Sounds like the OP has already offloaded his nuggets.... but I thought I'd throw this up here for anyone else.....
These guys have onsite assay capabilities for weird mixes or unknown purity precious metals.....http://www.paciron.com/precious-metals/
Unfortunately, they only pay ~80% of spot, but it gets you out of the assay fees and turnaround time. They'll pay 90% if you set up an account with them.
I've got some platinum and palladium I need to offload and these guys seem like the only ones that can deal with it on the 'spot'.
Called into NW G&D to see what their rates are, but they lack onsite assays.