The historic Cauquenes and Colihues tailings impoundments are man-made deposits that were generated as sites for the containment of tailings produced during the processing of copper-molybdenum ore at the El Teniente mine owned by Codelco.

El Teniente Tailings
MVC currently receives approximately 130,000 tonnes per day of Fresh Tailings from El Teniente’s Colon concentrator. The Fresh Tailings are transported via gravity to MVC via a 36 km long concrete open channel launder.

MVC’s contract with El Teniente provides for the supply of Fresh Tailings up to the year 2037. Details are provided in Section 19.0. Every year, MVC receives an updated life of mine plan from DET and uses this plan to estimate the quantity and quality of Fresh Tailings available to be processed at MVC. Due to volumetric transport constraints in the tailings channel launder to the Caren impoundment, there is insufficient capacity to simultaneously process both Fresh Tailings and Cauquenes tailings at their maximum rates. Surplus Fresh Tailings material is planned to bypass MVC’s mill and be deposited into the voids created in the Colihues and Cauquenes impoundments.

A total of 856 million tonnes of Fresh Tailings at a grade of 0.110% Cu and 0.008% Mo is planned to be delivered to MVC’s processing facility.

Colihues Tailings
Extraction of material from the Colihues deposit ceased in 2015 and is planned to recommence in 2031 when the Cauquenes deposit is depleted. Tailings in the Colihues deposit were extracted at a nominal rate of 35,000 tonnes per day via a hydraulic monitoring system using high pressure water guns operating at 30 bar. The flow of water at high pressure water is directed onto the surface of the tailings in a sweeping motion in such a way as to create a ditch on the surface. The monitors work horizontally and vertically, operated by remote control using a hydraulic system of electronic valves that allow them to rotate and advance. A single monitoring unit is capable of sustaining a production rate of 8,000 to 10,000 tonnes per day. Mining bench heights are 10m high and access ramps are created to relocate the hydraulic monitors. The depth of the Colihues tailings deposit is approximately 50 m requiring four mining benches. The slurry drains to the center of the sump by gravity and is channelled by the ditches made by the monitor. The slurry has a density of approximately 45% solids and is pumped to the processing plant by means of vertical 150 kW sump pumps and 350 kW horizontal booster pumps, via 10” high density polyethylene (HDPE) pipelines. The operation of four hydraulic monitors and two sumps is necessary. In order to sustain a production rate of 35,000 tonnes per day.

A portion of the Colihues tailings deposit is submerged under water. To enable extraction to commence, zones have to be isolated with impermeable barriers and dewatered prior to extraction. A spillway facility has to be maintained to allow for excess rainfall to be released. Colihues is planned to be separated into four zones: I, II, III and IV (see figure 16-6). In 2016, Colihues zones I and III were depleted and zones IV and II are available for future extraction. Tailings will not be extracted at the margins of the deposit, at the interface of the tailings with the original ground surface level, safety barriers at the dam walls and the tailings left in-situ for internal water barriers. A total of 46 million tonnes at a grade of 0.323% Cu is not currently in MVC’s mine plans. This tonnage has been removed from the Colihues in-situ resource and a total of 98 million tonnes at a grade of 0.230% Cu and 0.010% Mo is planned to be delivered to MVC’s processing facility.

Cauquenes Tailings
The first phase of the Cauquenes expansion project was completed in 2015 enabling extraction of material from the Cauquenes deposit into the existing MVC process facility. The processing rate from 2019 onward is planned to be 62,500 tpd and extraction of the Cauquenes deposit is anticipated to be complete in 2031. Tailings are extracted from the Cauquenes deposit via a hydraulic monitoring system similar to Colihues. The general method of operation is as follows:

• Construct a sump in the tailings deposit and install vertical slurry pumps
• Commence extraction down to 10m using hydraulic monitors and allow slurry to drain to sump
• Pump tailings to the plant at a density of 43% solids
• Reposition the monitors sequentially away from the sump to advance the extraction.

This procedure is repeated until the bottom of the tailings deposit is reached, approximately 50m deep. Safety zones are maintained near the walls to ensure the integrity of the walls.

Due to volumetric transport constraints in the tailings channel launder to the Carén impoundment, MVC is not expected to be able to simultaneously process the Fresh Tailings and Cauquenes tailings at their maximum rates. The sum of the feed streams will exceed the capacity of the Carén tailings channel, which is limited to 181,000 tonnes per day (equivalent to approximately 65 million tonnes per year). Therefore the surplus fresh tailings are planned to be discarded and deposited into the voids created in the Colihues and Cauquenes impoundments.

MVC recovers copper and molybdenum from Fresh Tailings and Cauquenes Tailings in separate plants. The tailings slurry is classified into coarse and fine fractions and then processed in ball mills and flotation cells to produce a combined bulk copper concentrate. The tailings from the Fresh and Cauquenes rougher flotation circuits report to the cascade scavenger flotation circuit. The concentrate from the cascade circuit is pumped to the fine rougher flotation circuit.

Final tailings from the cascade flotation circuit are delivered to three 100m diameter thickeners. The tailings are thickened to a density of 53% solids and returned to the El Teniente tailings channel for delivery to the Caren impoundment. Thickener overflow water is recirculated back to the plant. The bulk copper concentrate is treated in the molybdenum separation facility to produce a molybdenum concentrate. The final molybdenum concentrate containing 40% Mo is filtered, dried and packaged for dispatch in bu ........