56. Does the Mining Industry Employ Interns?

employing interns
Over the couple of years I have been working on a side project in the tech industry.   One of the things that struck me was the hiring of interns, both paid and unpaid.
I’m now aware that interns are being hired in other industries such as legal, politics, journalism, and marketing.  However I have never come across the use of interns within the mining industry.
Intern

Why hire interns?

I was recently talking to a marketing consultant about tips on tech marketing and one of the suggestions she made was to hire an unpaid intern.  They would do much of the legwork of finding sales contacts and establishing contact with them.
My first question was why would anyone work for free?  There are  three main reasons:
  1. For school credit; as part of a course credit in college or university where an internship is part of the program requirement.
  2. For experience; it is difficult to get a real job without experience and so the internship teaches, builds  experience, and establishes a portfolio of work.
  3. Networking; building up industry connections can possibly lead to permanent work down the road.

Its the right thing to do

At first I was taken aback at the thought of asking someone to work for my company for free.  Are we that cheap?
Thinking about it further, if you are paying someone a salary the expectation is that they should be somewhat skilled at their job.  I have come to realize that the internship may actually be a win-win for both parties.

Its a win-win

The company gets a chance to learn about potential employees and also gets productive service from them.
The intern gains employment experience and learns about the realities of the business world.  Students have already paid the schools to teach them.  Now businesses can help teach them more, but at no cost.   It’s a win-win for both.
So how did our unpaid intern search go?  We posted a free ad on indeed.ca.  Within 72 hours we received over ten replies, of which only 2-3 came close to meeting the actual qualifications.  Some of the applicants had no relevant experience at all.
Possibly in today’s job market people are willing to work for free on the hope that they can get some experience, which will hopefully lead to a permanent job in the future.

Conclusion

The question is whether the mining industry can make use of interns in the areas of geology, engineering, marketing, presentation graphics, websites, etc?
There may be many students or recent grads looking for an opportunity and are willing to do whatever it takes to  advance their careers.
Even if your operating budget can’t afford the cost of hiring another person, you may still have a chance to help out someone new in the industry.
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53. Ore Stockpiling – Why are we doing this again?

ore stockpile
In many of the past mining studies that I have worked, stockpiling strategies were discussed and usually implemented. However sometimes team members were surprised at the size of the stockpiles that were generated by the production plan. In some cases it was apparent that not all team members were clear on the purpose of  stockpiling or had preconceived ideas on the rationale behind it. To many stockpiling may seem like a good idea until they saw it in action.
Mine Stockpile
In this blog I won’t go into all the costs and environmental issues associated with stockpile operation.  The discussion focuses on the reasons for stockpiling and why stockpiles can get large in size or numerous in quantity.
In my experience there are four main reasons why ore stockpiling might be done. They are:
1. Campaigning: For metallurgical reasons if there are some ore types that can cause process difficulties if mixed  with other ores. The problematic ore might be stockpiled until sufficient inventory allows one to process that ore (i.e. campaign) through the mill. Such stockpiles will only grow as large as the operator allows them to grow. At any time the operator can process the material and deplete the stockpile. Be aware that mining operations might still be mining other ore types, then those ores may need to be stockpiled during the campaigning.  That means even more ore stockpiles at site.
2. Grade Optimization: This stockpiling approach is used in situations where the mine delivers more ore than is required by the plant, thereby allowing the best grades to be processed directly while lower grades are stockpiled for a future date. Possibly one or more grade stockpiles may be used, for example a low grade and a medium-low grade stockpile. Such stockpiles may not get processed for years, possibly until the mine is depleted or until the mined grades are lower than those in the stockpile. Such stockpiles can grow to enormous size if accumulated over many years.  Oxidation and processability may be a concern with long term stockpiles.
3. Surge Control: Surge piles may be used in cases where the mine may have a fluctuating ore delivery rate and on some days excess ore is produced while other days there is underproduction. The stockpile is simply used to make up the difference to the plant to provide a steady feed rate. These stockpiles are also available as short term emergency supply if for some reason the mine is shut down (e.g. extreme weather). In general such stockpiles may be relatively small in size since they are simply used for surge control.
4. Blending: Blending stockpiles may be used where a processing plant needs a certain quality of feed material with respect to head grade or contaminant ratios (silica, iron, etc.). Blending stockpiles enables the operator to ensure the plant feed quality to be within a consistent range. Such stockpiles may not be large individually; however there could be several of them depending on the nature of the orebody.
There may be other stockpiling strategies beyond the four listed above but those are the most common.

