Dr. Flint on Graphite Deposits: Potential Based on Processing
An analysis of the current junior mining projects, both public and private, around the world suggests that the following production figures are theoretically available. Thus, it is possible to produce the graphite required by the battery industry by 2020 (rounded to the closest 50,000).
All processing assumes purification only to 90-93% with the remaining upgrading done at a specialized refinery. Costs are not considered in this review.
The most common source of graphite currently being explored originates from carbonate rocks. Calcium carbonate contains 12% carbon by mass. Pure calcium carbonate as a limestone, as it converted to a marble, dolomite, or schist and gneiss sheds this carbon. Thus, a completely converted carbonate will have 12% graphite contained within it. As the process is not homogenous the usual upper limit is about 9% before lenses and pods of graphite form. These rocks form the Class 1A rocks that are typically marbles with smaller (0-150 micrometer) graphite crystals. As the metamorphism increases so does the grade and size of the graphite flakes. These are usually located within specific metamorphic temperature zones. As the crystals are found individually and the carbonate rocks are soft processing is generally easy. However, any inflow of other minerals during the metamorphic process, such as a Mississippi type zinc deposit, can significantly complicate the processing. These deposits tend to be very large with potential mine sizes in excess of 100kT per year. There are suggestions that this type of graphite has a greater degree of amorphism which may restrict its usage.
Very often these deposits have corundum occurrences close to them as well as area that may contain more highly metamorphosed rocks and vein like structure of graphite at contact boundaries. To date there are five known deposits could produce, in total, up to 300,000 tonnes annually.
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Class IB Unweathered:
Schist and gneiss rocks contain graphite that has been partially mobilized. The graphite grade of these rocks can be concentrated in pods or lenses sometime to grades over 25%. However, the presence of silica, mica, and garnets significantly complicates processing especially if they are inter-grown into or through the graphite. These complications often lead to low process recoveries and grades. The graphite tends to be of a higher order (closer spacing between graphene layers) and of a larger crystal size and some pockets may contain many crystals of graphite closely packed together that are often mistaken for a single crystal.
Approximately 500,000 tonnes of potential annual production of this type of graphite has been located.
Approximately 200,000 tonnes of annual production of weathered 1B deposits have been identified. These have a much lower cost and higher recovery rates then their parent rocks (1B).
Approximately 650,000 tonnes of annual production of weather 1B rocks that also contain vanadium mica. These may be mined for the vanadium resulting in a graphite by-product. The costs are a bit more expensive then1B-W but credits are added for the value of the Vanadium.
These are complex rocks that form a bit of a catch all. Mining costs are usually minimal, but processing costs can be very high if even possible. These include rocks that have been replaced with other minerals, where inter-growth with the graphite is extensive, or that have very high mica, sulfur, or oxide components. 130,000 tonnes of annual production has been identified.
Gases from deep melting carbonates flow through tension fractures in the rock. This dissolved or gaseous carbon precipitate under the certain temperature and pressure regimes in a reducing environment to form veins of almost pure graphite ranging in width up to several meters. While these veins are common in Sri Lanka, they are also found in many locations in the world and all show similar properties. These include the purest natural graphite known. However they have particular problems in processing not found in other graphite ores. Generally, they are underground mines. There are also a few complex veins that have kaolin, oxides and carbonates associated with them resulting from oxidation and replacement at the surface or by later intrusion of other rock types. The total known worldwide 2A deposits could produce up to 200,000 tonnes of graphite.
These are deposition deposits from off-gassing of melting metamorphic rocks, like the vein type deposits, but where the deposition is in a form that is not a vein. As a result, there rocks have very pure graphite micro veins, or zones of very pure graphite that has to be separated at the processing level rather than during mining.
Dr. Flint has been active in the graphite/graphene industry for over 25 years with experience ranging from engineering review, test work, pilot plants, process design, ... <Read more about Dr. Ian Flint>