Having worked in the potash industry for many years, I have reviewed numerous geological reports for projects in Canada, Asia, Russia, and Africa. One of the curious things that I have seen is the reporting of resource grades in two different units; either as potassium oxide (K2O) or potassium chloride (KCl). Standard practice in the Saskatchewan potash mines is reporting ore grades using K2O units, with typical head grades in the range of 25% K2O. It seems that many of the international projects, but not all, use the KCl units. Therefore when comparing potash resource grades between deposits, one must be cognizant of the units being used since there is a significant difference between the two.
The conversion from K2O to KCl is based on the formula K2O = 0.6317 x KCl. So a grade of 25% K20 is equal to 25/0.6317 = 39.6% KCl. The KCl grade value is significantly higher, easily recognisable on a high grade deposit. The issue is more relevant with a low grade deposit, with say an actual grade of 15%K2O, which may be reported as 23.7% KCl. One could conceivable see the ore grade in KCl and assume it is comparable to Saskatchewan potash grades, when in reality it is quite different.
When looking at various potash projects, particularly those involving underground mining, a key economic factor is the concentration ratio. This ratio represents the tonnes of ore that need to be mined and processed to produce a tonne of final saleable product. Typically the final potash product has a grade of 60% K2O, so an ore with a head grade of 25% would have a concentration ratio of about 2.4:1 (60%/25%). This means that 2.4 tonnes of ore must be processed to produce 1 tonne of product (ignoring the process recovery factor). For a lower grade ore with a head grade of say 15% K2O, the concentration ratio is 4:1 (60%/15%). This gives a rough sense for the comparable operation size required to meet the same final product production levels. This also gives a indication for the relative amounts of salt tailings requiring disposal for both high grade and low grade potash ores. Low grade ore can generate a lot of tailings, the disposal of which is becoming a bigger issue on the environmental permitting side.
In the past gold grades have been reported as “oz/ton” or as “g/t”, but most geological reports today use “g/”t. Sometimes US based projects may still use “oz/ton” however the differences in reported grade are fairly obvious between grams and ounces. That is not necessarily the case with potash grades.
My bottom line is that potash is one of the commodities that will use different units when reporting ore grades and the investor or reviewer must be aware of which ones are being used.