FGM, as a London-based company, was established in Segovia by émigré Cornish miners in 1852 and has been in continuous operation since. Total gold production by FGM to date is officially recorded at 5.5 Moz, with an overall estimate for the region of between 8-9 Moz. FGM has worked a large number of veins within its licence area and currently operates three principal underground mines:
• Mina El Silencio, worked since 1852 and currently producing from pillar robbing operations. The vein strikes NNE-SSW, dipping at 35º to the east. Mined strike length is up to 3 km and workings reach a maximum depth of over 800m below surface (mined over nearly 2,000m on dip).
• Mina Providencia, worked since 1980 and currently the main production operation for FGM. The vein strikes WNW-ESS, dipping at 35º to the north. The strike length mined is up to 2,000m and workings are currently 240m below surface.
• Mina Sandra-K, has worked since 1995 and remains under development with limited production.
In addition, Frontino Gold Mines has reserves and resources at a further ten mines (Mina La Santillana, Las Brisas, Puente Tierra, Los Escalantes, La Pitosina, Cecilia, Los Naranjos, La Laguna Azul, Cristales and Marmajito).
Various estimates of the current status of reserves are available for FGM, with the most commonly quoted dating from 2006:
Providencia, proven 538,000t @ 11.3 g/t gold; nil probable:
Sandra K, proven 55,000t @ 13.0 g/t gold, probable 660,900t @ 13.1 g/t gold.
Gold grades are highly variable within veins and the main gold production in artisanal mines has been to follow high grade ore shoots. In the case of FGM, gold grades vary from <1 g/t to >100 g/t gold within high grade “Criaderos” over the standard 2m sampling interval along level drives within its mines.
Typically, veins also contain variable quantities of simple sulphides; pyrite pyrrhotite- marcasite, sphalerite and galena. High sulphide content is often associated with areas of high gold grades, although no other direct correlation exists between gold and base-metal grades.