TL;DR: Lunar Helium-3 is a main entry in the 外星矿物知识引擎 database.
He-3 is implanted in lunar regolith by solar wind. While the total quantity is large, concentrations are extremely low (1-50 ppb). Economic viability depends entirely on the development of practical He-3 fusion reactors, which remains uncertain.
Location
Lunar surface regolith (global, concentrated in mature mare soils)
Estimated Quantity
~1 million tonnes total
Extraction Method
Solar wind degassing of heated regolith
Economic Value
$3-5 billion per tonne (if fusion reactors developed)