The rings are definitely riveted with some kind of metal. Already cleared back the plastic overlay (you can see the cut edges of the plastic in the bottom of the picture). The rivets pictured are metal - you can see on the left side where I've hit it with a punch a few times (and you can see silver divots). The rivets look the same from both sides of the crank.
I don't have a drill press or special titanium nitride bits. Hopefully alloy rivets as HillRider and dprayvd mentioned. Sounds like dprayvd has some experience with this crank. And yes it's 100gs. And they look equivalent to the chainrings on Exage, down to the spacers on the granny gear, which leads me to think they have normal-sized bolt holes.