Read the passage.

the city of butte, montana, is situated in an area rich in minerals. the area was settled by prospectors who came to mine gold in the 1860s. later, silver- and copper-mining brought prosperity to the area. the town is named for a nearby butte, or flat-topped hill.
which detail is least relevant to someone researching the history of montana mining?

a: silver and copper have been mined in butte.

b: the town is named after a nearby butte, or flat-topped hill.

c: butte, montana, is in an area rich in minerals.

d: gold prospectors settled the area.