Colors that are directly across from each other on the color wheel complement each other. In this case, gold/yellow is directly across from purple on the color wheel. The exact color will depend on how much of each color you use, but either way you will end up with a brown color. You may even see a tiny bit of gray depending on the color of the gold.
The more purple you use, the darker the brown will be, but if you use more gold, it'll be a lighter color.
Using the same amount of paint/material in proportion to the other will create a muddy brown color. It truly depends on the specific color of purple and gold you use, and the undertones in each.