Using gold as collateral to get a mortgage

[Nick Strauss]

I've just started looking into buying a duplex. One side for myself and the other for a tenant. I am self employed so it's harder to get a mortgage. I have no other assets except for gold - my money is made through trading currencies so I have no business to put up for collateral. 

What are the odds I could negotiate a mortgage with a lender with terms that might look something like 30% cash down and then offering 25-50% of collateral for the loan amount? My credit is very good - 782.

Just looking for some opinions or things to consider that might make this work. I'm new to this, so maybe this is an absurd idea, but I'm looking for options other than paying for the duplex in full up front.