Just using those quoted figures some math:1390000 x 0.0292 x 0.5...

Just using those quoted figures some math:

1390000 x 0.0292 x 0.5 / 0.483 = 42,100 (close to 37,500)

tonnes of tails mined at 2.92% zinc sent to the processing plant from which 42,000 or 37,500 tonnes of material at 48.2% grade was recovered.

1390000 x 2.92% = 40,588t contained zinc in mined tails

37500 x 48.3% = 18,113 contained zinc in concentrate

18,113 / 40,588 = 45% recovery not 50% so appears these numbers include inaccuracies and rounding errors