SANTIAGO, June 4 (Reuters) - The union of workers for BHP's sprawling Escondida mine said on Friday it had delivered an initial proposal for a new collective labor contract, marking the opening salvo in much-watched negotiations at the world's largest copper deposit.

BHP confirmed receipt of the proposal in a brief statement on Friday. The company now has 10 days to respond to the union.

The fresh negotiations at Escondida come as copper prices have spiked amid soaring demand and tight supply for the red metal, handing workers additional leverage as they enter into the high-profile talks.

"This negotiation takes place in a highly favorable economic environment for the industry, which is estimated to be projected over time," the union said in a statement.

The union has requested a one-time signing bonus equivalent to "1% of dividends paid to the mine's owners" - BHP, Rio Tinto and Jeco Corporation - plus a 5% salary increase, a "just and objective" system of career of development, and ongoing merit-based worker bonuses.

"Our Union will undertake this process knowing that the result affects not only the company and the workers, but also the country in general," adding that there "there is no reason why BHP cannot make good on our requests."

A separate union of BHP's remote operations workers who service Escondida and the smaller Spence mine have been on strike since last Thursday, contributing to a charged environment at the company's operations.

That strike has yet to impact production, BHP said earlier this week.

(Reporting by Dave Sherwood and Fabian Cambero Editing by Marguerita Choy)