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The San Rafael zinc-lead-silver underground mine is located in the Cosalá mining district in Sinaloa, Mexico.
Americas Silver Corporation (formerly Scorpio Mining) is the owner/developer of the mine. Construction of the mine started in October 2016 and ore production commenced in September 2017. The project achieved commercial production in December 2017.
The mine is expected to produce approximately 1Moz of silver, 50 million pounds (Mlb) of zinc, and 20Mlb of lead over the initial mine life of six years.
San Rafael zinc-lead-silver mine geology
San Rafael is a lime-bearing siliceous rock deposit formed through a contact between calcareous sediments and overlying volcanic rocks. Most of the sulphide mineralisation appears to be hosted in the volcanic tuff.
The main minerals are pyrite, pyrrhotite, sphalerite, and galena with minor marcasite, chalcopyrite, and magnetite. The deposit contains silver, lead, and zinc mineralisation with traces of gold and copper.
Mineralisation at San Rafael
The San Rafael deposit mineralisation is identical to the massive volcanogenic sulphide deposits, especially the Guerrero Terrane in central Mexico. The mineralisation occurs in three distinct zones, namely upper, main, and the low-sulphide 120 zone.
The upper zone is characterised by moderate sulphide silver-gold mineralisation, while the low-sulphide 120 zone comprises silver, copper and gold mineralisation.
The main zone comprises high-sulphide zinc and lead ore with significant amounts of silver. The mineralisation is associated with quartz, sericite and pyrite alteration minerals.
San Rafael mine reserves
The proven and probable reserves at San Rafael mine are estimated to be 3.74Mt containing 12.1Moz of silver, 139.6Mlb of lead, and 337.6Mlb of zinc.
Mining and processing of ore at San Rafael
Conventional underground cut-and-fill mining method, along with drill and blast, is being applied at the mine. The underground mine is accessed through the main portal located south of the deposit and a main ramp connecting to haulage drifts.
Mining is mainly focused on the main zone, which is anticipated to produce high amounts of zinc and lead concentrates using conventional flotation. Ore in the southern lobe of the Main Zone of the mine is being recovered by five development headings and will be stockpiled.
Americas Silver started processing the San Rafael ore at its existing Los Braceros facility in November 2017. The Los Braceros processing plant is a conventional polymetallic concentrator equipped with a three-stage crushing plant, a primary ball mill, two secondary grinding mills, two vertical concentrate regrind mills, rougher and cleaner cells, and drum filters. Flotation tanks have also been installed to increase the flotation and concentrate regrind capacity.
The facility is producing at an average of 1,400 tonnes per day (tpd) of zinc and lead concentrates. It is estimated to have a throughput of 1,500tpd in the first quarter of 2018.
The final lead-silver concentrate and zinc-silver concentrate is proposed to be conveyed by truck to buyers in Manzanillo, Mexico.
Infrastructure facilities at San Rafael
Americas Silver is using the existing infrastructure at its operations in the Cosalá district. The mine is accessed through an existing road from the town of Cosalá. A 1.5km road section was improved to connect the final section to the San Rafael main portal.
Power supply for the portal construction and the first 16 months of mining is provided through portable diesel power generators. The mine is proposed to be connected to the national electric grid at the town of La Estancia, approximately 9km south of the San Rafael main portal.
Water for the San Rafael mine is being sourced from a dam located in a nearby creek, which is pumping to a storage tank placed above the main portal for distribution within the mine.
Other facilities include a 12,500l fuel storage tank, a security station, and a standard leaky feeder radio communication system.
Financing of San Rafael
Americas Silver received a $15m concentrate prepayment facility in January 2017 from Metagri, a subsidiary of Glencor, for the development of the mine.
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