It's also worth remembering that proven reserves are thought of in the context of current and projected global population and consumption. The thought experime

It's also worth remembering that proven reserves are thought of in the context of current and projected global population and consumption. The thought experiment begins with a "post-global calamity/collapse" situation, in which the total population is much, much smaller. So even what we currently think of as "small" or "negligible" deposits might be more than enough for productive use within the now-smaller population.