Test Stockpiling Strategies

Using today’s production scheduling software, one can test multiple stockpiling strategies by applying different cutoff grades or using multiple grade stockpiles. The scheduling software algorithms determine whether one should be adding to stockpile or reclaiming from it. The software will track grades in the stockpile and sometimes be able to model stockpile balances assuming reclaim by average grade, or first in-first out (FIFO), or last in-first out (LIFO).
ore stockpile
Stockpiling in most cases provides potential benefits to an operation and the project economics. Even if metallurgical blending or ore campaigning is not required, one should always test the project economics with a few grade stockpiling scenarios.
Unfortunately these are not simple to undertake when using a manual scheduling approach and so are a reason to move towards automated scheduling software.
Make sure everyone on the team understands the rationale for the stockpiling strategy and what the stockpiles might ultimately look like. They might be surprised.
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50. Landslide Blog – If You Like Failures

slope failure blog
For those of you with a geotechnical background or have a general interest in learning more about rock slides and slope failures, there is an interesting website and blog for you to follow.
The website is hosted by the American Geophysical Union the world’s largest organization of Earth and space scientists. The blogs on their site are written by AGU staff along with contributions from collaborators and guest bloggers.

Landslide Blog screenshot

The independent bloggers have editorial freedom in the topics they choose to cover and their opinions are those of their authors and do not necessarily represent the views of the American Geophysical Union. This provides for some leeway on the discussions and the perspectives the writers wish to take.

Landslide Blog

One specific area they cover well in their Landslide Blog are the various occurrences of rock falls and landslides from any location around the globe. They will present commentary, images, and even videos of slope movements as they happen.
Often they will provide some technical opinion on what possibly caused the failure event to occur. The Landslide Blog has a semi-regular email newsletter that will keep you updated on new stories as they happen.
The following links are a few examples of the type of discussions they have on their website.
Here is a description of a small water dam failure in Greece.
Here is some video of the Samarco tailings runout in Brazil.
From time to time the Landslide Blog will examine mine slopes, tailings dams, and waste dump failures, however much of their information relates to natural earth or rock slopes along roads or in towns.
Some of their videos are quite fascinating, illustrating the forces behind some of earth’s natural erosion processes. Check it out for yourself.
The bottom line on all of this is that the less the mining industry is mentioned in the Landslide Blog, the better it is.
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49. Remote Sensing of Ore Grades

mining automation
Update:  This blog was originally written in March 2016 and has been updated Jan 2019. 
The mining industry must continually find ways to improve and modernize. The most likely avenue for improvement will be using new technologies as they become available.
One of the players on the scene is a start-up company called “MineSense Technologies Ltd.”  They are a British Columbia company looking to improve ore extraction and recovery processes based on the sensing and sorting of low-grade ore. They hope their technology will improve mine economics by reducing the consumption of energy, water, and reagents.

Minesense

Having first written about this in 2016, its still not entirely clear to me how developed their technology is in 2019. Thus far they appear to be secretive with respect to their testing and performance results.  Certainly they are able to raise financing to keep them going.

Sensors are the answer

It appears MineSense is relying on a combination of ground-penetrating sensors with other technology in order to measure and report the grade of ore in real time.
Existing ore sorting technologies seem to focus on distinguishing mineralized material from gangue, but MineSense seems to be targeting using actual ore grades as the defining factor.
They hope to be able to eventually integrate their technology into equipment such as shovels, scooptrams, conveyors, feeders, and transfer chutes.
Their proprietary technology is based on High Frequency Electromagnetic Spectrometry and High Speed X-Ray Fluorescence sensors. Reportedly these can deliver better sensitivity and operate at high speeds. They plan to develop two distinct product lines; shovel-based systems; and conveyor belt-based systems.

