More on metals. From the description of the machine People on page 30
of the Creatures book, it says:

"...are limited by scarce natural resources and plurality of their
domain. Metals are rare, strip-mining operations essential, and major
reclamation projects common."

So there we go. There are metal ores in the Ringworld rock and soil but
they are difficult to find and exploit due to the scale of the
Ringworld. Therefore, scavenging metals and other materials in the
ruins is an important way to supplement strip mining. Good.

The reason I was looking into this in the first place was that I was
contemplating the creation of a culture like the machine people, only
less technologically advanced. I want steam power. Steam powered
tractors pulling trading caravans, paddle steamers, and so on. I just
wondered how likely it was that such a metal-hungry technology would
emerge.

John