Sadly such information is going to be tough to come by. Most of the NCNG records went up in smoke with the Grass Valley depot. There are a handful of expense books and other documents that I have not yet been able to read through.
I can however give you this:http://www.pacificng.com/template.php?page=/ref/comrep/index.htm
I spent some time compiling the state railroad commission reports. While I have more to find, nearly all of them from 1876 to 1922 is available. These reports will list income totals and other pieces of information which will help you find what you're looking for in a general sense. Specific breakdowns of freight types would have been noted in NCNG records, which as I mentioned perished many years ago. Currently I don't have much more to help you, but I will note anything I find on PacificNG.