Read the qtrly for the best understanding but negative cash...

Read the qtrly for the best understanding but negative cash costs occur when a by product is sold (copper in this case) that covers all cash costs of production and leaves a profit margin as well, even before the gold revenue is factored in.

Pretty good when just your byproduct gives you a profit before you even get paid for the gold when others are struggling to get a profit from the gold in their gold mines.