ShovelSense

Their ShovelSense system would be a real-time mineral telemetry and decision system and used for measurement of ore quality while material is being scooped into the dipper, then reporting the ore quality and type to the grade control/ore routing system, and then enabling real-time online ore/waste dispatch decisions. Additional features may include tramp metal and missing tooth detection.  Sounds like a good idea, albeit some practical operating issues will need to be overcome.

BeltSense

Their belt conveyor systems (BeltSense) will use high-speed multi-channel sensing to characterize conveyed ore and waste in real time, allowing grades and tonnages to be reported and allowing ore to be diverted to correct destinations based on the sensor responses.
MineSense say that pilot units are operating at 20 tph and systems of up to 2000 tph are in the development stages.
Ore sorting has been around for a long time, with companies like Tomra, but possibly the MineSense technical approach will be different.

Conclusion

The bottom line is that we should all keep an eye on the continued development of this technology, especially as MineSense completes larger field trials.  Hopefully they will soon share results with industry since it will be critical for operators to see more actual case study data on their website.
I recognize that developing new technology will have its successes and failures. Setbacks should not be viewed as failure since innovation takes time. Hopefully after fine tuning their technology they can advance to the commercialization stage.
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44. Higher Metal Prices – Should We Lower the Cut-Off Grade?

When metals prices are high, we are generally told that we should lower the cutoff grade. Our cutoff grade versus metal price formula tells us this is the correct thing do. Our grade-tonnage curve reaffirms this since we will now have more ounces of gold in the mineral reserve.

But is lowering the cutoff grade really the right thing to do?

Books have been written on the subject of cutoff grades where readers can get all kinds of detailed logic and calculations using Greek symbols (F = δV* − dV*/dT). Here is one well known book by Ken Lane, available on Amazon HERE.
Recently we have seen a trend of higher cash costs at operating mines when commodity prices are high. Why is this?
It may be due to higher cost operating inputs due to increasing labour rates or supplies. It may also be partly due to the lowering of cutoff grades.  This lowers the head grade, which then requires more tonnes to be milled to produce the same quantity of metal.
A mining construction manager once said to me that he never understood us mining guys who lower the cutoff grade when gold prices increase. His concern was that since the plant throughput rate is fixed, when gold prices are high we suddenly decide to lower the head grade and produce fewer and higher cost ounces of gold.

Do the opposite

His point was that we should do the opposite.  When prices are high, we should produce more ounces of gold, not fewer. In essence, periods when supply is low (or demand is high) may not be the right time to further cut  supply by lowering head grades.
Now this is the point where the grade-tonnage curve comes into play.
Certainly one can lower the cutoff grade, lower the head grade and produce fewer ounces of gold.  The upside being an extension in the mine life.  A company can report more ounces in reserves and perhaps the overall image of the company looks better (if it is being valued on reserves).

What if metal prices drop back?

The problem is that there is no guarantee that metal prices will remain where they are and the new lower cutoff grade will remain where it is. If the metal prices drop back down, the cutoff grade will be increased and the mineral reserve will revert back to where it was. All that was really done was accept a year of lower metal production for no real long term benefit.
This trade-off  contrasts a short term vision (i.e. maximizing annual production) against a long term vision (i.e. extending mineral reserves).

