Silver Bow Reopens a Butte Portal After 35 Years

Silver Bow Mining Corp. (NYSE American: SBMT) has reopened underground access at its Rainbow Block project in Butte, Montana, after finishing rehabilitation of the historic Chief Joseph Portal, as Engineering & Mining Journal first reported. The company says the milestone marks the Butte Mining District’s first underground exploration access in roughly 35 years.

At a glance

• Silver Bow Mining finished rehabilitating the Chief Joseph Portal at Rainbow Block, restoring underground access in the Butte Mining District for the first time in about 35 years.
• The portal measures roughly 12 feet wide by 14 feet high and reaches historic workings on the eastern side of the property.
• Rainbow Block carries an inferred resource of 11.48 million tons grading 14.8 ounces of silver equivalent per ton, an early-stage estimate rather than a proven reserve.
• Next steps include rehabilitating the underground decline behind the portal, building drill stations on the 200 Level, and starting surface work on a second portal about 1,000 feet north.
• The Butte stop on Mining Our Future’s Season 1 route is anchored at Silver Bow Mining.

Why has Butte gone 35 years without underground exploration?

Butte’s “Richest Hill on Earth” ran on underground shafts for nearly a century before mining shifted to the open Berkeley Pit in 1955, and that pit defined the district’s output into the early 1980s. Our Montana master report covers that shift in full: once large-scale mining moved to the surface, the older underground workings that had carried the district for generations were largely left in place rather than actively explored.

That is what makes this rehabilitation notable. Reopening a specific historic portal for safe entry is a deliberate, multi-month engineering project, not a routine reopening, and Silver Bow says no company had put people back underground in the Butte Mining District to explore in roughly 35 years.

What did Silver Bow just complete, and what’s next?

Silver Bow signed a contract with contractor MES Mining in May 2026 to rehabilitate and modernize the Chief Joseph Portal and the underground decline behind it. Work mobilized by the end of May, and the company confirmed completion of the portal rehabilitation on August 19, calling it the first step toward safely re-establishing underground operations at Rainbow.

Chairman and CEO Travis Naugle called the achievement “an important milestone” in advancing the Rainbow Block resource, while Chief Operating Officer Kevin Shiell described the completed portal as the first step in safely restoring underground access. The company’s next phase covers rehabilitating the Chief Joseph Decline itself, establishing underground drill stations on the 200 Level to support resource definition drilling, and starting surface preparation for a second, larger portal about 1,000 feet north. Silver Bow says the work is authorized under a federal MSHA mine identification number issued for underground activity at the site.

Why do silver and zinc from Butte matter?

Rainbow Block’s resource is a silver-lead-zinc system, the kind of polymetallic ore body common across the Butte Mining District. Silver carries the highest electrical conductivity of any metal and shows up in solar cells and electronics, while zinc galvanizes steel with a sacrificial coating that keeps guardrails, rebar, and bridge beams from rusting through. Both are metals the United States still leans on imports to fully supply.

Butte’s copper legacy is what put the district on the map and on Mining Our Future’s Season 1 route, but Rainbow Block is a reminder that the same hill carries more than one strategic metal. An inferred resource is still an early-stage estimate, and Silver Bow’s own disclosures note it is not yet a proven or measured reserve, but reopened underground access is what lets a company like Silver Bow test that resource directly instead of relying only on surface data.