A colleague of mine who works with the International Crisis Group based in Beijing recently sent me a copy of the contract between the DRC and China on exploitation of mines and construction of infrastructure. You can find a copy of this document here: drc-chinese-contract (In French).
I also found the following links to be quite useful in shedding light on the DRC-China partnership:
IMF to study China's Congo deal before any accord
China, Congo Trade For What the Other Wants (part of a great NPR five-part series on China's rising power in Africa)