Articles for April 2016

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.

52. Mining Press Releases – Where to Get Them

There are numerous sources of mining information on the internet, encompassing topics such as technical articles, analyst opinions, and company press releases. It can be overwhelming sometimes. Now if your main interest is just seeing company news releases in a timely manner then what is the best way to do this?
One way is to go to the individual company website and sign-up one their email list. This approach generally works well but it forces you to sign up on a myriad of websites if you intend to follow a lot of companies. There are alternatives however.
One option is to sign-up for a free account with a newswire service where you can select the specific companies that you want to follow and then will get emailed news releases as soon as they are disseminated. The nice thing here is that you can select mining companies, non-mining public companies, as well as entire industries. Here are a few that I personally make use of.
Since different companies may use different news release distributors, the three websites that I track are:
Marketwire: There you can create a “Hot Off the Wire” account and then select your companies of interest. You can also select entire industries to add to your company list.
CNW Group Ltd.  Create an account there and search various companies to add to your “My Subscriptions” list.
Junior Mining News is another source to get general news updates via their daily newsletter, a screenshot is shown below. Their daily email gives a brief summary of events that happened recently and includes “Read More..” links if you want to read the entire press release. This website accesses some of the same news release distributors as mentioned above so there could be some repetition from time to time.


Junior Mining News screenshot

Using the services described above, it’s very easy to sign up for a lot of companies, too many companies in fact, and then get inundated with emails. We know that public companies need to keep the news flow active and some companies are very good at continually issuing news alerts. However by using the press release distribution websites you are consolidating your requests, thereby making it easier to control the amount of information you want to receive.
Feel free to share your method for tracking companies, whether using the same websites or something entirely different and better.

51. Pre-Concentration – Savior or Not?

Can pre-concentration become a key savior for the mining industry and help in lowering metal production costs?
Pre-concentration is a way to reduce the quantity of ore requiring higher cost downstream processing, i.e. grinding in particular. By using a low cost method to pre-concentrate mineral-bearing particles into a smaller volume, one can attain significant cost savings in overall energy consumption and operational expenses. A previous blog “Remote Sensing of Ore Grades” discussed a new pre-concentration method under development.
Pre-concentration is nothing new and has been around for many years but is generally limited in the techniques available. Hence many ore types are not amenable to it..unfortunately. The main methods being used are:
Ore sorting can be done using automated optical, electrical, or magnetic susceptibility sensors to separate ore particles from waste particles. The different sensor types can include colour recognition, near infrared radiation sensors, x-ray fluorescence, x-ray transmission, radiometric, or electromagnetic sensing. The sensors can determine if a particle contains valuable mineral or waste, thereby sending a signal to activate air jets to deflect material into ore and waste bins.
Density or specific gravity difference is another property that some pre-concentration methods can rely on. Gravity based systems such as dense media separation (DMS), jigs, or centrifugal concentrators are currently in production use.
Another simple pre-concentration method used is scrubbing, whereby simply washing away fines may remove some deleterious materials prior to final processing.
 Jig Plant 1
Pre-concentration can provide several benefits to an operation:
-If done underground or at remote mine site, the net ore hoisting and ore transport costs can be reduced.
-If the pre-concentration rejects can be used as mine backfill, this can reduce backfilling costs.
-Processing of higher grade pre-concentrated mill feed can reduce total energy costs and ultimately reduce the cash cost of metal produced.
-Grinding costs can be reduced if waste particles are harder than the ore particles and they can be removed beforehand.
-Minimizing waste through the process plant will reduce the quantity of tailings that must be disposed of.
-Lowering operating costs may potentially allow lowering of the cutoff grade and increasing mineral reserves.
-Higher head grades would increase metal production without needing an increase in plant throughput.
Not all ore types are amenable to pre-concentration and therefore a rigorous testing program is required. In most cases the pre-con method would be relatively obvious to the metallurgical engineer but testing is still required to measure performance. Testing is required to determine the amount of waste rejection that can be achieved without incurring significant ore loss during the process. Generally one can produce a higher quality final product if one is willing to reject more ore with the waste, so it becomes a trade-off of recovery versus total processing cost.
Fine particles from the primary and secondary crushing stages might require bypassing the pre-con circuit. If this bypassed material is sent for downstream processing, one may need to examine crushing systems that minimize fines generation to avoid too much material bypassing the pre-con circuit.
One must also decide if the pre-con system should reject waste particles from the material stream or reject ore particles from the stream since the overall recovery and product quality will be impacted depending on which approach is used.
My bottom line is that the mining industry is continually looking for ways to improve costs and pre-concentration may be a great way to do this. Every process plant design should at least take an initial look at it to see if is feasible for their ore type. While the existing pre-concentration methods have their limitations, future technologies may bring in new ways to pre-concentrate and so this is probably an area where research dollars would be well spent.

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.
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.