El Mochito — 2018 Technical Report

Operating profile from the May 25, 2018 Technical Report (effective January 1, 2018) describing the El Mochito concentrator and crushing circuit in Honduras. Process route: crushing, rod/ball mill grinding, differential lead-zinc flotation, thickening and vacuum disc filtration.

Report context

This profile is drawn from Section 17.0 (Recovery Methods) of the Ascendant Resources Inc. 2018 Technical Report on the El Mochito Mine, prepared by P&E Mining Consultants Inc. and Mercator Geological Services Limited. The report is dated May 25, 2018 with an effective date of January 1, 2018. The report describes operating conditions observed during a February 2018 site visit, and all data and observations show that period unless stated otherwise. No later expansion study or December 2018 modifications are incorporated.

Processing route

Crushing facility

Run-of-mine ore is hoisted in 10 t lifts via the #2 shaft into a small surge bin, with a reciprocating feeder drawing ore onto conveyor belt #1. A metal detector stops this belt for manual tramp-iron removal. Ore passes along a long conveyor (#2) to the coarse ore bin. Draw from the coarse ore bin uses a vibrating grizzly feeder with 2-inch bar gaps. Oversize (+2 inch) reports to the primary crusher: a Pioneer 3042 single-toggle jaw crusher set at 2 inches. Undersize (-2 inch) bypasses the jaw crusher. Both streams discharge onto conveyor #3, which passes under a static magnet for magnetic metal removal.

Conveyor #3 discharges onto conveyor #4, then onto a double-deck vibrating screen. The top deck has 1¼-inch apertures, the bottom deck 5/8-inch (temporarily replaced with ¾-inch in February 2018 to address plugging from wet ore). Screen oversize reports to a tertiary 5½-foot Symons short-head cone crusher set at 5/8-inch, in closed circuit with the screen. Screen undersize (-5/8 inch) reports to conveyor #6, then to five fine ore bins. Two 30-tonne capacity Dux trucks transport crushed ore 1.5 km by road to the mill feed bin.

The crushing circuit also includes a secondary 4-foot Symons standard cone crusher in open circuit with a single-deck vibrating screen (2-inch apertures). This secondary portion was not operating as of February 2018; the report states El Mochito intended to recommission it in the near future. Average crushing throughput was 154 t/h over 11 or more hours per day.

Wet ore (the mine discharges about 1,800 m³/h of water) contributes to significant conveyor spillage, transfer-point blockages, and reduced bin capacity due to wet packing. The report notes that both coarse and fine ore bins are flat-bottomed with single discharge points, causing extensive dead ore zones. Very large rocks (“big rocks” exceeding 0.5 m) on conveyors #1 and #2 were being stopped and broken by hand-operated hammer as an interim measure. The report recommends installation of wash systems on conveyor head pulleys and consideration of an ore fines washing facility.

Grinding circuit

The mill feed bin provides 2–4 hours of live capacity. Minus-5/8-inch crushed ore is drawn in parallel by feed chutes and conveyor belts to two rod mills (Denver, 6 ft diameter × 12 ft, 200 HP each). Weightometers on each rod mill feed belt record tonnage. Rod mill product (nominally 1 mm) reports to a primary Krebs cyclone. Cyclone underflow feeds a secondary ball mill (Marcy, 9 ft × 10 ft, 500 HP) in open circuit. The secondary ball mill discharge combines with tertiary ball mill discharge and is pumped to a second Krebs cyclone. Underflow from this second cyclone feeds the tertiary ball mill (Marcy, 8 ft 6 in × 12 ft, 500 HP) in closed circuit. Cyclone overflow reports to lead flotation. Final grind target is 80% passing 65 mesh (212 microns) and 54% passing 200 mesh (74 microns). A zinc regrind ball mill (Marcy, 7 ft 6 in × 12 ft, 300 HP) operates in closed circuit with a cyclone, with overflow returning to zinc rougher feed. Bond Work Index values are reported as 10–14 kWh/t for rod mills and 10.04 kWh/t for ball mills; the regrind mill is 14–16 kWh/t.

Flotation circuits

Differential flotation is practiced: lead is floated first while sphalerite is depressed with a mixture of sodium cyanide and zinc sulphate. Zinc is then activated with copper sulphate and floated from the lead flotation tails.

The lead flotation circuit comprises:

• Two 12 m³ Gallagher rougher cells
• Two 12 m³ Gallagher middling cells
• Four 12 m³ Gallagher scavenger cells
• Four Denver cleaner cells

Rougher concentrate reports to the cleaner cells. Final lead concentrate from the cleaners goes to the lead thickener. Cleaner tails return to rougher feed. Middling concentrate returns to rougher feed; scavenger concentrate goes to middlings feed.

