Dateline Resources (ASX:DTR) started preparations for a rare earth element-focused drilling program at the Colosseum Mine in California, according to a Monday filing with the Australian bourse.

Exploration work by the company and its US subsidiary, Colosseum Rare Metals, confirmed a broad zone of rare earth mineralization at the mine, the filing said.

The drilling plan is expected to be finalized within a month, and quotations from the drilling contractor are expected to be sought after, according to the filing.

Shares fell 11% in afternoon trade Monday.