I assume it's for bikes. The way things should be.
Mining technology is an interesting line of study and employment. When I worked for The Imperial College of Science in London, I often walked around the Mining Department and saw how ore is extracted - floatation etc. This, along with all the Klondike and Western movies, must have caused me the allure of GOLD. I have even found it native, along with many other minerals in my days spent at mine tailings.