It's not a "slave burial" but the African Burial Ground in Manhattan where blacks- both free and slave- were interred for most of the 18th century- a time whan slavery was legal in all of North America.

No news or "spin" involved- a gradual emancipation law was passed in 1799 and slavery existed in New York State until 1827.

More info on the burial ground HERE
or a 'google' search for "Manhattan Afrcan Burial Ground" should turn up 500+ hits.

Best, Greg