56. Does the Mining Industry Employ Interns?

Over the last year or so I have been working on a side project I founded within the tech industry.   One of the things that recently came to the forefront was the use of interns, unpaid interns, that is.   I know that  interns have been used for years in other industries including legal, politics, journalism, and marketing; however I have never come across the use of interns within the mining industry.
Intern
I was recently speaking with a marketing consultant about how to undertake tech marketing and one of the suggestions she made was to hire an intern to do much of the legwork of finding contacts and making contact with them.  My first question was why would anyone work for free?  I was told there were three reasons:
  1. For credit; as part of a course credit in college or university where an internship is part of the programme requirement.
  2. For experience; one can’t get a real job without experience and so the internship teaches something, builds up experience, and creates a portfolio of work.
  3. Networking; building up network connections can possibly lead to permanent work.
At first I was taken aback at the thought of asking someone to work for me for free.  Are we that cheap?   On the other hand if you are paying someone a salary, the expectation is that they should be relatively skilled at their job.  Giving it some further thought, , I have come to realize that the internship may actually be a win-win for both parties.
The company gets to better know potential employees and also gets some productive service from them at no cost.  The intern grows their employment experience and learns about the realities of the business world.  The students are paying the schools to teach them, and now businesses can help teach them as well, but at no cost.   It’s a win-win.
So how did our intern search go?  We posted a free ad on indeed.ca.  Within 48 hours we received eight replies, of which only 2 came close to meeting the 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 chance they can get some experience on their resumes which will hopefully lead to a job in the future.  We’ll maintain the job ad for a couple more weeks and see what the overall response will be.
My bottom line is asking whether the mining industry can make use of interns in the areas of geology, engineering, marketing, graphics, etc?  There may be a lot of young students out there looking for opportunity and willing to do whatever it takes to help advance their careers.   Even if your payroll budget cannot afford the cost of another person, you still may be able to help out someone within the industry.
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53. Ore Stockpiling – Why are we doing this again?

In many of the past mining studies that I have worked, stockpiling strategies were discussed and eventually implemented. Sometimes study team members were surprised at the size of the stockpiles that were generated by the production plan. It became apparent that not all members of the team were clear on the purpose of the stockpiling strategy or else they had preconceived ideas on the rationale. To them stockpiling may have seemed to be 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 but will focus simply on the reasons for stockpiling and why stockpiles may get large or numerous .
In my experience there are four main reasons why stockpiling might be done at an operation. They are:
1. Campaigning: For metallurgical reasons, there may be certain ore type(s) that can cause process difficulties if mixed in with other ores. Therefore the problematic ore(s) might be stockpiled until sufficient inventory is built up until it makes sense to process that ore (i.e. campaign) through the mill. Such stockpiles will only grow as large as the operator allows them to, before processing the material and eliminating the stockpile. Be aware that if the mine operations are still delivering different ore types to the crusher area, then those ores may need to be stockpiled during the campaigning period.  More different ore types may mean more stockpiles.
2. Grade Maximization: This stockpiling approach is used in situations where the mine delivers more ore than is required by the plant, thereby allowing the best material to be processed directly and the lower grade material to be stockpiled for a future date. Possibly one or more low grade stockpiles may be used, for example a low grade and a medium-low grade stockpile. Such stockpiles may not be processed for years, possibly remaining in place until the mine is depleted or until the mined head grades are lower than those in the stockpile. Such stockpiles can grow to enormous size if accumulated over many years.
3. Surge Control: stockpiling 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 and provide a steady primary crusher feed rate. These stockpiles are also available as short term emergency feed 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 mainly used for operational 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 consistent and uniform. Such stockpiles may not be large individually; however there could be several of them depending on the orebody character.
There may be other stockpiling strategies beyond the four listed above but those four capture the bulk of the situations.
Using today’s automated production scheduling software, one can test multiple stockpiling strategies by applying different cutoff grades or using multiple grade stockpiles. The scheduling software will have algorithms to determine whether one should be adding to the stockpile or drawing from it. It will track the 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).
Stockpiling in most cases will provide some potential benefits to an operation and the project economics. Even if metallurgical blending or campaigning is not required, one should always test the production schedule and project economics with a few grade stockpiling scenarios. Unfortunately these are not simple to undertake when using a manual scheduling approach and so are another reason to move towards automated scheduling software. Also 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

