OreWin's 2021 technical report for SSR Mining on the Marigold mine in Humboldt County, Nevada, describes a ROM heap leach with seven carbon column trains and a 120-day leach target.
The Marigold 2021 Technical Report was prepared by OreWin Pty Ltd for SSR Mining Inc. under NI 43-101 and filed in 2022. Marigold combines run-of-mine (ROM) heap leaching, carbon adsorption, carbon desorption and electrowinning to produce doré. The report describes the heap leach and gold recovery circuit as typical in the industry for treating gold cyanide solutions. The heap leach pad was first built in 1990 and has been expanded as needed, and the solution processing facilities have grown to match production and leach area.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Report | Marigold 2021 Technical Report | Not applicable | OreWin Pty Ltd for SSR Mining Inc. |
| Process | ROM heap leach, CIC, elution, electrowinning | Not applicable | Not applicable |
| Lift height | 6.1 to 12.2 | m | Pebble lime added in the haul trucks |
| Barren application rate | 0.122 to 0.143 | L/min/m² | Drip tubing on top, sprinklers on slopes |
| Area under leach | About 0.5 | million m² | At any one time |
| Barren pumping capacity | 53 | m³/min | Two independent systems |
| Leach cycle | 120 | days target | Primary cycles of 90 to 120 days historically |
| Carbon adsorption | Seven trains of five columns | Not applicable | Not applicable |
| Strip vessels | Two 3 t | Not applicable | Two 2.1 m³ electrowinning cells |
| Recovery, March 1990 to December 2021 | 71.1 | % | Solution to ore ratio 1.28:1 |
| Site power draw | 5 | MW | 120 kV line from NV Energy |
| Fresh water make-up | 2.4 | m³/min average | Water rights up to 3.134 Mm³/a |
Overview
Haul trucks deliver ROM ore to the leach pad and stack it in lifts of 6.1 to 12.2 m. Pebble lime from a silo is added to the trucks before dumping to control pH. Fresh ore is ripped and cross-ripped before leaching. The pad is divided into cells for inventory and irrigation control, which lets operators manage the irrigation time and the interval between lifts. About 0.5 million m² is under leach at any time, while other areas drain or are prepared for the next lift.
From March 1990 to December 2021, the heap recovered 71.1% of the gold, with primary leach cycles of 90 to 120 days and an overall solution-to-ore mass ratio of 1.28:1. New ore is now leached for a targeted 120 days.
Key Process Stages
Solution distribution. Headers and sub-headers distribute barren solution through drip tubing on the pad surface and impact sprinklers on the side slopes. Two independent barren systems together pump 53 m³/min. Sodium hydroxide is added to the barren pond after the carbon columns, and sodium cyanide at the spillway between barren ponds 1 and 2.
Ponds. The solution facilities comprise two barren ponds, six pregnant ponds and a stormwater and overflow pond. Pregnant pond 1 is inactive because of a leak. There are two cyanide addition facilities, two sodium hydroxide systems and four antiscalant addition points.
Carbon adsorption. Pregnant solution is pumped to seven parallel carbon column trains of five columns each, and column discharge returns to the barren ponds.
Elution and electrowinning. A dedicated truck carries loaded carbon to the carbon processing facility. Gold is eluted in two 3 t strip vessels, and the solution passes through two 2.1 m³ electrowinning cells in parallel, recirculating until each batch is complete.
Refining. The electrowinning sludge is collected in a filter press, retorted to dry it and remove mercury, mixed with flux and smelted in a propane-fired furnace.
Carbon regeneration. Stripped carbon is screened to remove fines, acid washed to remove carbonate scale and thermally reactivated as needed before returning to the columns.
Additional Interesting Data and Summary
Mercury control is a feature of the refinery. Vents from the strip solution tanks, electrowinning cells, retort and furnace pass through a deep bed scrubber of sulphur-impregnated activated carbon. Kiln exhaust passes through a wet scrubber that condenses elemental mercury, then through more sulphur-impregnated carbon. The planned improvements are barren booster pumps to hold 53 m³/min as the heap grows taller and farther from the pumps, telemetry to monitor application rates and the main flowmeters remotely, and further refinery ventilation upgrades. The report says reagent use is within industry norms, with cyanide and lime consumption varying by ore type.
In summary, Marigold is a long-running Nevada ROM heap leach whose pad has grown since 1990, recovering about 71% of the gold through carbon columns and a compact strip and electrowinning plant with layered mercury controls.
