** Perpetual Resources PEC.AX soars 45.5% to A$0.016, highest since March 21

** Stock eyes best day since August 9, 2023

** Critical-minerals explorer anticipates presence of caesium, a relatively scarce metal, at its Igrejinha project in Brazil

** Finds a 200-metre stretch of pegmatite, a rock formation that hosts pollucite, the main source mineral for caesium

** Stock sees busiest session since October 22, 2024, with ~18.6 mln shares traded - more than 19x the 30-day avg

** YTD, PEC gains 23.08%

(Reporting by Shruti Agarwal in Bengaluru)

((Shruti.Agarwal@thomsonreuters.com;))