more soil questions, noob strikes again! Options

[fenixsmom]

So I've been digging at this river for a few days and I've noticed some interesting soil deposits. I'm wondering if they are even worth my time. In one area there is an eroding man made rock slide area that backs to a willow covered plain. I went digging into it today and found a decomposing vegitation/mud/black sand layer underneath there I found a rusty sandy lome layer. It seems to be untouched by others judging by the red stained rocks I went through.
There is another section I played in across the river where there is a dark black sand area that has black stained rocks with silver streaks running through the stones. Above the dark sand area is a normal river sand layer.
Do either of these sound like it's better to dig through? Or if I need to provide more information?