Lithium Australia NL (‘LIT’) has long recognised the potential of the gneissic terrane of the southwest of Western Australia to host repetitions of the world-class Greenbushes pegmatite mine. Indeed, LIT already holds exploration titles in the Greenbushes mineral field.
Complementing LIT’s already extensive exploration position in this prospective mineral province are new applications by Stanifer Pty Ltd (‘Stanifer’), a wholly owned subsidiary of LIT. Said applications cover some 780 square kilometres (km2).
At Greenbushes, lithium pegmatites are closely associated with north/northwesterly-trending shear zones within high-grade metasedimentary and metabasic igneous rocks. The prospectivity of the Stanifer applications is enhanced by the fact that they overlie high-grade gneissic rocks and are traversed by major structural corridors: the Bridgetown-Donnybrook Fault, which is associated with pegmatite emplacement at Greenbushes, and the Boyup Brook Fault.
Stanifer, through LIT, has an indirect strategic alliance with a major bauxite explorer, which allows access to retained drill material in the form of sample pulps from bauxite exploration over the applications. Over the past two years, LIT has pioneered the use of Laser Induced Breakdown Spectroscopy (‘LIBS’) – a technique for achieving rapid, real-time lithium geochemical measurements – at projects in both Western Australia and Mexico. LIBS should prove an ideal tool for rapidly analysing the large number of bauxite sample pulps, with the aim of delineating lithium-anomalous target zones. Using proprietary techniques, the application of LIBS to this extensive sample database has the potential to delineate buried pegmatites in deeply weathered environments, overcoming a problem that has impeded previous explorers.
With a combined area of 784 km2, the seven Stanifer tenements in the southwest of Western Australia are some 300 km by road south of Perth. A combination of privately held agricultural land and state controlled forestry reserves, they lie between the towns of Nannup and Boyup Brook, in a region of established infrastructure that includes major roads and power transmission corridors (see Figure 1). Located between those Stanifer applications is Talison Lithium Limited’s Greenbushes pegmatite mine, the longest continually operating mine in the state.
Figure 1: Location plan.
For ease of description, the applications can be divided into three groups, as follows.
Nannup – E70/5032, E70/5036 and E70/5047.
Bridgetown – E70/5023
Boyup Brook – E70/5024-5026
All lie within an area of Archean-aged, high-grade metamorphic rocks known as the Western Gneiss Terrane. Regionally, the Western Gneiss terrane forms the southwest corner of the extensive Yilgarn Craton and is one of the four major divisions of the Craton. Lithologies comprise granitoid, gneiss, migmatite and metasediments (see Figure 2).
Figure 2: Geological plan (1: 2.5 m scale, GSWA geology).
Within the Nannup and Bridgetown tenements, the topography consists of moderately incised valleys separating remnants of the original lateritic upland. Further east, the landscape is more mature, with wide valleys and intervening hills topped by small areas of preserved laterite. The area is deeply weathered, with fresh rock exposure limited to the major drainage valleys. Surface expression is mainly saprock and saprolite, with some relict material comprising ferruginous and siliceous duricrust.
The Nannup and Bridgetown applications lie within the Balingup Metamorphic Belt (a sub-division of the Western Gneiss terrane), which consists mainly of metasedimentary rocks comprising interlayered quartzite, quartz-mica schist, banded quartz-feldspar-biotite-garnet gneiss and banded iron formations, together with minor quartzofeldspathic gneiss, amphibolite, calcsilicate gneiss and ultramafic rock. In addition, about 30% of the area is orthogneiss largely derived from deformed porphyritic granite. The metamorphic grade of most rocks is amphibolite facies.
The Greenbushes pegmatite occurs within the 15 to 20-km wide, north/northwest-trending regional lineament known as the Donnybrook-Bridgetown Fault. This significant structure extends south from the Greenbushes area into E70/5023, enhancing the prospectivity of the tenement.
The Boyup Brook applications lie immediately to the east of the Balingup Metamorphic Belt, in an area dominated by metamorphosed granitic rocks. A large part of the tenure overlies undivided gneisses, quartz monzonites and gneisses of metasedimentary origin. Permian-aged Collie Basin sediments occupy a small area in the northwest of E70/5024.
During the past 10 years, exploration for pegmatites and associated mineralisation was sporadic and achieved little success, being been hampered by unexposed pegmatites obscured by thick lateritic crusts and recent alluvial deposits. More recently, some companies have reported encouraging targets generated via high-resolution aeromagnetic data and geochemical sampling of laterites, the latter using indicator minerals to detect potential lithium-bearing pegmatites.
Mafic and ultramafic complexes in the Bridgetown and Yornup areas were explored in the 1960s and ’70s for base metals, with a focus on nickel. From the 1990s to the present day, exploration activity picked up, with Pancontinental Mining Limited, Teck Cominco, BHP Billiton and Hampton Hill Mining using various airborne, ground and downhole electromagnetic surveys to explore for sulphide-hosted base-metal deposits.
Exploration for gold – which concentrated on an area running south from Donnybrook to Nannup and immediately east of the Darling Fault – targeted a repetition of auriferous quartz reefs within the Donnybrook sandstone. Gold-bearing reefs near Donnybrook were mined for a short time from 1897.
Vam Limited and others held large areas of the southwest under tenure in the early part of the 1960s and ’70s and were actively evaluating the area for economic bauxite deposits. However, the bauxite was judged to be too thin and inconsistent for exploitation. More recently, the Bauxite Alumina Joint Venture between Bauxite Resource Limited and Yankuang Resources Limited has undertaken extensive drilling on bauxite occurrences in the Nannup and Boyup Brook applications.
Based on a combination of geological environment and structural setting, all the Stanifer applications are deemed highly prospective for pegmatite-hosted lithium mineralisation.
The Nannup and Bridgetown applications are located within the Balingup Metamorphic Belt, which is intruded by numerous pegmatite dykes, including the Greenbushes pegmatite swarm. That world-class deposit is closely related to the Bridgetown-Donnybrook shear zone, which extends through E70/5023.
Stanifer’s Boyup Brook applications overlie gneissic rocks, with two identified structural lineaments traversing the tenements in a northwest/southeast direction. The Boyup Brook Fault is a major structural corridor that may well be associated with controls on pegmatite emplacement.
In areas of deeply weathered rocks, a combination of geochemical and geophysical methods will be used to explore for lithium-bearing pegmatite intrusions. High-resolution aeromagnetic datasets will be acquired and interpreted to target potential structural complexities that may indicate areas favourable for pegmatite emplacement. Initially, work will focus on areas peripheral to the major structural corridors, concentrating on the Bridgetown-Donnybrook Fault and the Boyup Brook Fault.
Stanifer, through LIT, has an indirect strategic alliance with a major bauxite explorer, allowing it access to retained drill material in the form of sample pulps from bauxite exploration. The pulps, which are representative of drilling over the Boyup Brook applications and large areas of E70/5032, provide a unique and cost-effective geochemical database that can be used to direct rapid-reconnaissance pegmatite exploration.
As noted above, LIT has in the past two years used Laser Induced Breakdown Spectroscopy (‘LIBS’) – a technique for achieving rapid, real-time lithium geochemical measurements – at projects in both Western Australia and Mexico. The LIBS technology is ideal for rapidly analysing this extensive bauxite sample database to delineate lithium-anomalous target zones, and there is the potential to delineate buried pegmatites in deeply weathered environments that proved problematic for previous explorers.
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