really have no clue...
off the top of my head i can't think of any 10 pin headers, or 5x5, that don't have one blank.
check with Gigabyte.
it could be some proprietary extension module for adding extra USB headers/ports or some other type of device.
i know ASUS always used to include a proprietary fan extension card header on their boards that i've seen many freak trying to determine what it was for.
but i have never seen a board that didn't include at least one USB 2.0 header.
just looked at the manual images and it shows "USB 2.0 Hub" just behind the PCIe locking tab where i originally thought it may be but in your phone image that looks to be just an onboard chip.
i would definitely get Gigabyte support on this ASAP.