For those of you with a geotechnical background or have a general interest in learning 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. Their website screenshot is shown below.
Landslide Blog screenshot

Landslide Blog web page 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.
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.
Landslide
The following links are a few examples of the type of discussion that they have on the website.
Here is a description of a small water dam failure in Greece.
Here is some video of the Samarco tailings runout in Brazil.
Here is some video of boulders raining down on some buses along the Karakorum Highway in Pakistan.
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 and cities. Some of their videos are quite fascinating, illustrating the forces behind some of earth’s natural erosion processes. Check it out for yourself.
My bottom line on all of this is that the less the mining industry is mentioned in the Landslide Blog, the better it is for all of us.
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49. Remote Sensing of Ore Grades

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 new 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 (pre-concentration in other words). They hope their pre-concentration methods will improve mine economics by reducing the consumption of energy, water, and reagents.

Minesense

 It’s not entirely clear to me how developed their technology is, but MineSense is relying on a combination of ground-penetrating sensors with other sensor 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.
More specifically 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.
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.
Their belt conveyor systems (SortOre and 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 (www.tomra.com), but possibly the MineSense technical approach will be different.
My 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 readily share the results with us since it will be critical for industry players to see more actual case study performance data on their website. I recognize that developing new technology will have its successes and failures. Setbacks should not necessarily be viewed as fatal flaws since it takes time to work out all the kinks. Hopefully after being able to fine tune their technology they can advance to their next stage which will be to convince the mining industry to adopt it.
P.S. Unfortunately it appears MineSense don’t have a newsletter sign-up form on their website to help us in following their progress.
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44. Higher Metal Prices – Should We Lower the Cut-Off Grade?

When metals prices are high, we are generally taught that we should lower the cutoff grade. Our cutoff grade versus metal price spreadsheet tells us this is the correct thing do. Our grade-tonnage curve reaffirms this since we will now get 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 that sells for $998 on Amazon the last time I checked. You can also download a 38-page abridged sample of this book at THIS LINK and the full version is available for $150 at the COMET Strategy web site.

Theory of COG

Recently we have seen higher production cash costs at operating mines when commodity prices are high. Why is this? It may be due to higher operating costs inputs caused by increasing labour rates or supplies costs. It also may be partly due to the lowering of cutoff grades, thereby lowering the milled 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 rationale was that, since the plant throughput rate is fixed, when gold prices are high you suddenly decide to lower the head grade and produce fewer ounces of gold and at a higher cash cost. His point was that we should be doing the opposite; when prices are high you should produce more ounces of gold, not fewer. In essence, in times when supply is low (or demand is high) may not be the right time to further cut back on 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 now with the upside being extending the mine life. By doing this a company is able to report more ounces in their mineral reserve and the overall snapshot of the company looks better if it is being valued on reserve ounces.
The problem with this is that there is no assurance that metal prices will remain where they are or that the new lower cutoff grade will remain where it is. If the metal prices dip back down next year, the cutoff grade will be increased and the mineral reserve is back to where it was. All that was really done was accept a year of lower metal production for no real benefit. Such a trade-off essentially contrasts a short term vision (i.e. annual production) against a long term vision (i.e. mineral reserves).
My bottom line is that there is no simple answer on what to do with the cutoff grades, hence the 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 adjustments on their orebody. I would like to caution that one should be careful when taking your cutoff grade spreadsheet, plugging in new metal prices, and then running off to the mine operations department with the result. You need to fully understand the long term and short term impacts of that decision.
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32. Using Sand to Build Roads

