I have reread the URHG press releases and reports which I used for my estimates, and I may have misused some terminology. Not being any kind of mining expert, it would be no surprise. When I used the terms “primary" and “secondary” I meant having a first circuit and later building a second circuit in a separate location on the mining property. If there were two separate circuits, each would operate independently and therefore each one would run 100 yards an hour.
If “primary" and “secondary” mean having just one circuit that processes the same ore two different times, then that would be a different set of calculations than the one I was using. The December 3rd press release does mention a "secondary gold recovery circuit” which sounds like an additional piece of equipment which would augment the “primary” circuit but still be a part of that one circuit. That one circuit I suppose would run 100 yards an hour by itself, but I suppose having more parts to the circuit might slow the processing time.
However, from the latest press release I see “After exploring possible retrofits and upgrades to the current circuit, it was determined that a new circuit should be assembled at the Dun Glen site “. I interpret that to mean that they were considering adding to or modifying the existing single circuit (which matches the December 3rd PR mentioning a secondary gold recovery circuit) but have now decided to just replace the old inadequate circuit with a new circuit. This circuit includes a longer trommel, “screen section”, dual screens, magnetic separator, jigs, sluice box, screw. I am assuming that the old circuit doesn’t have all of those parts (otherwise why replace it) and that those new parts each play a role in increasing the production.
I did a web search for “Placer Gold Recovery” to see if there was information on what kind of recovery numbers one might expect; and it turns out to be a lot more complicated than that. I did find two reports (they appear to have been written around 1985-1986) which discussed increasing the recovery rate of mine machinery. I would assume there must be more recent research on it, but I didn't find it. (Most of what I saw appeared to be ads for different mining equipment companies which claimed their equipment had the best recovery rates). From reading these two reports, it appears that the sluice box plays a big role, and that a circuit can improve its recovery rate by adjusting the “riffles” in the sluice box to match the particular conditions of the ore being mined and the machinery being used. In other words, there is no “one size fits all” solution, so I imagine any newly installed Dun Glen equipment would need an experimentation period to adjust these “riffles” the right way.
(And maybe the jigs, screens, screw and magnetic separator need that, too, I don’t know… but if they do, it could be that this new Dun Glen circuit will run at a lower recovery rate at first, and then as the different sections are added to the circuit,or as the sections are fine-tuned, the recovery rate will rise over time). Maybe there are some miners on this board who can explain it to us.
If you want to read these technical reports for yourself see: http://goldrushgang.com/fine_gold_recovery_sluiceboxes.pdf. This is entitled Fine Gold Recovery of Selected Sluicebox Configurations, 73 pages, from the University of British Columbia. It describes different riffle types, sizes and shapes. The second one is at: http://www.scribd.com/doc/61880538/The-Clarkson-Study-Fine-Gold-Recovery#scribd, and its name is Placer Gold Recovery Research prepared for the Klondike Pacer Miners Association by Randy Clarkson, 49 pages. This guy used "nuclear tracers” and he discusses Angle Iron riffles, flat bar riffles, expanded metal riffles and riffle spacing, and some experiments at actual mines where adjusting these on existing circuits led to larger recovery rates.
Now to return to the “19 ounces/day” number - I think that might depend on how many hours the machines are run a week. I think I used a conservative 40 hours a week (5 days at 8 hours or 6 days at around 6.5 hours), but on Facebook it says they “hope the new plant will process ... 50 hours a week”. I attended a United Milling shareholder meeting where they discussed the number of hours and shifts a milling plant could run and there are many options. I assume Dun Glen also has several ways they could organize production. One thing I did notice is that a lot of time is devoted to maintenance. So in a day you might run a certain number of hours, then close down for a certain number of hours to check and keep up the machinery, then run more hours.
In the December 3rd PR Kilroy stated: “Dun Glen anticipates gold production of at least 19 ounces per day “ and "Dun Glen estimates a range of gold recovery in 2015 to be a low of 1872 oz. with a potential upside to 5990 oz.” The April 20 PR says “The new circuit is designed to run at 100-yards per hour with a recovery rate of 80%.” and the April 15 Facebook posting says they hope to run 50 hours a week.
For this all to happen, you would have to have ore run at 100 yards-per-hour X 50 hours a week X 80% = 4000 yards. To get 95 ounces a week (let’s say 5 days at 19 ounces each day) you would then have to have an assay-grade of about 0.025 for the ore. Thus, 4000 yards/week X 0.025 = 100 ounces. If you can run that circuit for 10 months a year (call it 40 weeks), that would be 100 ounces/week X 40 weeks = 4000 ounces/year which fits into their “1872 low - 5990 high” estimated range for one year of production. (I assume the estimated range is a broad one because there are so many variables there... yards per hour, hours per week, weeks per year, grade of the ore).
If (and that might be a big “if”) they can go at that rate for half of 2015, then that would be about 2000 ounces for 2015, or something over $2,000,000 with one circuit running, and $4,000,000 for one circuit in 2016. If they were to add a second, similar circuit to the mine late in 2015, then the two circuits together would produce $8,000,000 in 2016.
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