Project Details
The Cerro Prieto Project, located in the Cucurpe Mining District, Sonora, Mexico, is comprised of severa mineral concessions covering approximately 6879ha. The Cerro Prieto Project is 52 road kilometers from the regional center of Magdalena de Kino and 150 kilometers northeast of the city of Hermosillo.
Cerro Prieto commenced small-scale trial mining and leaching in December 2013. During the three and nine months ended September 30, 2014 Cerro Prieto produced 1,076 and 4,174 ounces of gold, respectively. The Company is working to ramp-up mining operations to commercial production rates.
Heap leach pads consist of a geomembrane with an overlying drainage system, and then a heap, a large of precious metal bearing ore or waste rock above. A cyanide or sulfuric acid solution is sprayed on top of the ore, leaches through it reacting with the metals, and carries the solution to the underlying drainage system where its collected in a sump. Separation of the ore from the leachate occurs at an on-site processing plant. The leaching solution is then renewed, and the process is repeated until it is no longer economical.
The liner placed at the bottom and around the sides of the pad prevents pregnant leach solution leaks and stop chemicals from leaking into the soil and contaminating groundwater. The geomembrane utilized for these liners must be capable of withstanding the excessive weight of stacked ore, the continuous application of corrosive chemicals, and harsh weather conditions over the long term.
| Property | Weighting | HDPE | LLDPE | fPP-R | PVC | CSPE-R | |||||
| Chem. Resist. | 10 | 5 | 50 | 3 | 30 | 3 | 30 | 1 | 10 | 4 | 40 |
| Durability | 5 | 5 | 25 | 3 | 15 | 3 | 15 | 1 | 5 | 4 | 20 |
| UV Stab. | 5 | 5 | 25 | 4 | 20 | 4 | 20 | 1 | 5 | 5 | 25 |
| Shear Strength | 10 | 5 | 50 | 5 | 50 | 4 | 40 | 4 | 40 | 4 | 40 |
| Stress Crack | 10 | 2 | 20 | 5 | 50 | 5 | 50 | 5 | 50 | 5 | 50 |
| Seameability | 8 | 3 | 24 | 4 | 32 | 4 | 32 | 5 | 40 | 4 | 32 |
| Seam Behavior | 6 | 4 | 24 | 4 | 24 | 3 | 18 | 2 | 12 | 3 | 18 |
| Strength | 4 | 5 | 20 | 4 | 16 | 3 | 12 | 2 | 8 | 3 | 12 |
| Elongation | 7 | 3 | 21 | 4 | 28 | 3 | 21 | 5 | 35 | 3 | 21 |
| Tear | 10 | 5 | 50 | 5 | 50 | 3 | 30 | 3 | 30 | 3 | 30 |
| Puncture | 10 | 5 | 50 | 5 | 50 | 2 | 20 | 5 | 50 | 2 | 20 |
| Impact | 8 | 5 | 40 | 5 | 40 | 3 | 24 | 5 | 40 | 3 | 24 |
| Solu. Diffusion | 8 | 5 | 40 | 4 | 32 | 4 | 32 | 2 | 16 | 4 | 32 |
| Constructability | 8 | 3 | 24 | 4 | 32 | 4 | 32 | 5 | 40 | 4 | 32 |
| Benefit | n/a | – | 463 | – | 469 | – | 376 | – | 381 | – | 396 |
| Cost/m2 | n/a | – | 10.00 | – | 10.50 | – | 11.25 | – | 9.00 | – | 13.00 |
| B/C ratio | n//a | – | 46.30 | – | 44.70 | – | 33.40 | – | 42.30 | – | 30.50 |
Tabla 1. Matriz Coste/Beneficio para un patio de lixiviación (ref., Geosynthetic Applications Used in Heap Leach Mining by George R. Koerner)
The use of a Benefit/Cost selection Matrix (GRI White Paper #12) appoint HDPE geomembranes as the best option for a Heap Leach Pad. For all that reasons Atarfil HD 1.00mm geomembrane was selected as the client needed a geomembrane with high chemical resistance, long lifetime, as well as good mechanical properties.
