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You can trust SGS to provide you with unparalleled global expertise in the field of grinding circuit design, optimization and production forecasting using tools such as the SAG Power Index (SPI®) test.


Conducted in a bench-scale comminution mill, the SPI test measures the energy needed to perform a standard size reduction and is expressed as an index.  It is a measure of the hardness of the ore from a SAG or AG milling perspective.

The test is a batch test, run with 2 kg of ore in a standard 10 cm diameter by 30 cm long mill, and it measures the time (in minutes) required to grind a sample from 80% passing 12.5 mm to 80% passing 1.70 mm.

The key to the scale-up applicability and widespread international success of the SPI test is that all four breakage mechanisms found in the industrial SAG mill are represented in the SPI test: 

  • Impact breakage
  • Single particle nipping
  • Abrasion breakage
  • Autogenous compression

The SPI test, in combination with Bond ball mill data, are used in the advanced Comminution Economic Evaluation Tool (CEET) grinding simulation system for design, optimization, and production forecasting studies. The SPI has the advantage of requiring a low sample weight, and is therefore well suited for geometallurgical mapping of ore deposits

The SPI test has been widely used in recent years. Hundreds of deposits from a wide range of commodities have been tested and the results collated into an extensive database of hardness and variability profiles. SGS experts have conducted over 25,000 SPI tests on ore samples from deposits across the world.

SGS regularly conducts the SPI test in combination with other bench-scale tests and circuit simulation projects.  The use of many methodologies provides you with a bankable solution that is unmatched in its rigor. Contact us to optimize the comminution design for your orebody and maximize your return.

Feed Sample Requirements

At least 2 kg of passing 3⁄4” ore for the SPI mill feed (with no more than 80% passing 1⁄2”). 10 kg is required for the Crusher Index (Ci) determination.

* Dobby G, Kosick G, and Starkey J, “Application of the Minnovex SAG Power Index Test at Five Canadian SAG Plants”, in International Autogenous and Semiautogenous Grinding Technology 1996, Mular A.L., Barratt D.J., and Knight D.A., eds.,1996.