BIOGEOCHEM PAYS OFF FOR MARMOTA
New ore zone discovered following biogeochem reconnaissance.
Marmota Ltd announced recently the interception of a new gold ore zone, remote from previously identified mineralisation, which was drilled on the basis of a biogeochem anomaly.
Aaron Brown, Senior Exploration Geologist with Marmota Ltd has been an exponent of the technique for some years and has recently been applying it to the Goshawk Zone at Marmota’s Aurora Tank gold exploration prospect, near the Challenger gold mine in northern South Australia. From the Company’s release:
“The reconnaissance component of the drilling program was designed to see if new gold mineralisation can be found outside the known mineralisation area at Aurora Tank.”
Following an earlier trial in the area last year, Brown selected Senna artemisioides (known as desert cassia, and prevalent throughout central Australia) for Marmota’s reconnaissance program, looking for signals of mineralisation away from the known target zone. The presence of transported cover rendered traditional surface geochemistry (such as soil sampling) ineffective, with no detectable signals penetrating the cover, and it was anticipated that the deep-penetrating roots of desert plants such as Senna and mulga would access elevated metal concentrations found near covered orebodies.
The leaf samples were collected and sent to LabWest in Perth for analysis. An anomalous gold result was determined in one Senna sample, approximately 450m from the zone of known mineralisation at Goshawk, and this anomaly was subsequently drill-tested with a reconnaissance hole adjacent to the tree. Drilling intersected a previously-undetected ore zone, returning 6m at 3.4g/t from 44m below surface, and remaining open below 50m. In the company’s recent announcement, chairman Dr Colin Rose said “The new high-grade zone on the NW flank occurs over a gold-in-calcrete surface low. It was picked up by Marmota’s innovative tree sampling (biogeochem) program. I find it particularly exciting and remarkable that we have identified a new discovery hole 450m from known mineralisation, at 44m below surface, based entirely on tree leaves from one Senna tree, with 6m at 3.4g/t, from 44m to end of hole”.
Marmota’s full release can be viewed here: http://marmota.com.au/component/docman/doc_details/663-gold-grades-over-30-gt–tree-leaves-find-new-gold-zone-31-july-2019.html
Marmota chose LabWest in Perth for their biogeochem work, based on previous experience.
Aaron Brown says: “I have used LabWest for over 5 years for analysis of a variety of biogeochemical sample media from projects in W.A, N.T and S.A. With respect to analysis of vegetation samples, the application of microwave assisted digestion results in a complete digestion of samples, provides a significantly higher level of confidence in low level element concentrations of many elements of economic interest than traditional open beaker digest or ashing of samples, as the risk of cross contamination is minimal and volatile elements are retained. In addition to their reliable cost competitive ICP-MS analytical results, LabWest’s customer service is second to none, and I would recommend them to anyone seeking high quality low-level analysis for mineral exploration.”
Helen Waldron (Xenocryst Geoscience Consulting), with >30 years’ experience in biogeochemistry, explained that “Vascular plants have evolved over ~ 425 million years in a wide range of physical and chemical conditions and they are capable of absorbing and scavenging elements and translocating them, in varying amounts, to stems, twigs, foliage, bark, flowers and seeds, while blocking some other elements, and eliminating others. The roots integrate the signature of large volumes of soil, rock and groundwater and therefore plants are sophisticated geochemical samplers.
The collection and analysis of the leaves, or other plant tissue, is used in biogeochemistry to give information on the subsurface lithology and mineralisation.
Biogeochemistry has been used in the Northern Hemisphere since ~ 1930’s and in Australia mostly from the 1970’s, particularly for uranium exploration. The use of modern sensitive multielement analysis methods has seen a resurgence of biogeochemical exploration for many commodities in the past ~20 years in Australia.
Sampling uses mostly simple equipment and has a low environmental impact. Orientation studies are important to establish the vegetation coverage and select the species and tissue types that give the best chemical signature. Levels of target elements are generally lower than in soils, so careful collection and laboratory preparation, digestion and analysis practices are important.”
Boutique Services for Specialist Biogeochem Analysis
LabWest has been at the forefront of biogeochemical analysis for much of its 11 year history, working with leading exponents of the science to ensure the analytical results are as good as can be obtained anywhere.
Customers have sampled a wide range of plants, including:
- Mitchell Grass
For a range of commodities, including:
- Rare-earth elements
LabWest’s MSA digestion methodology, using state-of-the-art microwave systems for digestion and determination by current-generation ICP-Mass Spectrometry, provides high recovery and low detection limits even in difficult botanical matrices such as spinifex and saltbush.
Work undertaken by Prof. Ken Collerson in the Simpson Desert funded by the Queensland Government (insert link to brochure) demonstrated that chondrite-normalised rare-earth element signatures in spinifex mimic those of underlying rocks, enabling detection of LCT pegmatites underneath transported cover. Given the potential for spinifex root systems to penetrate to depths exceeding 100m, a useful tool is thus provided for regional lithium and REE exploration in areas of transported cover.
Read more here: Biogeochemistry as a Vector to LCT Pegmatites