declare the jewellery? issues with receipt

what happens if you loss the receipt for some jeweller-silver and with pearl bought from China as gifts - . Value is less than 600 RMB. I've requested again the receipt from the shop but they will send in fax version.
I don't know the weight of them - 2 neckless and 2 pair of earrings . I need to declare them , will it be ok if I have only the fax receipt? I will pay duty- on for them but what is the percentage? Thank you so much