Set on a future Earth taken over by an alien race. Humans reduced to prisoners/cattle? (memories of a bunch being kept in a fenced area ala pow's) The aliens have stripped most of the planets resources and are now turning to any buried refuse sites etc to remove all metals for their use.
I recall part of the plot where the aliens have a small base and are tunneling into a hill trying to reach what turns out to be an old army weapons cache. Our guy (human/ish) manages to get into the base through the hill? (not realising the value/use of the weapons crated up in the cave thing) where he finds a clinic of sorts where the aliens are force breeding the humans and modifying the offspring? He discovers he has 3 dots on his arm like the modified babies and must be one himself.
I think there are chases, fights etc that lead through radioactive hot zones so he can escape. Though I may be mixing this in from another plot?
Any assistance would be great, this has been nagging me off and on for years.
I have read a lot of the other queries on the forum also, but they are not what I am looking for, nor have I been able to help anyone else..... yet!