Sotkamo silver mine (formerly Taivaljarvi silver mine) is a polymetallic mine under construction in the Sotkamo municipality of Eastern Finland, roughly 575km away from Helsinki.
Discovered in 1980, the silver-gold-lead-zinc deposit is being developed by Sotkamo Silver, a Swedish mining company that acquired the property in 2007.
Sotkamo Silver prepared a bankable feasibility study (BFS) for the project in 2012 and completed environment impact assessment (EIA) for the same in 2013.
An updated BFS for the project was completed in 2016, which predicted average annual production of 5,000 tonnes (t) of silver, lead and zinc concentrates over 11 years of mine life. The estimated investment of the project was $53.8m, according to the updated BFS.
Sotkamo Silver announced the financial closure and start of construction of the project in March 2018.
The mine is scheduled to commence operation in 2019.
Sotkamo silver mine geology
The Sotkamo silver polymetallic deposit covers an area of 530ha and stretches up to a depth of 1,500m, in the Taivaljärvi greenstone belt within the southern part the Tipasjärvi-Kuhmo-Suomussalmi greenstone complex in Eastern Finland.
The deposit will be mined using open-pit as well as underground mining methods.
The north-south trending 200km-long and up to 15km-wide Tipasjärvi-Kuhmo-Suomussalmi greenstone complex is enclosed with Archean basement rocks mostly dominated by tonalite-trondhjemite-granodiorite (TTG) and granodiorite-granite conglomerates.
Sotkamo silver mine reserves
The proven and probable ore reserves of the Sotkamo mine were estimated to be 2.75 million tonnes (Mt) grading 122g/t silver, 0.42g/t gold, 0.43% lead and 0.90% zinc, as of June 2017.
The open-pit proven and probable reserves were estimated to be 853,952t, grading 88.0g/t silver, 0.28g/t gold, 0.25% lead and 0.53% zinc.
The proven and probable reserves for the underground mine were estimated to be 1.9Mt, grading 137.3g/t silver, 0.5g/t gold, 0.5% lead and 1.1% zinc.
Mining methods for Sotkamo silver mine
Sotkamo silver mining operation will simultaneously adopt open-pit and underground mining methods in the initial phase, while underground mining alone will be continued in the later phases.
Conventional open-pit mining involving drill, blast, load and haul operations will continue for the first 1.5 years, with a target to produce up to 500,000t of ore. The open pit of the Sotkamo silver mine will be 300m-long, 80m-wide and 80m-deep.
The mining fleet for the open-pit operation will include two (45t and 25.3t) excavators, two articulated trucks, one front-end loader, one grader, one bulldozer, and auxiliary trucks for maintenance.
The underground mine will be accessed from the surface through a 2.5- long, 5m-wide and 5m-high decline.
The mining fleet for the underground operation will include one drilling jumbo, one longhole drill rig, one cable bolting rig equipment, one concrete spraying device, two load-haul-dump (LHD) loaders, and up to six trucks.
Ore processing at Sotkamo silver mine
The run-of-mine (RoM) ore will pass through two-stage crushing and two-stage grinding before undergoing sequential silver-lead flotation, zinc flotation and pyrite flotation processes.
Further, the concentrates obtained from each floatation circuit will undergo three-stage cleaning and dewatering.
The milling capacity of the processing plant will be 450,000t a year.
The mine is expected to produce up to 1,981t of silver-lead concentrates, 5,477t of zinc concentrates and 8,579t of pyrite concentrates a year.
The silver-lead and zinc concentrates will be sent to smelters in Europe for the production of final metals.
The tailings will be pumped to the 28ha tailings storage facility located adjacent to the processing plant.
Infrastructure facilities for Sotkamo silver mine
The Sotkamo silver mine is accessed using two independent roads that connect the national road 9005 near Sotkamo municipality. One of the two roads is meant only for heavy vehicles.
Water required for the mining operations will be sourced from Lake Pieni Tipasjarvi.
Electricity supply for the mine will be from UPM Energy’s Katerma hydro-power-station through a 20.2km transmission line connecting a 45kV/20kV transformer station near the mine site.
Contractors involved with Sotkamo silver mine
Outotec agreed to provide the grinding mill circuit for the Sotkamo silver in January 2018. Vapo was contracted for providing a bio energy-based heating solution for the air ventilation of the Sotkamo silver mine, in July 2018.
ABB is responsible for the engineering, design and delivery of electrification, automation and instrumentation systems for the mine.
PCS Engineering was contracted for the design electrification and instrumentation systems for the processing plant.
RPK Rakennus Kemppainen was contracted for the foundation and associated construction work. Ruukki Construction was contracted for the construction of the beneficiation plant. Power Mining was contracted for the underground mine infrastructure.
Kainuun Sora was engaged for rock crushing and extraction for the construction.
Pöyry Finland provided dam design for tailing ponds, while E. Hartikainen was awarded construction contract for the road and turf structures.
Insinööritoimisto Savolainen provided construction planning services, while
Teollisuustaito provided water treatment planning services.
Ramboll Finland was hired for the environmental impact assessment (EIA) and environmental permit application for the project.
CTS Engtec prepared the updated BFS for the project in 2016, whereas, the original BFS was prepared by Wardell-Armstrong International in 2012.