Hi @TrendTracker The low carbon roaster (LCR) was first...

Hi @TrendTracker

The low carbon roaster (LCR) was first envisaged during the roaster audit done in April 2016. They first started investigating the LCR project in 2017. It is not a seperate roaster it is a technology that gets implememted to the main roster plant to capture and agglomerate the fine carbon rich calcine dust that in the absence of the LCR technology escapes the roaster early and goes through to the CIL circuit where the carbon dust leads to a significant drop in gold recovery in cyanidation (a phenomenum known as peg robbing). In presentations given in 2017 they indicated they could get CIL recoveries as high as 95% in test work with the LCR technology in place. They also indicated that the project could be implemented with "minimal distruption to production", whatever that actually means.

Currently from what I understand carbon enriched concentrate is being produced at rate of about 6t/h with an organic carbon weight percentage of ~4.7%. This material according to what I remember JW saying in the recent conference call grades at about 20g/t gold (but I also remember seeing a figure as low as 16.1g/t) and is stored in a tailings pond abutting the calcine tailings pond not far from the roaster. The roaster can be fed carbon enriched concentrate with a percentage weight of ~2% organic carbon at a rate of 27t/h. You need to remember that the stockpiled carbon enriched concentrate has already been subject to crush, grind and flotation. I'm not sure of any intermediate processes that the carbon enriched tailings need to go through before being able to be fed into the roaster other than the proposed LCR technology which will be able to agglomerate the carbon enriched concentrate at a rate of 6t/h and simultaneously agglomerate the fine carbon dust leaving the roaster before it makes it to the CIL circuit. The agglomeration allows the carbon in the roaster to oxidise thoroughly thereby minimising the peg robbing in the downstream CIL circuit.

So to your question.

With the LCR technology in place it is my understanding that the stockpiled carbon enriched concentrate can be processed at theoretical rate of 6t/h. At a grade of 20g/t and a recovery of 90% that is 24 hours x 6t/h x 20 g/t = 83 ozs per day or about 30,295ozs per year if my calculation is right. I think JW in the conference call (from memory) said there was ~70kozs of gold in circuit and most was in the form of a carbon enriched concentrate. So on this basis it would take about 2.3 years to process the carbon enriched tailings once the LCR technology is implemented.

Remember also that we have stock carbon enriched concentrate (~2% weight organic carbon) that in theory can go through the roaster at 27t/h currently and I think JW mentioned a grade of 35g/t for this material in the conference call (it would probably pay to listen to this again). On that basis you have 24 hours x 27t/h x 35g/t = 729ozs per day or 656ozs per day at 90% recovery or 239,500ozs per year (assuming concentrate grade of 35g/t, recovery of 90% and continuous roaster ultilisataion through 365 days per year, 24 hours per day). So that's potentially a total of about 270,000ozs per year under these same theoretical assumptions.

In 2017 presentations they also talked about a "future supercharged roaster" where O2 could be added to the roaster air flow stream which could add 3 to 4t/h to the roaster feed. Taking the stock grade concentrate (of 35g/t and 90% recovery) that could add a additional ~96koz per year of production based on 365 days 24 hours per day of roaster utilisation. So potentially 366,000ozs per year from the current roaster with all working modifications and assuming 90% recovery and 365 days per year 24 hour per day roaster utilisation. If ultimately they achieve 95% recovery as per completed test work the production rate from the roaster could in theory also improve further.

Looking at this, in theory the roaster is not a bottleneck to Syama's scalability to 4Mt per annum of UG sulphide ore production, because at 366,000ozs of production (under the above assumptions) that corresponds to a mining rate for Syama UG sulphides of 4.7Mt which is above the ideal mining rate of 4Mt/annum calculated by independent consultants.

I don't know why they haven't implemented the LCR yet but I suspect they want to debug the new components of the Project85 circuit first and see how it performs once it gets fed wholly from the Syama UG ore before making the modification to the roaster which could also cause a minor distruption to production while getting fitted. I think JW mentioned a figure of about $20 million to implement the LCR so a very high internal rate of return once built and working successfully.

It would be a good question for JW at the next conference call, ie when the implementation of the LCR is planned? It seems to me that if what JW said is correct and most of the GIC is locked up as carbon enriched concentrate then then LCR should become a priority very soon after the UG mine reaches steady state ore production and Project 85 hits its target recovery of 85%. Esh