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There have been recent heap leach pad failures in the Yukon and Turkey and tailings dam failures in Chile and the Philippines. As a result I have been seeing more posts on LinkedIn about the application of satellite based InSAR deformation monitoring. Prior to that I had never heard of InSAR, so thought a little bit of background study might be worthwhile.

The following are my observations on what InSAR is and where it may be going. I am by no means an expert in this technology. I am merely viewing it from the perspective of a mine design engineer.

What is InSAR

InSAR is satellite-based “Interferometric Synthetic Aperture Radar”. It can measure the distance from a satellite to a ground feature. With repeated imaging it is used to detect changes in distance and measure displacements to within 5-10 millimetre accuracy. Hence it can be used as a potentially cost-effective slope monitoring tool, albeit it cannot be the only tool, as discussed later.

The relevant satellite images have been available for years. Currently the availability of analytical software to interpret the satellite data is improving. It can detect millimeter-scale displacements, however only in the line-of-sight (LOS) direction of the satellite. Using two or more satellites in different orbits, displacements in horizontal and vertical directions can be defined.

An example of a satellite being used is the Sentinel-1, launched in mid-2015 by the European Space Agency. This satellite information is open-source data. It will have a 6 to 12 day revisit cycle in many locations.

The results of an InSAR displacement survey are typically shown as a series of colored data points, typically coloured green for the stable points, trending to yellow and red for points that are moving.

This blog has some example images.

Some Limitations With InSAR

There are some limitations with InSAR, so it can only be part of a monitoring program. These limitations are:

The displacement direction is only measured in the direction of the satellite. Hence one may not know in which direction the movement is occurring. The magnitude of displacement could be underestimated depending on the apparent angle of measurement.
The movement being measured could consist of vertical settlement due to material consolidation and may not be horizontal and related to impending failure.
The displacement magnitude measured on opposite sides of a facility may have different accuracy, depending on the slope orientation versus the line-of-sight.
Areas with heavy vegetation may be difficult to monitor
Areas with heavy or persistent cloud cover can be difficult to monitor.
Areas with snow cover will be difficult to monitor.
The satellite return period may be weekly or every two weeks, so one is not able to analyze daily movements if a situation is critical. If the return visit day has cloud cover, there will be no new satellite data collected.
Areas with on-going construction or tailings deposition will lead to erroneous results.
Due to the line of sight, not all slope failure modes may be detectible (for example piping failure).

Regardless of these limitations, InSAR can still play a role in any monitoring program since it is able to monitor large areas quickly. Consider it as a pre-screening tool, being aware that not all failure modes may be detectible with it.

Discussion

On LinkedIn, one can see numerous posts where independent experts are examining historical InSAR data for recent failures to see whether early movement should have been detected. The results seem to be quite positive in that areas that have failed might have been red-flagged prior to failure.

There are also zones that showed critical displacements but have not failed.

Typically, there are four ways to monitor displacement in pit slopes, tailings dams, heap leach pads, and waste dumps. They are:

Insitu monitoring using embedded instruments, for example slope indicators, extensometers, and settlement gauges. These instruments provide information on what is happening internally within a slope, where actual movement is occurring, and they can be used in warning alert systems.
Surface monitoring using radar (ground based InSAR) systems and survey prisms. These tools measure only surface movements in selected areas, can be monitored as frequently as needed on an automated basis, and integrated into warning alert systems.
Drone or aerial surveys can be used to measure topography and monitor movements over large areas. This method requires a data processing delay (not real time) to derive the movement information, but such surveys can be done as frequently as needed.
InSAR from satellite can be used over very large regions to highlight areas with movement. That should trigger the implementation of one or more of the other monitoring approaches (if not already in place).

Conclusion

A mining site consists of numerous constructed embankments and slopes of all types and heights. Many of these slopes may be creeping and moving all the time – it’s a living beast.

The operator’s awareness about their site will be better the more monitoring tools they use. This awareness is important given the critical role that slope stability plays. We will see if InSAR technology achieves much wider adoption in the mining industry as a first phase of a stability monitoring programs.

Since InSAR monitoring is done from space, it does not require access to a property. Hence it can be used by third parties or NGO’s to “spy” on facilities of concern anywhere.