Key Processes
- Run-of-mine stacking in 6.1 to 12.2 m lifts with pebble lime
- Ripping and cell-by-cell drip and sprinkler irrigation
- Cyanide heap leaching on a 120-day target cycle
- Seven trains of carbon-in-column adsorption
- Elution and electrowinning
- Retorting and propane-fired smelting
- Acid wash and thermal carbon reactivation
- Mercury scrubbing on refinery and kiln vents
Source: Marigold 2021 Technical Report, prepared by OreWin Pty Ltd for SSR Mining Inc. (NI 43-101), 2022.
Technical report and processing history
The following archived source profiles have been consolidated here to preserve the project’s processing history and study context.
Mineral Processing Circuit of Marigold Mine
Processing and Recovery Methods
The Marigold Mine employs a Run-of-Mine (ROM) heap leaching process combined with Carbon Adsorption/Desorption/Recovery (ADR) and electrowinning to produce a final doré product. The oxide ore is processed entirely via heap leaching, a cost-effective method for gold recovery.
1. Ore Stacking on Leach Pad
– Ore Handling: ROM ore is hauled by trucks and stacked in 6.1 m to 12.2 m lifts on the leach pad.
– pH Control: Pebble lime is added to haulage trucks from a silo to maintain optimal pH before dumping.
– Leach Pad Preparation: Fresh and spent ore are ripped and cross-ripped to enhance permeability.
– Solution Application:
– Drip tubing and impact sprinklers distribute barren solution at 0.122 to 0.143 L/min/m².
– Header and sub-header lines ensure uniform solution distribution.
2. Leaching Solution Distribution
– Pond System:
– Two barren ponds, four pregnant ponds, and one stormwater/overflow pond.
– Ancillary Systems: Sodium cyanide (NaCN) addition (two locations), sodium hydroxide (NaOH) for pH adjustment, and antiscalant injection.
– Leach Pad Expansion:
– Originally constructed in 1990, expanded to 20 cells (with permitting for an additional cell).
– Active Leaching Area: ~0.5 million m² at any given time.
– Solution Pumping:
– Two barren solution distribution systems (total capacity: 43.5 m³/min).
– One lean solution system (max flow: 5.7 m³/min), recycled from low-grade pregnant solution.
– Total flow to pad: 49.2 m³/min.
3. Pregnant Solution Processing
– Carbon Adsorption:
– Pregnant solution is pumped to five parallel carbon column trains (each with five columns).
– Total flow rate: 37.9 m³/min (handled by six vertical turbine pumps).
– Gold Recovery Efficiency (2017): 95.4% from carbon columns.
– Solution Recycling:
– Discharge solution reports to barren ponds for reconditioning (NaCN/NaOH addition) before recirculation.
4. Carbon Processing (Strip Circuit)
– Carbon Elution:
– Loaded carbon is stripped in two vessels (2-ton and 3-ton capacity).
– Stripping Conditions:
– pH 13 (adjusted with NaOH).
– Temperature 141°C (heated via boiler and heat exchangers).
– Solution flow rate: 114–151 L/min.
– Gold Recovery Efficiency (2017): 95.6% from strip circuit.
– Electrowinning:
– Pregnant eluant passes through two parallel 2.1 m³ electrowinning cells.
– A third cell is used for cathode replating.
– Barren solution is recycled until stripping is complete (target: <17.1 g/t gold).
5. Refining
– Retorting & Smelting:
– Electrowinning sludge is retorted (mercury removal) and smelted in a propane-fired furnace.
– Flux is added to produce final doré bars.
– Carbon Reactivation:
– Stripped carbon is screened, acid-washed, and thermally reactivated before reuse.
6. Ventilation & Emissions Control
– Mercury Scrubbing:
– Exhaust gases from stripping, electrowinning, retort, and smelting pass through:
– Deep bed scrubber (sulfur-impregnated carbon) for mercury capture.
– Wet scrubber (water mist) for additional mercury condensation.
Key Equipment & Capacities
– Carbon Columns:
– Existing (2017): 20 columns (five trains).
– Post-2018 Expansion: 30 columns (additional two trains).
– Pumping Systems:
– Barren solution pumps upgraded to 597 kW motors (increasing flow from 43.5 to 53.0 m³/min).
– Pregnant solution pumps expanded to match flow rates.
– Pond Volumes:
– Pregnant ponds: 137,059 m³ (post-expansion).
– Barren ponds: 40,648 m³.
Recovery Rates & Performance
– Heap Leach Recovery (1990–2017): 70.3% (90–120-day leach cycles).
