So a quick google and 20,000 cubic metres of concrete is approx 48,000 metric tonnes.
Average grade of gold per tonne in the release was 21.98g/t
48,000 * 21.98 = 1,055,040 g
1,055,040g / 31.1 (Troy Ounce) = 33,924
33,924 * $1,217 = $41,285,648 USD
= $56,416,582 NZD
I don't know how accurate that would be but that's what I would assume is approximate