6% is not much, really... imagine you invest 1 mil in the gold bond. within a year, they probably make about 50% more with it and pay you $3000.
You mentioned "probably" but this is guaranteed, meaning fixed income, very high return leh. I also heard that some banks can lend you money for short term without interest and cost. Don't know what the catch is but combining the two, you can make money from nothing.
Normally these two conditions do not happen together, not even once in a blue moon but across countries, there is a slim chance for a short period where some smart people will try to arbitrage.
To be able to offer high interest, the bank must be short of money and there are many borrowers willing to pay high interest or their investment team has good investment prospects.
For banks to offer zero interest loans, they must be flushed with money with zero return from their normal investments or very few borrowers. They wish to transfer the holding risk to you and in case of default payment, they will charge you a penalty and high interest. Such loans are only offered to selected retail customers who are not likely to result in bad debt. The amount is normally very small and available only for a very short period.
It is very unlikely both conditions can happen at the same time except in different countries. I understand at the moment they are some banks offering the zero interest loans. So 6% guaranteed interest probably cannot be offered at this time.