Conclusion

The bottom line is that there is no simple answer on what to do with the cutoff grades.  Hence there is a need to write books about it.
Different companies have different corporate objectives and each mining project will be unique with regards to the impacts of cutoff grade changes on the orebody.
I would like to caution that one should be mindful when plugging in new metal prices, and then running off to the mine operations department with the new cutoff grade. One should fully understand both the long term and short term impacts of that decision.
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32. Using Sand to Build Roads

geogrids
Several years ago I did some geotechnical consulting for BHP’s bauxite mining projects along the north coast of Suriname.  The mines were located in swampy terrain, overlain by very soft clays.   The picture below shows the typical landscape when crossing a swamp.  Haul roads were needed to access the small satellite bauxite pits, which were spread several kilometres apart.
Sand road across swamp

Suriname swamp road for mine

Where haul road construction was concerned, there were no nearby gravel pits or road aggregate supplies but there were significant amounts of fine sand on the high ground “islands” in the swamp.  Road building mainly relied on end dumping truck loads of sand, allowing it to settle and sink into the swamp, and then continue adding more sand until the settling process stopped.  This resulted in high cost roads and very slow progress in construction.  Periodic rainfalls, particularly in wet season, would cause havoc with the trafficability on the fine sands.

Swamp vegetation to the rescue

backhoe on soft clays
How soft were the swamps clays?  See the photo to the right.
Where there was significant swamp vegetation (like in the photo above), it would be buried by the fill, helping to form a mat.  This supported the road fill and minimized the sand losses into the sub-grade.  However in some parts of the swamp the vegetation was minimal and therefore sand settlement losses could be high.
Geotextiles were applied in some areas, using a geogrid.  These were successful although large amounts of sand were still required as the entire road would compress the underlying clay.
Once a road was built, the next issue was the trafficability on the fine sand surface, especially after rains.  The sand would rut and require constant grading and repair.
Final road capping would consist of laterite when available.  Laterite is a high iron off-grade bauxite that could be compacted to form a hard surface but would still degrade and get slippery when wet. If coarse aggregate had been available locally, road performance would have been much better but one had to work with what was available.

Geo-cells would have helped

Geocell

A few years later I saw a video about a geo-cell solution for building roads with sand only.   The website is The PRS-Neoweb™ Cellular Confinement System (www.prs-med.com).  I think there are other similar geotextiles available but this is one that is well described on their website.   Sand is placed into the geoweb, which eventually forms a stiffer layer.  I assume that one could place the sand using mobile equipment or by hydraulically pumping coarse sand as a slurry.
In hindsight, I would have liked the opportunity to test the geo-cell system in the swamps of Suriname.  Potentially it would have been a good solution to prevent both sand losses and create a more trafficable surface.
I’m not certain if the best location for the geo-cell would have been along the sub-base of the road to support the sand load or near the surface to help create a more trafficable surface. Maybe it would have been beneficial in both locations.
Building a road over a swamp in South America is somewhat similar to building a road out onto a tailings pond.  Possibly the geo-cell would have application there too.

Conclusion

Geotextiles have many applications in the mining industry.  There can be significant up-front costs to purchase and install them but don’t let that scare you away.   The savings may been seen down the line. They are definitely worth a look.
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17. Directional Drilling Open Pit Dewatering Wells – Great Idea

open pit dewatering
I read an interesting article in the Mining Magazine May 2015 edition called “Top 10 Technologies”.  One of the new technologies that jumped out at me is the capability to directionally drill open pit dewatering wells.   This is an oil field technology from Schlumberger Water Services that was going to be applied to mining.
One of my past roles was engineering for the Diavik diamond mine in northern Canada.  The granitic rock mass was geotechnically very competent with a limited amount of jointing and fracturing.
Groundwater seepage from a partly permafrost pit wall could create a host of operational problems in winter. Most of the groundwater flows were predicted to be along a few main structures or along single open joints.
Generally these structures were near vertical, which created a problem when trying to intercept them with vertically drilled pumping wells.  Either you hit one or you didn’t.

