THE MINING PROCESS
How We Mine
Finding new mineral reserves is critical to the success of our company. Careful planning in locating, extracting and processing these natural resources is a multi-year process that involves complex scientific, environmental and social planning.
Golden Queen’s mission is to build a sustainable mining business while leading in safety, environmental stewardship and social responsibility. Golden Queen primarily mines gold and silver metals from crushed, agglomerated ore by utilizing conventional open-pit mining methods, cyanide heap leach and Merrill-Crowe processes.
Follow along as we walk you through our mining process.
Mining for Gold
Mining for gold is a complex, scientific and time-intensive process. A great deal of studies, research, planning, organizing and prep work must occur before any mining can take place. Soledad Mountain was previously mined using underground mining techniques to extract the gold and silver bearing ore. Today, the mining is done by open pit surface mining techniques requiring large equipment to excavate the mine in 20 foot benches. During this process, the drifts, tunnels and stopes from the previous underground mining will be encountered requiring precautions to be taken to avoid an unplanned collapse of underground workings.
Old Underground Tunnel (Then)
Open-Pit Surface Mining (Now)
The bench is divided into blocks or patterns. Drill patterns are designed and drilled on a certain spacing (i.e. 14’X14’, 16’X16’, etc.) to enable accurate sampling of the material being drilled. Since we mine 20’ benches, each hole is drilled to a predetermined depth, usually 23’ to ensure the bench is completely blasted. The cuttings from each drill hole are sampled to determine if that hole is ore (pay dirt) or waste. Once a pattern has been completely drilled, the holes will be loaded with a booster and ANFO (ammonia nitrate fuel oil) and capped with stemming. When all the drill holes have been filled, the loaded holes will be tied together and blasted. Watch our blasting videos here.
Once the samples from each drill hole have been analyzed by the on-site lab, the Ore Control department will create ore polygons and dig maps based on that information and release the material to be mined. The dig maps, both paper and digital, will allow the loader/shovel operators to know exactly what material they are digging, which helps reduce the dilution of the ore. The material is loaded into 100-ton haul trucks. The drivers receive the material type information by way of a computerized dispatching system and delivers the material to the appropriate destination. Waste material is placed on a dump outside the pit limits and ore (pay dirt), is delivered to the Primary Crusher to be either direct dumped in the crusher or stockpiled.
Ore passes through 3 stages of crushing before it is stacked on the leach pad. The first stage is the Primary Crusher were ore is crushed down to minus 6”. The second stage is the Secondary Crusher where the ore is screened and crushed to minus 1.5”. The third and final stage of crushing is the Tertiary Crusher were the ore is processed through a HPGR (high pressure grinding roll). The HPGR breaks the ore down to 75% passing minus ¼”. The ore then passes through the agglomeration drum where cement and water are added to assist in binding the clays and fines together. The ore is then transported to the leach pad via conveyors and is stacked in 30’ lifts in preparation for leaching.
After the ore has been crushed and stacked it is leveled out and drip emitters are installed. Process solution is then added at a certain application rate for an initial 90 day period. The process solution permeates through the ore and dissolves the gold and silver into the solution. The process solution, through gravity, is transported to the recovery plant through solution collection piping.
The gold and silver are extracted from the process solution using the Merrill-Crowe process. The first step in the process is the solution is pumped through clarifiers to remove and turbidity. The next step is to remove the dissolved oxygen from the solution. The final step is to add zinc dust to the solution. The solution is pumped through filter presses where the zinc combines with the gold and silver to create a zinc precipitate. After the gold and silver has been removed from solution, the solution is pumped back to the leach pad to start the process over.
Periodically the filter presses are cleaned out and the zinc precipitate is placed in trays. The zinc precipitate is placed in a mercury retort to remove any mercury. When this step is complete the zinc precipitate is combined with refining reagents and put into the furnace. The material is heated to approximately 2000F and is poured into mold. Up to 8 bars can be poured at a time. The bars are cooled, cleaned and prepared for shipment.