Overview
The Los Filos mine consists of two open pit mines (Los Filos and El Bermejal) with common heap leach, wet plant and ancillary facilities. Los Filos is located in the Nukay mining district of central Guerrero State in southern Mexico. Commercial production for Los Filos commenced January 1, 2008 and in 2009 Los Filos became Mexico's largest producer.
Gold production for 2009 totaled 239,000 ounces. Los Filos is forecast to produce an average of 300,000 ounces of gold per year.
On 31 March 2005, Goldcorp completed the acquisition of El Bermejal deposit, located some two kilometres south of the Los Filos deposit. The Los Filos and El Bermejal deposits will be developed as a twin open pit-heap leach operation, with two different methods of ore processing. Higher grade ore from within the Los Filos deposit will be crushed to 19mm and agglomerated before being conveyor stacked and heap leached. Lower grade ore from Los Filos and El Bermejal deposits will be hauled from the open pit directly to the leach pad to be bulk heap leached. The recovered solution will be treated to produce a final gold doré product on site.
Location
The Los Filos Project is located in the Nukay mining district of central Guerrero State in southern Mexico, approximately 230 kilometres south of Mexico City. This district hosts the Nukay, Aguita, Subida, Guadalupe, El Carmen, Lucero, and San Juan mines.
The property is located at the Village of Mezcala and is accessible from Highway 95, a major paved route between Mexico City and Acapulco. A former 8.5 kilometre dirt road leading to Los Filos and El Bermejal areas was widened and paved as part of the Los Filos project scope. Driving time from Mexico City is approximately three hours.
The project area is served by a network of local roads and the principal centre of population is Mezcala. International airports are located at Mexico City and Acapulco and there are a number of regional airports, principally serving the southern Pacific coast. The Nukay district is served by hydroelectric power from the Caracol dam on the Balsas River. Potable water is available from local springs and wells.
Geology and Mineralization
The Los Filos Project is located in the Morelos-Guerrero Basin in southern Mexico. The roughly circular basin is occupied by a thick sequence of Mesozoic platform carbonate sediments comprising the Morelos, Cuautla and Mezcala Formations, and has been intruded by a number of granitoid bodies.
Regional Geology
The region of southern Mexico is underlain by a cratonic assemblage, approximately 2,000 metres thick of moderately to strong folded Mesozoic platform carbonate and clastic rocks. The deposits lie near the centre of a large circular-shaped feature known as the Morelos- Guerrero Basin. The basinal sequence is composed of the Morelos, Cuautla and Mezcala Formations. The carbonate sequence of the Morelos-Guerrero Basin is underlain by Precambrian and Paleozoic basement rocks. The majority of the metallic mineralization (gold and massive sulphide) is hosted by the Morelos Formation which is a Cretaceous-age medium-bedded to massive fossiliferous limestone up to 900 metres thick. The Cuautla and Mezcala Formations are made up of shales and thin-bedded limestones.
The sedimentary formations were subsequently intruded by granodioritic plutons and related phases of dioritic stocks and dike intrusive bodies. The associated hydrothermal activities lead to the local development of alteration halos in the sediments surrounding the intrusives, including the formation of hornfels in argillaceous formations and, more importantly, marble within calcareous formations.
The Cretaceous sediments and granitoid intrusions are unconformably overlain by a sequence of intermediate volcanic rocks and alluvial sediments (red sandstones and conglomerates) which partially cover the region.
Regional structures in the Morelos-Guerrero Basin include sets of northeast-and-northwest-striking faults and fractures which cut both the carbonate sequence and the intrusives. The distribution of intrusive bodies in northwest-trending belts is thought to reflect the control on their emplacement by northwest trending faults.
Gold, silver and base metal mineralization in the Nukay area is spatially and temporally related to the emplacement of early Tertiary porphyritic diorites, tonalites and granodiorites into the carbonate sequence of the upper Cretaceous Morelos Formation. Mineralization is either hosted by or spatially associated with, marble formed during contact metamorphism of the carbonates. Massive magnetite, hematite, goethite and jasperoidal silica, with minor associated pyrite, pyrrhotite, chalcopyrite and native gold typically occur in the veins and metasomatic replacement bodies that developed at the contacts between the platform carbonates and intrusives.