Possibly over the next few years we will see independent donor-funded organizations monitoring tailings facilities around the globe. They will be able to notify the public and mine operators “Hey, there is some movement on this mine site that needs to be addressed”. An organization called World Mine Tailings Failures has started some discussions on this concept. Check it out.

Finally, it is great for a mine site to collect a lot of displacement data, hopefully to forewarn of movement, displacement acceleration, and imminent failure. However, this assumes that someone experienced is interpreting the data and its not just generating graphs for the file cabinet. Perhaps AI can play a role here in the future, if the technical personnel to do this are lacking.

Note: You can sign up for the KJK mailing list to get notified when new blogs are posted. Follow me on Twitter at @KJKLtd for updates and other mining posts. The entire blog post library can be found at https://kuchling.com/library/

Springpole Project

I recently saw an investor presentation from First Mining Gold about their Springpole Project. The situation is that their open pit is located within a lake and will require the construction of a couple of small cofferdams to isolate the pit area from the lake. The concept is shown in this image.

Over the last couple of years I have been involved in a few early-stage studies for mining projects in which nearby bodies of water play a role in the design. In Canada’s north there are thousands of lakes and rivers, so its not surprising to find mines next to them.

That got me thinking about how many other mines are in the same situation, i.e. projects that may be located very close to, or within, a lake, river, or ocean. Hence I have compiled a short list of a few such mines.

I have been directly involved with some of those in the list, while others are only known to me with limited detail. Some mines I had never heard of before, but their names were provided to me by some Twitter colleagues.

My observation is that building a mine within, or adjacent to, a body of water is nothing new and this has been done multiple times successfully.

Some of these projects may refer to the dams as “dikes”, “cofferdams”, “sea walls” but I assume they are all providing roughly the same function of holding back water for the life of the project. They are not viewed as permanent dams.

This is Part 1 of a two-part blog post. Part 1 provides some examples of projects where water bodies were involved in the design. Part 2 provides a discussion on specific geotechnical and hydrogeological issues that would normally have to be examined with such projects.

Some Lake Mining Examples

The following are some examples of operating mines involving lakes. I have captured a few Google Earth images, unfortunately some have only low resolution vintage satellite imagery.

This is a project I was working on with in 1997 to 2000 while it was still at the design and permitting stage. My role focused on pit hydrogeology and geotechnical as well as mine planning.

The project would require the construction of three dikes in sequence to mine four lakebed kimberlite pipes.

The three dikes were named after the associated kimberlite pipe being mined inside it; A154, A418, and A21.

The first dikes were built in 2002 and the last dike (A21) was completed in 2018.

The total dike length for the three dikes is about 6.2 km.

For those interested in learning a bit more about Diavik, I have posted an earlier article about the open pit hydrogeology there, linked to at " Hydrogeology At Diavik – Its Complicated".

This is a project I was involved with several years ago. The bauxite deposit extends beneath the Suriname River and the goal was to mine as much ore as possible.

Given the flow rates in the river, especially during the wet season, it would be difficult to maintain a cofferdam out into the river.

The shoreline overburden consisted of sands and soft clays, so the decision as made to construct a sheet piling wall along the river bank to protect the pit from river erosion. This was mined out successfully and eventually reclaimed.

Conclusion

As one can see, the idea of mining into a body of water is nothing new. Its not a preferred situation, but it can be done economically and safely. The technical challenges are straightforward, and engineers have dealt with them before. However there also are instances where the design could not economically address the water issue, and thus played a role in the mine not getting built.

If you know of other mines not listed above that have successfully dealt with a water body, please let me know and I can update this blog post.

This concludes Part 1. Part 2 can be read at this link " Mining Under Lakes – Part 2: Design Issues" discusses some of the concerns that engineers need to consider when building a mine in these situations.

Finally, the worst-case scenario is shown in this grainy video of a tin mine (Pantai Remis Mine) pit slope failure. It seems they mined too close to the ocean. Watch to the end, its hard to believe. Its looks like something out of a Hollywood disaster movie.

Note: You can sign up for the KJK mailing list to get notified when new blogs are posted. Follow me on Twitter at @KJKLtd for updates and other mining posts. The entire blog post library can be found at https://kuchling.com/library/

The following are my observations on what InSAR is and where it may be going. I am by no means an expert in this technology. I am merely viewing it from the perspective of a mine design engineer.

