The Yaxtché deposit shows alteration assemblages typical of high sulfidation epithermal deposits whereas the metal content and sulfide assemblages are characteristic of mineralizing fluids with an intermediate sulfidation state.

The transition from high- to intermediate-sulfidation state is thought to define an evolving epithermal system as high-sulfidation state metal-bearing fluids cooled and interacted with host rocks as they moved vertically and laterally though the Yaxtché structure. This is depicted with three stages of primary fluid evolution:

• Alteration and gangue mineral assemblages related to acidic magmatic–hydrothermal fluids created permeability through acid leaching (i.e. vuggy silica)
• High-sulfidation state mineral assemblages (namely enargite–luzonite–famatinite) and metal contents (copper–gold dominant) formed at lower elevations within the Yaxtché structure
• Transition of high- to intermediate-sulfidation state as metal-bearing fluids ascended and further interacted with host rocks. The final phase of fluid evolution was critical for precipitation of silver-bearing minerals as tennantite–tetrahedrite became stable.

Sillitoe and Hedenquist (2003) defined the following key features of intermediatesulfidation systems:

• Intermediate-sulfidation deposits occur in calc-alkaline andesitic–dacitic arcs, although more felsic rocks can locally act as mineralization hosts
• The arcs typically display neut ........

Preliminary work was performed on four possible mining systems: post-pillar cut-andfill, transverse with pillars, transverse with cemented fill, and sublevel with end slicing.

The post-pillar cut-and-fill mining method was selected for the PEA evaluation.

This mining method relies on using 5 m x 5 m rooms and 5 m x 5 m square pillars. The pillars of one level are planned to align vertically with the next mining level to provide support. Mining starts at the lowest elevation in a mining area and is completed working upward. Some pillars can be extracted when they occur in an area of the stope where there will be no mining above.

Productivity calculations and unit costs for the final selection of a post-pillar cut-and-fill mine plan are based on the following criteria:

• Two 10 hr shifts per day, which yield 16 hr of actual work time
• The ground is considered medium–hard for the drilling and blasting variable
• Drilling of 18 ft (5.5 m) holes (providing 16.6 ft (5.1 m) of advance) with a two-boom production jumbo. Hydraulic drifter (drill) penetration rate is assumed to be 3.5 ft/min (1.1 m/min)
• No standard ground support is indicated; however, 1.5 hr per cycle is allotted for ground control (e.g. rock bolting), spot bolting or other cycle interruptions
• Blasting will be carried out using gelatin-class dynamite and ammonium nitrate/fuel oil (ANFO) as the primary blasting agent. Non-electric (non-el) type de ........

- subscription is required.