AIM-specialist Numis had built up a presence in the small-midcap mining sector, acting as UK broker to companies including Shanta Gold, Pan African Resources, Yellow Cake and Base Resources.
Staff have been placed on a consultation period until the end of next week.
An analyst from fellow broker SP Angel said the withdrawal "may reflect a lack of critical mass and expertise in the sector, high business overheads and a lack of commitment to the natural resources space in a firm that was founded on the rescue and recapitalisation of syndicates in the Lloyds insurance market and the media and retail sectors".
"We suspect more firms will continue to cut costs in the oil & gas and mining sectors as increased regulation in recent years has effectively reduced commissions paid by investment funds to unsustainable levels in certain areas," said the analyst.