– Carbon Column Recovery (2017): 95.4%.
– Strip Circuit Recovery (2017): 95.6%.
Innovations & Challenges
– 2018 Expansion Projects:
– Upgraded pumping capacity to 53.0 m³/min (eliminating lean solution system).
– Added two carbon column trains to increase throughput.
– Challenges:
– Managing gold-in-solution inventory in the pad.
– Optimizing reagent consumption (NaCN: 0.17 kg/t ore; lime: 0.68 kg/t ore).
Throughput & Capacity
– Solution Flow Rates:
– Pre-2018: 37.9 m³/min (pregnant), 49.2 m³/min (total to pad).
– Post-2018: 53.0 m³/min (matched pregnant/barren flows).
– Power Consumption: 2.3 million kWh/month (2017 average).
Reagent Consumption (2017 Averages)
| Reagent | Consumption (kg/t ore) |
|——————|———————–|
| Sodium Cyanide | 0.17 |
| Lime | 0.68 |
| Caustic Soda | 0.01 |
| Activated Carbon | 0.01 |
This summary provides a comprehensive technical breakdown of the Marigold Mine’s processing circuit, emphasizing operational parameters, recovery efficiencies, and planned optimizations. Let me know if you need further details on any section.
Marigold Mine — 2017 Technical Report
Marigold Mine — 2017 Technical Report
| Company | SSR Mining |
| Date | 2017 |
| Region | Nevada, USA |
| Commodities | Gold |
| Mine Type | Open Pit |
| Status | Operating |
Executive Summary
The Marigold Mine is a long-standing oxide gold operation utilizing a ROM heap leaching process combined with a Carbon Adsorption/Desorption/Recovery (ADR) circuit. The facility has been in operation for approximately 28 years, with gold recovery from the heap leach pad historically averaging 70.3%. The process involves stacking oxide ore on a leach pad with lime addition for pH control, followed by solution application and collection into pregnant and barren ponds.
The ADR circuit recovers gold from the pregnant solution using carbon columns, followed by elution and electro-winning to produce a doré product. The text details specific equipment upgrades planned for 2018, including increased pumping capacity and additional carbon column trains to match barren solution flow rates. Reagent consumption for sodium cyanide and lime remains within industry norms, with power supplied from the local grid.
Operational data indicates a consolidated gold recovery of 95.4% from carbon columns and 95.6% from the strip circuit in 2017. The mine does not utilize a crushing circuit, relying instead on the ROM heap leach method which is deemed cost-effective for the current ore types. Ventilation systems are in place to manage mercury vapors from the refining and stripping processes.
Processing Profile
- Leaching: ROM Heap Leach
- Recovery: Carbon Adsorption/Desorption/Recovery (ADR)
- Refining: Electro-winning and Smelting
Reports
Website: https://www.ssrmining.com/operations/production/marigold/
Report Date: 2017
Region: Nevada, USA
Project Status: Operating
Commodity: Gold
Throughput:
Mine Life:
Mine Type: Open Pit
Ore type:
Marigold Mine — 2014 Technical Report
Marigold Mine — 2014 Technical Report
| Company | Silver Standard |
| Date | 2014 |
| Region | Nevada, USA |
| Commodities | Gold |
| Mine Type | Heap Leach |
| Status | Operating |
Executive Summary
The Marigold processing plant utilizes industry-standard ROM heap leaching combined with carbon adsorption, desorption, and electro-winning circuits to produce a final precious metal doré product. Ore is delivered by haulage truck and stacked on leach pads with pH control via pebble lime. Solution application is managed through header lines and drip tubing, with a total solution flow rate to the leach pad of 13,500 gpm.
Gold recovery is achieved through pregnant solution collection and pumping to five parallel carbon column trains. Loaded carbon is transported to the process facility for elution in strip vessels, followed by electro-winning cells where metals are plated out. The stripped carbon is reactivated and returned to service, while the plated material is retorted and smelted for final recovery.
Historical gold recovery from the heap leach pad from 1990 to 2014 was 71.6%, with current strip circuit and carbon column recovery rates exceeding 96%. The process relies on sodium cyanide and lime reagents, with power supplied from the local grid and propane used for refining and heating.
Processing Profile
Website: https://ir.ssrmining.com/investors/news/press-release-details/2014/Silver-Standard-to-Purchase-Marigold-Mine/default.aspx
Report Date: 2014
Region: Nevada, USA
Project Status: Operating
Commodity: Gold
Throughput:
Mine Life:
Mine Type: Heap Leach
Ore type:
