Lithium Australia has identified lithium-anomalous pegmatite dykes at its Dudley prospect at the Kangaroo Island Project in South Australia.
|Gem-quality elbaite (lithium tourmaline) from the Dudley mine|
The company reports that despite strong weathering of outcrops and exposures in shallow historical tourmaline and tin-mine workings, the host pegmatites exhibit local, anomalous lithium, rubidium and tantalum.
Lithium Australia considers this significant, as lithium, which is very mobile, is usually leached from weathered rocks. The Dudley pegmatites intrude the Cambrian metasediment Tapanappa Formation and are variably exposed at surface. Currently, lithium pegmatites in Australia are attracting investment from some of the world’s largest lithium companies.
Reconnaissance exploration was undertaken at Dudley in October 2018 and March 2019. The area had not previously been explored for lithium or tantalum.
LIT Managing Director, Adrian Griffin, says that early results from the Dudley prospect indicate good potential for a new LCT pegmatite field.
“we look forward to extending our exploration coverage later in the year,” commented Mr Griffin.
In all, 66 rock-chip samples were collected from outcrops and another 35 samples from float material, with assays now been received for all samples. Both the fieldwork and assays confirmed the presence of lithium pegmatites in the shallow, historical Dudley tourmaline mine workings, as well as the broader surrounding prospect area. The Dudley mine has produced gem-quality elbaite (lithium tourmaline) since 1899, with kaolin also mined after 1906.
The main known Dudley pegmatite trend strikes northeast-southwest in line with regional foliation, and consists of approximately 30 dykes ranging up to 80 metres thick and a strike estimated to be more than 450 metres.
Also observed was a new cross-cutting northwest-southeast striking trend of pegmatite dykes up to approximately 40 metres thick, which correlates with trends in geophysics images.
This contrasting trend extends about 1 kilometre southeast into LIT’s adjacent tenement, EL 6213, where pegmatites were unknown until now. A previously unreported ‘Black Spider’ tin mine (name supplied by elderly local farmer) with shallow workings over pegmatites in EL 6213 was also sampled (tin mineralisation is common in lithium-mineralised pegmatites such as the Greenbushes mine in Western Australia).
The two pegmatite trends appear to intersect at the broader Dudley mine area, where variably anomalous chip assays were returned from the LIT samples.
Despite the strong weathering of material sampled by LIT, the outcrop rock-chip assays included results up to 0.43 per cent Li2O, 1,600 ppm rubidium, 770 ppm tantalum, 460 ppm niobium (0.046 per cent assay) and 180 ppm caesium; float samples returned assays up to 0.11 per cent Li2O, 1,100 ppm rubidium and 560 ppm caesium (rounded).
The tantalum values in the outcrop rock chips are also highly significant, as values above 200 ppm are considered economic grades.
The lithium mica lepidolite, which was previously reported from marialitic cavities within the pegmatites (Mindat and specimens in the Sorrell collection), was not observed during the fieldwork programmes. Data suggest that the workings and outcrops only expose the upper extremities of the pegmatite system, indicating the potential for spodumene mineralisation at depth.
All data from this programme indicate that the Dudley prospect has the potential to host a lithium deposit in a location not previously identified for its lithium potential.