Spying on Tailings Using Satellites

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.


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:
  1. 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.
  2. 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.
  3. 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.
  4. 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).


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.
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Filtered Tailings Testing Checklist

I have always been a big proponent of filtered (or dry stack) tailings over conventional tailings disposal. Several years ago I had written a blog (Fluid Tailings – Time to Kick The Habit?)  that this is the tailings disposal approach the mining industry should be moving toward.
Recently I have been seeing more mining studies proposing to use the dry stack approach. In some cases, they no longer even do the typical tailings trade-off study that look at different options. The decision is made upfront that dry stack is the preferred route due to its environmental acceptability and positive perceptions.
Recently I came across a nice document prepared by BHP and Rio Tinto titled “Filtered Stacked Tailings – A Guide for Study Managers (March 2024)”. I will refer to this document as “The Guide”. You should definitely get a copy of this Guide if your project is considering a dry stack operation. An information link is included at the end of this post.

A Guide for Study Managers

The Guide covers several topics, including tailings characterization; site closure concepts; filtered tailings stack design; material transport, stacking systems; and tailings dewatering methods. The Guide covers all the basics very well. The one area that jumped out at me is the tailings characterization and testing aspect.
Many assume that dry stack is simply filter, haul, dump, then walkaway. Its all very easy! However, in reality, the entire dry stack approach is complex.
One needs to be able to consistently dewater tailings from different ore types, then transport it under different climatic conditions, and then place and compact the tailings efficiently.
One also needs to be able to deal with plant upsets, when the filtered tailings don’t meet the optimal product specifications. So its not really that simple.
One of the chapters in the Guide details the different test work that should be done to understand the dry stack approach.  The list of tests is a lot longer than I had envisioned.  I previously knew some of the types of lab testing required, however the Guide outlines a very comprehensive list.
The Guide also categorizes the tests according to study stage, be it concept study, order of magnitude study, or Pre-Feasibility level. Interestingly, the concept study can rely mainly on published information. However, the more advanced mining studies require the lab testing of actual tailings material.

Testing Checklist

To help organize the complexity of testing, I have listed their suggested tests as to whether the test is related to material characterization, process characterization, or filtered product characterization. Each aspect serves a different purpose in understanding the workings of the filtered tailings approach. The engineer will decide at which study stage they wish to do each of the tests, or which of the them they actually need to do.
To keep the blog post brief, I am not describing the details for each test. Most geotechnical or process engineers will already be familiar with them, or anyone can search the web to learn more.


  • Chemical composition Testing: using atomic absorption or spectroscopy, identify the elements within the tailings stream to highlight contaminants and potential flocculation issues.
  • Conductivity Test: increase knowledge of the tailings stream.
  • Mineralogy Testing: identify mineral types and clay minerals (if any) that could impact on performance.
  • Particle Shape Analysis: are there fibrous minerals present, as well as settling and rheology effects.
  • Particle Size Distribution: are the tailings coarse, or mainly fine silt and clay sized particles that can impact on filtering and product performance.
  • pH Test: determine the acidity of the tailings steam, can relate to flocculant selection.
  • Tailings Slurry Density Test: assess the pumpability and amount of thickening and filtering that will be required.
  • Tailings Solid Mass Concentration and Moisture content: required for process mass balances.
  • Specific Gravity Testing: assess the SG of the tailing particles, i.e. light or heavy minerals.
  • Total Dissolved Solids Test: assess the fluid composition, are minerals dissolvable.
  • Zero Free Water Test: relates to the solids concentration at which the sample is fully saturated and may relate to transportability.


  • Total Suspended Solids: assess the quality of the return water from thickening or filtration.
  • Drained and Undrained Settling Test: to assess the thickening aspects and stack performance.
  • Setting Cylinder Tests: used to assess thickener settling performance.
  • Raked Setting Cylinder Tests: used to assess thickener settling performance.
  • Dynamic Continuous Settling Tests: used to assess thickening under continuous feed situation.
  • Minimum Moisture Content: assess the minimum moisture content achievable in filtration.
  • Vacuum/Pressure Filtration Test: often done by vendors, assess the filtering performance.
  • Compression Rheology: design consolidation / permeability data for filtering and disposal design.
  • Shear Rheology: provide information for pump and pipeline design.
  • Shear Yield Stress: provide processing insights for slurry dispersion and flocculation.


  • Leaching Tests (long term): assess whether the tailings stack will continue to leach metals and contaminants over the long term.
  • Leaching Tests (short term): assess whether the tailings stack will rapidly leach metals and contaminants.
  • Acid Base Accounting Tests: will the stack be an ARD concern.
  • Net Acid Generation: relates to ARD and neutralizing potential.
  • Air Drying Tests: determine the rate of natural air drying and dry density.
  • Atterberg Limits Testing: determine the plastic limit, liquid limit with respect to moisture content and stackability.
  • Consolidation Tests (one-dimensional): to assess the consolidation and settlement of the stack over time.
  • Proctor Density Tests: assess the optimal compacted density and moisture content vs the moisture content delivered by filtration.
  • Critical Void Ratio Tests: assess compaction, consolidation, and liquefaction potential.
  • Shear Testing: determine the geotechnical strength of the filtered product for stack height design.
  • Permeability Testing: assess the internal drainage characteristics of the filtered product.
  • Soil-water characteristics Tests: assess the unsaturated behavior of the filtered product.
  • Flow Moisture Point Tests: assess how well the material can be transported and placed.
  • Conveyance Testing: assess how well the material can be conveyed (troughing, steepness).
  • Minimum Angle for Discharge: used in the design of hoppers and chutes.
  • Angle of Repose Tests: used in hopper design and dry stack design. Ground Bearing Pressure: used to assess the trafficability of the deposit.


A dry stack operation might be just as complex as conventional tailings disposal, although that might not be the perception. Certainly, the processing side of filtered tailings is more complex than conventional tailings. The transportation design may also be more complex, as is the tailings placement methodology. The main complexity missing from the dry stack is the need for a large sludge retaining dam, albeit that is a huge and important difference.
Some might view the suggested testing checklist as overkill and decide that not all test work is necessary. That is most likely true for some situations, especially for small mines not dealing with large quantities of tailings. However for a project with a high capital investment, one doesn’t want to see the entire mill off-line because the tailings disposal system isn’t functioning.
Major miners, such as BHP and Rio Tinto, typically spare no expense on material testing for metallurgical or geotechnical purposes. They have the funds available to test and engineer to a high level to adequately de-risk the project to meet their investment thresholds.
Junior miners often don’t have the time or funds to spend on such comprehensive testing programs. “Good enough” is often good enough.
One reason why junior miners sign 5-year JV deals with the Major is the amount of technical work required to properly evaluate a project.
The Major understands the amount of time needed for sample collection, testing, analysis of results, and follow up with more testing. It takes a fair bit of time to reach a comfort level for moving forward. Even then, there are no guarantees of success.
Each tailings disposal project is unique in size, location, type of mineralization, site layout, and throughput rate, so each company must decide what level of testing is “good enough” to address their risk tolerance.
For those that would like to get a copy of the the Guide, you can find more information at this LinkedIn link.   I thank BHP and Rio Tinto for putting their heads (and wallets) together to prepare (and share) this document.


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/