No, debit cards are generally tied to bank accounts which would hold some form of cash though this may be in various denominations such as US Dollar, Yen, Canadian Dollar, Euro, etc.
Something to consider in what you are proposing is to handle a few main points. Does the bank convert the asset to cash? Does the payment processor convert this? Does something else handle this transaction? Secondly, does one get to choose a currency as in parts of Canada, one could use US dollars or Canadian dollars for payment. Does the hard asset auto convert to local dollars or is there something else to wire in here?
Lastly, consider how you are assuming there would exist a 24/7 conversion that would be interesting to see how that is handled. Is the price of the metal at 2 pm the same at 4 pm? How about 2:30pm? There is something to be said for when are the rates being updated and pushed out properly to the millions of debit machines out in the US and Canada, this is if I just stick to North America where I'm more familiar with banks.
If you could get past the technical headaches, have governments pass the legislation to approve these kinds of transactions and get banks on board with this arrangement, then perhaps this could exist but I see a lot of road blocks in the way.