Below is a link to a “typical flowsheet for processing refractory gold ore”:
A typical flowsheet for processing refractory gold ore (Sulphidic Gold… | Download Scientific Diagram (researchgate.net)
A lot of this talk about “refractory” ores and “flotation” and “DIRECT SMELTING” can be confusing but it’s really not that complicated. Most gold ores are destined for the smelter (ultra-hot reverberatory furnace) eventually. “Refractory ores” are gold ores that are typically encapsulated in “sulfide” or “arsenic” minerals like arsenopyrite or “apy”. Sometimes it is the gold’s association with “carbon” in “carbonaceous minerals” that makes it more difficult to recover. Other times, it’s the size of the gold particles, “fines” and “ultra-fines”, that make it tougher to recover and less amenable to processes like “gravity separation”. As noted, eventually the final destination is likely to be a “smelter”. The main difference is the pathway to the smelter. It can be “DIRECT” as in what Enami calls “DIRECT SHIPPING ORE” or INDIRECT involving preliminary steps prior to smelting.
Is ”refractory ore” a bad thing? If you recall the typical layers to a hydrothermal vein deposit like that of Auryn’s, at surface you have the “gossan”. This is a colorful area often composed of “altered” clays that make up “argillic alteration”. These are illite, smectite and kaolinite. This is the “X marks the spot” for prospectors because rich deposits often show this at surface right above the deposit. The DL2 Vein has a corridor of “argillic alteration” with a width of up to 200-meters. The next layer down from surface is the “leached zone”. Not much valuable material is found here because, as the name implies, it has been “leached” by surrounding acids, and the sought after metals have been dissolved and they drift lower in the structure. Next comes the “oxide” layer. Now things start getting interesting. “Oxides” are relatively easy to process and the recovery rates are high in mining operations. The thing that does the “oxidizing” is the oxygen contained in “meteoric water” which is rain water. If you look at that “typical flow sheet for processing refractory ore” you’ll notice that several of those steps for dealing with “refactory” ore involved “forced oxidation” of sulfide material. These include “pressure oxidation” or “POX” and “biological oxidation” or “BIOX”. Even “smelting” involves “forced oxidation”.
The next layer lower is the “SUPERGENE ENRICHMENT ZONE” if a deposit is lucky enough to have one. This is where the material that has been “leached” by acids piles up in large very high-grade mineral assemblages down by the historical water table. Auryn got lucky in this respect with all of that high-grade copper known as “BORNITE” (the blue stuff) you saw in the “photo gallery” of Auryn’s website.
The layer underneath the SGE zone is called the “sulfide” layer. This is where Auryn is currently mining. As the name implies, this layer is inhabited by gold, copper and silver “sulfides” which are often “refractory” because the gold can hide within the crystalline lattice of these sulfide minerals, especially arsenopyrite or “apy”. Most mines are mining “sulfide” ore.
In “mesothermal” vein systems like these, as you go deeper into the “sulfide” layer, BOTH the grades and the widths of the veins tend to improve. Both Dick Sillitoe and Rob Cinits of ACA Howe have noted this happening at the DL2 Vein. Auryn is currently mining level 3. When they start mining, let’s say, level 5 or 6, the grades are likely (but not assuredly) to be higher and the vein widths more favorable.
The question becomes, IS “REFRACTORY” ORE A BAD THING. The answer is easy, it depends upon the GRADE of the “refractory” ore. “Refractory” ore will cost more to process because more steps are involved. The GRADE of the ore is still, by far and away, the primary determinant of the ECONOMICS. Would you rather average grade oxide ore or would you rather have off the chart grade sulfide ore? It’s not even close. The Auryn story is all about EXTRAORDINARILY HIGH-GRADE SULFIDE ORE. Sure, it would have been great if we were mining EXTRAORDINARILY HIGH-GRADE OXIDE ORE.
On the flowsheet that is linked to, if you draw a straight line between “comminution” (crushing and grinding) to “smelting”, this represents the path for Auryn’s “DIRECT SMELTING” ore, i.e. DIRECTLY to the smelter. For those Enami (a branch of the Chilean government) clients that have qualified to be “registered” with the Chilean Mining Registry, like Auryn did on July 4, 2023, they have the right to send their DIRECT SMELTING ore to the nearest CODELCO (another branch of the Chilean government) smelter. Codelco runs 4 of the 7 smelters in Chile. This policy, which was approved by the Chilean legislature’s Lower House Mining and Energy Committee, is very important for a producer like Auryn. The Las Ventanas Smelter, in Valparaiso, is being shut down, for reasons associated with environmental concerns. There are 2 Codelco smelters located within about 100 miles of the ADL.
