The caustic fusion circuit is used to process samples weighing up to 500 kg to recover diamonds greater than 0.10 mm in size. The process sequentially utilizes attrition milling, heavy liquid separation and complete digestion of the rock by subjecting it to a strong basic solution at high temperature (caustic soda). During the final step, virtually all the minerals that constitute the kimberlite are rendered soluble except for the diamonds. The resulting residues are then observed microscopically to identify and recover the diamonds. The diamonds are measured in millimetres by sieving through square mesh screens. Because of the small sample size, diamonds recovered by caustic fusion typically range in size from 0.10 mm to 1.70 mm.


Kimberlite samples are processed through Stornoway's 5 tonne per hour dense media separation (“DMS”) plant in North Vancouver, our 10 tonne per hour DMS plant on-site at the Renard Project, or in our 1.5 tonne per hour facility in Thunder Bay (operated by Microlithics Laboratories) to recover diamonds greater than 0.85 mm, as measured by a square aperture screen. (Cut-off sieve size may vary with sample size.)

Samples are first disaggregated through a reiterative crushing process designed to limit the risk of diamond breakage. The crushed kimberlite is then processed through a sequence of washers and screens, and fed into the core of the DMS plant. In essence, this device consists of a high-pressure centrifuge or “cyclone”. In the operation of the DMS plant, the kimberlitic material is mixed with water and ferrosilicon, a dense, fine-grained powder, which effectively increases the density of the process water. The resulting slurry is spun at high speeds, creating a very effective density gradient. As a result, the lighter materials rise to the top of the cyclone and are discarded as waste. The higher density indicator minerals, including diamonds, concentrate at the lower levels of the device and leave the cyclone through an opening at the bottom.

The concentrate is then examined for diamonds using the X-ray flow sorter and grease table.


The X-ray diamond flow sorter located in Stornoway's North Vancouver laboratory is a unit that is based on the property of diamonds to fluoresce when exposed to X-rays. In the X-ray flow sorter, wet, heavy mineral concentrate is fed into the unit where it is exposed to X-rays. When a diamond fluoresces, the resulting light is detected by a photo multiplier, amplified, and converted into an electrical signal. This signal is then transmitted to an ejection gate which mechanically separates the diamond from other material and diverts it into a locked canister. The diamonds are then measured, weighed and characterized in the observing laboratory.

The X-ray diamond flow sorter can detect diamonds ranging from 1 mm to 25 mm in size. Although many factors influence the efficiency of diamond recovery, the X-ray flow sorter typically recovers more than 98% of diamonds present in a sample.


Diamonds are hydrophobic (repel water) and readily adhere to grease or oil. A “grease table” uses these physical properties to separate diamonds from alluvial gravels or kimberlite concentrate. The grease table at Stornoway's laboratory is used as a final recovery circuit for diamonds not removed by the X-ray flow sorter. After two passes through the X-ray unit, kimberlite tailings are flushed over a vibrating table covered with a layer of specially formulated grease. While waste rock fragments and minerals are washed away by flowing water and sprayers, diamonds resist being wetted and adhere to the greased surface instead. The diamond-laden grease is scraped off the table, boiled in water to remove the grease and cleaned using a solvent degreasing machine. Resultant diamond concentrates are sent to the observation laboratory for hand sorting.


Concentrates from the DMS plant are examined for diamonds in a separate laboratory area specifically designated for diamonds. The stones recovered at this stage (for samples under 100 tonnes) are greater than 0.85 mm in size as measured by a square aperture screen. They are verified, described and measured in the same manner as the diamonds recovered from the caustic fusion residues.

Technical staff also observes the residues from the caustic fusion circuit in a specific area of Stornoway's laboratory. After separation from the dust-like residues, each diamond is verified, morphologically described and precisely measured before storage.

North Vancouver

The North Vancouver facility was originally established in 1994 by Ashton Mining of Canada (“Ashton”). At that time, the laboratory consisted of a 1 tonne/hour dense media separation ("DMS") plant, equipment for conducting heavy mineral processing and diamond observation circuits. In 1997, a microdiamond circuit was added to aid in the assessment of new kimberlite discoveries. In 1998, an X-ray flowsort circuit was added for extraction of diamonds from the DMS concentrates.

The laboratory was moved to its current location (Unit 116, 980 West 1st Street) in 2004 and the DMS was upgraded to a 5 tonne/hour plant. After Stornoway’s 2007 purchase of Ashton, the X-ray flowsort circuit was upgraded, a grease table circuit was added and much of the heavy mineral processing equipment was removed.

In 2007, a 10 tonne/hour DMS was built on-site at the Renard Project in Québec to process the bulk sample kimberlitic material to a concentrate, which was then shipped to the North Vancouver lab for final processing and diamond recovery.

Microlithics in Thunder Bay

Located in Thunder Bay, Ontario, Microlithics Laboratories is an independent mineral process laboratory that provides services to Stornoway and our affiliates including:

Dense media separation
Caustic fusion
Indicator Mineral processing
Indicator Mineral extraction from rock
Diamond picking

The Microlithics DMS plant is rated at 1 tonne per hour and is owned by Stornoway. Purchased new from Dowding, Reynard and Associates of South Africa and delivered in November of 2005, it is used to assess and evaluate diamond exploration properties primarily in the grassroots stage and is specifically configured for a high recovery of diamonds in the smaller size categories that are typically under-sampled in larger pilot plants.

Quality Assurance and Quality Control Statement

Stornoway utilizes industry-standard quality control (“QC”), quality assurance (“QA”) and “chain of custody” procedures in all aspects of our field and laboratory operations.

Strict quality control and chain of custody procedures are followed in the field before samples are shipped to any laboratory. Field practices are designed to reduce the possibility of sample contamination and include the use of unique sample numbers, bar codes, security seals and secure storage.

Industry-standard chain of custody procedures are followed for all aspects of shipping and handling from the time a sample leaves the field until it arrives at the laboratory.

Stornoway’s internal laboratory utilizes standard quality assurance and quality control (“QA/QC”) procedures in all aspects of its operations. The QA/QC programs were developed from guidelines published by the Standards Council of Canada (“SCC”) and the International Standards Organization (“ISO”), commonly referred to as ISO Guide 25 (1990) and the ISO-9000 series Guidelines. All QA/QC work is monitored by the Process Geologist/Quality Control Specialist who reports directly to the Laboratory Manager.

QA/QC testing is conducted on 5–10% of the samples and includes blind spiking of samples and regular testing and calibration of all equipment using reference standards and blank samples. Records generated at all stages are archived, and corrective measures are implemented whenever any aspect of the laboratory procedure does not conform to standards.

QA/QC and security programs are also maintained in the diamond recovery circuits. They include testing and calibration of all equipment using standards and blanks; audits of reject material; archived record-keeping of all procedures and data; and corrective guidelines to correct a procedure that does not conform to standards.

Robin Hopkins, Professional Geologist and Stornoway’s Vice-President, Exploration, is responsible for the design and conduct of field programs and the verification and quality assurance of the analytical results generated in the laboratory.