Looks like the it might be a Downies issue but I really have no idea. Just going by the look of the certificate being similar to silver sets issued by Downies and the silver medallion looking similar to the koala/crocodile stuff Downies did around the same time Check the back of the certificate if it says Downies or Macquarie Mint (also Downies) or Sherwood (Sydney store that merged with Downies)
no it doesn't have any indication of who minted it plus the weight is wrong, it says 1 gram on the nugget but it weighs 1.3 grams