Multi-element ratios to define estimation domains: Kvanefjeld

Kvanefjeld is the flagship orebody of Greenland Minerals and Energy Ltd’s (GMEL) Northern Ilimaussaq project. Kvanefjeld contains the world’s largest mineral resource of rare earth elements, as defined by the reporting standards of the JORC Code or NI 43-101.

In 2011, SRK Australia prepared a Mineral Resource estimation for the project. SRK updated this estimation in 2015. The resource inventory is 1,010 Mt @ 1.1 % Total Rare Earth Oxide (TREO): lanthanide series plus yttrium, and 266 ppm U3O8. Based on SRK’s resource model, a feasibility study was completed and the maiden Ore Reserves were reported in June 2015.

The host rock for Kvanefjeld mineralisation is lujvarite – a form of nepheline syenite unique to this complex in southern Greenland. The lujavrite occurs in a layer about 250m thick, shallow dipping, and extending laterally for several kilometres. The visual contrast between the dark lujavrite, and adjacent, lightly coloured host makes it easy to identify from surface mapping.

A challenge for GMEL was to identify higher grade zones within the lujavrite that could be accessed early in the mining schedule, to improve the economic viability of exploiting a very large but essentially low-grade orebody. Defining subdomains would also be critical for focusing metallurgical studies developed from the resource model.

Early work to establish criteria for subdividing the lujavrite, based either on core logging or statistics from the uranium and REE assays, yielded inconclusive results.

By the time SRK became involved in the project, GMEL had made substantial additions to the drill hole database, including reassaying historical core and broadening the analyses to include 14 rare earth elements, yttrium, uranium, zinc and 23 more elements.

SRK worked with GMEL to test the usefulness of elements, singly or combined, to define estimation domains. SRK’s skills using Isatis software for statistical analysis and Leapfrog software for 3D visualisation were particularly suited to this task.

The key breakthrough came when we divided mineralised samples into subpopulations, based on the ratio of zirconium or hafnium to heavy rare earth elements.

The hafnium to ytterbium ratio was adopted as a geochemical marker for dividing the lujavrite into five layers that became the estimation domains. Analysing multi-element ratios justified estimating these domains separately with hard boundaries between them.

Of particular financial importance for GMEL, the upper two layers that will be accessed first when mining starts are the highest grade: mean TREO is about 50% greater than the lower layers. The improved domain definition in the SRK resource update meant that these high grade zones were not obscured by the influence of lower grades during estimation.

Robin Simpson: rsimpson@srk.ru.com

 


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