Been looking for tin for hours. Gone through several prospecting picks before I finally found an area that gave something above a "poor" rating for casserite. Kept picking around until my last reading before quitting the game for the day read as "decent."
When I booted up the game the next day, I continued prospecting, but didn't seem to be getting any closer to the high point of the casserite distribution. In fact, no matter which direction I walked, I only got poor readings. Eventually I went back to the place I had the decent reading, and dug right next to it, and got another poor reading in the very same spot I got a decent one the previous day.
Maybe I'm confused on how ore generation works. I assumed they were generated according to some vaguely circular shaped probability mass function assigned at initial terrain generation. Now though, it almost appears as though it can change each time you boot up, but I can't imagine how that makes any sense from a technical perspective...
EDIT: never mind. I was mistakenly reading "0.1%" as "0.01%"