Only where a group of mines operates in a single district are costs comparable and then only with reservations. In general, cost systems are fairly uniform, yet in studying costs of a number of plants it is noticeable that in some cases there is a tendency to omit certain operations which are proper charges against ore dressing and treatment. These should cover the first stage of coarse crushing, whether it be underground or on the surface, as well as the disposal of the residue, the recovery of bullion, and returns from products sold and must include the cost for labor, power, supplies, repairs, and compensation.
In 1936 when data were being compiled for Cyanidation and Concentration of Gold and Silver Ores, considerable published information was available on milling costs in various parts of the world. At the present time, however, it is extremely difficult to obtain reliable figures on the cost of ore treatment owing to the fact that during a period of rising prices and wages the mine managements do not consider current cost data typical of normal operation and are unwilling to release them for publication.
Another factor which applies particularly to the United States and Canada and which tends to make cost-per-ton figures unreliable is the disparity between the rated capacity of many of the mills and the actualtonnage being handled today. This is partly attributed to shortage ofunderground labor and partly to the fact that during the war period not only was maintenance heavier than normal but opportunities for improvements in technique were lacking.
Figure 97 shows the relationship between the tonnage capacity and total milling cost, per ton based on the 1939 figures for a number of typical Canadian plants. Saving in overhead and labor is the principal factor that enters into the decreasing cost per ton for the larger operations.
Considerable variation will be found in individual cases depending upon hardness of ore, fineness of grind, hours of treatment required, reagent consumption, and the situation of the property in its bearing on cost of supplies, etc.
The total cost of producing an ounce of gold in Canada increased from $22.35 in 1939 to $32.07 in 1945, according to the report of the director of the Ontario Mining Association for 1945. This represents a 43.5 per cent increase. From various other data which are available, however, it appears that milling and treatment costs (mining excluded) have probably not risen on the average over about 30 per cent. The broken line in Fig. 97 indicates estimated present (1948) average cost on the basis of this 30 per cent rise.
Kerr Addison, for instance, is milling 2800 tons per day for a total of 72 cents per ton. Hollinger in the 40 weeks ending Oct. 6, 1948, milled an average of 3627 tons per day at a total cost of 77.29 cents per ton, of which 37.90 cents was labor cost.
Where a combination of flotation and cyanidation is used, the combined cost approximates this same percentage. This includes such items as heating and lighting, sampling, assaying, experimental work, repairs, and various indirect costs, depending upon the system of cost distributions in use. It is partly because widely different methods of charging out such costs have been adopted that considerable divergence in overall cost distribution is to be found.
Consolidated Beattie gold mines is a good example of a large plant employing flotation, roasting, and the cyanidation of concentrates. Approximately 1300 tons per day of arsenical gold is treated for an overall cost of $1.05 per ton, distributed as shown in Table 98.
The roasting cost works out at approximately $1.22 per ton of concentrate, distributed as shown in Table 99. At MacLeod Cockshutt Gold Mines, Ltd., the cost of roasting in 1941- 1942 was 32 cents per ton milled or $1.25 per ton of ore roasted, while at Lake Shore mines for the same year the cost was about 80 cents per ton roasted.
The 700-ton mill operated by the Standard Cyanide Co. in Nevada between the years 1939 and 1942, when it was closed as a result of government order during the Second World War, succeeded in making a profit from ore carrying as little as 0.06 oz. gold per ton. Cheap, open-pit mining methods were used, and good extractions were obtained when grinding to only 3 mesh. These, among other factors, made for extremely low-cost operation. The 596,482 tons milled yielded $1.86 per ton at a total cost of $1.18 per ton of which $0.52 was milling cost.
The power required in cyanide plants varies with type of ore, fineness of grind, etc., but in general the range is 20 to 30 kw.-hr. per ton of daily capacity. The power distribution at Preston East Dome mines in Ontario, Canada, is shown in Table 102. The relative distribution of power between the crushing and grindingsections will vary according to the fineness of crushing and the type of plant, but on the average these departments will together consume 60 to 70 per cent of the total power.
Flotation. The power consumption for straight single-product flotation plants varies, according to A. M. Gaudin, from 12 to 20 kw.-hr. perton, depending on the fineness to which the ore is ground. The average percentage power costs for the various.departments of seven United States producers is given in Table 103.
The power consumption at Randfontein Estates, which is milling 13,000 tons per day by the older sand-slime process, is shown in Table 104. Distribution figures for the new 2100-ton-per-day Marievale plant are shown in Table 105.
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Amidst the general fall in metal prices over the last few years, the gold price has remained comparatively stable in the US$1,000-1,250/oz range. Gold bulls were disappointed that the price did not break through the $2,000/oz ceiling; nevertheless the current stable price run has helped to maintain a strong interest in gold projects.
