Lithium Pegmatites – Is This the Right One?

by | Feb 26, 2019

Over the last 10 years, lithium has become a hot commodity due to its significant role in the production of lithium-ion batteries. Market projections show that the renewable energy industry will need more lithium carbonate and lithium hydroxide, the raw materials required to produce cathode material, which is typically used in the production of rechargeable lithium batteries.

Many junior and mid-tier exploration companies recognise this as an opportunity to refresh and expand their exploration portfolio, raise money and find the new deposits. Finding a good prospect is key for the success of every exploration company. Joint venture deals, mergers, and acquisitions are part of the life cycle of a junior exploration company and more and more investors are financing the acquisition of lithium prospects. There are now hundreds of different mineral prospects for sale and advertised online – some can even be found on Kijiji!

What is a Pegmatite?

One of the main sources for lithium is pegmatite crystals. A pegmatite is an igneous rock that is created underground when interlocking crystals form during the final stages of a magma chamber’s cooling. The name pegmatite has nothing to do with the mineral composition of the rock, but rather describes a rock’s physical structure. To be called a pegmatite, the rock should be composed almost entirely of crystals that are at least one centimetre in diameter. Pegmatite lithium deposits, also known as hard-rock lithium deposits, can contain a number of elements, including lithium, tin, tantalum and niobium. Lithium is extracted from hard-rock lithium deposits using conventional open-pit or underground mining techniques with the mineral processed and concentrated using a variety of methods prior to direct use or further processing into lithium compounds, such as lithium carbonate or lithium hydroxide.

If a company or individual wants to explore for hard-rock lithium, or any other commodity, usually there are two choices: either acquiring a brown field project or finding an area with good potential for lithium-bearing pegmatites and applying for an exploration licence or staking the ground.

Lithium-bearing pegmatites are not easily identified with airborne geophysical surveys, so the acquisition of a brown field exploration project may be an attractive way forward. The company can review historical mining records, find lithium past producers and negotiate to acquire the property from the current land owner or licensee.

Property acquisition should include a site visit for a high level or in-depth due diligence. Pegmatites are quite easily recognized if there is an outcrop or other rock exposure. Relatively large crystals of lepidolite (purple to pink mica), spodumene, petalite, quartz, feldspar or the presence of holmquistite (violet to blue amphibole (Li2)(Mg3Al2)(Si8O22)(OH)2) in the host rocks are a good indication that the property is within a pegmatite field.

Are All Lithium Pegmatites Equal?

Recently, a junior exploration company was planning to apply for an exploration licence that would encompass a former lithium mine in Uganda. Before submitting the application, its exploration team conducted a short sampling program of a pegmatite that hosted a historical columbite-tantalite-lithium mine.

The pegmatite around the entrance of the mine was sampled and 32 grab samples were sent to a reputable laboratory in South Africa. The samples were processed using sodium peroxide fusion with ICP-MS finish. The results varied from 14 ppm Li to 8,270 ppm (0.83% Li or 1.78% LiO2) and the acquisition of the property seemed to be the next step.

In the meantime, five field duplicate samples were sent to Dorfner ANZAPLAN (a specialist in testing and engineering services based in Germany) for ICP-MS and whole rock analyses. The Li content ranged from <50 mg/kg (below the detection limit) up to 8,430 mg/kg (0.84%Li or 1.81% LiO2). These results verified the elemental analyses from the South African laboratory.

XRD Graph for Sample JA006

In addition to elemental analysis, these samples were analysed using X-Ray Diffraction (XRD) to identify the mineral composition of the samples. The richest sample from the pegmatite returned the best results (1.81% Li2O), which compared well with the corresponding chemical analyses.

The XRD analyses clearly showed the Li-bearing mineral to be a phosphate, from amblygonite (LiAl(PO4)OH)–montebrasite (LiAl(PO4)F) series. Montebrasite is a fluophosphate containing aluminum and lithium and is common in pegmatites in Manitoba (Canada), California (USA) and Uganda. The big clear crystals are used as semi-precious gemstones, while non-gem quality occurrences are used as a source of alumina phosphate and lithium in the ceramics industry. Despite being a high-grade lithium pegmatite, the presence of fluorine (F) in the montebrasite could compromise the quality of lithium compounds for the battery industry. At present, therefore, this type of pegmatite rock is not used as a source for the production of lithium chemicals for lithium-ion batteries and proves that not all lithium hard-rock deposits are equal in respect to the lithium battery market.