What is InSAR

An example of a satellite being used is the Sentinel-1, launched in mid-2015 by the European Space Agency. This satellite information is open-source data. It will have a 6 to 12 day revisit cycle in many locations.

The results of an InSAR displacement survey are typically shown as a series of colored data points, typically coloured green for the stable points, trending to yellow and red for points that are moving.

This blog has some example images.

Some Limitations With InSAR

There are some limitations with InSAR, so it can only be part of a monitoring program. These limitations are:

The displacement direction is only measured in the direction of the satellite. Hence one may not know in which direction the movement is occurring. The magnitude of displacement could be underestimated depending on the apparent angle of measurement.

The movement being measured could consist of vertical settlement due to material consolidation and may not be horizontal and related to impending failure.

The displacement magnitude measured on opposite sides of a facility may have different accuracy, depending on the slope orientation versus the line-of-sight.

Areas with heavy vegetation may be difficult to monitor

Areas with heavy or persistent cloud cover can be difficult to monitor.

Areas with snow cover will be difficult to monitor.

The satellite return period may be weekly or every two weeks, so one is not able to analyze daily movements if a situation is critical. If the return visit day has cloud cover, there will be no new satellite data collected.

Areas with on-going construction or tailings deposition will lead to erroneous results.

Due to the line of sight, not all slope failure modes may be detectible (for example piping failure).

Regardless of these limitations, InSAR can still play a role in any monitoring program since it is able to monitor large areas quickly. Consider it as a pre-screening tool, being aware that not all failure modes may be detectible with it.

Discussion

On LinkedIn, one can see numerous posts where independent experts are examining historical InSAR data for recent failures to see whether early movement should have been detected. The results seem to be quite positive in that areas that have failed might have been red-flagged prior to failure.

There are also zones that showed critical displacements but have not failed.

Typically, there are four ways to monitor displacement in pit slopes, tailings dams, heap leach pads, and waste dumps. They are:

Insitu monitoring using embedded instruments, for example slope indicators, extensometers, and settlement gauges. These instruments provide information on what is happening internally within a slope, where actual movement is occurring, and they can be used in warning alert systems.

Surface monitoring using radar (ground based InSAR) systems and survey prisms. These tools measure only surface movements in selected areas, can be monitored as frequently as needed on an automated basis, and integrated into warning alert systems.

Drone or aerial surveys can be used to measure topography and monitor movements over large areas. This method requires a data processing delay (not real time) to derive the movement information, but such surveys can be done as frequently as needed.

InSAR from satellite can be used over very large regions to highlight areas with movement. That should trigger the implementation of one or more of the other monitoring approaches (if not already in place).

Conclusion

A mining site consists of numerous constructed embankments and slopes of all types and heights. Many of these slopes may be creeping and moving all the time – it’s a living beast.

Since InSAR monitoring is done from space, it does not require access to a property. Hence it can be used by third parties or NGO’s to “spy” on facilities of concern anywhere.

Note: You can sign up for the KJK mailing list to get notified when new blogs are posted. Follow me on Twitter at @KJKLtd for updates and other mining posts. The entire blog post library can be found at https://kuchling.com/library/

I recently saw an investor presentation from First Mining Gold about their Springpole Project. The situation is that their open pit is located within a lake and will require the construction of a couple of small cofferdams to isolate the pit area from the lake. The concept is shown in this image.

Over the last couple of years I have been involved in a few early-stage studies for mining projects in which nearby bodies of water play a role in the design. In Canada’s north there are thousands of lakes and rivers, so its not surprising to find mines next to them.

That got me thinking about how many other mines are in the same situation, i.e. projects that may be located very close to, or within, a lake, river, or ocean. Hence I have compiled a short list of a few such mines.

I have been directly involved with some of those in the list, while others are only known to me with limited detail. Some mines I had never heard of before, but their names were provided to me by some Twitter colleagues.

My observation is that building a mine within, or adjacent to, a body of water is nothing new and this has been done multiple times successfully.

