The Trinidad silver-gold deposit at the San Jose Mine is a typical low-sulfidation epithermal deposit according to the classification of Corbett (2002), having formed in a relatively low temperature, shallow crustal environment. The deposit is characterized by structurally controlled hydrothermal breccias, crackle breccias and quartz-carbonate veins hosting silver-gold mineralization plus trace to minor base metal mineralization.

Precious metal mineralization at the San Jose Mine is hosted by hydrothermal breccias, crackle breccias, quartz-carbonate veins and zones of sheeted and stockwork-like quartz-carbonate veins emplaced along steeply dipping north and north-northwest trending fault structures.

The mineralized structural corridor extends for greater than 3 km in a north–south direction and has been divided into two sectors. The Trinidad Deposit area located between 1846500N and 1847800N, and the San Ignacio area located between 1845000N and 1846500N. The Victoria mineralized zone is located approximately 350 m to the east of the Trinidad Deposit.

The major mineralized structures or vein systems recognized in the Trinidad Deposit area are the Trinidad and Bonanza structures and the Stockwork zones. In addition to the major mineralized structures, secondary vein systems are present between the Trinidad and Bonanza systems and locally in the hanging wall to the Bonanza system and also in the footwall to the Trinidad system. To-date, drilling has defined the Trinidad and Bonanza mineralized structures over a strike length of approximately 1,300 m and to depths exceeding 600 m from the surface, with average thicknesses of the veins ranging from 1.5 m up to 50 m in some areas of the main Stockwork Zone.

Trinidad vein system
The Trinidad vein system (Tv) is emplaced in the footwall fault zone of the extensional system hosting the mineralized vein systems at the San Jose Mine. The Trinidad vein system strikes 355 degrees and dips 70 to 80 degrees to the east–northeast. The vein system ranges from less than one meter to locally over 15 m in true width, with higher grade mineralization generally being present in zones with greater widths. Significant portions of the Trinidad structure are characterized by late, black matrix, silicified fault breccias with only trace to weak mineralization. Higher-grade precious metal zones in the Trinidad vein system vary from 200 g/t to as much as 1,300 g/t Ag Eq across the width of the vein. Combined copper, lead and zinc values are generally less than one percent but locally higher concentrations are present. At approximately 1,100 masl in the central portion of the Trinidad Deposit, four drill holes intercepted higher-grade base metal mineralization. Fault gouge seams are commonplace at the footwall and hanging wall of the Trinidad vein system. The Trinidad hanging wall splays and the Trinidad footwall veins are considered to be part of the Trinidad mineralized structure.

Since late 2017 it has been observed that fluorine levels are not consistent throughout the Trinidad vein, with levels varying from 500 ppm in the central and lower portions of the vein system to above 5,000 ppm and even 10,000 ppm in certain areas in the north. High fluorine concentrations are generally, but not always, related to low silver–gold mineralization, and are thought to be related to a late stage of mineralization. Stopes where the highest fluorine levels have been encountered include J, R, S, G1 and the northern part of H1, located between elevations 1000 to 1300 masl.

Bonanza vein system
The Bonanza vein system (Bv) is emplaced in the hanging wall zone of the structural corridor hosting the mineralized vein systems in the Trinidad Deposit. The Bonanza vein system generally strikes 350 degrees and dips steeply to sub-vertical to the east. The Paloma vein (Pv) is considered to be part of the Bonanza vein system. Mineralization within the Bonanza vein system is present in the form of shoots plunging shallowly to moderately to the north-northwest, reflecting the dominant dip-slip movement of the controlling fault structures. Combined copper, lead and zinc values for the Bonanza vein range from negligible in the upper portions of the vein system to approximately 0.1 to 0.5 % at depth.

Stockwork Zone
The main Stockwork Zone (Swk) is located between 1846550N to 1847200N and 1,000 masl to 1,300 masl, being situated in an extensional environment between the principal Bonanza and Trinidad structures. The main Stockwork Zone is present over 650 horizontal meters and 300 vertical meters being elliptical in shape, with a variable thickness ranging to greater than 50 m.

The primary silver-bearing mineral in the main Stockwork Zone is acanthite, usually in association with traces of pyrite. Secondary minerals accompanying the acanthite are silver-rich electrum, fine-grained galena, sphalerite, chalcopyrite and gangue minerals including hyaline quartz, white quartz, and calcite, together with minor concentrations of adularia and fluorite.

In addition to the main Stockwork Zone, exploration has identified the Stockwork 2 (Swk2) and Stockwork 3 (Swk3) zones, located in the north of the Trinidad Deposit area between the Trinidad and Bonanza veins. Definition drilling has demonstrated that the Stockwork 2 and Stockwork 3 zones are similar to the main Stockwork Zone and appear to be interconnected.

Fortuna vein system
The Fortuna vein (Fv) strikes north–south and, in contrast to the other major veins in the Trinidad Deposit, dips steeply to the west. The Fortuna vein has been extensively mined on levels 2, 3 and 4 of the historic mine workings with vein widths ranging from approximately 2 to 5 m.

Secondary vein system
In addition to the Trinidad, Bonanza, Paloma, Stockwork, Stockwork 2, Stockwork 3, and Fortuna veins, a number of secondary veins have been intersected by exploration and definition drilling. These include the Bonanza Hangingwall (Bhws), Trinidad Footwall (Tfw), Trinidad Footwall 2 (Tfw2), Trinidad Footwall 3 (Tfw3), and Trinidad Hanging Wall (Thws4) veins.

