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SGS's approach is to understand the variability in your deposit and map it using proven grindability technologies such as Rock Quality Designation (RQD). We then design and optimize your grinding and grinding circuit for throughput and recovery.


RQD was developed in 1964 by D. U. Deere*. It is determined by measuring the core recovery percentage of core chunks that are greater than 100 mm in length. Core that is not hard or sound should not be counted even if they are 100 mm in length. RQD was introduced for use with core diameters of 54.7 mm (NX-size core). It is a leading indicator for low-quality rock zones. Today RQD is used as a standard parameter in drill core logging and forms a basic element value of the major mass classification systems:  Rock Mass Rating system (RMR) and Q-system**.

RQD is defined as the quotient:
"RQD = (Sumof10)/Itot * 100%"

Where (Sumof10) = Sum of length of core sticks longer than 10 cm
Itot = Total length of core run

Classification Table
From the RQD index, we can classify rock mass:
RQD Rock mass quality
<25% very poor
25-50% poor
50-75% fair
75-90% good
90-100% excellent

SGS's team of experienced engineers use RQD data in combination with bench-scale comminution tests and circuit simulation. The use of many methodologies provides you with a bankable solution that is unmatched in its rigor. Contact us to understand the variability of your orebody and ensure your processing circuit will handle the variability in your ore over the life of the project.

* Deere, D.U. 1989. Rock quality designation (RQD) after 20 years. U.S. Army Corps Engrs Contract Report GL-89-1. Vicksburg, MS: Waterways Experimental Station.
* Deere, D.U. and Deere, D.W. 1988. The rock quality designation (RQD) index in practice. In Rock classification systems for engineering purposes, (ed. L. Kirkaldie), ASTM Special Publication 984, 91-101. Philadelphia: Am. Soc. Test. Mat.
** Directly from Wikipedia contributors, ‘Rock Quality Designation’, Wikipedia, The Free Encyclopedia, 14 September 2009, 19:44 UTC,“” [accessed 26 October 2009]