Finding the Right Pegmatite Field

The difference in the mineral composition and the ratio between the different minerals will significantly affect their potential for acceptance for use by the lithium battery market and, thus, the value of the lithium prospect. As the example discussed above demonstrates, a simple XRD test early in the exploration phase can prevent the project owner or investor from wasted efforts by mistakenly exploring for, or investing in, a common industrial mineral. Although lithium may have become a hot commodity, finding a good prospect that yields the necessary mineral composition to produce lithium carbonate and lithium hydroxide for the battery market is the key to success.

.
.
.
.
.

.
.
.

11 Comments

  1. George Roach

    About time someone started highlighting the importance of differentiating Li bearing pegmatites. Perhaps the author could consider more on this and perhaps a matrix of the good and the bad?

    Reply
    • Tania Ilieva

      Dear George, thanks for your interest. We will follow up with more articles about the different types of final products that can be produced from different pegmatites and their technical specifications..

      Reply
      • Dennis Waddington

        Hi Tania. I think George’s question might have been focused on how to initially identify a pegmatite that is prospective for Lithium and therefore worthy of exploration. If that was not his question, then it is mine anyway. Your answer to him focused more on different Lithium products from known productive pegmatites, I think. Thanks

        Reply
        • Tania Ilieva

          Dear Dennis, lithium-bearing pegmatites have a very distinct geochemical signature. A proper geochemical survey can provide a very valuable information about the presence of a pegmatite field and the different types of pegmatites within the field.

          Reply
  2. Muhammad Yaqub Shah

    Do the mafic and ultramafic pegmatites bear any significance for finding Lithium in those?

    Reply
    • Tania Ilieva

      No, the lithium pegmatites are related to granitoids, the mafic and ultramafic are related to gabbros and ultramafic rocks.

      Reply
  3. Hazel

    Insightful, my question is: is ICP MS and XRD best analytical methods to detect lithium in pegmatites or there are other methods….if there which are they?

    Reply
    • Tania Ilieva

      Dear Hazel, it depends on the stage of the exploration.
      Portable XRF analyzer can be used to detect pathfinders. Handheld XRF cannot detect Li directly, because the lithium is too light, however most of the XRF units can detect elements associated with lithium-bearing pegmatites (LCT Pegmatites), such as rubidium (Rb), cesium (Cs), tantalum (Ta), niobium (Nb).
      In more advanced stage, when the pegmatites are identified a full mineralogical analyses and QEMSCAN (quantitative evaluation of materials by scanning electron microscopy) identify not only the main minerals (quartz, feldspar, spodumene, lepidolite, petalite, microcline, and muscovite), but also accessory minerals, such as columbite, tantalite, spessartine, biotite, pollucite, iron-titanium oxides, tourmaline, chlorite, apatite.

      Reply
  4. Adeolu Ahmed

    Very interesting read, I have been working on some LCT pegmatites in Nigeria and geochemistry has been a very good tool in the exploration of these pegmatites, I found the K/Rb ratio particularly important as it highlights highly fractionated pegmatite zones.
    Ground Mag doesn’t seem to be particularly useful except where the pegmatites have been weathered and imprints of gossans are identified.

    Question
    Is there any geophysical methods or satellite remote sensing technique available to streamline pegmatite zones?

    Reply
    • Tania Ilieva

      Dear Adeolu,

      usually the LCT pegmatites have lower magnetic susceptability, lower density and higher gamma.signature. It depends on the host rocks. In some cases the geophysical survey can be very useful, in other cases it will be less reliable.

      Reply
      • Adeolu Ahmed

        Thank you, very helpful

        Reply

Submit a Comment

Your email address will not be published. Required fields are marked *

Opinion

VIEW ALL

Case Studies

VIEW ALL