Exploration company Six Sigma Metals (ASX: SI6) has confirmed the intersection of “exceptional” grades of mineralisation during a drilling and rock sampling campaign at the high-priority Bonnyvale prospect, within the Shamva lithium project in northern Zimbabwe.
The campaign was designed to drill and collect sections of continuous, unbiased samples across the Bonnyvale pegmatites as part of Six Sigma’s due diligence assessment of the project, prior to acquiring an 80% interest from Botswana-based company Mirrorplex.
The five-hole, 287-metre reverse circulation program returned significant intersections of high-grade lithium oxide within spodumene-rich zones continuing at depth below surface outcrops and old workings.
Best results were 8m at 3.08% lithium oxide from 1m, including 5m at 4.38% lithium oxide from 2m.
Other assays returned were 32m at 1.42% lithium oxide from 0m including 12m at 2.45% lithium oxide from 18m, and 5m at 3.83% lithium oxide from 19m.
Assay results were also received from further rock sampling of pegmatite outcrops from the Loch Ness North and Loch Ness South prospects, within the Shamva tenement package.
Six Sigma non-executive director Steve Groves said the due diligence program had successfully identified areas of high-grade mineralisation across the project area.
“Mapping and surface rock sampling have shown at least five large areas containing extensive lithium mineralisation at surface from multiple pegmatite dyke outcrops exist across the entire project,” he said.
“This program has been very successful in intersecting thick zones of high-grade mineralisation to at least 30m below surface and has achieved everything it was designed to do.”
The due diligence drill program at Bonnyvale was conducted as a first pass to test the morphology, thickness and depth extent of the prospect’s pegmatite dykes.
It targeted a small area of the large field where outcropping pegmatite dykes containing historic mine workings have been mapped.
The first four holes were drilled perpendicular to the interpreted strike direction of outcropping pegmatites and the fifth hole was drilled parallel (or down dip) of a thick pegmatite outcrop to ascertain continuity and tenor of mineralisation with increasing depth.
Previous rock sampling of Bonnyvale has revealed a large area of approximately 550m x 160m, containing a broad spread of lithium-mineralised samples.
Based on this spread, Mr Groves is confident the discovery of further pegmatite dykes related to surface mineralisation is likely.
“It is worth remembering that drilling targeted a tiny portion of one pegmatite in the large Bonnyvale field, and that at least four other pegmatite prospects showing high-grade lithium mineralisation across broad areas remain to be drill tested,” he said.
Pegmatite dyke region
The Shamva project acreage comprises various pegmatite dykes including Bonnyvale, the northerly-striking Loch Ness suite (1a, 1b, IV), Ronspur (Mkana) and several other unnamed dykes in the Hereford area.
The cumulative strike length of dykes identified to date is approximately 3km, with the widest ranging up to 250m in width.
Some of the dykes were exploited in the 1960s for beryl, cassiterite and tantalum mineralisation.
Spodumene mineralisation is reported to be present in the central portion of Loch Ness IV, occurring as fine-grained prismatic aggregates interspersed with quartz, albite-oligoclase and accessory beryl, apatite and columbite-tantalite.
According to historical records, a pegmatite to the east of Ronspur (Mkana) contains a “substantial” tonnage of spodumene, making it an area of high interest for Six Sigma’s lithium exploration activities.
Loch Ness sampling
A single north-south traverse across the north area of the Loch Ness prospect collected 18 samples for analysis as part of the campaign.
The samples revealed “extremely encouraging” results, containing grades of up to 2.89% lithium oxide.
At Loch Ness South, 71 grid-patterned samples were collected, returning grades of up to 4.82% lithium oxide and further demonstrating the potential of the area.
These results, coupled with previous sampling across the Bonnyvale pegmatites to the east and the Hereford pegmatites to the south, have shown that all pegmatites identified in the licence to date have a “large surface footprint” with highly-significant levels of lithium mineralisation from exposed rock outcrops.
Extending due diligence
Six Sigma’s board has elected to extend the due diligence assessment at Shamva for 14 days after receipt of final assay results to enable “full interpretation of the geological merits” of the promising lithium project.
At the same time, the board will consider all aspects of the proposed three-stage acquisition announced in July of Shamva and the neighbouring Chuatsa vanadium-titanium project from Mirrorplex.