The mineralization at ESM has been classified as sedimentary exhalative (Sedex) in origin. The composition of the mineralization is unique, composed of primarily massive sphalerite and only minor galena and pyrite. Massive and semi-massive sphalerite-bearing deposits occur in siliceous dolomitic and evaporite-bearing marbles of the Upper Marble Formation of the Balmat-Edwards marble belt. These zinc-sulphide deposits lie in the core of the Sylvia Lake Syncline, a major poly- deformed fold lying between Balmat and Edwards. Zinc mineralization tends to follow evaporate deposition in the stratigraphic sequence. The region has experienced multiple metamorphic and intrusive events and large-scale ductile structures are common.

The property contains 14 known zones of sphalerite mineralization. Three clusters have been defined consisting of three to five deposits each. Geometry of mineralization varies, ranging from tabular to podiform and shallow to steeply dipping. Areas defined to date contain tonnages ranging from roughly 0.5 Mt to over 10 Mt. Typical thickness ranges from 2 ft to 12 ft thick. Mineralization tends to be very continuous along strike, ranging from 50 ft to 800 ft Plunge-lengths may exceed 6,000 ft.

There are two mineralization styles recognized in the district. Stratiform high-grade massive sphalerite is interpreted as primary mineralization contemporaneous with deposition of the Upper Marbles. Discordant breccia-like “durchbewegung” texture ........

The mine utilizes a combination of selective longhole stoping, modified or stepped room and pillar and mechanized Cut and Fill as mining methods, based on the geometry and the grade of the mineralized zones:
- Longhole stoping (“LH”) for mining blocks dipping steeper than 45°, which represents about 50% of the mine plan tonnage. This is the preferred mining method from a productivity and operating cost perspective;
- Mechanized Cut and Fill (“C&F”), for mining blocks with dips of less than 45° and zones not amenable to LH stoping, is more selective and represents about 7% of the mine plan tonnage;
- Modified or Stepped Room and Pillar (“RP”), for mining blocks with dips of less than 45° and grades, do not warrant the application of a fill to permit multiple panel extraction, representing 11% of the mine plan tonnage.

The mine plan tons at the ESM deposit will be extracted using a combination of longitudinal retreat stoping (LGS), Cut and Fill (C&F), Panel Mining – Primary and Secondary (PAP & PAS), and development drifting underground mining methods with rock backfill. Longhole backstopes (BCK) are also used in the design where applicable. The proposed combined underground and open pit mine plan is expected to reach an initial target production rate of 1,200 t/d for 2021 and ramp up to 1,800 t/d in 2022. Open pit mining will be completed in Year three (2024). The overall mine life will be seven years.

Underground
The ESM deposit will ........

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Mineralized material mined in the ESM deposits is processed at the existing ESM concentrator that was commissioned in 1970 and last shut down in 2008. The concentrator was refurbished in late 2017 and began processing mineralization in 2018. The concentrator flowsheet includes crushing, grinding, sequential lead and zinc flotation circuits, concentrate dewatering circuits, and loadout facilities.

The design capacity of the concentrator is 5,000 t/d. Through-out the history of the Balmat operation (now ESM), the capacity of the concentrator has exceeded that of the mines’ capacity. The operating strategy is to operate the concentrator at its rated hourly throughput of 200 t/h to 220 t/h, but for only as many hours as necessary to suit mine production. It currently is processing between 6,500 to 7,000 tons per week operating on a schedule of one shift per day, four days per week. The concentrator suffers no notable losses from intermittent operation.

Lead flotati ........