RE: RE: Vale targets pristine lake for tailingsThe topic of tailings treatment re environmental impacts caused me to go back and re-read the initial mettalurigal tests which were published in August.
It was a mettalurgical ipiphany.
Having decided to convert from u/g to open pit mining, I had assumed that the gold would be processed by heap leaching.
Heap leaching is the most common form of extracting gold from low grade bulk mineable deposits.
Recoveries are low ( 60-70 % ) but the process is cheap and requires much less capex than convenional milling.
This process is very economical for low grade ore ( less than 1.5 gms/ton ) that is typical of most gold open pit deposits.
However, at higher grades, the additional recovery rate of conventinal milling ( 90 % or so ) makes conventional milling an attractive and more economic option.
Now, back to the initial mett tests for VL.
My former profession trained me to speed-read , a good skill to have when perusing the extensive literature accumulated by equities over their life time.
It is not infallable.
In normal re-read , what jumped out at me was the average grade..............and I quote
" Approximately 50 kg of split drill core was selected by Marathon for the metallurgical test work program. The samples chosen for the metallurgical composite were selected to represent typical mineralization at about average grade for the Leprechaun Gold Deposit. The average grade of the composite samples was 4.16 g/t Au."
4.16 gms/ton is extremely high for an open pit gold mine ( I know of no other, but there may be others ) and obviously heap leaching would not be the most economical or appropriate recovery method.
Instead, conventional milling will be used for the open pit mine, a revelation to me.
The third revelation was the fact that conventional milling means a cheap transition to underground mining , once the open pit is depleted.
And, the results of gravity separation followed by cynanide leaching of the tailings were superb.........up to 58 % recovery by the initial phase ( gravity separation subsequent to crushing ) , with cynanide leaching removing.
Standard cyanide bottle roll leach tests undertaken on the tailings from the gravity separation tests gave total gravity plus leach recoveries of between 93% to 94% for the finer sample and 89% to 91% for the coarse ground material.
The high gravity recoveries means that far less ore will need to be cynanide leached , with commensurate benefits to mine costs.
These are top-end recovery rates and, along with the vey high head-grades, means that cash costs for the VL open pit mine will be quite low.
Now, on to the enviromental issues.
Alhough we are a mining friendly province, our EIS requirements are no different than those of the EU or elsewhere.
There are options for conventional milling to recycle the cynanide leach water and there are alternatives to using natural standing water......afterall, we will be creating a pit as part of the mining process , and which will be amenable to constructing a secure tailings repository.
As such, I do not foresee that environmental issues other than normal EIS requrements will be a problem for the VL gold mine.