There is something very appealing about the burble of a big V8, poke the beast with a sharp pedal and the roar is just too delicious. You will find a few in racy sports cars, but the truth is that most of these wonderful power plants were created out of necessity to drag ridiculously huge automotive bodies around. Used to carry a family of ten perhaps? No, mostly just one person commuting to the office.

Sensibilities and sheiks have seen to it that we will just have to get excited about the purr of a V-4 or even the pesky squeak of a V-2, and in the end, it isn’t such a bad idea. You see, getting to the fair is no fun at all if it cost you your last cent to get there. And what has this to do with processing? An awful lot actually, and it has taken a ride over the most atrocious roads in Siberia to finally bring it all into jarring focus. Minimalism!

Take a drive south of Johannesburg, tailings to the left, tailings to the right, and in the distance the ubiquitous headgear and process plants. Huge tank farms. In fact, I recall the boast that “my tank’s bigger than your tank”. All that capacity to churn around over 90% of their contents for thirty six hours for - absolutely nothing! You see, virtually all of a typical Wit’s ore’s value can be put into less than 10% of the mass, on some into less than 3%. And let us not forget that all 100% of the ore was required to be milled to a very fine size, not only for dissolution, but to prevent it sanding out in those huge tanks.

Back to bumpy Siberia (lots of driving in this article), and in the distance looms a process plant building, all covered, because here it is 40 below on an average winter’s day. What the heck, that’s not in the distance its right here, I thought this guy said they did 120 tonnes per hour, but this puny cube would almost fit into one of our dissolution tanks. And not a single dissolution tank in evidence here either! In fact, as I am lead in respectful silence through this amazing plant I can tot up no more than 2 minutes residence time in the whole building. Recovery? Over 82% and climbing! No chemistry anywhere, ladies and gentlemen, this is all gravity, Extreme Gravity we call it, all Knelson gravity at that.

I had heard about this concept, read the brochure, even written some of the script, but seeing the real thing is something else – profound, because there is so little to see, or hear. It all begins with high-pressure rolls, followed by disintegration of the pressure cake in a scrubber and closed circuit milling of the coarsest fraction thereafter. Most of the coarse gold is at the mineralization boundaries and the pressure results in fracture to release it, very smart. There are in fact three stages of gravity concentration: 1) in the scrubbing circuit to recover the coarse free gold, 2) in the milling circuit where the primary gravity tails are milled finer to liberate the occluded component, and 3) on final plant tailings where the very fine gold is recovered. Four Knelson XD48’s in all, one in the first stage, two in the second and one in the third.

Okay, okay, small doesn’t necessarily mean smart, so let’s quantify this lot and see how it stacks up: Pressure rolls, 5kwh/t. Scrubber, 0.5kwh/t. Mill, 1.6kwh/t. Knelsons 0.75kwh/t. Pumps etc 0.5kwh/t. I make that about 8.5kwh/t and let’s add in 3.5kwh/t for the primary crushing down to -19mm and we are right on the plant’s estimate of 12kwh/t! We consume that in our big ball mills alone, ladies and gentlemen. Add in the conventional pre-crushing, tank farms, cyanide, elution, etc, etc and the comparison becomes just too ridiculous.

Go and get a cup of tea to calm yourself, because we are now going to blow any remaining perceptions with some cost information. This entire plant was built for less than US$8 million and to arrive at a processing cost per tonne lets amortize that over 8 years and add in spares at 5% per annum (process staff costs are almost negligible, it’s all automated you see). I am also assigning a power cost of US$0.05/kwh.
Ready? How does US$1.95/tonne grab you, all of 0.15 grams per tonne! Anyone who had claim to being the world’s lowest cost processor had better start bowing, I think you just came second.

And did I hear you mention the remaining 18%? I tell you what, you recover that conventionally and I will give you the change. Our new FLEX*Flo® cones will soon be eating into it anyway.