewrite this, but we now know that a large part of the crust may date back to 3.6 Ga, and the zircons located not only in the Jack Hills, but also 200 miles to the South, suggests that a large segment of the Yilgarn craton dates back to 4.4-4.27 Ga. Comments?Valich 02:24, 2 August 2006 (UTC)

For an economic geology page

he following text has been removed, prior to placing it somewhere else perhaps more in line with an article on the economic geology of W.A.;

The Yilgarn Craton gold endowment is considered to be a process of a prolonged period of cratonic development during a series of orogenic episodes beginning at about ~2.9Ga and culminating in ~2.67Ga. These events saw the assembly of the Yilgarn Craton from several 'proto-cratons' or unconsolidated terranes of perhaps older earlier-formed granite-gneiss, probably of similar nature to the Narryer Gneiss Terrane. These have been mostly destroyed by the voluminous tonalite-trondhjemite-granodiorite (TTG) magmatism of c. 2.75-2.85Ga, which saw vast quantities of essentially uniform igneous-derived granitoids intruded into the existing greenstone belts, thus forming the cratonising event. These granites now form pillow-like flatly-dipping to steeply dipping sheath-like margins to the greenstone terranes, and may have contributed to the gold mineralisation either during the metamorphic decarbonation-dehydration reactions or as heat engines to drive thermal convection and hydrothermal fluid flow.

The greenstone-granite terranes of the Yilgarn Craton have subsequently been affected by several later metamorphic events and deformations, which have now overprinted the craton with zones of steeply-dipping foliation and vertically thrust-offset fault blocks. These later events tend not to cause mineralisation, instead causing structural disruption of the gold lodes. Gold mineralisation in the Yilgarn Craton usually occurs at the contact between the veins and wallrocks. Formation of these deposits is linked to mid-crustal level processes during regional metamorphism.

Nickel and PGE's in the Yilgarn Craton are associated primarily with an hypothesised plume event which occurred at or around the Kambalda Dome at ca. 2.85 Ga. This resulted in a voluminous thoeliitic basalt event, with widespread deposition of thick sequences of mafic volcanic rocks. This may represent the broad, voluminous plume head erupting through a cratonic margin which separated a slightly older western section of the Yilgarn from a younger eastern section. Closer to the centre of the plume, the plume tail erupted much hotter, and caused voluminous ultramafic and komatiite volcanism. This was submarine volcanism and occurred over the top of sulfidic sediments, cherts and silts. These sediments tended to melt from the komatitic lava, which was at temperatures in excess of 1600°C, causing sulfur saturation in the lava. This caused precipitation of molten nickel-iron-copper sulfides.

Today, these deposits are heavily sheared and mechanically disrupted, often occurring many metres away from their original position in a lava palaeo-channel. Massive nickel sulfide lodes are mined at Kambalda, Widgiemooltha and disseminated nickel sulfides are mined at the Black Swan-Silver Swan deposit and at Leinster and Mount Keith. Nickel laterite has also been formed on top of significant accumulations of forsteritic ultramafics, such as at Murrin-murrin and in Ravensthorpe, during prolonged tropical weathering.Rolinator 02:53, 16 August 2007 (UTC)

Gold

Before 6 November 2020, this article stated, in the "Economic geology" section, that the Yilgarn Craton "contains some 30% of the world's known gold reserves" and in the "Gold" section it stated "The Yilgarn Craton is host to around 30% of the world's economically demonstrably recoverable reserves (EDR) of gold". Then on 6 November 2020, the text in the "Gold" section was changed to "The Yilgarn Craton is host to around 4% of the world's economically demonstrably recoverable reserves (EDR) of gold." by IP editor 134.7.244.1. Both versions are unsourced.

I searched the web for some statistics about gold reserves and I found that, according to Geoscience Australia at https://www.ga.gov.au/data-pubs/data-and-publications-search/publications/australian-minerals-resource-assessment/gold , Australia's gold resources of 9,900t accounted for 18% of the world's total gold resources of 54,500t. That Geoscience Australia webpage also stated that Western Australia accounted for 43% of Australia's Economic Demonstrated Resources of gold and total resources of gold. These data imply that Western Australia accounts for about 8% of the world's total gold resources. I found no figures for the Yilgarn Craton's share of Australia's or Western Australia's gold resources.

Resources is a geological term, reserves is a mining term, but I do not know if they have a one-to-one correspondence in tonnage. EDR is used as an abbreviation for Economic Demonstrated Resources (the only place I have seen claims that it means "economically demonstrably recoverable reserves" is in this Wikipedia article). GeoWriter (talk) 22:13, 6 November 2020 (UTC)