It doesn't matter at what price you have project that are...

It doesn't matter at what price you have project that are economic viable when the projects are small. What does matter is at what production cost you can fill demand and how much production that disapears from big old mines.

Here grade are a key, lower and lower grade means that you have to move more and more rock to get the same amount of copper.

Sum all together and you see where price of copper will go. Just look at copper price latest 20-30 years.

Good video on the topic