Copper & Zinc
Site visit: Somincor Neves-Corvo mine, near Castro Verde, Portugal
The Neves-Corvo mine is located in the southern Alentejo region of Portugal, in a semi-arid landscape. The underground mine, which has operated since the late 1980s, taps into five orebodies rich in copper and zinc. The mine is one of the largest in Europe, yielding roughly 2.3 million tonnes of copper and 1.2 million tonnes of zinc per year. The mine is owned by the Portuguese company Somincor, a subsidiary of Lundin Mining.
I was hosted by Nelson Pacheco, Chief Geologist for the Neves-Corvo mine. In his office, Nelson explained the geological processes that created the 350 million-year-old mineral ore in the area. The sulfide deposits formed on (what was then) the seafloor as material was carried up by volcanic activity within the earth’s core. Veins of glimmering mineral in the extracted ore samples indicate the pathways of the minerals being pushed up by the bubbling gasses.
The mine employs 2000 people and operates 24 hours per day in three shifts. There are 200 km of roads inside, descending anywhere from 500 to 1000 meters below the ground. The material is extracted through a process of drilling and blasting. There are three explosions per day, initiated at the end of each shift after all workers are cleared from the area. The blasted rock, called muck, is carried out of the mine through a shaft with two lifts, each with a capacity of 17.5 tonnes. Once a section of the mine has been exploited to capacity, it is backfilled with tailings, concrete and sand.
From the lifts the material is poured onto a conveyor belt that takes it to the ore park for separation. There are two processing plants onsite, one for copper and another for zinc. The sorted material is sent to either facility depending on its composition, where it is crushed and refined. Once processed, the minerals are prepared for transport by rail to the port of Setúbal, outside of Lisbon. The majority of the mined material is exported by ship, mainly to Sweden, Germany and China, for smelting.
Mining tailings, the waste slurry consisting of ground rock and chemical effluent, is a major environmental hazard. When exposed to oxygen and water, the sulfide minerals in the slurry become sulfuric acid, a highly corrosive substance that is hazardous to both humans and the environment. To control the reactions and minimize the environmental impact, the slurry must be stored either underground or underwater. Much of the tailings from Neves-Corvo are sent back into the mine to be used as backfill. The remaining waste is sent to an onsite tailings dam. The dam is isolated with no discharge to natural waterways (except during large storm events when the dam is over capacity).
Second to management of the tailings, water usage is an environmental concern in the mining process. The water, both the water used for drilling and natural groundwater, must be continually pumped out to avoid flooding the mine. Much of this water is cleaned in an onsite treatment plant for reuse with the mining and refining activities.
With current ore refining techniques, the process is only about 85 percent efficient and 15 percent of the minerals are discarded with the tailings. As copper and zinc concentrations in the mine decrease over time, the quantity of minerals in the tailings dam grows. Somincor is considering future methods of mining the tailings, which become more valuable as the underground deposits become harder to source. The reversal of the process chain illustrates the constraints and consequences of raw mineral extraction. The earth is not is a not a limitless well, and as we move forward new means of material sourcing through reuse and remanufacturing becomes all the more critical.
Thank you to Somincor for allowing me to visit, and particularly to Nelson Pacheco for his time. The thoughts and information in this post are based on my visit to the facility and have not been externally verified unless otherwise noted.
All photos by Irmak Turan.
