Estrella Resources has embarked on a comprehensive evaluation of the potential for its Carr Boyd project in Western Australia’s Goldfields region to host lithium-caesium-tantalum (LCT)-style pegmatites – primarily for lithium.
The company has today revealed that it is examining all available geological and geophysical datasets in a bid to determine the likely presence and potential extent of pegmatites within its 250-square-kilometre tenement holding, which includes the renowned Carr Boyd layered intrusive complex (CBIC).
Historically, the CIBC is better known for its mafic-ultramafic-hosted nickel potential than for mineralisation such as LCTs, which are typically associated with acidic and late-stage granitic rocks. That almost certainly explains why no specific work programs have ever been undertaken to target pegmatite-hosted lithium and related mineralisation within the project.
Estrella Resources managing director Chris Daws said: “The Carr Boyd complex has previously been the focus of extensive nickel-copper-PGE and to a lesser extent gold exploration programs which are still ongoing. To my knowledge no previous exploration has focussed on the pegmatite-hosted lithium potential. The presence of the Carr Boyd Monzogranite immediately on the northern contact to the Carr Boyd ultramafic/mafic intrusive complex provides a particularly compelling geological setting for the location of pegmatites.”
The Carr Boyd nickel project, 80km north-east of Kalgoorlie, takes its name from the CBIC – a mafic igneous complex with a 78sq km surface expression that hosts several nickel and copper sulphide occurrences. The most significant is the Carr Boyd Rocks nickel mine.
The mine was discovered in the late 1960s by Great Boulder Mines and was actively exploited by a shaft and small underground workings by Western Mining Corporation between 1973 and 1977. After repeatedly changing hands during the next 40 years, the site was acquired by Estrella in 2017.
The nickel project has become a major focus for the company since it made a significant nickel-copper discovery while drilling its T5 electromagnetic target, intersecting 11m of mineralised basal contact zone, including 5m of strong matrix-style nickel and copper sulphides. The discovery is its most significant result at the project and it is now planning future drilling for the area.
During most of the site’s exploration and mining history, there has been little proven understanding of how the nickel resource, often described as “breccia pipes”, had formed. The abandoned pit and surrounding prospects are hosted within the mafic-ultramafic layered intrusion informally known as the CBIC, which has chemical compositions ranging from a peridotite to a leucogabbro.
The CBIC is a series of lobate bodies. The western, southern and eastern lobes are composed of ultramafic rocks, while the central and northern sections are occupied by layered mafic rocks with some ultramafic units. The mined Carr Boyd nickel deposit lies on the western margin of the complex.
Recent collaborative research with the CSIRO has investigated the generation and emplacement of the CBIC and its contained sulphide mineralisation to help deliver a better understanding of the geometry of the complex, its potential ore processes and to evaluate prospective areas within it.
A detailed geochemical study generated a new litho-geochemical classification of the mafic-ultramafic rock types within the complex. It is being used to single out previous drillholes to study and sample and it is also useful to study internal variations within the intrusive complex that are associated with its magmatic history.
Results from the new classification and its 3D visualisation confirm Estrella’s current interpretation of the orientation and geometry of the CBIC. It has the complex lying on its side, having been rotated 90° from its original orientation along a north/north-west, south/south-east rotational axis.
It means primary igneous layering that would have originally been sub-horizontal is now steeply dipping and that the south/south-west edge of the complex potentially represents the original floor or basal contact of the CBIC.
Importantly, that brings us back to the lithium story.
On broad terms, the CBIC intrudes rocks of the Morelands Formation and is, in turn, intruded on its northern margin by an Archaean granitic or monzonitic batholith. It is that more acidic environment that has the potential to host potentially lithium-mineralised pegmatites around its upper cupola.
It could also be the source of late-stage emanations of pegmatitic fluids that may have hydraulically ruptured and intruded other surrounding rocks, including the mafic and ultramafic rocks of the complex.
Other geochemical classification work has revealed that sulphide compositions show clear differences, with higher nickel tenors, but lower palladium and platinum tenors in the sulphides from the Carr Boyd breccia pipes compared to those at T5. It is interpreted as the sulphides having been produced by two distinct magmas with varying metal compositions, suggesting that there are two separate mineralising events within the CBIC.
The T5 intrusions represent a sulphide accumulation at the basal contact of a different magma pulse to the one that created the nickeliferous mineralised Carr Boyd mine style of breccia pipes. It suggests the CBIC may host more magmatic nickel sulphides along the contacts.
Plainly, that revelation opens up a significant new field of exploration for Estrella to look for new nickel sulphide deposits, in addition to the potential for other sulphide breccia occurrences within other parts of the CBIC.
And if that was not enough to be going on with, the company now also has the drill-bit between its teeth to evaluate its northern granitoid intrusive for any related LCT-type pegmatites and their lithium-bearing characteristics.
The significance of the new line of thinking has clearly also attracted attention from abroad, with the company revealing it had already received multiple “unsolicited” expressions of interest from third parties to take on LCT-type pegmatite exploration within its Carr Boyd tenure.
Is your ASX-listed company doing something interesting? Contact: matt.birney@businessnews.com.au
By Doug Bright
