The Merian Operations lie within Lower Proterozoic-aged rocks of the Guiana Shield. The northeast portion of Suriname is dominated by rocks of the Marowijne Supergroup which comprise the Rosebel Formation and the underlying Armina Formation. Mineralization discovered to date is consistent with an orogenic gold deposit model.

The deposits are structurally-controlled by a northwest-trending, southeast-plunging antiform (the Merian antiform) that has been interpreted from mapping and geophysical data. Northweststriking, moderate- to steeply-dipping faults and shear zones occur along the axial trace and limbs of the Merian antiform. Gold mineralization occurs in association with quartz veins, stockworks and breccias along these northwest-trending structural zones. Minor disseminated mineralization can occur adjacent to the quartz vein zones. A set of low-angle veins also occurs throughout the Project area and is interpreted to occupy low-angle imbricate thrust fault zones. The veins may be cross-cut by later, mineralized, quartz breccia bodies. Northeast and east–west-trending faults, which are also interpreted to have pre- and post-mineral displacement, cross-cut the Merian antiform and may, in part, bound or localize mineralization along the northwest-striking structural fabric.

At both Merian II and Maraba, gold mineralization is associated with quartz veins and breccias. Higher gold values are associated with higher vein density at both deposits. At Merian II, the highest gold values correlate with quartz breccias. Quartz veins range from several percent to 60–80% of the rock volume. Mineralization at Merian I is associated with quartz veins, but the breccias that are common in Merian II and Maraba do not occur.

In fresh rock, trace-to-several percent pyrite, pyrrhotite, and magnetite locally occur in, and adjacent to, quartz veins and breccias. Trace amounts of chalcopyrite, bornite, and molybdenite have been identified in fresh rock and in drill core.

In core and thin sections, gold has been observed in quartz veins, late fractures in quartz, in quartz vein selvages, and along mineral grain boundaries such as quartz/ankerite and quartz/pyrite. Gold appears to be late in the paragenetic sequence. Gold also occurs disseminated in the wall rock associated with pyrite and/or chlorite–carbonate–ankerite forming lower grade halos which can extend from a few to tens of meters around zones of higher vein densities. Intense white clay (kaolinite) alteration is indicative of some of these disseminated zones or halos in the saprolite or saprock.

Merian II is currently in production and is mining above and below the saprolite–fresh rock interface.

Gold mineralization at Merian II occurs over a strike length of approximately 3.5 km, is elongate in a northwest–southeast direction, is 200–600 m wide and has been drill-tested to a depth of 675 m. The deposit is interpreted to occur along the axial trace of the Merian antiform.

Two distinct structural styles of mineralization are identified:
• Gold mineralization associated with northwest striking, shallow- to moderatelynortheast-dipping sheeted and/or tabular quartz vein zones and quartz stockworks;
• Gold mineralization associated with higher-angle, northeast-dipping veins and irregular quartz breccia bodies.

A northwest-striking, northeast-dipping quartz breccia body referred to as the “92 shoot” forms the core or central portion of the deposit. The “92 shoot” quartz breccia consists primarily of white to gray quartz, albite, ankerite, wall rock clasts and clasts of earlier-formed quartz veins; it is irregular in geometry and ranges in thickness locally from meters to tens of meters. Higher gold grades are associated with the “92 shoot” and quartz breccias. Overall, gold grade increases predictably with increasing quartz vein density and quartz breccias (>90% quartz veins) tend to correlate with higher gold grades.

Moderately dipping sheeted and irregular quartz veins and stockwork zones and minor quartz breccia occur in the footwall and hanging wall of the “92 shoot”. These sheeted and irregular quartz veins may be massive, banded, or have a sugary texture. Individual veins range in thickness from millimeters to 1–2 m thickness and generally occur as mappable zones of veining ranging in thickness from several meters to ±50 m.

All veins and quartz breccias may be locally folded and faulted. Observations made from core logging and mapping of field exposures show that the “92 shoot” quartz breccia is a later event that cross-cuts the earlier-formed sheeted and irregular quartz veins that occur in the footwall and hanging wall of the “92 shoot”.

Saprolite thickness ranges from 20 m to as deep as 140 m (50% ranging from 60–90 m). Deep oxidation or saprolite development occurs both within and adjacent to zones of more intense quartz veins.

Saprock ranges in thickness from zero to tens of meters. Fresh rock occurs below the saprock.
Maraba
Gold mineralization occurs over a strike length of 1.5 km, is elongate in a northwest direction, ranges in width from 50–200 m and has been drill-tested to about 560 m depth. Mineralization at Maraba is interpreted to be located on the east limb of the Merian antiform. The Maraba deposit includes the Kupari sector that is along strike from Maraba and interpreted to be hosted in the same structure but with a non-mineralized gap between the two areas. The Maraba deposit also includes the Maraba South zone to the south of Maraba Main.

Gold mineralization at Maraba occurs with a relatively continuous zone of steeply-dipping sheeted quartz veins with a lenticular core of increased vein density and higher gold grades. Individual veins range in thickness from millimeters to 2-3 m thickness. Vein textures are massive or sugary.

