This 2022 Technical Report Update for the Wind Mountain project describes the recovery design for a conventional Run of Mine (ROM) cyanidation heap leaching and Merrill Crowe processing facility.
The Wind Mountain project, as described in this 2022 Technical Report Update, is designed around a conventional Run of Mine Cyanidation Heap Leaching process followed by Merrill Crowe solution processing. The design basis is set for a daily production rate of 20,000 tons per day with metal head grades of 0.011 opt gold and 0.254 opt silver. The process design targets metal recoveries of 62 percent for gold and 15 percent for silver, respectively. Capital and operating cost models were developed using a factored approach based on this 20,000 tpd leaching operation.
The process requires a leach pad built with suitable linings and a solution collection network of perforated piping for efficient drainage. Leach pad irrigation is done through an HDPE pipe header network with drip line emitters for solution application. ROM leach material is dumped directly in place by mine haul trucks, eliminating the need for crushing or milling prior to leaching. Prior to placement, each truck drives under the Lime Silo for lime addition to maintain proper pH. A dozer maintains the heap surface gradient, stacking ore to a depth of 27 feet. After placement, the material is ripped to minimize compaction and promote solution percolation.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Daily production rate | 20 | ktpd | Design criteria |
| Head grade (Au) | 0.011 | opt | Design criteria |
| Head grade (Ag) | 0.254 | opt | Design criteria |
| Gold recovery | 62 | % | Design criteria |
| Silver recovery | 15 | % | Design criteria |
| Total leach material | 30,300 | K tons | Total over production schedule |
| Gold production | 43 | K Ozs Au / yr | Average annual over five years |
| Silver production | 239 | K Ozs Ag / yr | Average annual over five years |
| Heap lift depth | 27 | feet | Stacked ore depth |
| Solution pH range | 10-10.5 | Not applicable | Leaching efficiency range |
Project website: https://miningrecord.com/preliminary-economic-assessment-for-the-wind-mountain-project/
Overview
This Technical Report Update provides the process design basis for the Wind Mountain project's recovery methods. The process is conventional and uncomplicated, utilizing ROM heap leaching followed by Merrill Crowe processing. The report details process flow diagrams, equipment lists, and mass balances to support preliminary sizing. The process production schedule has been developed from a detailed monthly mine production schedule, incorporating a lag time for recoveries to model the time it takes to produce gold and silver after placement.
Key Process Stages
The leaching process begins after pad preparation with the application of dilute sodium cyanide solution, also called barren solution, to the surface of the ore. The solution is pumped from the Barren Solution Tank through header pipes and drip irrigation lines. As the solution percolates through the stacked ore, it leaches metals and is collected through the collection system into a pregnant leach solution (PLS) pond.
The PLS is then transferred to the Merrill Crowe circuit. Three pressure leaf filter clarifiers, operating in parallel, remove suspended solid contaminants from the PLS. These filters are sized so that two operating filters can handle 100 percent of the process design throughput while the third is being cleaned. Diatomaceous earth is used to precoat the clarifiers. Clarified PLS then reports to a deaeration tower.
Following clarification and deaeration, powdered zinc is added to the PLS solution. The zinc reacts with metal cyanide complexes, precipitating the precious metals as a metal-rich sludge. The sludge is separated from solution using pre-coated plate and frame filter presses.
The processing of the metal begins when the metal precipitates are removed from the filter presses, placed into trays, and retorted to remove moisture and elemental mercury. Mercury vapors are condensed for collection, and any remaining vapors pass through a mercury scrubber containing sulfur-impregnated carbon. Retorting is followed by batch flux-smelting in an induction furnace. The molten metal and slag are poured into cast molds. After cooling, the slag is broken away, and the doré buttons are collected, remelted, and poured into doré bars, which are then weighed, stamped, and readied for shipment.
After metal removal from the PLS, the solution is returned as barren solution to the Barren Solution Tank. Cyanide is added to maintain the concentration before recycling to the heap.
Additional Interesting Data and Summary
The process production schedule, developed from a detailed monthly mine production schedule, incorporates a lag time for recoveries. This lag delays recovery from placed material during the month it is placed, with the following months allowing for 85%, 7%, 5%, and 3% recovery of total recoverable ounces. This effectively provides a lag of recoveries over a period of five months or about 150 days. During construction, 0.6 million tons of crushed leach material are placed on the pad, with recovery delayed until the start of production year.
The production schedule shows approximately 43,000 ounces of gold and 239,000 ounces of silver per year of production for five years, based on a total leach material tonnage of near 30 million tons. The design of the leaching facilities, process hydrology, and recovery facilities has not been completed for the PEA, with sufficient water assumed to be obtained. Reagent consumptions are based on test work data and industry norms.
Key Processes
- ROM Cyanidation Heap Leaching
- Merrill Crowe Solution Processing
- Clarification using Pressure Leaf Filters
- Deaeration and Zinc Precipitation
- Precipitate Filtration and Retorting
- Induction Furnace Smelting
Source: Wind Mountain , 2022 Technical Report Update, 2022. Project website: [project name](URL)
Project website: Wind Mountain, 2022 Technical Report Update
