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A geochemist's view on lithium exploration and some promising paths

Lithium explorers : where next?

IMEx Consulting has been working with a number of clients over the past couple of years in the Lithium space in Australia & Canada and we thank them for permission to use their data in this post.

So you’re a little late to catch the initial wave of hard rock Lithium enthusiasm and it appears that every old mine, prospect or occurrence in the state/province that you’re working in has been pegged/staked.  So what do you do?  “Nearology” seems to be the first reaction but that really only works when you’re in the right terrain and have the right rocks.

So what else can you do? Where are we going to find the next (photo above) Greenbushes ?  The following are some of the techniques that IMEx has been using with its clients to look a little bit outside the square.

1. Li/Cs/Ta association

There is an excellent volume of Elements (v.8 issue 4, August 2012) that discusses the association of Li with the above elements in pegmatites.  Very useful if the geochem data you have (see 3 below) is predominately lithium/borate fusion XRF i.e. Li not analysed.  Presence of anomalous Cs and/or Ta can be indicative of Li mineralisation.  A high correlation of Ta versus Cs is regarded by Möller & Mortenai (1987) as a strong indicator of Ta mineralisation - may not be so good for Li.  Note that Ta associated with tungsten and/or tin can be discriminated from the above – geologically and geochemically.

2. K/Rb ratio

Analysis for Li, Cs and Ta is not

IMEx Consulting has been working with a number of clients over the past couple of years in the Lithium space and we thank them for permission to use their data in this post.

So you’re a little late to catch the initial wave of hard rock Lithium enthusiasm and it appears that every old mine, prospect or occurrence in the state/province that you’re working in has been pegged/staked.  So what do you do?  “Nearology” seems to be the first reaction but that really only works when you’re in the right terrain and have the right rocks.

So what else can you do? The following are some of the techniques that IMEx has been using with its clients to look outside the square.

3. Li/Cs/Ta association

There is an excellent volume of Elements (v.8 issue 4, August 2012) that discusses the association of Li with the above elements in pegmatites.  Very useful if the geochem data you have (see 3 below) is predominately XRF and a lithium/borate fusion i.e. Li not analysed.  A high correlation of Ta versus Cs is regarded by Möller & Mortenai (1987) as a strong indicator of Ta mineralisation.  Note that Ta associated with tungsten and/or tin can be discriminated from the above – geologically and geochemically.

4. K/Rb ratio

Analysis for Li, Cs and/or Ta is not ubiquitous unfortunately and often the digestion and analytical methods are not ideal.  Work by Trueman & Cerny (1982) described a number of useful correlations to differentiate rare metal bearing pegmatites from barren pegmatites.  The basis of the K/Rb ratio is that Rb substitutes for K in micas and K-feldspar in the final stages of crystallisation.  They noted that a K/Rb <160 indicates increasing fractionation.  Ratios of <15 were found in highly fractioned pegmatites and were usually indicative of rare metal mineralisation – Ta, Nb, Be, Cs, Li

5. Whole rock database

Many states/provinces/countries have these available.  These are often a compilation of government field mapping as well as university data with some company data.  The prevalence of Li analysis tends to be low due to whole rock / major element chemistry being the focus but these data can be useful for K/Rb and Cs/Ta analysis.  Where there has been Li analysis, a number of “curious” occurrences have been identified e.g. anomalous Li associated with ignimbrites that warrant further investigation.

6. Exploration geochemistry databases

Also, some states have exploration geochemistry databases where rock, soil, stream, till and/or drill hole geochemistry has been captured.  Analysis of one state’s geochemistry database (just under 1 million records!) revealed a cluster of rock samples described as pegmatites with anomalous Li on open ground with no previously recorded Li mineralisation.  Subsequent rock sampling confirmed this

7. Pegmatites

Interrogation of one particular state database showed that not one of the pegmatites identified from field mapping had ever been geochemically analysed.  One client saw this as an opportunity and initiated a program of pegmatite sampling with encouraging results.  This open range sampling

 This is by no means a definitive list nor is it “the” formula for success.  The occurrence of Li as amblygonite, spodumene, petalite and lepidolite is worthy of separate article.  Also (because someone will or should ask) I have not presented thresholds due to client privilege. 

Would be good that this post initiates discussion on the topic and allows those who feel “locked out” of the Lithium space an opening.  Would also be good for the government agencies to pull their rock pulps out of storage and analyse for Li (and other elements) in potentially fertile terrains.....

 

References

Möller, P. & Morteani, G. 1987 Geochemical Exploration Guide for Tantalum Pegmatites Econ. Geol. Vol 82 pp 1888 - 1897.

Trueman, D. & Cerny, P. 1982 Exploration for Rare - element Granitic Pegmatites in Granitic Pegmatites in Science and Industry. Ed. P. Cerny. Min. Assoc. of Canada. pp 463 - 494.

 

[This text was first published on LinkedIn and is posted here with the approval of the author, for the information of the geochemist's community]

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