Lake Johnston Project
- Project Highlights
- Lithium Potential
- Gold Potential
- Proposed Exploration Programme and Budget
- Geological Setting
- Previous Exploration
- Lithium Exploration
- Gold Exploration
Charger was attracted to the area as pegmatite fields were known, and due to its proximity to Covalent Lithium Pty Ltd’s Earl Grey/Mt Holland lithium deposit, located approximately 70km west.
- Charger’s most advanced project
- Project will initially focus on the Medcalf Spodumene Deposit, located approximately 450km east of Perth, and 150km southwest of Coolgardie in WA
- Tenements cover approximately 25km of prospective ground
The Lake Johnston region has not been subjected to long periods of intense exploration like most other greenstone belts in Western Australia due to the difficult access and the lack of outcrop.
Lake Johnston Project overlain on the regional aeromagnetic image (left) and regional geological map (right).
A positive feature of the Lake Johnston Project is the large area of unexplored granite intrusions with associated pegmatites. The fact that pegmatites containing anomalous Li, Cs & Ta located and sampled during reconnaissance exploration is encouraging.
The most prospective area is clearly at Lake Medcalf around Bontempelli Hill where spodumene-bearing pegmatites are members of a pegmatite swarm centred upon a topographic high. Not all pegmatites occur as topographic highs and the flat ground is also prospective as LCT deposits typically occur in clusters.
The potential for the discovery of gold mineralisation still remains high despite the extensive gold exploration activity following the discovery of the Bounty Gold Mine in 1985 within the nearby Forrestania Greenstone Belt. The Bounty mine was discovered by systematic sampling of old RAB hole spoil and soils following along a large shear zone. A high-level gold-in-soil anomaly was RAB drilled resulting in the discovery. By contrast many of the gold deposits discovered in the Southern Cross Greenstone Belt have very subtle gold-in-soil anomalies with thresholds in the order of 50 ppb. Experience in the Southern Cross Greenstone Belt has shown that the shape and coherency of the anomaly is more significant that the level of gold.
The gold anomaly identified by Okapi of E63/1903 is certainly of interest and appears to be offset from, and therefore untested by, earlier drilling by LionOre in 2003.
PROPOSED EXPLORATION PROGRAMME AND BUDGET
LCT deposits typically display zoned mineralogical and geochemical halos. Lithium anomalies define the widest halos adjacent to pegmatites which can be in excess of 100 m and are a direct test, but while the dispersion of vector-elements Rb and Cs is more restricted, these elements are readily detected using hand-held pXRF instruments (Li is not detectable) making first-pass exploration very cost effective. Spodumene is typically found in close proximity to the deposit whereas biotite is an abundant metamorphic/ metasomatic mineral in the country rocks that surround LCT pegmatites.
In areas of good outcrop, geological mapping, in conjunction with the use of pXRF instruments, is a good first pass when assessing the prospectivity of an area. For larger areas in arid terrains hyperpectral remote sensing data obtained from satellites as these are known to work particularly well in identifying specific minerals Li-bearing silicate minerals such as spodumene.
Ensuing targets can be further tested by RC drilling followed where necessary with diamond drilling.
The geology of the Lake Johnston Greenstone Belt is recognised as an Archaean supracrustal sequence dominated by mafic volcanic rocks. Most of the belt has been metamorphosed to amphibolite-facies assemblages and is strongly deformed and intruded by at least three generations of granitic rocks, including pegmatites. Proterozoic dolerite dykes are common in the Lake Johnston region and occur variable with east-west orientations.
While the region hosts a variety of mineral commodities, the focus for Charger is currently gold and minerals associated with LCT-pegmatites.
