I agree, looks sedimentary, if the choice is between shale and basalt, I pick shale.
It is possible that the sandstone is derived from eroded gold bearing rock and contains some gold.
The other line of thinking is that the diorite made the gold flow into the sandstone. If it is fractured the gold may have been part of a hydrothermal system. Stick to that area and look at the contacts where the diorite meets the sandstone. Is there any baking along that edge, contact metamorphism, then you may be able to put together a geologic history, sandstone laid down, uplift, erosion, faulting, then intrusion by diorite causing mobility of gold particles.