Here's a little piece of trivia... The Maple Leaf is darker than the U S one ounce because it is one ounce. The US coin is lighter in color and heavier than one ounce. It has one ounce of gold and then "additives" to make it stronger, making it slightly more than one ounce. TTC
Karat utilized is your answer and the mixture of metals to dilute or geology of natural occurance is the absolute answer. And Shep them righteously rough lookn' devils are pure pleasure to a old dredge dog eyes sir. Nice to see Motherload(mariposa county) gold? lookn' so darn good. Still have a few oz stashed in the sdbox from days a old but NOT them fantastic gnarly specimens tons a au 2 u 2 -John