The Lake Johnston region was never an area of intense gold exploration during the gold booms of the late 1800s and early 1900s due largely to the remoteness of the area and the lack of water. The first episode of significant mineral exploration took place in the 1960s during the nickel boom. During the late 1980s and 90s mineral exploration resulted in the discovery of the Maggie Hays and Emily Ann nickel deposits now operated by Poseidon Nickel Ltd. Much of the exploration work leading up to these discoveries was by Goldfields Exploration Pty Ltd, LionOre Australia (Nickel) Limited and Norilsk Nickel NL. While there has been a large amount of exploration work completed in the region it is almost all focussed on the greenstone belts, with the main work within the granite areas having been completed by GSWA geological mapping and regional geophysical datasets available through the GSWA GIS portal Geoview.
Target generation work by LIT initially highlighted the Mt Day area where GSWA mapping and subsequent company field sampling and mapping located numerous, sometimes large, (>200 m long by >15m thick) pegmatites with massive lithium mica cores at a number of locations. Rock-chip sampling of these zones returned some highly anomalous assays, with individual results up to 3.94% Li2O, 8,600 ppm Cs up to, 43,000 ppm Rb and up to 6,900 ppm Ta. These targets contained zones of outcropping massive lepidolite and zinnwaldite; altered petalite was also tentatively identified, and spodumene was also thought to be present.
The most promising target to date is the Lake Medcalf Prospect where LIT geologists identified a large zone of very strongly mineralised spodumene pegmatite at Bontempelli Hill which forms a prominent topographic feature. The Bontempelli Hill outcrops consist of near fresh, stacked pegmatites, containing 20-30% spodumene. Rock-chip samples from the pegmatite dyke swarm average 3.6% Li2O, and up to a maximum of 7.15% Li2O from spodumene outcrop.
The mineralised pegmatites at the Lake Medcalf Prospect cover a 450 x 250 m area, with soil sampling and geology indicating possible extensions to the southeast under adjacent cover. Individual dykes range from about 20 to 120 m in length and 1 to 5 m in thickness. At least three spodumene zones within the thicker centres of the dykes range from 3 to 5 m wide and may increase at depth.
A programme of 137 soil samples were collected on a 100 m by 100 m, or 50 m by 50 m grid over Bontempelli Hill where the known spodumene bearing pegmatites outcrop. Samples were collected from a depth of 10 cm and sieved to -10 mesh (2 mm). The samples were analysed for Li, Rb, Cs, Bi, Be & Ta determined by ICP with 19 additional elements (Al, As, Ba, Ca, Cl, Fe, K, Mn, Na, P, Pb, S, Sb, Si, Sn, Sr, W, Zn and Zr) analysed by XRF analysis. The results show very strong coincident lithium and tantalum anomalies over Bontempelli Hill (Spitalny, P. 2019)
Tenement E63/1903 is located at the southern end of the Lake Johnston Greenstone Belt in central Western Australia. To date, no significant gold mineralisation has been found. The Project is located approximately 10 km from the Maggie Hays and Emily Ann underground nickel owned by Poseidon Nickel Ltd.
Okapi has identified a structural target from the magnetics, that is coincident with anomalous gold in a soil anomaly over a 10 km strike length. Limited historical drilling by LionOre in 2003 appears to have targeted outcropping material and historical workings and is offset from the soil gold anomaly which is yet to be tested by drilling.
Okapi is progressively advancing soil geochemistry programmes to accelerate target definition at the Mount Day Project, targeting both gold and nickel. Charger is able to use these same samples for its lithium exploration activities.
Drilling results from drilling undertaken by LionOre in 2003 include:
- LJPC004 (RC): 26-28m, 2m at 11.04 g/t Au
- LJPC005 (RC): 26-27m, 1m at 1.64 g/t Au
- LJPC0058 (RC): 71-74m, 3m at 1.74 g/t Au
- LJPC0094 (RC): 52-59m, 3m at 0.88 g/t Au, including 1m at 1.48 g/t Au from 56m
- LJPD0105 (DD): 43.85-44.15m, 0.3m at 1.14 g/t Au
In addition to the gold opportunity, the region remains prospective for nickel deposits in the same geological sequence that hosts the Maggie Hays nickel deposits where it occurs within the Mount Day Project.