This article was written by Executive Consultant, Andrew Scogings.
Flake graphite projects are essentially no different from other mineral exploration projects, which require targets to be ranked before committing to costly drilling, assaying and metallurgical tests. Graphite exploration follows a similar path to other minerals, often from discovery of an outcrop or geophysical anomaly, followed up by methods such as field mapping, trenching, more detailed geophysics, drilling, analysis of the graphite content, mineralogical examination and metallurgical testing. Data generated in this way, if successful, could lead to the estimation of a Mineral Resource and Ore Reserve which underpin technical studies such as Scoping, Pre Feasibility or Feasibility Studies.
But the question to be asked right at the outset is: what constitutes the best graphite exploration target at a project?
Many junior graphite explorers over the past few years have espoused the notion that 'biggest is best'. So, should graphite exploration targets be ranked on possible tonnage and grade similar to the way other commodities such as metals often are?
My opinion is that, although resource tonnes and graphitic carbon content (grade) are important metrics in evaluating exploration / mining projects, the overall picture is more complex and there are other factors to be considered.
This is because natural graphite is an industrial mineral and is a lot more complex than it appears at face value - as there are a diverse (and sometimes bewildering) number of market-related specifications. At the bare minimum, flake size may be used to describe graphite products - see table below:
Natural graphite is an example of a truly multi-functional industrial mineral. It has specific physical properties such as flexibility (and hence the ability to be rolled into tiny spheres for battery anodes), it’s soft and hence a lubricant, it conducts electricity, is stable at high temperatures and it can be expanded and made into foil for heat sinks in computers - this list is almost endless as are the specifications for individual markets.
The mention of the word 'markets' reminds me of that well-known saying by Peter Harben "Without a market, an industrial mineral deposit is merely a geological curiosity". Similarly, as noted by Border and Butt (2014) concerning the modifying factors for industrial minerals “Without a potential market, there can be no resource; without a good knowledge of the planned market (volume, price and competition), there is no reserve”.
This says a lot about ranking of graphite exploration targets, as the graphite will need to meet market specifications such as: moisture, chemical purity, particle size distribution, particle shape, mechanical strength, bulk density, thermal resistance, expandability and conductivity.
Therefore it is potentially misleading to simply rank graphite exploration targets based on tonnage and the contained mineral percentage for flake graphite projects. For example, a graphite explorer may hope to define a Mineral Resource of 100 million tonnes at 10% total graphitic carbon (TGC) at greater than 94% purity, but this conveys very little about the quality of product that may be possible to liberate. It's all well and good to have a huge tonnage of contained graphite (the example above has 10 million tonnes of contained graphite) but bear in mind that the global flake graphite market is under 1 million tonnes per year, hence the scale of production and expected market penetration should be realistic. In this regard, it's worth noting that many successful flake graphite mines currently produce around 7,000-20,000 tpa (e.g. Africa, Europe and China), though there are exceptions that turn out 50,000-70,000 tpa (e.g. China and Brazil) and a mine in Mozambique that is targeting ~300,000 tpa.
The explorer should therefore devote some time and money up front evaluating not only potential tonnage and grade, but also potential product quality before spending big dollars on drilling and further evaluation such as metallurgy / process tests.
Other considerations when evaluating graphite targets include the economics of mining and processing, as these are impacted by factors such as the size and geometry of the deposit, contained graphite and recoveries. The deposit geometry affects the strip ratio and, the higher the contained graphite, the less ore has to be mined and processed, as long as saleable product is delivered. Processing less ore results in lower production costs and less waste going to tailing dams, all of which can have a major impact on capital and operating expenditure. But the overriding factor is likely to be PRODUCT QUALITY as, without markets, the project is doomed to failure.
Finally, the explorer should consider logistics and accessibility to power, water, labour and transport routes as the cost of trucking and shipping often exceeds the value of industrial mineral products.
The TanzOz example
TanzOz is a private Australian company with a graphite exploration project in southern Tanzania. The tenement was initially surveyed regionally by means of VTEM (an airborne EM method known as Versatile Time Domain Electromagnetics) which highlighted numerous conductive targets that might be associated with graphitic rocks.
But the question then was - how to rank the VTEM targets and where to spend the exploration dollars on drilling and subsequent metallurgical / process tests? TanzOz adopted the following sequence:
1) Dig trenches across the most conductive VTEM anomalies
2) Map the trenches, estimating visual graphite flake size and concentration and collect samples of graphitic rocks
3) Submit samples for chemical anlaysis of graphitic carbon and also have thin sections cut of selected samples for microscope examination
4) Fixed Loop Electromagnetic (FLEM) surveys were carried out over several targets, to determine dip and strike of conductive rocks. This assisted with predicting the expected depth of mineralisation when drilling.
Following this process, Targets CD and NP were selected for diamond core and reverse circulation drilling; these locations are about 3km apart and interestingly turned out to have quite different characteristics.