The second is the sustained, and dare I say sustainable, use of cyanide for gold leaching in the last 100 years or more in a world of increasing environmental concerns and general aversion to the use of toxic chemical like cyanide. Alternatives to cyanide are not the subject of this article, but it is suffice to say that recent applications of alternatives to cyanide, e.g. thiosulfate at Goldstrike Nevada, have been driven by technical rather than environmental imperatives. In the case of Goldstrike, this was a double-refractory ore combining sulphide-occluded gold with preg-robbing carbonaceous material that rendered the ore unsuitable for conventional cyanide leaching and carbon adsorption.
In most cases, gold processing with cyanide leaching, usually with carbon adsorption, is still the core technology and the critical thing is understanding the mineralogy in order to optimise flowsheet selection and cost drivers, and get the best out of the process.
Traditionally, the process selection choice was between a conventional, well-tried, three-stage crushing circuit followed by ball milling, or single-stage crushing followed by a semi-autogenous (SAG) mill and ball mill. The latter is preferred for wet sticky ores to minimise transfer point chute blockages, and can offer savings in both capital costs and long-term operating and maintenance costs. However, the SAG route is more power-intensive and, for very hard ores, comes with some process risk in predicting performance.
Now that initial wear issues have largely been overcome, they offer significant advantages over a SAG mill route where power costs are high and the ore is very hard. They can be attractive too in a heap leach where the micro-cracking induced by the high pressure has been demonstrated in many cases to improve heap leach recovery.
The hashing stage (corresponding to metal extraction and recovery stages) is a little more complex for gold ores, as the optimal process flowsheet selection choice is heavily dependent on a good understanding of two fundamental geometallurgical parameters, the gold mineralogical associations, and the gold particle size and liberation characteristics. These are summarised in Table 2, where the processing options that correspond to the various combinations of mineral associations and liberation are shown along with some examples.
This is common in tropical environments (e.g. West Africa) and typically oxidises gold-bearing sulphides down to 50-100m, transforming commonly refractory gold in sulphides to free-milling gold, behaving in a similar fashion to gold associated with quartz.
Refractory ores are typically treated by flotation and the resulting flotation concentrate may be sold directly to a smelter (common for example in China) or subjected to downstream processing by pressure oxidation or bio-leach.
An ore containing 1% sulphur will produce a mass pull of approximately 5% by weight to a bulk flotation concentrate where recovery is the key driver. If this ore also contains 1g/t Au (for GSR =1), and 90% recovery to concentrate is achieved, then 0.90g will be recovered and with a concentration ratio of 20 (5% to concentrate) this corresponds to 18g/t Au in concentrate.
Both smelter treatment charges and oxidation or bio-leach costs are at least $200/t of concentrate and payables/recovery in the 90% range, so a minimum GSR for effective downstream processing is around 0.5. Clearly this is a function of gold price, but in the current gold price and cost environment, a good rule of thumb is that a minimum GSR of 0.5 is required for downstream processing of a gold-bearing concentrate.
A lower GSR can be tolerated if the flotation concentrate is amenable to direct cyanide leaching without the costly oxidation stage to release the gold from the sulphides. And on-site dor production avoids the off-site costs of transport and smelter charges, but usually with lower recovery (flotation recovery then oxidation-leach recovery) so a trade-off analysis is required.
Smelters typically pay >95% (Au) and 90% (Ag) in copper and lead concentrates, but will only pay 60-70% (maximum, depending on degree of Pb/Zn smelter integration) for gold and silver in zinc concentrates.
It can be seen that the key cost elements are: power, cyanide and grinding steel plus, for refractory ores, the costs associated with pressure oxidation or bio-leaching. It should also be noted that, where cyanide destruction is required (increasingly the norm), then cyanide detox unit costs are usually of a similar order of magnitude to the cyanide unit cost.
In summary, and of particular relevance to project screening, an early appreciation of gold mineralogical associations and liberation can provide considerable insight into metallurgical process flowsheet selection and processing costs.
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Hengcheng offers complete solutions for Rock Gold Processing Plant. We are one of the leading project suppliers for Rock Gold Processing Equipment and we work closely with our customers to fulfill their specific needs for customized package solution. Specialized in the fabrication of these machines for 15+ years and this enables us to be in a leading position in the field of Rock Gold Processing/Mining.
At Hengcheng, we provide more than just gold gravity processing machines, but constantly strive to assist you in achieving overall business excellence. This is why when you partner with Hengcheng, you dont just get a diversified product offering, but form a relationship based on product refinement, a true understanding of gold process flow sheets and field service and maintenanceensuring that together we will create a solution that is suited specifically to your individual needs and that will optimize your process and lower your overall operating costs.
At Hengcheng, we provide more than just processing equipment, but constantly strive to assist you in achieving overall business excellence. This is why when you partner with Hengcheng, you dont just get a diversified product offering, but form a relationship based on product refinement.etc
PCF Capital Group, a provider of corporate advisory services to the mining and resource sector, has released a report, highlighting current gold all in sustaining costs (AISC) for Australian and New Zealand gold operations.
While we provide profiles of high performing mines and companies featured in the report, it is important to gain a thorough understanding of what makes up AISCs, and how important this metric can be especially during periods of commodity price volatility.
