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Caustic Fusion

SGS stands behind our exploration- to evaluation-stage services to the international diamond exploration community.


Commissioned in the early 1990s, we developed and have continuously expanded our caustic fusion laboratory, so it is specifically set-up for diamond and indicator mineral extraction.

Macro- and micro-diamond extraction is done on exploration (outcrop, drill core) and evaluation (mini-bulk and bulk) stage samples by attrition milling and caustic dissolution.

The minimum recommended sample size is 24 kg per sample or rock type. Sample aliquots of 5 - 8 kg are dissolved in molten caustic soda in stainless steel fusion pots heated in kilns to 500-600 degrees Centigrade. The molten mix is poured onto 0.105 mm screens and the residue is washed and treated with acids leaving a small concentrate that is picked for diamonds. Micro diamond counts and weights are reported for each size class using a root-two progression of square mesh sieve sizes from 0.105 mm up in accordance with CIM (Canadian Institute of Mining and Metallurgy) guidelines. Individual stones are measured (X, Y, Z dimensions), and described in terms of color, clarity, percentage preservation and stone morphology.

Caustic fusion at SGS is among the procedures included in SGS’s ISO/IEC 17025 scope of accreditation which is reported on the Standards Council of Canada website. Quality Assurance procedures include standard operating procedures for all aspects of the process and training and monitoring of staff. ONLINE LIMS is used for detailed worksheets, batch and sample tracking including weights and labeling for all the products from each sample.

Quality control procedures include:

  • Sample spiking with synthetic diamond SG 3.52
  • Balance and screen calibrations
  • Quality control repicking of 50% of samples

When you require more confidence in the economic potential of your diamond bearing rock, trust SGS’s diamond experts for a reliable, independent and thorough evaluation.

  • SGS Canada Inc.

6755 Mississauga Road, Suite 204,

, L5N 7Y2,

Mississauga, Ontario, CA-ON, Canada

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