Cool Graphite | Borrowdale, Lake District

Previously unknown conditions for the origin of rare graphite deposits found in ancient volcanic rocks near Borrowdale, Lake District, have been revealed recently.

This new, collaborative research by the British Geological Survey and the Crystallography and Mineralogy Department of Complutense University, could have implications for the industrial synthesis of high quality graphite for specialised products, currently obtained by heating petroleum or coal tar residues to greater than 2000°C.

Graphite is listed on the Critical raw materials for the EU 2010. The EU is up to 95% dependent on imports, mainly from China. Graphite recycling is very limited while the abundance of graphite on the world market inhibits increased recycling efforts.

catalyst

About Borrowdale Graphite

Steeply dipping fault with quartz-andesite breccia on left and narrow massive chlorite-graphite vein in the centre

The Borrowdale Graphite deposit is located at Seathwaite in the picturesque valley of Borrowdale, in Cumbria. This occurrence is unique in the UK and it is one of only two graphite vein deposits hosted by volcanic rocks worldwide — the other is in southern Spain.

At Seathwaite, the graphite occurs in a set of mineralised faults hosted by andesite lavas and sills belonging to the 450 million year old (Ordovician) Borrowdale Volcanic Group. Narrow veins filling fault fissures contain massive graphite and chlorite, but the richest deposits containing nodules of graphite, altered wall rock and brecciated quartz are in pipe-like bodies developed at the intersections of faults.

History

pencils

Graphite was first discovered at this Lake District locality; mining at Seathwaite began at least as early as the late 16th century, continuing intermittently until it was abandoned in the late 19th century.

The remarkably pure graphite was at first used for marking sheep, but its main use for many years was in moulds for the casting of coins and cannonballs; in the 19th century it formed the basis of the renowned pencil industry in Keswick.

Findings

Graphite nodules; the matrix is altered diorite

Spherulites of graphite seen under a scanning electron microscope.

Key findings of this research, which used a wide range of modern analytical techniques, are:

  • This is the first reported volumetrically large occurrence of highly crystalline graphite deposited from fluids at moderate temperatures (c. 500°C);
  • Fluid inclusions in quartz that formed during the mineralising event indicate the mineralising fluids evolved from CO2-CH4-H2O to CH4-H2O mixtures;
  • The deposit contains the widest range of graphite morphologies known from any deposit worldwide; colloform graphite is reported for the first time from any deposit worldwide; the predominant morphology is flakes, while others present include spherulites, dish-like forms, rings, graphic-like intergrowths with chlorite and cryptocrystalline aggregates;
  • Isotope data indicate that the carbon has a biogenic origin and was incorporated into the mineralising fluids by assimilation of carbonaceous-bearing mudrocks that underlie the volcanic rocks;
  • Borrowdale graphite is as highly crystalline as the highest quality graphite currently mined from its main source in vein-deposits from granulite-facies terranes.

Contact

For further information contact:

David Millward, British Geological Survey (BGS) or Javier Luque at Universidad Complutense Madrid (UCM)