The use of directional drilling of pumping wells is a great innovation

It gives the opportunity to bend the pumping well to a angled orientation, allowing the well bore to cut across vertical structures rather than paralleling them.   In addition, one could drill pumping wells near the pit crest targeting the ultimate pit bottom.  This may help improve drainage near the operating benches as the pit deepens and may eliminate the need to install inpit pumping wells.
Some open pits have constructed underground drainage galleries around the pit circumference to help intercept groundwater seepage.  Possibly directionally drilling aligned parallel to the pit wall can replace the need for these high cost drainage galleries.
The bottom line is that the directional drilling innovation makes a lot of sense and mine operators should take a look at it.  It might help improve their pit dewatering systems.
If anyone has experience with directionally drilled dewatering wells, please let us know.
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13. Pit Wall Angles and Bench Width – How Do They Relate?

open pit slopes
The wall of an open pit wall will consist of a series of stacked benches.  Geotechnical engineers will normally provide the pit slope design criteria based on the inter-ramp angle (“IRA”) for various sectors around the pit.  The IRA represents the toe-to-toe slope angle, as shown in the diagram below.

Pit Slope Image for post

The inter-ramp angle can be created in many ways, depending on the bench height (“BH”), bench face angle, and the catch bench or berm width.  Different combinations of these can be used to develop the same inter-ramp angle.
Typically the bench face angle (“BFA”) will be dictated by the rock strength, the structural fabric, and whether controlled blasting is used (minimizing damage to the walls).   The BFA may vary around the pit or in different rock types, but it typically is in the range of 60° to 75°.

Open Pit Slope

The catch bench (“CB”) or berm is used to catch spalling rock and prevent it from rolling down the pit wall,  creating a safety hazard.  A rule of thumb is that the catch bench width should be according to the formula 4.5m + 0.2H, where H is the height of the bench.   This means the recommended catch bench width for a 5m high bench should be about 5.5m; for a 10m high bench it should be 6.5m; and for 15m high bench it should be 7.5 metres.
Double benching (or triple benching) is used where the inter-ramp slopes angles are steep enough that single benching would result in an overly flatten slope.   For example if the inter-ramp slope is 50° and the BFA is 70°, then the corresponding calculated catch bench width would be 2.4 metres to achieve the 50° IRA.  However such a small catch bench would be ineffective in catching ravelling rock.
If one double benched (i.e. left a catch bench every 10m instead of every 5m), then the calculated catch bench width would be 4.8 metres.  If one triple benched (i.e. left a catch bench every 15m), then the recommended width would be 7.1 metres.  Hence triple benching would be suggested in this case, assuming the rock mass is of sufficient strength to sustain a 15m high face.
A simple interactive calculator (Bench Slope Calculator) has been prepared to show the relationship between all of these factors.  A screenshot of the calculator is shown below.  It allows one either to calculate the IRA given a set of bench height, BFA, and catch bench criteria; or calculate the catch bench width given the height, BFA, and IRA criteria.  The yellow shaded cells represent input cells.

Bench Slope Calculator Pic

Single Bench Height (BH):  this is the input height of a single operating bench.
No. of Benches between catch benches:   this is the input for single, double, or triple benching.
Total Height (TH):  this is the calculated total height (# of benches X single bench height)
Bench Face Angle (BFA):  this is the input bench face angle, in degrees
Catch bench (CB):  this is the width of the catch bench, either as an input or a calculated value.
Inter-Ramp Angle (IRA): this is the slope angle in degrees, either as a calculated value or an input.
When double or triple benching, sometimes a small 1-2m berm may be left between benches due to the inability of the blasthole drill to get right against the pit wall when drllling off the next bench.  The width of the drill berm can possibly be eliminated by drilling the entire double bench or using smaller drills.
Sometimes one may see the term “geotechnical berm”.   In some pit designs a large bench is introduced periodically, e.g. every 120m-180m in height, which acts as another means with which to catch ravelling rock.

Conclusion

The bottom line is that the inter-ramp angle can be achieved in different ways depending on various components of the slope profile.  Safety is of the utmost importance and therefore the adequate sizing of the catch bench is important, as is the ability to access the benches and clean up the rubble buildup.  Double and triple benching maybe required in some circumstances to achieve the design wall angles yet maintain safety catch bench widths.
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