Some of these projects may refer to the dams as “dikes”, “cofferdams”, “sea walls” but I assume they are all providing roughly the same function of holding back water for the life of the project. They are not viewed as permanent dams.

This is Part 1 of a two-part blog post. Part 1 provides some examples of projects where water bodies were involved in the design. Part 2 provides a discussion on specific geotechnical and hydrogeological issues that would normally have to be examined with such projects.

Some Lake Mining Examples

The following are some examples of operating mines involving lakes. I have captured a few Google Earth images, unfortunately some have only low resolution vintage satellite imagery.

Diavik Diamond Mines, NWT

This is a project I was working on with in 1997 to 2000 while it was still at the design and permitting stage. My role focused on pit hydrogeology and geotechnical as well as mine planning.

The project would require the construction of three dikes in sequence to mine four lakebed kimberlite pipes.

The three dikes were named after the associated kimberlite pipe being mined inside it; A154, A418, and A21.

The first dikes were built in 2002 and the last dike (A21) was completed in 2018.

The total dike length for the three dikes is about 6.2 km.

For those interested in learning a bit more about Diavik, I have posted an earlier article about the open pit hydrogeology there, linked to at " Hydrogeology At Diavik – Its Complicated".

Gahcho Kue, NWT

Meadowbank, NWT

This is an Agnico-Eagle gold mining operation built in 2010 that required a cofferdam to be built around one of their open pits (see image).

The total dike length is about 2000 metres. I don't know much more about it than that unfortunately.

Cowal Gold Mine, Australia

Yes, a lake in Australia ! This is a former Barrick operation, now owned by Evolution Mining, and is another example where the mine is located within the shoreline of a lake (Lake Cowal). I don't know much about this, the name was kindly provided to me by a colleague.

The total dike length appears to be about 3000 metres.

Rabbit Lake Sask

The historical Rabbit Lake uranium mining operation required the construction of cofferdams around a few of their open pits. They are now reclaimed and flooded.

St Ives Gold Mine, Australia

This is a unique situation in that several pits are located within an ephemeral (intermittent) salt lake and dikes were required to prevent pit flooding during wet season.

Some River Mining Examples

Gorevsky Mine, Siberia

This lead-zinc operation has an orebody that extends into the Angara River.

This mine has built a fairly large cofferdam into the river, and is currently mining a large pit within it. The total cofferdam length appears to be about 4000 metres.

It would be interesting to see how close the pit will get to the cofferdam. We'll check back in a few years.

BHP Suriname Bauxite Mine

This is a project I was involved with several years ago. The bauxite deposit extends beneath the Suriname River and the goal was to mine as much ore as possible.

Given the flow rates in the river, especially during the wet season, it would be difficult to maintain a cofferdam out into the river.

The shoreline overburden consisted of sands and soft clays, so the decision as made to construct a sheet piling wall along the river bank to protect the pit from river erosion. This was mined out successfully and eventually reclaimed.

McArthur River, Australia

In situations where the river (creek) is small enough and the topography allows, one can divert the entire river around the mine.

There are several examples of this in Canada and elsewhere. Here’s the McArthur River lead-zinc mine in Australia, where they channeled their small river around the open pit.

An Ocean Example

Cockatoo Island Mine, Australia

This interesting iron ore mine has an ore zone that dips 60 degrees, is 35 metres wide, with a strike length of more than one kilometre.

A sea wall was constructed to prevent any tidal water from entering the open pit that was to be mined, with reportedly high tidal fluctuations there.

Conclusion

If you know of other mines not listed above that have successfully dealt with a water body, please let me know and I can update this blog post.

This concludes Part 1. Part 2 can be read at this link " Mining Under Lakes – Part 2: Design Issues" discusses some of the concerns that engineers need to consider when building a mine in these situations.

Pantai Remis tin mine

Finally, the worst-case scenario is shown in this grainy video of a tin mine (Pantai Remis Mine) pit slope failure. It seems they mined too close to the ocean. Watch to the end, its hard to believe. Its looks like something out of a Hollywood disaster movie.

Note: You can sign up for the KJK mailing list to get notified when new blogs are posted. Follow me on Twitter at @KJKLtd for updates and other mining posts. The entire blog post library can be found at https://kuchling.com/library/

Pantai Remis Mine