Underground Feasibility Forecasts vs Actuals

underground costing
I recently attended a CIM Management and Economics Society presentation here in Toronto discussing the differences between actual underground production versus the forecast used in the feasibility study. The presenter was Paul Tim Whillans from Vancouver Canada.
His topic is interesting and relevant to today’s mining industry.  Paul raised many thoughtful points supported by data. He gave me permission to share his information.
The abstract for his paper is inerted below.  The paper can be downloaded at this LINK and here are the presentation slides.

ABSTRACT

An underground mining study that is done in accordance with NI43-101, JORC or similar reporting code is generally assumed by the public to be representative, independent and impartial. However, it has been well documented by academics and professionals in our industry that there is a sharp difference between the forecasts presented in these underground studies and the actual costs when a mine is put into production.
For underground mines, the risks associated with obtaining representative information are much greater than for surface mining and the cost of accessing underground ore is also proportionally much greater. There is a pressing need to align expectations, by improving the accuracy of projections. This will result in reduced risk to mining companies and investors and provide more reliable information to government agencies, the public, and more importantly, the communities in which the proposed mine will operate.
The objective of this article and an article currently being written titled “Mining Dilution and Mineral Losses” is to:
– Discuss the dynamics of intention that lead to over-optimism;
– Provide simple tools to identify which studies are likely to be more closely aligned with reality;
– Identify some specific points where underground mining studies are generally weak;
– Discuss practices currently in use in our industry that lead to a composite or aggregate effect of over optimism;
– Describe the effects of overly optimistic studies;
– Outline specific changes that are necessary to overcome these challenges; and
– Stimulate discussion and awareness that will lead to better standards.”

Conclusion

I agree with many of the points raised by Paul in his study. The mining industry has some credibility issues based on recent performance and therefore understanding the causes and then repairing that credibility will be important for the future.
Credibility ultimately impacts on shareholder returns, government returns, local community benefits, and worker health and safety; so having a well designed mine will realize benefits for many parties.
If you need more information Paul’s website is at http://www.whillansminestudies.com/
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Do Any Junior Producers Model a Gold ETF?

junior mining company
I have often wondered if any of the smaller gold producers have ever considered modelling their business plan similar to a gold Exchange Traded Fund (“ETF”).
This hybrid business model may be a way for companies to provide shareholders a way to leverage themselves to physical gold rather than leveraging to the performance of a mine.

Let me explain further

Consider two identical small mining companies each starting up a new mine. Their projects are identical; 2 million gold ounces in reserves with annual production rate of 200,000 ounces with a 10 year mine life. On an annual basis, let’s assume their annual operating costs and debt repayments could be paid by the revenue from selling 180,000 ounces of gold. This would leave 20,000 gold ounces as “profit”. The question is what to do with those 20,000 ounces?

Gold Dore

Company A

Company A sells their entire gold production each year. At $1200/oz, the 20,000 oz gold “profit” would yield $24 million. Income taxes would be paid on this and the remaining cash can be spent or saved.
Company A may decide to spend more on head offices costs by adding more people, or they may spend money on exploration, or they could look at an acquisition to grow the company. There are plenty of ways to use this extra money, but returning it to shareholders as a dividend isn’t typically one of them.
Now let’s jump forward several years; 8 years for example. Company A may have been successful on grassroots exploration and added new reserves but historically exploration odds are working against them. If they actually saved a portion of the annual profit, say $10M of the $24M, after 8 years they may have $80M in cash reserves.

Company B

Company B only sells 180,000 ounces of gold each year to cover costs.  It puts the remaining 20,000 ounces into inventory. Their annual profit-loss statement shows breakeven status since their gold sales only cover their financial commitments. In this scenario, after 8 years Company B would have 160,000 gold ounces in inventory, valued at $192 million at a $1200 gold price.
If you’re an investor looking at both these companies in the latter stages of their mine life, which one would you rather invest in?
Company A has 400,000 ounces (2 years) remaining in mineral reserves and $80M cash in the bank. Company B also has 400,000 ounces of mineral reserves and $192 million worth of gold in the vault. If I’m a bullish gold investor and foresee a $1600/oz gold price, then to me Company B might theoretically have $256M in the vault (160k oz x $1600). If I’m a super bullish, their gold inventory could be worth a lot more..theoretically.

Which company is worth more?

