Overview

Deposit type

• Porphyry

Summary:

The Henderson mine is a porphyry molybdenum deposit with molybdenite as the primary sulfide mineral.

The Henderson deposit is composed of two partially overlapping ore bodies beneath the summit of Red Mountain. The ore bodies are entirely within a Tertiary rhyolite porphyry intrusive complex that has intruded the Precambrian Silver Plume granite. The mineralization is relatively continuous in the ore bodies and consists of molybdenite and quartz in random intersecting closely spaced veinlets.

Mining Methods

• Block caving

Summary:

The Henderson operation consists of a large block-cave underground mining complex feeding a concentrator with a current capacity of approximately 32,000 metric tons per day.

The available underground mining equipment fleet consists of fifteen 9-metric-ton load-haul-dump (LHD) units and seven 73-metric-ton haul trucks, which deliver ore to a gyratory crusher feeding a series of 3 overland conveyors to the mill stockpiles.

The Henderson mine is located in a mountainous region with the main access shaft at 3,180 meters above sea level. The main production levels are currently at elevations of 2,200 and 2,350 meters above sea level.

The Henderson mine and mill are connected by a 10-mile conveyor tunnel under the Continental Divide and an additional five-mile surface conveyor.

Comminution

Crushers and Mills

Summary:

The available underground mining equipment fleet delivers ore to a gyratory crusher feeding a series of three overland conveyors to the mill stockpiles.

Processing

• Vacuum filtration
• Crush & Screen plant
• Flotation
• Dewatering
• Roasting

Summary:

Henderson has the capacity to produce approximately 15 million pounds of molybdenum per year. The majority of the molybdenum concentrate produced is shipped to our Fort Madison, Iowa, processing facility.

The mine and the Mill are connected by a fifteen-mile elevated belt that passes underneath the Continental Divide through an old train tunnel and then above ground to the mill. Molybdenite (the molybdenum containing mineral) is obtained from the ore by crushing, grinding, and flotation.

Flotation & Concentration
Chemicals are added to the slurry. These are called collectors and frothers. The collectors attach to the surface of the molybenite causing it to become hydrophobic or “water hating.” The slurry is poured into giant mixing tanks called flotation cells. Air is introduced to the mixing process to create air bubbles. The hydrophobic moly sticks to the air bubbles and floats to the surface of the tank where they are skimmed off. The frother that was added earlier makes sure that the bubbles are stable and don’t burst before the moly can be skimmed off.

The final concentrate, still in the form of a slurry, is processed through many filters where the water is removed. A vacuum pulls the water away and a “cake” of molybdenite is left behind. These cakes go through a heat drying process to make sure any remaining water is removed. A dry, concentrated gray-black powder remains. The powder is packaged into giant bags that weigh about 3,750 pounds when they are full. The bags are shipped to a “roasting” plant for further processing.

The waste or tailings from the milling process is still in the form of slurry. It flows down into an area where the particles settle out of the water and create a tailings dam. The water is returned to the mill and is recycled over and over again.

Roasting
The roasters are huge – tall as a six-story building and 21 feet in diameter. They run twenty-four hours a day at a temperature of approximately 1200 degrees Fahrenheit. At the roasting plant, about 120,000 pounds of molybdenum concentrate are processed daily.

Even though the moly can be 98% pure when it leaves the mill, it needs to be purified even more so it can be used in hundreds of products. The heat of the roasting process removes all remaining impurities.

Production

Operational metrics

Personnel

Job Title	Name	Profile	Ref. Date
Chief Geologist	Nyssa Loeppke		Feb 23, 2024
Mine Manager	Dave Loring		Feb 23, 2024
Mine Production Superintendent	Josh Gresham		Feb 23, 2024
Sr. Mine Engineer	Dino Febiawan		Feb 23, 2024
Supply Chain Superintendent	Catherine Patti		Feb 23, 2024