Would have dated this to the Shang instead of the Zhou,but the Feng Peacock double incised on both sides of the flat Jade(Nephrite) is usually linked to the early Bronzes of the early Zhou Dynasty. Interesting is that the plaque is irregular in outline and there is a hole at top for attachment.Same Feng Peacock design on both side.
Can read furthur about the Feng Peacock in article The ''Feng" Peacock by John F. Moffitt and Peter Voris in Arts of Asia July-August 1988.