About one-fourth of all gold ores are considered “refractory”. The great equalizer in gold ore processing is that “refractory” ores tend to have grades approximately 1.86-times the grades of non-refractory ores. This has nothing to do with the stellar grades being found at the DL2 Vein. Those “RUN OF MINE” grades are simply off the chart whether, from a processing point of view, the ore be “refractory” or non-refractory. As noted, by far and away, the most important characteristic from an ECONOMIC point of view is GRADE. At the end of the day, pretty much all of the gold will be recovered. It’s mainly a matter of how many intermediate steps between comminution and smelting need to be taken.
“Smelting” is what’s called an “extractive metallurgical process” that produces a metal from its ore. Smelting uses heat, usually from a reverberatory furnace, in order to decompose the ore and drive off unwanted waste material and gases, leaving the desired metals behind. Those “sulfides” that give ore its refractory nature will be volatilized and the “sulfur dioxide” gases will carry away those impurities. In the case of the unwanted “carbon” material, they will be volatilized away as carbon monoxide and carbon dioxide gases. Toxic gases released by smelting will be “scrubbed” later in order to detoxify them. The operating costs for Codelco’s newly updated smelters is only 10-cent per tonne for Codelco. I personally find this hard to fathom but it is what it is.
At the DL2 Vein project, Auryn will be shipping their RELATIVELY LOW-GRADE ORE (below 20 gpt gold but still actually very “high-grade” ore) to Enami’s FLOTATION FACILITY. NOTE THAT 18 TO 20 GPT GOLD ORE IS NOT “LOW GRADE” BY ANY MEANS. At the DL2 Vein, this material is “RELATIVELY” low-grade. The average grade of gold being mined worldwide today in underground vein operations is 4.18 gpt gold. When you factor in above ground “open pit” operations, the average grade of gold being mined worldwide today is a little bit over 1 gpt gold. The ore that Auryn will be shipping to the Enami FLOTATION FACILITY will be somewhat “high-grade” ore derived from the less well-mineralized wall rock just lateral to the DL2 VEIN PROPER. This ore will be very ECONOMIC but just not to the degree that the super high-grade ore from the VEIN PROPER will be. The good news is that, after all of this time, we’re about to find out the ECONOMICS involved.
At the DL2 Vein project, the highest grade-ore is that located within the vein itself. You already know what types of grades that this ore is running in the area where Auryn is currently mining. The “channel sampling” or “channel chip sampling”, which measures only the grade of the VEIN ORE itself, ran from 150 gpt to 164 gpt gold. But do not expect the SHIPPING GRADE of a truckload of Auryn’s DL2 Vein ore to approach these kinds of numbers. This kind of grade will become DILUTED because what is shipped will include some of the “RELATIVELY” low-grade wall rock.
On any given working face, the ore located lateral to the vein and within the surrounding “wall rock” is less well-mineralized and of a LOWER grade. This does not translate into this ore being of “LOW-GRADE”, i.e. perhaps 1 to 2 gpt gold. When you mine a 3-meter-wide adit working face, the miners have to remove all 3-meters of rock so that men and equipment can access the next upcoming “working face”. Visibly non-mineralized rock near the lateral borders of the adit can be visually sorted and discarded prior to crushing.
The only grade that matters is the grade that Enami will pay you for. In the recent shipment of an unknown quantity of ore to Enami/Codelco’s DIRECT SMELTING facility, the “settled upon” grade or “agreed to liquidation grade” was 73 gpt “gold equivalent” when you add to the gold grade, which was 57 gpt gold, the contributions from silver and copper. Do not expect the grades of the ore being shipped to Enami’s FLOTATION FACILITY to be that high.
SOME POINTS BEING CURRENTLY DISCUSSED ON THE MININGPLAY FORUM
- CRITIQUE: Management should have known that the ore had a refractory nature to it.
What management KNEW or DIDN’T KNOW about any potential refractory nature of the ore isn’t the issue. The potential offtake partner, Goldlogic, had to learn about the refractory nature or lack of a refractory nature to the ore LOCATED AT WHERE AURYN WAS ABOUT TO COMMENCE MINING. Auryn has never been at this 1,840 meters above sea level depth before so, of course, COMPREHENSIVE METALLURGICAL STUDIES needed to be done.
Auryn tested a well-known “gravity plant” model known as the Sepro-Falconer. This was done at an unknown depth over at the Merlin 1 Vein to the west of the DL2 Vein. The results were great and they saw an over 90% recovery of “even the fines”. Whatever technology that Goldlogic insisted on utilizing for the ore located at the 1,840 meters above sea level at the DL2 Vein did not show the results that Goldlogic was looking for. Was Goldlogic looking for ore that made THEIR PARTICULAR TECHNOLOGY look like the new ultimate “better mousetrap” of the future, I don’t know. Would Auryn have had to purchase this new better mousetrap technology through Goldlogic? I don’t know. What was wrong with the standard “mousetraps” (gravity plants) available right there in Chile i.e. Sepro, Knelson, etc? I don’t know.
