The Merian Operations process plant in the Republic of Suriname is a conventional gold processing facility designed to treat blends of fresh rock and saprolite ore using well-proven industry-standard comminution and recovery technologies.
The Merian Operations process plant flowsheet design was based on testwork results, previous study designs, and industry standard practices for handling combinations of fresh rock and saprolite. The process flowsheet is based on process units that are well proven in the minerals and gold processing industries. Material handling of the saprolite ore is intentionally simplistic in order to avoid mass flow problems with this material, and conventional industry engineering practices were incorporated in the design and sizing of equipment. The process method is conventional to the industry, with comminution and recovery processes widely used and no significant elements of technological innovation.
The plant was designed with a throughput rate of 877–1,725 t/h depending on ore mixture, and a design availability of 91%, equating to 7,983 operating hours per year, with standby equipment in critical areas. The plant was designed with sufficient flexibility for treatment of a blend of ore types. When fed 100% fresh rock, throughput is 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, throughput is capped from operational experience at 1,725 t/h. The process plant design feed grade is 1.6 g/t Au, with an average life-of-mine grade of 1.22 g/t Au.
The comminution circuit consists of a primary gyratory crusher, a semi-autogenous (SAG) mill, a pebble crusher, and a ball mill. Fine ore particles are delivered to a trash screen and thickened prior to leaching, while coarser material is re-circulated through the grinding circuit. Classification is achieved using hydrocyclones, with gravity concentration incorporated via centrifugal concentrators. The slurry then goes to the tailings processing facility, and the carbon is delivered to the elution circuit where gold is recovered using an electrowinning process. Tailings produced from the plant are treated using a combination of cyanide detoxification and tailings storage facility management.
Energy requirements for the SAG and ball mills vary by domain and deposit. Raw water is supplied by rain water recovered from process plant, power plant, and administration building rainwater runoff, and augmented in the dry season by a groundwater well field.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Plant throughput range | 877–1,725 | t/h | Depending on ore mixture |
| Design availability | 91 | % | 7,983 operating hours per year |
| 100% fresh rock throughput | 992 | t/h | Approximately 7–8 Mt/a |
| Saprolite-only throughput cap | 1,725 | t/h | Based on operational experience |
| Design feed grade | 1.6 | g/t Au | Process plant design basis |
| Average life-of-mine grade | 1.22 | g/t Au | LOMP basis |
| Crushing availability | 70 | % | Both saprolite and rock |
| Crushing throughput | 1,631 | t/h | Both saprolite and rock |
| Crush size | 125 | mm | P80, both saprolite and rock |
| SAG mill energy requirement | 3.75–13.17 | kWh/t | Varies by domain and deposit |
| Ball mill energy requirement | 3.17–13.50 | kWh/t | Varies by domain and deposit |
| Average annual mill power | 165,000 | MWh | To support LOMP |
| SAG mill installed power | 13 | MW | 10.40 m x 5.33 m EGL dual pinion |
| Ball mill installed power | 13 | MW | 7.3 m x 12.65 m EGL dual pinion |
| Gyratory crusher installed power | 600 | hp | 62-inch x 75-inch |
| Pebble crusher installed power | 300 | kW | HP4 |
| Operating cyclones | 12 | units | 26-inch Krebs, 4 spares |
| Gravity concentrators | 3 | units | 48-inch centrifugal |
| Gravity scalping screens | 3 | units | 1.5 m x 3.6 m |
| Elution columns | 2 | units | 10 t capacity each |
| Electrowinning cells | 11 | units | 2,000 amp |
| Carbon regeneration kiln | 1 | unit | 1700 kg/hr diesel-fired |
| Carbon elution circuit capacity | 20 | t | 2 x 10 t circuits |
| Concentrate leach reactor | 1 | unit | 9 t capacity |
| Lime consumption (saprolite) | 1.8 | kg/t | As quicklime |
| Lime consumption (rock) | 0.8 | kg/t | As quicklime |
| Cyanide consumption (saprolite) | 0.3 | kg/t | As NaCN |
| Cyanide consumption (rock) | 0.25 | kg/t | As NaCN |
| Reagent – metabisulfite (saprolite) | 0.57 | kg/t | Not stated |
| Reagent – metabisulfite (rock) | 0.33 | kg/t | Not stated |
Overview
The Merian Operations process plant is located in the Republic of Suriname and processes ore from open pit mining operations. The plant was designed to treat combinations of fresh rock and saprolite, showing the varying material characteristics of the deposits. The flowsheet design drew upon testwork results, previous study designs, and industry standard practices for handling these ore types.
