In the Continental area, Butte Quartz Monzonite is host to low-grade, porphyry style, copper and molybdenum mineralization exposed at surface in the footwall of the Continental Fault. This style of mineralization was intercepted by underground workings beneath the Berkeley pit at about the 2,000 level. Subparallel strands of the Continental Fault, collectively thought to have as much as 3,500 feet of dip-slip displacement, are exposed, along strike, in the bottom reaches of the Continental pit and in “cross section” in the north highwall. The deposit is bounded on the west by the Continental Fault and on the East by the Klepper Fault. In the Butte District, two mineralizing events are recognized as important relative to reserve definition: PreMain Stage (PMS) and Main Stage (MS). The Pre-Main Stage veinlet swarms and crackles with distinctive secondary green biotitic selvages, typify the potassium feldspar metasomatism associated with the early quartz-chalcopyrite-molybdenite porphyry style mineralization. Swarms of barren quartz, molybdenite crackles (slicks), and various styles of banded quartzmolybdenite veinlets marked the end of the Pre-Main Stage event and set the structural pattern for the classic mesothermal Main Stage veining to follow. These east to northeasterly trending, steeply dipping, massive copper sulfide veins, characterized by wide sericitic envelopes, often offset by conjugate northwest trending MS veins with gouge in both the hanging wall and footwall, sustained the historic underground mining in Butte, but occur only as small veinlets in the Continental pit. The bulk of the Continental orebody that sustains ongoing mining was mineralized by interlacing Pre-Main Stage crackles and veinlet swarms. Deepening of the current pit continues to exploit this mineralization. Ongoing research over the past 30 years, however, has further quantified another facet of Butte geology that is important to reserve definition. As a result of deep drilling in the District, a massive quartz-sericite-pyrite plug was delineated at depth in the southeast corner of the Berkeley pit that was contemporaneous with MS mineralization. It is thought that fluids from this intrusive mixed with meteoric water and sericitized a massive area above the PMS porphyry system. The swarms of pyrite and quartzpyrite veinlets associated with this intervening mineralization prepared the ground for subsequent supergene copper enrichment that occurred with ongoing weathering as the district was uplifted and faulted by the mountain building processes along the Rocky Mountain Front. These events produced the copper enrichment blankets conformable with ancient ground water tables both east and west of the current Continental pit. The upper eastern pushback visible from uptown Butte is scheduled to expose near-surface enriched reserves between the current Continental pit and I-15 over the next 5 years. The enrichment blanket between the Continental pit and the Berkeley pit is scheduled for exploitation mid-2050, allowing mining to progress downward to the ultimate design depth mid-2060.

Step 1: Rotary drills bore 48 foot holes, 9-7/8 inches in diameter, into the granite host rock.

Step 2: Drill cuttings are assayed to verify composition.

Step 3: Drill holes are loaded with explosives to blast and fracture the rock.

Step 4: Electric shovels load ore into haul trucks.

Step 5: Ore is hauled to the crusher in 240 ton capacity trucks. Waste goes to a designated waste rock repository.

The primary crusher reduces large chunks of raw ore to dimensions under six inches. The secondary crushers then reduce the size of the rock further to three-quarters of an inch.

The crushed ore is then routed through rod mills and ball mills where it is pulverized to a fine powder. Water is added to the process which makes the pulverized rock slurry.

The slurry is then pumped into the flotation cells in the concentrator where lime and other chemicals are added to liberate the metal sulfides. Molybdenum and copper is extracted, separated and dried for shipping.

High-grade molybdenum concentrate is bagged and transported to roasting facilities in the US. Copper concentrate is loaded into 100 ton rail cars and shipped to smelters in North America and overseas.