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. Currently, feed to the plant is derived from two sources: fresh rougher tailings from the Codelco’s El Teniente concentrator and hydraulically recovered tails from the Cauquenes tailings impoundment. The mineralogy of the feeds varies, and the most recent mineralogy indicates that the main copper and molybdenum-bearing minerals are sulfide in nature. In the fresh tailings the majority of the copper (47%) occurs as chalcopyrite, with significant secondary copper sulfide forms: chalcocite, bornite, and covellite (40%). In the historic tailings, approximately 75% of the copper occurs as secondary copper minerals and about 17% of the copper occurs in the form of chalcopyrite. The portion of poor floating copper minerals (copper in iron oxides and sulfates) ranged from 7 to 13% for the historic and fresh tailings, respectively. In both tailings streams, the molybdenum occurs as molybdenite.

MVC has been in operation since 1992 and produces copper (Cu) and molybdenum (Mo) concentrates by reprocessing tailings produced by the El Teniente mine. Sources of mill feed include the fresh tailings from El Teniente and the tailings from the Cauquenes historic tailings deposit and Colihues historic tailings deposit.

MVC has valid contracts with Codelco’s El Teniente Division (DET) to process Fresh Tailings, the Colihues deposit and the Cauquenes deposit. MVC has the right to process tailings up to 2037.

Currently, feed to the plant is derived from two sources: fresh rougher tailings from the Codelco’s El Teniente concentrator and hydraulically recovered tails from the Cauquenes tailings impoundment.

El Teniente Tailings
The Fresh Tailings are transported via gravity to MVC via a 36 km long concrete open channel launder. The target fresh tailings concentrator throughput is 140,000 tpd. The term of the Fresh Tailings Agreement was extended from December 31, 2021 to December 31, 2037.

Colihues Tailings
In 2003, MVC commenced production from the Colihues deposit, and, in 2015, suspended operations from Colihues. The total tonnage of material extracted from the Colihues deposit, up to the end of December 2016 was 72,742,245 tonnes. The total quantity of copper produced from Colihues, up to the end of December 2016 was approximately 55,975 tonnes. Extraction of material from the Colihues deposit 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. 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.

The term of the Colihues Agreement was extended from the earlier of December 31, 2019 or depletion of the Colihues deposit, to the earlier of December 31, 2037 or depletion of the Colihues deposit. MVC has the right to treat up to 45,000 tpd of ore from Colihues.

Cauquenes Tailings
In 2015, MVC commenced production from the Cauquenes deposit. The total tonnage of material extracted from the Cauquenes deposit, up to the end of December 2021, was 123,692,310 tonnes. The total quantity of copper produced from Cauquenes, up to the end of December 2021, was approximately 98,739 tonnes.

The term of the DET Agreement is to the earlier of December 31, 2033 or depletion of the Cauquenes deposit. MVC has the right to treat up to 85,000 tpd of ore from Cauquenes.

Tailings in the Cauquenes tailings impoundment are planned to be removed at a rate of 45,000 tonnes per day via a hydraulic monitoring system using high pressure water guns operating at 30 bar. High pressure water is directed onto the surface of the tailings in a sweeping motion 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 benches are 10 metres high, and access ramps are created to relocate the hydraulic monitors. The depth of the Cauquenes tailings deposit is approximately 50 metres, requiring five mining benches. The slurry drains to the center of the sump by gravity and is channeled by the ditches made by the monitor. The slurry has a density of approximately 47% solids and is pumped to the processing plant by means of vertical 150 kilowatt (kW) sump pumps and 350 kW horizontal booster pumps, via 10-inch high density polyethylene (HDPE) pipelines. The operation of four to six hydraulic monitors and two to four sumps is necessary to sustain a production rate of 45,000 tonnes per day.

The general method of operation is as follows:
- Construct a sump in the tailings deposit and install vertical slurry pumps;
- Commence extraction down to 10 metres using hydraulic monitors and allow slurry to drain to the sump;
- Pump tailings to the plant at a density of 47% 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 50 meters deep. Safety zones are maintained near the walls to ensure the integrity of the walls.

The ideal tailings extraction plan is to employ phases, based on the granular sizes. The location with highest granular particle sizes should be extracted first as the coarse material is preferential. The material with the lowest granular sizes will be extracted last. The overall target is to extract the all the available material.

The underflow of each primary cyclone reports to its corresponding ball mill (6) for grinding. These ball mills (N°1 through N°6) range in motor power from 1,866 KW to 2,611 KW (2,500 to 3,500 HP) and are in a closed circuit with a cyclone cluster. The cyclone overflow targets a P80 of approximately 180 µm and reports to a distribution box where the slurry is split for rougher flotation.

Concentrates from the rougher flotation cells pumped to the regrind mill discharge pump box which feeds the regrind cyclones. Regrind 1 and 2 are equipped with 970 KW and 933 KW motors, respectively (1,300 HP and 1,250 HP).

The underflow of each primary cyclone reports to its corresponding ball mill (2) for grinding. These ball mills (N°7 through N°8) range in motor power from 2,388 KW and 2,611 KW (3,200 to 3,500 HP) and are each in a closed circuit with a cyclone cluster. The mill cyclone overflow targets a P80 of approximately 130 µm and reports to a primary rougher flotation (Banks 100 and 200). Bank 100 and 200 consists of conventional cells with a total volume of 1,020 m3 .

MVC initially utilizes two separate circuits to produce copper and molybdenum concentrates from fresh and historic tailings: fresh rougher tailings from the Codelco’s El Teniente concentrator (TEN) and hydraulically recovered tails from the Cauquenes tailings impoundment (CQNS). Primary classification is performed on the tailings streams to separate the fine fraction for scavenging skim flotation in a cascade system and the coarse fraction is subjected to grinding before conventional flotation. The ground coarse fraction is transported to a conventional rougher/cleaner flotation circuit to produce a combined bulk copper-molybdenum concentrate. The bulk concentrate is reground and cleaned followed by selective flotation for molybdenum separation. Final tailings from both TEN and CQNS circuits report to thickening before final discharge to the El Teniente tailings channel and report to the Caren impoundment.

The current plant configuration treats approximately 185,000 tonnes ........