Maraba exhibits the same oxidation states as Merian II: saprolite, saprock and fresh rock. Saprolite thicknesses range from 25 m to as much as 150 m (50% between 60 m to 100 m), saprock thicknesses from zero to tens of meters. In general, the saprolite/saprock and/or saprolite/fresh rock contacts are irregular, but these can be fairly uniform in areas with weathering profiles undisturbed by veins or significant structures.

The Maraba vein zone and gold mineralization is open at depth but narrows along strike to the northeast and southeast.

Merian I
The Merian I deposit is located approximately 3 km to the southeast of Merian II. The geology of host rocks and mineralization is similar in style to Merian II but not as well understood. Three small deposits have been drilled fairly extensively. Mineralization at Merian I is not fully delineated and remains open in several directions.

Mineralization at Merian I has a northwest–southeast strike over a known distance of 2.1 km. Mineralization ranges in width from 25 to 200 m and has been drill tested to a depth of approximately 270 m. Based on geophysical interpretation, a northwest-trending fault may run parallel to, and possibly bound, the mineralization on the southwest side of the deposit but the structural control of mineralization is not well understood.

Mineralization is characterized by irregular quartz stockwork zones and moderate to strong white clay development. Unlike Merian II, there are very few breccia bodies. Oxidation and saprolite development are deeper at Merian I than at either Merian II or Maraba; this may be due to more fractured rock and stockwork veins at Merian I.

Open pit mining is conducted at Merian using conventional techniques and an Owner-operated conventional truck and shovel fleet. Currently, two open pits, Merian II and Maraba are being mined. Three smaller pits, Maraba South, Kupari, and Merian I are planned.

Pit slope design sectors are defined for the saprolite, saprock (transition), and fresh rock; and separate bench configurations are specified for each sector. Design parameters are the same for the Merian II, Maraba and Merian I pits. Bench face slope angles vary from 56–80º. All benches are assumed at 10 m heights.

There are five mining phases planned for the Merian II deposit. A starter phase in the main pit is planned within the final phase of the main pit with a small section of the west wall being common between the starter and main pits for a section of the pit wall. A minimum mining width of 50 m was targeted between the two phases and narrows to about 40 m for certain sections of the pit. The proposed Merian II main pit measures 2,800 m along strike and is roughly 1,000 m wide with a maximum depth of 390 m from 590 to 200 m elevation.

There are three mining phases planned for the Maraba deposit. A starter phase in the main pit is entirely centered within the final phase of the main pit allowing for at least 50 m between the two mining limits. The initial phase has shallower overall slopes than the final phase as it is only in saprolite. The proposed Maraba main pit measures 1,230 m along strike and is 860 m wide with a maximum depth of 300 m from 580 to 280 m elevation.

Merian I will consist of four small pits. The largest pit measures 600 m along strike and is 500 m wide with a maximum depth of 85 m from 590 to 505 m elevation. Merian I pit is expected to be added in 2021.

The double lane ramp width is designed to be 34 m wide and the single lane ramp width is designed to be 19 m wide. Ramp gradients are established at 10%.

A fleet of CAT 785D rigid haul trucks with a 136 t payload was selected to provide a good pass-match with the primary loading units.

Fresh rock from the open pits is crushed using a primary gyratory crusher to a product size of nominally 80% passing (P80) 150 mm. The crushed ore is fed onto a transfer conveyor, equipped with a self-cleaning magnet to remove steel and transferred to a stacking conveyor feeding a crushed ore conical stockpile with a live capacity of 16 hours. Ore from the stockpile is reclaimed using three apron feeders, each capable of feeding 75% of the peak fresh rock mill feed (750 t/h).

Three additional saprolite feeding stations, each comprising a static grizzly, a small bin and an apron feeder, are continuously fed using hydraulic excavators. The feeding stations supply a 13 MW SAG mill with dimensions of 10.36 m (34 ft) diameter by 5.33 m (17.5 ft) effective grinding length (EGL). Discharge from the mill is fed over a vibrating screen for classification and oversize is transferred to the pebble crushing circuit.

The ball mill is 7.32 m (24 ft) diameter with 12.65 m (41.5 ft) EGL and is operated in closed circuit with 650 mm hydro-cyclones. The nominal product size from the grinding circuit is a P80 of 75 µm.

The Merian process plant is designed to treat a range of 8–12 Mt/a of ore depending on the ore mix from mining operations.

The plant design is based on the following parameters:
• A throughput rate of 877–1,725 t/h depending on ore mixture;
• Design availability of 91%, which equates to 7,983 operating hours per year, with standby equipment in critical areas;
• Sufficient plant design flexibility for treatment of a blend of ore types. When fed 100% fresh rock, throughput will be reduced to the processing rate of the grinding area, approximately 7–8 Mt/a, or 992 t/h. If only saprolite is fed to the circuit, the throughput is capped from operational experience, at 1,725 t/h;
• The process flowsheet is based on process units which are well proven in the minerals and gold processing industries. Material handling of the saprolite ore is simplistic in order to avoid mass flow problems with this material; conventional industry engineering practices were inc ........