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Radioactive,
The reason for Verde’s high opex cost is because its potash is contained in otherwise useless glauconite based rocks (i.e. a silicate-based rock) and special mineral processing techniques need to be deployed to transform these rocks into useful product. Verde until August last year was looking to use a process which involves cooking potassium rocks at temperatures exceeding 1000 deg Celsius in order to produce product called Thermopotash. It wasn’t until January 2012 that Verde announced PFS for production of conventional KCl product. Nevertherless, glauconite must still undergo an energy intensive processing to break it down and produce KCl.

In contrast the primary potash-bearing ore for most (about 95%) of world’s major deposits is sylvinite, which is made up of sylvite (the marine salt based potash also known as potassium chloride) and halite. It is the most desirable ore due to its high KCl ranging from 15-40% content and the relative ease with which it can be extracted under standard conventional or solution mining depending on the depth of the deposit.

Carnallite is another potash-bearing ore, primarily composed of carnallite and halite. The main difference between sylvinite and carnallite, with respect to potash production, is that carnallite contains magnesium which is an impurity in the product and typically has much lower grading than sylvinite. Carnallite deposits generally range between 10-20% KCI content and is extracted through solution mining.

In regard to Colluli deposit, its potash mineralisation consists of sylvinite, carnallite and kainite ore. In fact the upper portion of STB deposits and the shallowest resource comprises mainly of high grade sylvinite and this resource has formed the basis for the Engineering Scoping Study (ESS) into open pit mining.

Also please note that due to easy availability of highly soluble marine potash salts in many countries as well as in the international market, no serious efforts have been made anywhere else in the world (except in India), to make use of glauconite as potash fertilizer.