An anonymous donor has dropped a wedding band and diamond engagement ring worth an estimated $3,500 into a seasonal Salvation Army collection kettle outside Boston, the charity group said on Tuesday.

The gift, dropped off at a supermarket in suburban Billerica, Massachusetts, will be auctioned off on Saturday, said the group, which sends out volunteers in organizational uniforms and dressed as Santa Claus to collect donations to support its work with the poor and homeless each Christmas.

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"We're excited and incredibly grateful to the individual who made such a generous and kind donation," said David Davis, a divisional commander of the group's Massachusetts arm.

In 2014, a widow's donation of her engagement and wedding rings sparked a spate of similar gifts to the group in Massachusetts, which raised some $30,000 for the Salvation Army.

Last month an anonymous Minnesota couple dropped a $500,000 check into one of the group's kettles, the group said.