Leopard Opal was (re)discovered in 1965. I say rediscovered because there is evidence that the mine had been active in the past, and that the opal was known by pre-Columbian habitants.
Leopard Opal is vesicular basalt impregnated with play-of-color opal from the state of Hidalgo, Mexico. Vesicular basalt forms when water vapor and gases cannot escape quickly enough from cooling lava, thus leaving open cavities, or vesicles. These gaps then fill with mineral and silica-rich run-off which eventually turn into opal. And in this case, also feldspar.