Material handling of saprolite ore is deliberately simplistic to avoid mass flow problems, a design consideration that influenced the sizing of equipment and the incorporation of conventional engineering practices. The process method is conventional to the industry, with no significant elements of technological innovation.
The plant design accounts for variability in ore characteristics across different domains and deposits. As mining operations trend deeper, there is potential for increased plant wear-and-tear due to harder material, which may also result in increased power costs. Blending of fresh rock and transitional material will need to be monitored to ensure that life-of-mine plan forecasts are met. There is an opportunity to optimize grind and recovery for harder materials to possibly increase mill throughput rate.
Key Process Stages
The process flowsheet begins with primary crushing using a gyratory crusher, followed by a grinding circuit comprising a SAG mill, pebble crusher, and ball mill. Fresh rock from the open pits is crushed and stockpiled, then reclaimed using three apron feeders, each capable of feeding 75% of the peak fresh rock mill feed rate of 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.
Discharge from the SAG mill is fed over a vibrating screen for classification, with oversize transferred to the pebble crushing circuit. The ball mill operates in closed circuit with hydrocyclones, with 12 operating cyclones and 4 spares. Gravity concentration is achieved using three 48-inch centrifugal concentrators preceded by gravity scalping screens. A 9 t capacity intensive concentrate leach reactor treats gravity concentrate.
The leach circuit processes slurry after pre-leach thickening. The carbon elution circuit consists of two 10 t columns operating with separate acid wash and elution columns. All eluted carbon is regenerated using a diesel-fired kiln with fine carbon recovery, with provision made for 100% carbon regeneration if needed. An electrowinning circuit recovers gold from pregnant solutions from both elution circuits and the intensive concentrate leach reactor. A gold refinery (gold room) recovers and smelts electrowinning sludge to produce doré bars.
Additional Interesting Data and Summary
Energy requirements for the SAG and ball mills vary by domain and deposit. SAG mill energy requirements range from 3.75 kWh/t in the Merian II saprolite zero quartz vein material to 13.17 kWh/t in the Maraba fresh rock 0–10 v domain. Ball mill requirements range from 3.17 kWh/t in the Merian II saprolite zero quartz vein domain to 13.50 kWh/t in the Merian II saprolite breccia domain. The estimated average annual mill power requirement to support the life-of-mine plan is 165,000 MWh.
Process water is supplied from multiple sources. The tailings wash thickener overflow is used for grinding dilution, gravity concentrator fluidization water, and some reagent mixing. Pre-leach thickener overflow water is used mainly for grinding dilution, with a small amount going to the leach tanks for emergency dilution when needed. TSF supernatant water is reclaimed using floating barge pumps and reticulated to the process operations. Raw water is supplied by rainwater recovered from process plant, power plant, and administration building runoff, as well as collected from rainwater catchment within the treated water storage facility. These sources are supplemented by treated water from the effluent treatment plant and potable water from the camp potable water system.
Low pressure air is supplied by individual blower installations for each leach train and the cyanide detoxification circuit. High-pressure air is provided by dedicated compressors.
Key Processes
- Primary gyratory crushing
- SAG mill grinding with pebble crushing and screening
- Ball mill grinding in closed circuit with hydrocyclones
- Gravity concentration using centrifugal concentrators
- Intensive concentrate leach reactor
- Pre-leach thickening and trash screening
- Carbon-in-leach (CIL) or carbon-in-pulp (CIP) leaching
- Carbon elution with acid wash and elution columns
- Electrowinning and gold refining to doré bars
- Carbon regeneration using diesel-fired kiln
- Cyanide detoxification of tailings
- Tailings storage facility with supernatant water reclaim
Source: Merian Operations , 2019 NI 43-101 Technical Report, January 2019.
Editorial Note: The source text presents differing figures for the Merian II saprolite ball mill energy requirement. One passage states a range of 3.17 kWh/t to 13.50 kWh/t, while the same passage attributes the upper value to the "Merian II saprolite breccia domain" and the lower value to "Merian II saprolite zero quartz vein domain." No direct contradiction is present; however, the presentation of the data in a single quoted range could be misread as applying to a single domain. The intended meaning is a range across different saprolite domains within the deposit.
Project website: Merian Operations, 2019 NI 43-101 Technical Report
