SENSOR DDS® technology applied to Leach Pad in gold mine

Leach Pad or Heap Leach Pad is used to recover precious metals like gold, silver, copper or uranium from their ore. The ore is placed on the geomembrane (an impermeable pad) in a heap and the a leaching solvent is distributed over the surface of the ore. Generally cyanide is the chemical of choice for this process, which dissolves the trace metal elements into a liquid solution. The cyanide trace element solution is then collected at the bottom of the pad, in a collection trench.

Geomembrane are often damaged during the placement of the gravel / ore, often by the ore itself or the by the mechanical equipment placing the ore. When the Leach Pad is leaking, the dissolved metals then soak into the ground instead of remaining in collection trenches. This means that the mining operation is continuously pour cash back into the ground, typically this amounts to $100,000 per acre per year (based leakage at the ASTM 'acceptable leakage rate for geomembranes'. In some cases government agencies can close down the mining operations that they suspect to be causing localised pollution.
Our permanent geomembrane leak location system installed on a Leach Pad can prove to those government agencies that the mining operation is not responsible for the pollution meaning it can continue to operate. One time surveys of the liner integrity can also help but only provide a snapshot of integrity and once the heap is in place there is no way to test by one time survey.

99.7% of completed geomembrane installations leak from day one...

LEACH PAD AT ASIAN GOLD MINE – SENSOR DDS® MIT

In the following example the Leach Pad’s design cross section (from bottom to top):

  • Compacted clay
  • Geomembrane HDPE (80mils)
  • Protective geotextile
  • Drainage layer – gravel (2ft)
  • Ore

The size of the Leach Pad was 3,005,000sqft and total number of leaks detected straight after geomembrane installation was 582, which is a typical finding and that's before the excavators move in! If this number of holes were not located before to the Leach Pad's went into operation, the mining operation would have lost more than $7,000,000 every year.

SENSOR DDS® MIT survey was completed in 27 days. The client repaired the leaks located, the repairs were retested and Sensor issue a Certificate of Integrity to show that the exposed geomembrane was free of penetrating damage, allowing the construction of the Leach Pad to continue.

Examples of detected and located damage at Leach Pad project

One operator can test around 7000m² of a leach pad a day depending on site conditions.

One operator can test around 7000m² of a leach pad a day depending on site conditions.

Once a leak is localised, the gravel is excavated and liner damage on the Leach Pad is repaired.

Once a leak is localised, the gravel is excavated and liner damage on the Leach Pad is repaired.

Many times multiple damage is detected in the same immediate vicinity.

Many times multiple damage is detected in the same immediate vicinity.

Once the leak is repaired using patches and extrusion welding, the area is re-checked with the MIT Tester

Once the leak is repaired using patches and extrusion welding, the area is re-checked with the MIT Tester

Gravel thickness of 2ft is the most common arrangement for Leach Pads.

Gravel thickness of 2ft is the most common arrangement for Leach Pads.

First step to zero leak on Leach Pad is to MIT test the exposed liner (SENSOR DDS® MIT).

First step to zero leak on Leach Pad is to MIT test the exposed liner (SENSOR DDS® MIT).

Most frequently leaks found in leach pad geomembranes are punctures caused by the gravel drainage layer penetrating the liner.

Most frequently leaks found in leach pad geomembranes are punctures caused by the gravel drainage layer penetrating the liner.

Many operators can be deployed to accelerate the programme.

Many operators can be deployed to accelerate the programme.