San Rafael Zinc-Lead-Silver Project, Mexico
The San Rafael zinc-lead-silver underground mine is a brownfield mine being developed in the Cosalá mining district in Sinaloa, Mexico.
Americas Silver Corporation (formerly Scorpio Mining) is developing the mine. Construction of the mine started in October 2016 and the first concentrate is expected to be produced in the third quarter of 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 massive 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 3.23Mt containing 11.44Moz of silver, 127.2Mlbs of lead and 303.2Mlbs of zinc.
Mining and processing of ore at San Rafael
Conventional underground cut-and-fill mining method, along with drill and blast, will be used at the mine. Access to the underground mine will be through the main portal located south of the deposit and through a main ramp connecting to haulage drifts.
Mining will be focused on the main zone, which is anticipated to produce high amount of zinc and lead concentrates using conventional flotation. Both the concentrates will contain silver as a by-product.
Americas Silver intends to process the ore at its existing Los Braceros facility and produce separate zinc and lead concentrates. 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.
The San Rafael ores will be processed at a nominal throughput of 1,800t a day to produce lead and zinc concentrates. 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 will make use of the existing infrastructure at its operations in the Cosalá district. The mine will be accessed through an existing road from the town of Cosalá. A 1.5km section of the road will be 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 will be made 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 will be sourced from a dam located in a nearby creek, which will be pumped to a storage tank placed above the main portal for distribution within the mine.
Other facilities will 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.