How Gilsonite Is Mined and Processed

Gilsonite occurs in narrow vertical veins that cut through surrounding rock. These veins can be a few centimetres to several metres wide and can extend for long distances. Mining and processing aim to recover the pure black material and turn it into consistent grades.

Mining

Because the veins are steep and narrow, gilsonite is usually mined by following the vein downward. Pieces are broken out mechanically, collected and brought to the surface. Care is taken to separate clean gilsonite from the host rock, because rock fragments raise the ash content.

Sorting and crushing

At the processing plant the run-of-mine material is sorted, and visible impurities are removed. It is then crushed into lump or granular sizes.

Milling

For powder grades, crushed gilsonite is fed to mills and air classifiers. Because gilsonite is brittle, it can be ground very fine — down to 600 mesh — without melting, provided temperature is controlled. The mill output is classified into grades such as 100, 200, 300 and 600 mesh.

Quality control

Every lot is tested for:

• Softening point (ring and ball)
• Ash content
• Moisture
• Solubility
• Particle size distribution

Results are recorded on the Certificate of Analysis that accompanies each shipment. See gilsonite quality control tests for details of each method.

Packing

Processed gilsonite is packed in 25 kg multi-wall paper or PP bags, or in 1 MT jumbo bags. Bags are stacked on pallets, stretch-wrapped, capped and strapped to protect them from moisture and damage during transport.

From vein to customer

The result is a clean, graded natural asphalt ready for drilling fluids, asphalt plants, foundries, ink factories and coating producers around the world.