A conceptual process plant design for the Converse Property, based on metallurgical testwork results, defines a base case consisting of 50,000 T/d crushing, two-stage heap leaching, and on-site gold and silver recovery.
The Preliminary Economic Assessment for the Converse Property includes a conceptual process plant design developed as the basis for preliminary capital and operating costs to support the economic evaluation. The base case plant design includes primary, secondary, and tertiary crushing and screening to produce 50,000 T/d of leach feed at a P80 of 0.25 inches, followed by two-stage heap leaching, carbon adsorption, stripping and regeneration, electrowinning, and smelting on-site to produce doré bars for shipment to third party refiners. Design criteria were developed from experience at similar projects coupled with the metallurgical test results presented in Section 13.0 of the report. The plant is designed to operate 24 hours per day, 7 days per week, with a design primary crusher availability of 75% and secondary/tertiary crushing and screening availability of 85%.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Design leach feed throughput | 50,000 | T/d | |
| Final crushed product P80 | 0.25 | inches | Nominally P80, P100 0.375 inches |
| ROM stockpile capacity | 100,000 | T | |
| Coarse leach feed stockpile capacity | 50,000 | T | Total |
| Crushed leach feed loadout pile | 5,000 | T | Surge pile adjacent to leach pad |
| Heap lift height | 25 | ft | |
| Ultimate heap height | 250 | ft | To be confirmed by testing |
| Irrigation rate | 0.005 | g/min/ft2 | |
| Primary leach cycle | 60 | d | 1.5 T solution per T feed |
| Secondary leach cycle | 60 | d | 1.5 T solution per T feed |
| Barren solution cyanide tenor | 2 | Lb/T | |
| Cyanide (NaCN) consumption | 1.4 | lb/T | |
| Lime (85% CaO) consumption | 1.2 | lb/T | |
| Moisture content of fresh ore | 2.5 | wt% | |
| Moisture content of saturated heap | 15 | wt% | |
| Evaporative loss from drippers | 10 | wt% | |
| Adsorption column sizing | 25 | g/min/ft2 | Design flow rate per unit area |
| Carbon stripping capacity | 10 | T/d | |
| Gold+silver loading on carbon | 200 | oz/T | |
| Daily (annual) gold production | 488 (178,120) | oz/d(y) | |
| Gold recovery (estimated) | 60 | % | From average head grade of 0.015 oz/T |
| Silver recovery (estimated) | 30 | % | From average head grade of 0.058 oz/T |
| Leach pad area | 25,000,000 | ft2 | Assumes 200,000,000 T of material |
Overview
The Converse Property PEA outlines a conceptual process plant design based on metallurgical testwork. The base case involves crushing and screening to produce leach feed at a P80 of 0.25 inches, followed by a two-stage heap leaching system. Gold and silver recovery is achieved through carbon adsorption, stripping, electrowinning, and smelting to produce doré bars. The process plant and solution ponds will be located adjacent to the leach pad, with the majority of process equipment housed in a single pre-engineered steel framed building that also includes the high security refinery area.
Key Process Stages
The processing flow begins with a run-of-mine (ROM) stockpile area of nominally 100,000 T capacity and a primary gyratory crusher (62 x 75 inch) set at seven inches, located on a bench on the south end of the eastern lobe of the waste dump. ROM leach feed will be hauled from the open pits and either stockpiled for subsequent reclamation by front end loader or direct dumped into the primary crusher feed hopper. Primary crushed ore will be reclaimed by an apron feeder below the crusher discharge pocket and conveyed to the coarse leach feed stockpile with 50,000 T total capacity.
Coarse material from the stockpile will be reclaimed by apron feeders (two operating, two standby) and conveyed to two double-deck vibrating screens (10 x 24 ft) ahead of two open circuit standard secondary cone crushers (MP1000 or equivalent) set at 1 inch. Screen undersize and crusher discharge will be conveyed to feed bins ahead of six tertiary vibrating screens (double deck 14 x 28 ft). Screen oversize will be conveyed to feed bins ahead of four shorthead cone crushers (MP1000 or equivalent), with crusher discharge returned to the tertiary screens. Screen undersize at P100 0.375 inches and nominally P80 0.25 inches will be conveyed to a small surge pile of 5,000 T capacity adjacent to the leach pad. Lime will be added to the conveyor immediately ahead of the pile. Crushed material will be withdrawn from the surge pile through clamshell gates, discharging onto a high capacity conveyor which loads it into haul trucks for transport to the leach piles.
The leach pad will be initially constructed in at least two stages but will ultimately cover an area of approximately 25,000,000 ft2, assuming 200,000,000 T of material. Based on testwork to date, the ore will not require agglomeration. Ore will be placed in 25 ft high lifts to an ultimate height of 250 ft, to be confirmed by load or percolation testing as part of the planned Feasibility Study. Operating heap faces will be contoured to 1.5:1 with intermediate catch benches and provision for failure to 3:1. Irrigation will use drippers at a rate of 0.005 g/min/ft2. The two-stage leach system is used to maximize the area under leach, minimize the size of the carbon adsorption plant, and accelerate production, while no preg robbers have been identified in the feed. Due to the region’s low rainfall, control of the water balance will be a critical issue in leach operations; a preliminary water balance that ignores rainfall indicates a negative water balance requiring 4,000 gal/min of fresh make-up water.
Carbon adsorption will consist of two parallel trains of five up-flow columns, each 17 ft diameter by 12 ft high with a design flow rate of 25 gal/min per ft2. Carbon loaded with approximately 200 oz/T of gold and silver combined will be advanced at a rate of ten tons per day to acid washing followed by pressure Zadra stripping, regeneration, electrowinning, and smelting to produce doré bars. The containment pond will be constructed with a single liner, and the design will comply with the requirements of the State of Nevada Division of Environmental Protection.
Additional Interesting Data and Summary
The process plant and solution ponds will be located adjacent to the leach pad, with most equipment in a single pre-engineered steel framed building. The design incorporates a water balance that will be critical to leach operations due to low regional rainfall. The planned Feasibility Study includes load and percolation testing to confirm heap height assumptions. The leach pad design includes a single liner for the containment pond.
Key Processes
- Three-stage crushing with primary gyratory, secondary and tertiary cone crushers to produce P80 0.25 inches
- Two-stage heap leaching with dripper irrigation at 0.005 g/min/ft2
- Carbon adsorption using two parallel trains of up-flow columns
- Pressure Zadra stripping and carbon regeneration
- Electrowinning and smelting to produce doré bars on-site
Source: Converse Property , Preliminary Economic Assessment, report date Unknown. Project website: Converse Property (URL not stated).
Project website: Converse Property, Preliminary Economic Assessment