I assume that the enterprise value (and stock price) of Company A would be based on its remaining reserves at some $/oz factor plus its cash in the bank. Company B could be valued the same way plus its gold inventory. So for me Company B may be a much better investment than Company A in the latter stages of its mine life. In fact Company B could still persist as an entity after the mine has shutdown simply as a “fund” that holds physical gold. If I am a gold investor, then Company B as an investment asset might be of more interest to me.
If Company A had good exploration results and spend money wisely, then it may have more value but not all companies are successful down this path.

Conclusion

It appears that most of the time companies sell their entire annual gold production to try to show profit on the annual income statement. This puts cash in the bank and shows “earning per share”.
My question is why not stockpile the extra gold and wait for gold prices to rise?  This might be an option if the company doesn’t really need the money now or doesn’t plan to gamble on exploration or acquisitions.
This concept wouldn’t be a model for all small miners but might be suitable for a select few companies to target certain types of gold investors.
They could provide an alternative mining investment that might be especially interesting in the last years of a mine life. Who really wants to buy shares in a company who’s mine is nearly depleted?  I might buy shares, if they still hold a lot of gold.
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Mining Fads and the Herd Mentality

minerals
Have worked in the mining industry for over the last 40 years it is always interesting to watch the herd mentality that exists.  Its obvious how easily the industry gets caught chasing the latest fads.
All it takes is a short term spike in a commodity price or a big discovery somewhere and then off we go running in that direction.  It doesn’t matter the rationale driving the event, companies know they need to be in there and  investors don’t want to miss out either.  Its FOMO; the fear of missing out.

Don’t be the last on the bandwagon

In my experience, the fads or crazes can be based on commodities, locations, or technologies. The mining industry is very flexible in that regard. I’ll give a few examples that I have seen.  You probably have even more from your own experience.

Commodity Fads

It seems that as soon as there is a price spike or positive market narrative, a commodity specific projects can take on a life of their own.  The following list gives a few examples and, when you reflect upon them, ask how many actually came into successful production.  These events occur at different times in different economic cycles.
  • Potash: a few years ago potash prices spiked and potash leases were all the fad no matter where they were located around the globe, be it Canada, Russia, Ethiopia, Thailand, Brazil, etc.  That craze has largely fizzled out as prices returned to normal.  But just wait for the next temporary price spike.
  • Lithium / Graphite:  as soon as green battery technology started to be promoted in the news in 2016, miners couldn’t run fast enough to pick up the lithium properties.  The same idea holds for battery metals such graphite, vanadium, cobalt, and also rare earth categories.   After a lull, the process repeats itself in 2022.
  • Uranium: years ago uranium prices spiked and Ur properties were hot everywhere.  Prices have dropped but seem to be ramping up in late 2018.
  • Cobalt Excitement Curve

    Cobalt: see the price chart on the right to see how cobalt went into a craze and then out of it.
  • Nickel: years ago a spike in nickel prices caused a surge in nickel properties, whether it was sulphide nickel, laterite nickel, or other forms.
  • Iron Ore: in conjunction with the Chinese construction boom, iron ore properties were hot around the globe, in high cost or low cost jurisdictions, it didn’t matter where the property was.  Iron is still being pursued but mega scale projects always overhang the market.
  • Diamonds: in conjunction with the first diamond discoveries in Canada in the 1990’s, diamond properties became hot, whether in the Canada or around the globe.  If you couldn’t get a property in Canada’s NWT boom area, anywhere else globally was fine too.
  • China in general: a few years ago every base metal project was thought of as either a potential supplier to China or a potential acquisition for Chinese companies.  As long as it could meet Chinese investor interest it was good.

Regional Exploration Fads

Mineral claim map exampleWe have all seen the staking rushes that occur when a world class prospect is discovered.  I’m sure we can all recall getting the large claim maps (as shown) with their multicolored graphics showing the patchwork of acquisitions around a discovery. PDAC was great for distributing these.  They were well done and interesting to study.
Picking up properties in hot areas became the fad and share prices would move upwards regardless of whether there was any favorable geology on the property.  Who recalls the following?
  • Voisey Bay: with a mad staking rush around there, with nothing else really paying off in the long run.
  • Saskatchewan:  the potash staking rush where almost every inch of the potash zone was staked with only a couple of companies eventually moving forward and only one going into production.
  • Indonesia: during Bre-X people could not acquire properties in Indonesia fast enough.
  • NWT:  where the diamond property staking rush was crazy in the mid 1990’s.

Technology Fads

Even mining or processing technologies could get caught up in somewhat of a wave and become a fad for further study.  Sometimes this is driven by suppliers or consultants. For the engineers out there, who can recall…
  • Paste Tailings: with numerous conferences and consultants promoting thickened or paste tailings technology as the panacea.  This lead to numerous studies related to thickening, pumping, and disposal at each mine.
  • Block Caving: whereby in order to deliver high tonnages at low cost, bulk underground mining was being promoted.  Everyone wanted their underground project to be a low cost caving style operation.
  • High Pressure Grinding Rolls (HPGR): where process consultants would highlight HPGR as the new replacement for conventional grinding mills.  I’m not sure this technology has taken the industry by storm as they were hoping in the 1990’s.
  • IPCC: whereby inpit crushing and conveying systems were being promoted in many articles and global conferences as the solution to operating cost issues.  I think implementation of IPCC technology isn’t as simple as envisioned and I’m not aware of many cases of its successful implementation.
  • Dot.com: in the early 2000’s many junior miners left exploration behind and transitioned to the dot.com boom, a fad that essentially went nowhere for most.
  • Pre-concentration: this seems to be a growing technology that may be gaining momentum.  It isn’t new technology and it will definitely have its benefits.  However a big stumbling block is how many deposits are actually suitable for its application.  I have written more about this technology “Pre-Concentration – Savior or Not?

Conclusion

Have I missed anything?
The bottom line is that over the years it has been interesting to watch the mining industry react to events.  Sometimes it seems like we’re passengers on a ship, almost capsizing the industry by running from one side to other side and then back again.  Unfortunately that doesn’t necessarily make for smooth sailing.
What’s the next fad going to be? I don’t know but if you can predict it you can probably make a lot of money.
Once the commodity fad is underway, the next aspect of the junior mining that comes into play is the ebb and flow of exploration and mine development.   This is illustrated by the Lassonde Curve, were a project’s value rises and falls simply based on the amount of exciting news coming from it.   You can read more on this at the blog post “Mining’s Lassonde Curve – A Wild Ride“.
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Global Tax Regimes – How Do They Compare?

mining economics
Update: This blog was originally written in Feb 2016, but has been updated in Aug 2019.
As a reminder for all QP’s doing economic analysis for PEA’s, don’t forget that one needs to present the economic results on an after-tax basis.
Every once in a while I still see PEA technical reports issued with only pre-tax financials.  That report is likely to get red- flagged by the securities regulators.  The company will need to amend their press release and technical report  to provide the after tax results.    No harm done other than some red faces.

Taxes can be complicated

When doing a tax calculation in your model, where can you find international tax information?  PWC has a very useful tax-related website.  The weblink below was sent to me by one of my industry colleagues and I thought it would be good to share it.
The PWC micro-site provides a host of tax and royalty information for selected countries.  The page is located at https://www.ey.com/gl/en/services/tax/global-tax-guide-archive
On the site they have a searchable database for tax information for specific countries.
The PWC tax and financial information includes topics such as:
  • Corporate tax rates
  • Excess profits taxes
  • Mineral taxes for different commodities
  • Mineral royalties
  • Rates of permissible amortization
  • VAT and other regulated payments
  • Export taxes
  • Withholding taxes
  • Fiscal stability agreements
  • Social contribution requirements
PWC has a great web site and hopefully they will keep the information up to date since tax changes happen constantly.  The website also has a guide related to the rules for the treatment of capital expenditures.   Check it out.  https://www.ey.com/gl/en/services/tax/global-tax-guide-archive
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Resource Estimates – Are Independent Audits A Good Idea?

mining reserves
Question: How important is the integrity of a tailings dam to the successful operation of a mine?
Answer: Very important.
Tailings dam stability is so important that in some jurisdictions regulators may be requiring that mining companies have third party independent review boards or third party audits done on their tailings dams.  The feeling is that, although a reputable consultant may be doing the dam design, there is still a need for some outside oversight.
Differences in interpretation, experience, or errors of omission are a possibility regardless of who does the design.  Hence a second set of eyes can be beneficial.

Is the resource estimate important?

Next question is how important is the integrity of the resource and reserve estimate to the successful operation of a mine?
Answer: Very important.  The mine life, project economics, and shareholder value all rely on it.     So why aren’t a second set of eyes or third party audits very common?

NI 43-101 was the first step

In the years prior to 43-101, junior mining companies could produce their own resource estimates and disclose the results publicly.  With the advent of NI 43-101, a second set of eyes was introduced whereby an independent QP  could review the company’s internal resource and/or prepare their own estimate.  Now the QP ultimately takes legal responsible for the estimate.
Nowadays most small companies do not develop their own in-house resource estimates.  The task is generally awarded to an independent QP.

Resource estimation is a special skill

Possibly companies don’t prepare their own resource estimates due to the specialization needed in modelling and geostatistics. Maybe its due to the skills needed to operate block modeling software.   Maybe the companies feel that doing their own internal resource estimate is a waste of time since an independent QP will be doing the work anyway.

The QP is the final answer..or is it?

Currently it seems the project resource estimate is prepared solely by the QP or a team of QP’s.   In most cases this resource gets published without any other oversight. In other words no second set of eyes has taken a look at it.  We assume the QP is a qualified expert, their judgement is without question, and their work is error free.

Leapfrog Model

As we have seen, some resources estimates have been mishandled and disciplinary actions have been taken against QP’s.   The conclusion is that not all QP’s are perfect.
Just because someone meets the requirements to be a Competent Person or a Qualified Person does not automatically mean they are competent or qualified. Geological modeling is not an exact science and will be based on their personal experience.

What is good practice?

The question being asked is whether it would be good practice for companies to have a second set of eyes take a look at their resource estimates developed by independent QP’s?
Where I have been involved in due diligence for acquisitions or mergers, it is not uncommon for one side to rebuild the resource model with their own technical team.  They don’t have 100% confidence in the original resource handed over to them.   The first thing asked is for the drill hole database.
One downside to a third party review is the added cost to the owner.
Another downside is that when one consultant reviews another consultant’s work there is a tendency to have a list of concerns. Some of these may not be material, which then muddles the conclusion of the review.
On the positive side, a third party review may identify serious interpretation issues or judgement decisions that could be fatal to the resource.
If tailings dams are so important that they require a second set of eyes, why not the resource estimate?  After all, it is the foundation of it all.
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Disrupt Mining Challenge – Watch for it at PDAC

Update:  This blog was originally written in January 2016, and has been updated for Jan 2018.

Gold Rush Challenge

In 2016 at PDAC, Integra Gold held the first the Gold Rush Challenge.  It was an innovative event for the mining industry.  It was following along on the footsteps of the Goldcorp Challenge held way back in 2001.
The Integra Gold Rush Challenge was a contest whereby entrants were given access to a geological database and asked to prepare submissions presenting the best prospects for the next gold discovery on the Lamaque property.  Winners would get a share of the C$1 million prize.
Integra Gold hoped that the contest would expand their access to quality people outside their company enabling their own in-house geological team to focus on other exploration projects.   In total 1,342 entrants from over 83 countries registered to compete in the challenge.  A team from SGS Canada won the prize.

Then Disrupt Mining came along

In 2017, its seem the next step in the innovation process was the creation of Disrupt Mining sponsoerd by Goldcorp.  Companies and teams developing new technologies would compete to win a $1 million prize.
In 2017, the co-winning teams were from Cementation Canada (new hoisting technology) and Kore Geosystems (data analystics for decision making).
In 2018, the winning team was from Acoustic Zoom, an new way to undertake seismic surveys.

The 2019 winners will be announced at PDAC.  The entry deadline has passed so you’re out of luck for this year.

Conclusion

At PDAC there are always a lot of things to do, from networking, visiting booths, presentations, trade shows, gala dinners, and hospitality suites.
Now Disrupt Mining brings another event for your PDAC agenda.
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Claim Fees Paid for a Royalty Interest – Good Deal or Not?

mineral property acquisition
In 2016 I read several articles about how the junior mining industry must innovate to stay relevant.    Innovation and changing with the times are what is needed in this economic climate.
One company that was trying something new is Abitibi Royalties.  They were promoting a new way for them to acquire royalty interests in early stage properties.  They were offering to fund the claim fees on behalf of the property owner in return for a royalty.
Their corporate website states that they would pay, for a specified period of time, the claim fees/taxes related to existing mineral properties or related to the staking of new mineral properties.
In return, Abitibi Royalties would be granted a net smelter royalty (“NSR”) on the property.  It may be a gamble, but it’s not a high stakes gamble given the relatively low investment needed.

Not just anywhere

Abitibi were specifically targeting exploration properties near an operating mine in the Americas. They were keeping jurisdiction risk to a minimum.   Abitibi stated that their due diligence and decision-making process was fast, generally within 48 hours.  No waiting around here but likely this is possible due to the low investment required and often the lack of geological information to do actually do a due diligence on.
To give some recent examples, in a December 14, 2015 press release, Abitibi state that the intend to acquire a 2% NSR on two claims in Quebec and will pay approximately $11,700 and reimburse the claim owner approximately $13,750 in future exploration expenses. This cash will be used by the owner towards paying claim renewal fees and exploration work commitments due in 2016.   Upon completion of the transaction, these will be the ninth and tenth royalties acquired through the Abitibi Royalty Search.  For comparison, some of their other royalty acquisitions cost were in the range of $5,000 to $10,000 each (per year I assume).   I think that those NSR interests are being acquired quite cheaply.
The benefit to the property owner may be twofold; they may have no other funding options available and they are building a relationship with a group that will have an interest in helping the project move forward.  The downside is that they have now encumbered that property with a NSR royalty going forward.
The benefit to Abitibi Royalties is that they have acquired an early stage NSR royalty quite cheaply although there will be significant uncertainty about ever seeing any royalty payments from the project.   Abitibi may also have to continue to make ongoing payments to ensure the claims remain in good standing with the owner.
It’s good to see some degree of innovation at work here, although the method of promotion for the concept may be more innovative than the concept itself. Unfortunately these Abitibi cash injections investments are not enough to pay for much actual exploration on the property and this is where the further innovation is required, whether through crowd funding, private equity, or some other means.   I’m curious to see if other companies will follow the Abitibi royalty model but extend it to foreign and more risky properties.
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Junior Mining – Are People Still Investing?

small mining companies
Update: This blog was originally written in June 2015, however many of the observations made then still hold in late 2018.
The general consensus over the last couple of years is that the junior mining sector is still in a state of flux.
I briefly touched on this in a previous article “12. Financings – It Helps to Have a Credible Path Forward”.
It is still difficult for junior miners to get funding and the stock prices of have been on a downward trend.   Some observers say this just a temporary phase and the stock prices will cycle, as they have in the past.   I’m not convinced that this will be the case, although I am hoping.

Metal prices may recover, but will stock prices?

I am reasonably confident that metal prices will improve over time, but I am not sure that alone will result in the junior mining sector invigorating.  I think there is a long term shift in how personal investments are being made and how the mining industry is being viewed.  The following blog has some personal opinions on the present and the future.
Mining companies are constantly in the media with stories of cost over-runs, mine shutdowns, fatalities, strikes & protests, and environmental incidents.
In addition, the junior mining sector has had a few notable scams that nobody ever forgets about.
In some instances management were over promoting sub-optimal projects simply for the purpose of raising the stock price and cashing out.  Not many companies fell into this category, but enough to create an unfavorable image of the industry.
I think it will take time to recover from the image being created by the events described above. Unfortunately new incidents only build on the perceived legacy.
The implementation of sustainable and green mining practices is an attempt to rehabilitate the image of mining, but is anyone out there listening?

Are investment practices changing?

Regarding today’s investment practices, I have three general observations:
  1. Yield Investors: When many of us baby boomers were younger with a steady job, we were willing to speculate on mining stocks hoping for the big payoff.  At the time there were some well publicized payoffs. Also there wasn’t much else to speculate on.
    Now those same baby boomers are moving into retirement and financial planners are push them into fixed income and dividend paying investments.  Be happy with a 2% to 5% yield.  The risk tolerance for many of these investors has shifted from speculation / growth to income / capital retention.
    I’m not sure how many of these people will ever re-enter the mining stock market.  The majority of miners don’t pay any significant yield.   Looking at the yield for Barrick (2%), Goldcorp (0.8%), and Yamana (0.85%), their yields are lower than those for the more conservative bank stocks (4%-6%).
  1. Where to speculate now?  Where might the 30 to 40 year old’s speculate today? Younger people today may still speculate with their free cash, but they are not hoping to be investors in the next Voisey’s Bay, Kidd Creek, or Hemlo.  They have never even heard of them.
    They are hoping to be investors in the next Apple, Google, or Facebook, or a cannabis company.  The dot.com bubble of 1999–2000 was a case of junior mining speculators jumping into technology and it was a bust.  However currently several of the new breed of dot.com companies that have IPO’d are getting huge share price increases.  Is it still a tech bubble? Not so much anymore.
    I don’t know whether the younger speculators will ever have interest in the mining sector since they never heard of it.  There is so much other investing activity happening out there.
  2. The perception of mining: The mining and energy news shown in the media is not helping the industry by focusing mainly on the negative aspects. The resource business appears to be somewhat analogous to the meat industry. Everyone likes their nicely packaged rows of chicken and beef at the grocery store but nobody wants to see how it actually gets to the store.  Everyone also loves their metallic gadgets and the energy used to power them, but please don’t show how it actually gets from mine to store shelf.  It can be quite upsetting.
  3. Complexity:  To invest in a mining stock or understand a mining IR presentation, one needs a basic understanding of mining and geology.   To understand a tech stock or bank stock, one does not need to be an expert in that industry. People will intuitively have a better comfort level with them.

Can mining companies provide more yield?

An interesting group of companies are the mid tier producers that have operating mines and generate profits, but do not pay a dividend.  I will be curious to see how these companies shares will perform since they don’t satisfy the yield investor nor may they satisfy the pure speculator looking for order of magnitude capital gains.
The larger mining companies will always have their investors like pension funds and mutual funds, however the junior miners may be a different story.
Possibly private equity and equity-based crowdfunding will be one of the long term solutions.
I have heard of one geological consulting firm that was trying to foster a plan to help crowdfunders with their 43-101 report even though they don’t yet have the money to pay for the report.
I also understand that Canada now has a few private equity stock exchanges that allow PE to change hands, which may facilitate more private equity involvement.

Conclusion

The bottom line is the mining industry needs to have a self-examination with respect to what the future holds.  There is talk that mining needs to change its business model, but very little suggestion regarding what changes to make.
The growing population changing demographics, competition for equity funding, and society’s urbanization may result in fundamental, and permanent, changes to how the financial side of the junior mining industry can function.  Just my opinion.
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Open Pit Optimization – How I View It

Mining feasibility study
One of the first steps in an open pit design is the pit optimization analysis.  Pit optimization is used to define the most profitable pit shell for a given set of economic parameters.  The economic parameters include the metal prices, processing recoveries, and site operating costs. Normally when optimization is done, a range of metal prices or Revenue Factors (“RF”) is used to develop a series of nested shells to understand how the pit will expand or contract with increasing or decreasing metal prices.
Once the optimization step is complete, mining engineers will then design the pit inside that shell, introducing benches and ramps.  The pit design should mimic the selected optimized shell as closely as possible.
The pit design may (or may not) closely replicate the optimization shell depending on the slope angles used in the optimization and where the haul ramps are located in the design.
Hence the actual ore and waste tonnages mined may be different that the tonnages defined by the optimizer.
Various experts in pit optimization will use approaches of differing complexity.  Some may apply variable mining costs with pit depth; apply variable process recoveries linked to head grade; apply variable pit slopes by sector or depth, apply dilution and ore losses; etc.   One can make the pit optimization step as simple or detailed as one wants it.
The question is whether detailed pit optimization is warranted.  My view is that overly detailed pit optimization is  not required, other than if one wants to test parameter sensitivity on the resulting pit size and shape.  There are just too many uncertainties in the parameters being used in optimization.

Open Pit Optimization Uncertainties

Some of the uncertainties involved in the optimization approach are listed below:
  • Pit optimization can generate large pits that would have a long mine life.  However one doesn’t really know the metal prices far into the future.   So will that final pit ever get mined, or might it even be larger than shown.
  • Pit optimization is typically done at the start of a study, so one doesn’t have the detailed operating costs yet. The size of the project may be unknown and one has to use rough estimates for future costs and possibly even assume preliminary process recoveries.
  • Operating costs will also change in the future, and the optimization step is just a snapshot using current information.
  • Sometimes the optimization includes the use of Inferred resources, which are uncertainty.   Sometimes optimization is done only using Measured and Indicated resource, yet there may be areas if Inferred resource that ultimately convert to M &I and these will have been ignored.  So, either way you do it, you are not sure what ore the pit can captured and will  to shape the pit.
  • The smaller pits, if developed, would consist of smaller operations and may have different operating costs than assumed in the optimization.   Similarly larger pits may have different throughput rates and  operating costs than assumed in the optimization.
  • The ore and waste split reported within the pit will be based on a specific life-of-mine cutoff grade.  This is based on the fixed metal price and operating cost assumptions applied.
  • Overall pit wall slopes may differ for shallow pits versus deep pits.  Slopes may vary above the groundwater table and below it.  In many instances during pit optimization the wall angles are maintained at the same angle irrespective of the pit depths.   Sometimes geotechnical programs have not yet been completed, so optimization slope angles are simply educated guesses.
  • Dilution may be applied globally during pit optimization (unless one is working with a diluted block model).  In reality, dilution may differ in different parts of the ore body, and that may not be considered in the optimization stage. For more discussion on dilution in general, read the blog “Ore Dilution Prediction – Its Always an Issue“.