AISCs are the costs attributed to production at operating mines, and they are an important focus in gauging a projects commercial viability. It is important to note, that they dont include the costs such as building a plant and establishing the infrastructure required to bring a mine into production, commonly referred to as upfront capital expenditure (CAPEX).
AISC is a similar measure to what you might find in anything from manufacturing to retail, only in other sectors acronyms such as CODB (cost of doing business) and COGS (cost of goods sold) are applied.
Different treatment processes that may be required because of the composition of the mineral or the amount of waste that needs to be separated to extract the ore also impact the cost of the end product.
Factors such as these can impact decisions such as the economic viability of mining higher grade ore at lower depths where the potential revenue generation is weighed up against the increased mining and processing costs.
While this isnt a metric that necessarily comes into play in calculating AISCs as foreign exchange rates impact the top line, it does become a significant factor where companies benefit from the sale of by-products.
Simplistically, a mine operating in the US generates revenues of about US$1280 per ounce based on the current spot price, whereas an Australian mine based on an unhedged sale price is receiving $1850 per ounce in Australian dollars.
As a case in point, a mine that produces 100,000 ounces of gold and 10,000 tonnes of copper per year at a cost of US$1000 per ounce, not including revenues generated from the sale of copper, will have AISCs well below US$1000 per ounce after the by-product credits are taken into account.
This would effectively provide the producer with a healthy margin of approximately US$900 per ounce at todays rates, making it a much more economical mine given a standalone gold operation would only be delivering a margin of about US$300 per ounce.
Of course, in the case of an Australian producer the cost of production offset would be in the order of $8700 per tonne of copper ($87 million based on production of 10,000 tonnes per annum) because of the favourable AUD:USD exchange rate.
This is only an overview of a much more comprehensive report, but it provides an interesting insight into the operations of companies of all sizes with one notable performance being an AISC of, believe it or not, negative $510 per ounce.
It also highlights some of the aforementioned contributing factors we referred to - bear in mind the current spot price is approximately US$1280 or AU$1850 based on an AUD:USD exchange rate of 68.8 cents.
Evolution Minings (ASX:EVN) part of the Ernest Henry operations was the lowest cost producer reporting an AISC of A$-510/oz followed by Newcrests (ASX:NCM) Cadia Valley operations with an AISC of A$206/oz, then by Kirkland Lakes' (ASX:KLA) Fosterville mine (A$442/oz).
The lowest cost gold only operations were Kirkland Lakes' Fosterville mine with an AISC of A$442/oz, then Westgold Resources' (ASX:WGX) Fortnum mine (A$937/oz) and Newmont's (NYSE:NEM) Tanami mine (A$953/oz).
Newcrests Cadia Valley operation took out top spot as Australias largest gold producer with 218,891 oz for the quarter, followed by Newmont's Boddington (155,000 oz) then Newmont's Tanami operation (131,000 oz).
Of the mines where gold is a by-product, Oz Minerals (ASX:OZL) Prominent Hill produced the most gold 32,947 oz followed by BHP's (ASX:BHP) Olympic Dam with 28,609 oz and Evolution's part of Ernest Henry 22,419 oz.
Grade wise, for the companies that report AISC, the average reported mill head/feed grade was 3.47 g/t (Open Pit (OP) - 1.71 g/t, Underground (UG) 5.33 g/t, Open Pit and Underground (OP/UG) - 2.35 g/t) which was down on the previous quarter, 3.91 g/t (-11.3%).
While March quarter production of 22,400 ounces at a very low head grade looks underwhelming on the surface, the production of 4800 tonnes of copper was instrumental in the group generating record net mine cash flow of approximately $60 million in the quarter.
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As the first digital publication dedicated specifically to this space, Finfeed soon became the most trusted publication in the market, quickly garnering over two million page views a number that continues to rise.
Finfeed.com provides its readers with informative articles that tackle the latest in market moving #ASX small cap news, plus exclusive content you wont find anywhere else. It is aimed at those with an interest in investing, market education, company performance, start-ups and much more.
Over the years, the website has expanded beyond exclusively reporting on small caps, to profile Australias leading ASX listed small, mid and large caps as well as some of the countrys most successful CEOs and business leaders to find out what makes them tick.
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Small-scale hard rock miners do not have the luxury of a fully equipped industrial-grade mill with flotation and cyanide leaching to process their ore and recover values. We are usually limited by practicality, finances and permitting to a simple crushing and grinding circuit, with a gravity recovery system for the free milling values and value-containing sulfides.
Mt. Baker Mining and Metals is focused on providing a cost-effective and durable ore processing plant that includes a jaw crusher, hammer mill, size classification equipment, and sluice/shaker table. This is the most efficient combination of cost, productivity, longevity, and recovery when the job calls for processing bulk samples, performing test runs, or an initial setup to generate revenue flow.
We have designed a turn-key ore processor with hands-free operation in mind. This cost-effective solution requires no computers nor electronics, making it easy to run and maintain. The system scales to your growth, as well, incorporating ball mills or flotation plants to keep up with commercially-viable mining operations. Visit our turn-key mining product page to learn how an MBMMLLC system can fit into your operation.
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