Butte: Bornite & Pisanite Rockhounding in Silver Bow County, Montana

Plan your visit

Generally open to casual rockhounding

County

Silver Bow County

State

Montana

Nearest road

Clark Street

Postcode

59701

Coordinates

46.02061, -112.54630

Coordinates are approximate. Confirm the exact ground in the RockHoundR app, where land overlays show which agency manages the area.

Land & collecting status

Generally open to casual rockhounding

Most public-tagged spots sit on BLM, U.S. Forest Service, or other federal land where reasonable hand collecting of common rocks and minerals is allowed. Confirm posted rules and active mining claims before you dig.

Access note: Do not enter mine workings, fenced areas, contaminated sites, or private property; collect only where public access and safety rules allow.

Public-land rules vary by agency, season, and field office. The RockHoundR app pulls live BLM, USFS, NPS, and tribal overlays so you can see exactly which agency manages the ground at this spot.

Best time to visit Butte

Comfortable months (45 to 90°F highs)

Best months: April to October. Typical highs run 80°F in midsummer and 31°F in midwinter, with winter lows near 7°F.

Climate normals: NOAA 1991-2020 monthlies, BUTTE BERT MOONEY AP station (4 mi away), adjusted for elevation.

Geology at Butte

This spot sits on Biotite-hornblende granodioritic rocks along the Continental Divide, Anaconda Range, Sapphire Mountains, and Flint Creek Range, mapped as biotite-hornblende granodiorite, biotite-hornblende monzogranite, and tonalite that formed roughly 145 to 66 million years ago. Plutonic rock like this weathers slowly into grus and boulders, and the most productive collecting is typically in weathered zones and drainages.

Mapped unit

Biotite-hornblende granodioritic rocks along the Continental Divide, Anaconda Range, Sapphire Mountains, and Flint Creek Range

Age

145–66 Ma (Cretaceous)

Rock types

biotite-hornblende granodiorite, biotite-hornblende monzogranite, and tonalite

Elevation

5,860 ft

Geologic mapping via Macrostrat and the underlying state geological survey maps (CC BY 4.0). Bedrock at the surface can vary within a mapped unit.

Sources & verification

Spot details combine the public RockHoundR location dataset, normalized mineral labels, agency land-status checks in the app, and community submissions. Coordinates are approximate until verified in the field.

State guidance last verified: April 1, 2026

• BLM Montana, Recreational mineral collecting
• Montana Bureau of Mines and Geology
• Gem Mountain Sapphire Mine (fee-dig operator)
• Community submissions reviewed against published agency rules