Conclusion

The bottom line is that pit optimization should be viewed as a guide to the pit design, but not as a highly precise calculation.  There are too many uncertainties in the parameters used.
There is always opportunity for future miner operators to examine pushback to grow the pit larger than initially envisioned.  Having said all that, one should still understand how future changes in metal prices can impact on the pit size, and then assess whether practical pushbacks are possible.   Thin sliver pushbacks are operationally difficult so this should be understood at the start.
While open pit optimization is not a precise science, there is still merit in examining how the pit size and shape reacts to changes in different parameters.  There are many ways to examine this and help select which shell should be advanced into the design stage. It can be more than just looking at the NPV versus Revenue Factor chart.   You can read this post at this link “Pit Optimization – More Than Just a “NPV vs RF” .
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Mining Project Economics – Simple 1D Model

mining desktop study
In a previous article I outlined my thoughts on the usefulness of early stage financial modelling (“Early Stage “What-if” Mine Economic Analysis – Its Valuable”).     My observation was that it is useful to take a few days to build a simple cashflow model to help your team better understand your project.

By “simple” I mean really simple.

This blog describes one of the techniques that I use to take a super-quick look at any project; whether it is for a client wishing to understand his project at a high level; or whether it is a project that I have read about.  There isn’t any actual study or production schedule available yet.  Maybe there is only a mineral resource estimate available.
It takes about 10 minutes to plug the numbers into my template to get fast results.  The image below is an example of the simple model that I use, but anyone can build one for themselves.

Screenshot of Simple Economic Model

I use the term one dimensional (“1D”) model since it doesn’t use the typical X-Y matrix with years across the top and production data down the page.
The 1D model simply relies simple on life of mine (“LOM”) totals to estimate the total revenue, total operating cost, and total profit.  This determines how much capital expenditure the project can tolerate.
The only caveat is that you need to have some sense for operating and capital costs for similar projects. This analysis can be on both a pre-tax and simple after-tax basis.
Using estimated metal prices and recoveries, the first step is to calculate the incremental revenue generated by each tonne of ore (see a previous article “Ore Value Calculator – What’s My Ore Worth?”).
Next that revenue per tonne is multiplied by the total ore tonnage to arrive at the total revenue over the life of mine.
The second step is to determine the life of mine operating cost, and again this simple calculation is based on estimated unit operating costs multiplied by the total tonnages being handled.
The third step is to calculate the life of mine profit based on total revenue minus total operating cost.
The potential net cashflow would be calculated by deducting an assumed capital cost from the life-of-mine profit.  The average annual cashflow is estimated based on the net cashflow divided by the mine life.  An approximate NPV can be calculated by determining the Present Value of a series of annual payments at a certain discount rate.
The reasonableness of the 1D model will be examined via benchmarking and this will be summarized once completed.  I will include a link to that future blog here.

You need to understand your project

One can easily evaluate the potential impact of changing metal prices, changing recoveries, ore tonnages, operating costs, etc. to see what the economic or operational drivers are for this project.  This can help you understand what you might need in order to make the project viable.

Conclusion

The bottom line is that a 1D economic calculation is very simplistic but still provides a vision for the project.  The next step in the economic modelling process would be a 2D model based on an annual production schedule.  The 1D approach is just a quick first step in looking at the potential.  You can do it even when you only know the head grades and some generalized orebody information.
The two ways you can apply the simple 1-D model are:
  1. evaluate the potential of early stage projects using cost inputs from other studies,
  2. examine a project’s sensitives (units costs, recoveries, prices) by calibrating your simple model to the published study (i.e. use the same parameters and make changes as needed.
The entire blog post library can be found at this LINK with topics ranging from geotechnical, financial modelling, and junior mining investing.

 

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