File:Alice Mine (Butte, Montana, USA) 6.jpg

English: The town of Butte, Montana (pronounced “byoot”) is known as the “Richest Hill on Earth” and "The Mining City". The Butte Mining District has produced gold, silver, copper, molybdenum, manganese, and other metals.

The area's bedrock consists of the Butte Quartz Monzonite (a.k.a. Butte Pluton), which is part of the Boulder Batholith. The Butte Quartz Monzonite ("BQM") formed 76.3 million years ago, during the mid-Campanian Stage in the Late Cretaceous. BQM rocks have been intruded and altered by hydrothermal veins containing valuable metallic minerals - principally sulfides. The copper mineralization has been dated to 62-66 million years ago, during the latest Maastrichtian Stage (latest Cretaceous) and Danian Stage (Early Paleocene). In the supergene enrichment zone of the area, the original sulfide mineralogy has been altered.

Seen here is the reclaimed Alice Mine (Alice Pit), which is in Walkerville, immediately north of Butte. The mine targeted the Alice-Rainbow-Black Rock Vein Systems. Ore minerals here included native silver (Ag), acanthite (Ag2S - silver sulfide), rhodochrosite (MnCO3 - manganese carbonate), rhodonite (MnSiO3 - manganese silicate), and sphalerite (ZnS - zinc sulfide).

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From on-site signage:

Pit Mining at the Alice

Taking a Bigger Bite

As mining technology improved the efficiency and viability of processing low-grade ore, copper mining entered a new phase. Several "open pit" mines were created in the 1950s to maximize the amount of ore shipped to the processor. The main pit was the Berkeley Pit, which opened about one mile southeast of here in 1955. But about that same time, open pit mining began at the Alice here. Like its siter the Berkeley, the Alice Pit grew so much that it began consuming first houses, then entire neighborhoods. Most of the North Walkerville had been swallowed by the Alice Pit by the time of its closure in 1960.

What is open pit mining?

Open pit mining involved large excavators (dirt diggers) and huge 35- to 50-ton trucks able to carry 35 to 50 times more material than a pickup truck. These massive trucks were initially used to take away the "overburden" (soil without metal ore in it). Overburden material was taken from the pit and placed in a "dump" or pile, next to the pit. Looking west beyond the pit, you can see the former Alice Dump, which now has been reclaimed into a grassy hill. Once the digging gets down to the ore (rock with metal in it), the large trucks then carried the ore out of the pit to a processing plant, or mill. Depending on the geologic conditions, open pit mining can be more cost-effective to extract metal ore from the ground. By opening the Alice and Berkeley pits to mining, many more years of mine production and jobs were provided.

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Locality: Alice Mine, Walkerville, hilltop above the town of Butte, peripheral zone of the Butte Mining District, northeastern Silver Bow County, southwestern Montana, USA