The precious metals-focused analyst's departure means BMO has dropped coverage of 18 companies across the LSE and TSX, including Acacia Mining, Centerra Gold and Sibanye-Stillwater.
The bank announced his departure with a statement listing the companies it would stop issuing updates on, without naming him.
Mining Journal confirmed he had left with a senior source at BMO.
The London-based analyst issued his last note on January 15, a positive look at Centerra's December quarter production results.
Before BMO, Breichmanas spent four years as an engineer at mining services firm Hatch.