When dissolving silver and base metal, don't rely on a formula for the amount of nitric required. You are at the mercy of the actual concentration of the acid, plus the unknown elements present in the inquarted material. You most likely have not allowed for the original base metals, and are most likely to not have a clue what they may be, anyway, aside from copper.
If you are in doubt, when you *think* you have eliminated all base metals and silver, pour off the solution and add a small amount of fresh dilute nitric and heat (keep it covered with a watch glass). If you can bring the solution to a boil with no signs of fumes, the job is done. If you see brown fumes, there's still metal to be dissolved. Do not rely on this test if you work without heating.
When you dissolve the resulting gold from inquartation, all of it should dissolve readily---and the color of the solution should be yellow to orange. If you have a green tint, it's obvious you have copper or nickel present---meaning you have either rinsed poorly, or there was still un-dissolved base metal present. If there's un-dissolved base metal, that usually results in some pieces that fail to dissolve in AR--and will be coated with a gray/green layer of silver chloride when you have finished the dissolution process.
There is little reason to expect anything less than about 99% pure gold if you dissolve and filter before precipitation. I can't begin to imagine how you're ending up with such low grade material unless you're melting things that didn't dissolve in AR.
Harold
Edit:
I am not one to support processing by the clock. Heating a solution that is barren of free acid for a prolonged period of time serves no useful purpose. You should become familiar with reactions so you can make visual observations that dictate if you should prolong heating, or if you should add more acid. I stronlgy advise you lose the notion that you have processed for a given amount of time, therefore the work must be done. It may or may not be.