Several years ago I did some geotechnical consulting work for various bauxite mining projects along the north coast of Suriname.  The mines were located in swampy areas and overlain by very soft clays.   The picture below shows the general terrain when crossing a swamp.  Such haulroads 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 haulroad construction was concerned, there were no hard rock or road aggregate supplies nearby but there were significant amounts of fine sand on the large “islands” within 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 would also cause havoc with the trafficability on the fine sands.
Where there was significant swamp vegetation (like in the photo), it would be buried and help form a mat to support the road and minimize the sand losses into the sub-grade.  However in other parts of the swamp the vegetation was minimal and therefore sand settling losses could be high.
Geotextiles were applied in some areas using a geogrid and these were successful although large amounts of sand were still required.  Once a road was built, the next issue became the vehicle trafficability on the fine sand surface, especially when rains occurred.  The sand would rut and require constant grading and repair. Final road surfacing would consist of laterite when available, which is a high iron off-grade bauxite and could be compacted to form a hard surface but would degrade and get slippery in the rain. Had coarse aggregate been available locally, road performance would have been much better but one has to work with what is there.
Recently 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 geotextile solutions available but this is one that is well described on their website.   Sand is placed into the geoweb and eventually forms a stiffer layer.  I presume that one could place the sand using mobile equipment or hydraulically by pumping coarse sand as a slurry.
Geocell

Geocell geotextile for road construction

In hindsight, I would have liked the opportunity to test this geoweb 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 using sand only.   I’m not sure if the best placement of the geoweb would have been along the base of the road to support the sand load from sinking into the swamp or near the surface of the road to help create a more trafficable surface.    Building a road over a swamp is similar to building a road out onto a tailings pond, so there could be application there too.
Geotextiles have many applications in the mining industry and may have many cost savings related to initial construction and subsequent operation.  There can be significant up-front costs to purchasing geotextiles but don’t let that scare you away.    They are definitely worth a look.
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17. Directional Drilling Open Pit Dewatering Wells – Great Idea

I recently 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 pit dewatering wells.   This is an oil field technology from Schlumberger Water Services that is being applied to mining.  More information is at this link (see Well Placement Technology for Mine Dewatering).
http://www.slb.com/services/additional/water/mines.aspx
One of my past projects was a diamond mine in northern Canada.  The granitic rock mass was geotechnically very competent with limited jointing and fracturing. Groundwater seepage into a partly permafrost could create a host of operational problems in winter as well as affect pit wall stability.  Most of the groundwater flows were predicted to be along a few main structures or along single open joints.   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 don’t.
The use of directional drilling of pumping wells can be a great innovation.    It gives the opportunity to bend the pumping well to a more horizontal orientation, allowing the well bore to cut across vertical structures rather than parallel to them.   In addition, one can drill wells near the pit crest bending them in towards the ultimate pit bottom.  This may help improve drainage near the operating benches in the pit as it deepens and may eliminate the need to install inpit pumping wells.
In addition, 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 replicate these drainage galleries at a much lower cost.
My bottom line is that the directional drilling innovation makes a lot of sense to me and mine operators should take a look at it, it might improve their pit dewatering systems.
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13. Pit Wall Angles and Bench Width – How Do They Relate?

The inter-ramp wall of a pit 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 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 Catchbench 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 to minimize damage to the walls.   Hence the BFA may vary around the pit or in different rock types, but it generally is in the range of 60° to 75°.
The catchbench (“CB”) is used to catch spalling rock and prevent it from rolling down the pit wall and creating a safety hazard.  A rule of thumb is that the catchbench width should be according to the formula 4.5m + 0.2H, where H is the height of the bench.   This means the recommended catchbench 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 catchbench width would be 2.4 metres to achieve the 50° IRA.  However such a small catchbench would be ineffective in catching ravelling rock.  If one double benched (i.e. left a catchbench every 10m instead of every 5m), then the calculated catchbench width would be 4.8 metres.  If one triple benched (i.e. left a catchbench 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 calculator (Bench Slope Calculator) has been prepared to show the relationship between all the factors.  A screenshot of the calculator is shown below.  It allows one either to back-calculate the IRA given a set of bench height, BFA, and catchbench criteria; or calculate the catchbench 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 Catchbenches:   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
Catchbench (CB):  this is the width of the catchbench, 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.
My 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 catchbench 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.
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