UPDATE 1 — Supervisors at BHP's Escondida mine in Chile to strike after contract talks fail

(Adds details, context) SANTIAGO, Oct 13 (Reuters) — The supervisors' union at BHP's Escondida copper mine in Chile said they will begin a strike on Wednesday after mediation efforts to tie up a new collective labor contract had failed, the union said on Tuesday. The strike at the world's largest copper deposit threatens to tighten global supply and has been supporting copper prices. The union said it made a final offer incorporating 90% of company proposals plus key union demands including salary increases and production bonuses. BHP declined to respond and ended mediation talks, the union said in a statement late on Tuesday afternoon. The union said the company demanded workers give up essential benefits and insisted on sharing private biometric data with third parties. "The responsibility for this strike lies solely with the company and its negotiating committee," the union said in its statement. The supervisors' union and Escondida have been embroiled in fraught contract negotiations for several weeks, and had been threatening a strike if talks were to fail. The mine did not immediately respond to a request for comment. (Reporting by Fabian Cambero; Editing by Natalia Siniawski