*I am using the newest Mindcrack pack, which has Forestry and Industrial craft installed, this applies to the question.*
I'm asking this question because my quarry, (16 x 16, starting at y = 63), gave me 4 copper ore. With this, it made me question the following: what is the chances of not getting any copper ore in a chunk, where y = 63? I know layers copper spawns in, but don't feel like doing the math. Similar questions to this involving something like diamond and iridium is asked often, I'm sure. However, with a common ore such as copper, such a question may come out odd indeed.
I would think that copper ore rarity is similar to that of iron, but with slightly more rarity.
Note: I have plenty of copper myself, so this question is purely hypothetical.