Victoria mineralized zone
The Victoria mineralized zone is located approximately 350 m east of the Trinidad vein and north of the current underground operations of the San Jose Mine. It is structurally related to the same extensional regime that dominates the Trinidad Deposit with a similar style of mineralization, corresponding to a low sulfidation epithermal deposit formed in a shallow crustal environment with a relatively low temperature resulting in the precipitation of silver and gold mineralization. Formation temperatures are believed to be on average less than 250°C with salinities less than 1.8 %wt NaCl. Mineralization is hosted in breccias and quartz–carbonate veinlets with a general northwesterly direction and an approximate dip of 65 degrees to the northeast. The dominant alteration within the structural system is argillic, grading to propylitic towards the periphery. The hosting lithology is related to effusive volcanoclastic facies and flows of andesitic/dacitic rocks possibly of Paleogene age.

The method chosen for underground mining is overhand cut-and-fill which removes ore in horizontal slices, starting from the bottom undercut and advancing upwards. When ore widths are greater than 8 m, a combination of overhan cut-and-fill and room-and-pillar methods has been selected as the most appropriate for the conditions encountered.

Mechanized mining uses a Jumbo drill rig to drill blast holes, scoop trams for loading and trucks for ore haulage. Rock support is provided through rock bolts and shotcrete. The deposit width ranges from 4.5 m to 17 m for the Bonanza and Trinidad vein systems and can be more than 30 m in the Stockwork Zone. Mechanized mining is regarded as the only methodology suitable for all veins based on the geological structure and geotechnical studies to date. The mechanized mining sequence includes: drilling (with a Jumbo drill rig), blasting, support, loading (by scoop tram) and haulage:

1. Ore is extracted from the stope in horizontal slices that span the entire width and length of the stope using pivot cuts of up to ±15 % gradient.

2. After the stope has been mined out, voids are backfilled with paste or waste rock. The key performance indicators for this activity sets 85 t/h production rates for rock waste and 100 to 150 t/h for paste fill.

3. Drilling of horizontal slices is conducted in sections of 6 m by 6 m by mechanized jumbos which have a boom length of 5 m.

4. The blast pattern is charged with an explosive made up of emulsion and ANFO. The average power factor applied in the blasting is 0.45 kg/t for stopes. After the mine face has been blasted and ventilated, scaling of loose rock is conducted. This is an important phase of the mining cycle in terms of safety due to the risk of falling rock.

5. Mucking is done by scoop trams (6 yd3 capacity) from the face to an underground stockpile in the stope. Trucks with 14 m3 capacity transport the broken ore from the stopes to the surface stockpiles using a paved ramp which allows speeds of up to 25 km/h.

6. Required support is defined by the Geomechanics Department.

Access to the San Jose underground mine is from surface through a main ramp with a total average gradient of 10 % and dimensions of 4.5 m width by 4.5 m height.

The San Jose Mine has been designed with a separation of 100 m between levels primarily to limit blast vibration but also to assist with hanging wall and footwall stability.

The ventilation requirements for the mine to produce 3,000 tpd is 548,169 cfm. The ventilation system brings all the intake air through the main ramp and three main airway networks. Exhaust air is forced to the surface from inside the mine by three principal fans, two operating at 250,000 cfm and one at 120,000 cfm.

Crushing
Crushing at the San Jose Mine is a dry process, where ore extracted from the mine is reduced in size from 406 mm to 12.7 mm to be fed to the mill.

The crushing process begins at the reception hopper, where ore from the mine is deposited. The ore is fed from the bottom of the hopper via a plate feeder into a jaw crusher that crushes the ore to a 102 mm product size prior to it being transported via conveyors to one 2.44 m by 6.1 m primary screen deck. The screen deck operates with one mesh of 35 mm opening. Material that does not pass through the 35 mm mesh is sent to a secondary crusher via a chute, where it is reduced to 25 mm and the product returned to the primary screen deck. The material that passes the 35 mm mesh is sent via a conveyor to one 3 m by 7.3 m secondary screen deck. The screen deck operates with one mesh of 12.7 mm opening. Material that does not pass through the 12.7 mm mesh is sent to a tertiary crusher where it is reduced to 12 mm size before being sent back to the jig to close the circuit. The fine ore that passes through 12.7 mm mesh is sent to fine ore storage, achieving a final product of 12.7 mm that is stockpiled before being fed into the milling circuit.

Milling and classification
The fine ore stock is sent via conveyor belts to either a 3.96 m by 5.94 m or 4.57 m by 6.6 m ball mill with 25 to 30 % of their volume filled with three inch wrought steel balls used to further reduce (grind) the ore size. The product of the mills is pumped to the classification process comprised of hydro-cyclones, where two products are generated; 1) a fine ore, which is expulsed thorough the top of the cyclones, and 2) a coarse ore that exits through the bottom and is recycled back into the mills for further grinding. The fine ore must comply with the metallurgical conditions for metal recovery, which indicates 80 % of the product must be under the 200 mesh size (equivalent to 74 µm), before being sent to the flotation process.

Expansion of the concentrate plant was successfully completed in June of 2016 taking the ore throughput capacity from 2,000 dry tpd to 3,000 dry tpd. The principal stages are follows:
1. Crushing
2. Milling
3. Flotation
4. Thickening, filtering and shipping.

Flotation
The pulp (water + mineral) received from the fine ore of the hydro-cyclone, is first sent to a flotation stage performed in ten mechanic cells, six 14.2 cubic meter and four 17 cubic meters in size, which generate agitation through a propeller and diffuser that distributes the pulp and injects air. The agitated pulp allows reagents to act on the elements of value and adhere to the bubbles formed by the injected air, freely spilling over the edges of the cells into a collection trough. The resulting product is known as the primary concentrate. Upon conclusion of this first stage, the pulp is sent by gravity to a second stage.

The second flotation stage is similar to the first ........