The Nukay area lies along the crest of an antiform or uplifted ridge, 6 to 8 kilometres wide and trending north-northeast. The age and genesis of the anticlinal feature has not been established but is believed to be related to compressional forces during the late Cretaceous Laramide orogenic event.
Regional mineralization styles comprise the skarn-hosted and epithermal precious metal deposits and volcanogenic massive sulphides. In Guerrero, these occur as two adjacent arcuate belts, with the gold belt lying to the east and on the concave margin of the massive sulphide belt. Both are approximately 30 kilometres wide and over 100 kilometres long, from northwest to southeast, between Mochitlán and Telolapan. Skarn hosted and epithermal precious metal deposits include Todos Santos, Nukay, Bermejal and Mochitlán. Volcanogenic massive sulphide deposits (gold-silver-lead-zinc-copper) include Campo Seco, Farallon and Rey de Plata.
Local Geology
In the Los Filos area mineralization, which includes both Los Filos and Bermejal deposits, is associated with three diorite to granodiorite stocks that were emplaced in carbonate rocks of the upper Cretaceous Morelos Formation. The stocks, known as East, West, and Bermejal are early Tertiary in age and resulted in high temperature calc-silicate and oxide metasomatic alteration (skarn) assemblages that were followed by distinct meso- to epithermal alteration. The Los Filos deposit formed along the north, east and southern margins of the East stock that geologic evidence and argon dating have indicated is slightly older than the West stock.
The differing morphology of the East and West Nukay stocks is believed to reflect different structural controls during emplacement. The exposure of the West stock is roughly circular and about 1.3 kilometres in diameter. The East stock is elongate in a north-south direction. It is about 1.4 kilometres long and 0.5 to 0.7 kilometres wide in the south but in the north, a western lobe extends for one kilometre in a west-southwest to east-northeast direction.
Similar to West stock, El Bermejal is a circular stock about 600 metres in diameter with an important structural control on the mineralization. The first structural system was regional northwest trending faulting, interpreted as being of deep seated origin. It is of late-Cretaceous age and does not cut Tertiary volcanics. This system appears to control the distribution of the ore-forming stocks at Gudalupe-Bermejal.
Marble beds consistently dip away from the margins of the East stock, indicating that the diorite was emplaced during active doming of the Morelos Formation. In contrast, the West and Bermejal stocks generally have steep-sided, simple contacts and do not show any sill-like extensions, suggesting that the diorite was passively emplaced during a period of tectonic quiescence.
Mining & Operations
A mine plan was developed for the project to process a total of 24 Mt/a of ore. Three ore types have been identified for processing discretely; these are: a) crushed and agglomerated leach ore from Los Filos only; b) run-of-mine ore from Los Filos; 3) run-of-mine ore from Bermejal.
Crushed leach ore from Los Filos will be processed at the rate of 4 Mt/a. ROM ore from both Los Filos and Bermejal is scheduled to make up the remaining 20 Mt/a to meet the total ore requirement of 24 Mt/a. The peak total material rate for the project is 66 Mt/a.
The mine is scheduled to work 365 days per year. Each day will consist of two 10 hour shifts and three mining crews will cover the operation.
The final pit designs are based on floating cones run at gold prices of US$425/oz for Los Filos and US$400/oz for Bermejal.
Processing
The project has been designed as a heap leach operation utilizing a multiple-lift, single-use leach pad. Crush leach (higher grade) ore will be processed by crushing, agglomeration and heap leaching. Low grade ore will be processed by ROM heap leaching.
Crushing of the higher grade ore will comprise a two stage, closed circuit system. The crushed product will discharge via a specially developed mine shaft to an overland conveyor and radial stacker system to a stockpile. Ore will be reclaimed from the stockpile and fed to an agglomeration drum where cement will be added to the crushed material together with barren process solution and mixed with high strength cyanide solution.
A series of pad overland conveyors will transport the agglomerated crushed material to a Rahco system that will construct the heap. ROM ore will be stacked using trucks and bulldozers. The stacked ores will be leached using a drip irrigation system for solution application.
Gold and silver recovery will take place in a carbon adsorption-desorption-recovery plant utilizing four trains of five cascade columns each. Commercial production at Los Filos began January 1, 2008.