Here’s what we know to be the facts. The Sepro-Falconer worked just fine at the Merlin 1 Vein which is located to the west of the DL2 Vein. It is part of the same VEIN SET as the DL2 Vein. The DL2 Vein ore located at the 1,840 meters above sea level did not meet the goals set forth by Goldlogic, whatever they were. Did they want a PERFECT MATCH for their technology that would make their technology look awesome for promotional purposes? I don’t know. The need to ship the ore to 2 “specialty labs” in Peru seemed a little bit weird but who the heck knows? WOULD I RULE OUT THE FUTURE USE OF GRAVITY PLANTS AT THE ADL MINING DISTRICT? NOT ON YOUR LIFE. When Auryn (hopefully) intersects the Don Enrique Vein very close to where the terminus of the Antonino Adit currently is, might this ore (from a different vein than the DL2 that is located closer to the Merlin 1 Vein) have results equal to those achieved by the Merlin 1 Vein with the Sepro-Falconer? Of course it might, but I certainly don’t feel qualified to handicap the odds.
CRITIQUE #2: Auryn took way too long to locate the DL2 Vein.
The plan was to locate and intercept the DL2 Vein at approximately the 1,840 meters above sea level elevation underneath where “Shaft C” of the “old workings” intersected level 2. You need to think in 3-dimensions here. They are looking for a certain “spot” in the belly of the mountain. You want adits to be fairly level with maybe a slight incline or decline. You don’t want low spots that will attract water. Next, you need to pick the location at which you want the transported ore to arrive at the plateau surface. The obvious choice would be at the junction of the North Road and the plateau. You then go to this area with a topographical map and locate where the 1,840 meters above sea level elevation is. This gives you a line that the adit to the portal is going to be on. You need to keep thinking in 3-dimensions. The elevation needed to be right and the proximity to the North Road had to be right. You also wanted to intersect the DL2 Vein at somewhat of a right angle so that you could establish 2 working faces, one oriented to the NNW and one to the SSE. Now you know where on this topographical “line” to construct the “portal”/entrance to the adit. This is where Auryn put it.
You start drifting the adit, in the direction of the “strike” of the DL2 Vein. You can’t miss it because you’re going to “broadside” it. Near surface, the DL2 Vein “dipped” from the surface to the NE at a 45-degree angle. Since management was coming from the NNE and heading to the SSW, from 2 o’clock to 8 o’clock on a watch dial with 12 o’clock being due north, if the DL2 Vein continued on that “dip” of 45-degrees to the NE, they should have hit it fairly early during the process IF THE VEIN DIDN’T CHANGE ITS EARLIER COURSE. As Mother Nature often does, She threw a bit of a curve ball and the Vein up-righted itself and started plunging straight down. The intersection point was much further to the SSW than originally anticipated. Veins are DISCORDANT. They can zig-zag all over the place just like the cracks through rock structures do before they became “veins”.
Three separate times, management declared that they thought that they intersected it and we are awaiting lab confirmation that this was indeed the DL2 Vein. Three straight times, the lab reported that the “DNA” (so to speak) of the vein you just intersected DID NOT MATCH. Keep in mind, you’re underground. There is no GPS. You’re looking for a specific “spot” in the belly of the mountain. Finally on Dec. 23, 2022 they intersected the DL1 Vein, the skinnier of the DL1 and DL2 Veins that the artisanal miners were mining. On January 4, 2023, they confirmed intersecting the main target, the DL2 Vein, and the “DNA match” was confirmed. They ran 2 “channel chip” sampling surveys about 10 days apart. Both came back with literally off the chart results. The original set of 4 “channel chip” samples came back with an average of 164 gpt gold and 4.5% copper. The second sample came back “as expected” (management’s terms) at approximately an average of 150 gpt gold. THE SIGNIFICANCE OF THIS WAS THAT THE STELLAR HISTORICAL SHIPPING GRADES AVERAGING 64 GPT GOLD, AS REPORTED BY ENAMI AND SERNAGEOMIN, HAD FINALLY BEEN CORROBORATED. This is a very, very high-grade mesothermal vein system.
CRITIQUE #3: Why didn’t management ship ore for the last 2 years if the grades were so wonderful? You can’t make regular shipments/”consignments” to Enami, over and above test shipments, until you qualify your project with the CHILEAN MINING REGISTRY and become a “REGISTERED” Enami participant. Auryn qualified and became a “REGISTERED” participant on July 4, 2023.
It is a simplification of a small section of Greg Corbett’s overview of structures in a classic copper porphyry model containing both high and low sulfidation zones with offshoot veins. Assays have clearly shown the presence of these ore types.