The zinc flotation circuit comprises:

• Three 12 m³ Gallagher rougher cells
• Three 12 m³ Gallagher middling cells
• Four 12 m³ Gallagher scavenger cells
• Two banks of Denver cleaner cells

Rougher concentrate is pumped to the second bank of cleaner cells. Middling and scavenger concentrates go to the first bank of cleaner cells. Final zinc concentrate from the final cleaner cells flows by gravity to the zinc thickener. Tails from final cleaners return to secondary cleaner feed. Tails from primary cleaner cells go to the regrind ball mill discharge pump box.

Zinc scavenger tails bypass an installed magnetic separator unit (two magnetic drum separators) designed for magnetite recovery. Magnetite recovery was suspended at the report date pending a potential sale or off-take agreement.

Observations during the site visit: Several flotation cells showed unstable froth conditions; Gallagher cells are described as “old school” and difficult to control, with cell level controllers being acquired. Zinc flotation was observed to be slow and incomplete with significant magnetite activation in scavenger cell froth. The report recommends considering replacement of rougher-scavenger cells with more modern units. Reagent feeders (Clarkson type) were in very poor condition due to corrosion and reagent crystallization; electronic feeders are recommended.

Concentrate dewatering and handling

Lead concentrate: one thickener, underflow pumped to one 5-disc vacuum disc filter. Filter cake (9.5–10.0% moisture) is conveyed to the lead concentrate shed. Thickener overflow is pumped to the milling circuit as process water.

Zinc concentrate: a primary and a secondary thickener; primary thickener underflow is pumped to two Eimco 5-disc disc filters. Filter cake (10.5% moisture) is conveyed to the zinc concentrate shed. Zinc thickener overflow is used as launder spray water in the zinc circuit. Flocculant is added to both thickeners.

Concentrate is trucked six days per week to a warehouse at Puerto Cortes, 140 km away, due to limited storage at site. Trucks are loaded with an average 24.5 short tons (22.2 t) of concentrate, weighed, and loaded to about 38 short tons (34 t) to comply with the Honduras road limit of 39 short tons (35 t). At port, concentrates are offloaded and stockpiled in warehouses, then transferred to ships via flatbed trucks and a mobile telestacker or truck-tipping. Ship draft surveys confirm loaded weight.

Tailings and water management

Fine tailings from the mine backfill plant (located near the crusher facility) are returned to the concentrator, where sodium metabisulphite is added for cyanide detoxification and lime maintains alkaline pH. Tailings are then pumped 3.5 km to the La Soledad lined valley tailings storage facility, discharged from the edge via spigots. Pond water is decanted from a floating barge and tested for compliance before environmental discharge. The report notes the facility was expected to contain tailings for up to three more years, with options including cycloning or thickened disposal to extend capacity. The report also notes consideration of recycling tailings water to the mill, potentially with activated carbon to remove copper if needed.

Two older tailings facilities exist on the property: El Bosque (from early 1970s, ~5 Mt) and Pozo Azul (~10 Mt, used until 2013). Both have received remedial work. The report states El Mochito tailings are neither acid generating nor metal leaching, with healthy natural vegetative cover on the El Bosque TSF.

Metallurgical performance

Reported actual 2017 recoveries: 74.25% lead in lead concentrate, 88.9% zinc in zinc concentrate, 52.06% silver in lead concentrate, 25.7% silver in zinc concentrate, total silver recovery 77.8%. Actual January–March 2018: 74.5% lead, 92.0% zinc, 49.1% silver in lead concentrate, 27.5% silver in zinc concentrate, total silver 76.6%. The report states that despite head grades below budget, 2017 recoveries exceeded budget and appeared to be increasing. P&E suggests reasonable recovery expectations of 75% lead, 89% zinc, and 72% total silver (51% to lead concentrate, 21% to zinc concentrate).

Key reported parameters

Technical qualifications

This profile is drawn exclusively from Section 17.0 (Recovery Methods) of the May 25, 2018 Technical Report effective January 1, 2018. All data, observations, and recommendations show conditions during a February 2018 site visit by P&E Mining Consultants Inc. The report describes installed equipment and operating practice at that time; some described improvements were planned or recommended but not yet implemented. The crushing circuit includes a secondary crusher not in service during the visit that the mine intended to recommission. Flotation cell level controllers were being acquired but not yet installed. Magnetic separators for magnetite recovery were installed but not operating. The secondary screen bottom deck was temporarily changed from 5/8-inch to ¾-inch in February 2018 to address wet-ore plugging,this temporary configuration is noted, not a permanent design. Tailings capacity estimates and options for extension are described as under consideration, not committed. The report acknowledges that observations during a short visit may be based on incomplete information. No resource or reserve calculations are included in this profile.

Source: Ascendant Resources Inc., 2018 Technical Report on the Mineral Resources and Mineral Reserves of Ascendant Resources Inc. Producing El Mochito Mine in Honduras, dated May 25, 2018, effective January 1, 2018. Section 17.0 Recovery Methods.