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Lump and or Vein graphite is commercially valuable, and highest quality types of natural graphite. It occurs in veins along intrusive contacts in solid lumps and is only actively mined in Sri Lanka (Moores, 2007). Given the carbon content typically found with lump/vein graphite recovery operations and costs will normally be lower than flake or amorphous graphite recovery. Lump graphite processing techniques can include everything from hand sorting of large concentrated samples to standard crushing, grinding, froth flotation and milling. Lump/vein graphite is suitable for many of the same applications as flake graphite giving it a distinct competitive edge in terms market prices and product applications.
In Sri Lanka, the vein deposits are in high grade metamorphic rocks of Archean age (greater than 2,500 m.y. old). The graphite commonly occurs as fracture fillings, especially in openings related to structural disturbances that posdate the high grade metamorphism. Some of this graphite is extremely high grade, having over 99 percent fixed carbon. Graphite from these deposits is markedted as "lump graphite" (chips, dust, and flying dust).*
Geological Characteristics
Veins are a few millimetres to over a metre thick in places, although usually less that 0.3 meter thick. Individual veins display a variety of forms, inlcuding saddle-, pd-or lens-shaped, tabular or irregular bodies: frequently forming anastomosing or stockwork patterns. The mines in Sri Lanka are from 30 metres to 400 metres deep; individual veins rarely extend more than ten of metres. Reference: British Columbia Geological Survey Branch
Texture/Structure
Rosettes, coarse flakes, "fibres" or "needles" oblique or perpendicular to wall rock, or in some cases schistosity subparallel to the vein walls.
Ore Mineralogy
Crystalline and microcrystalline graphite.
Typical Grade and Tonnage
Veins contain 40-90% graphitic carbon before hand sorting.
Product Applications
Graphite from viens is used in a broad range of applicationd due to crystalline structure and electrical and thermal conductivity. Main uses; powder metals, special refractories, copper graphite and carbon graphite brushes for electrical applications.
Product Pricing
Price is comparable to flake graphite pricing and is driven by carbon content, purity levels and mesh size. Lump occurs naturally across a uniform size range resulting in a higher than average, but narrow price range.
Importance
The only current source of crystalline lump graphite is Sri Lanka; it is exported world-wide.