Выражение встречается в следующем контексте:

A drill program has been designed to confirm and recheck #10 vein tonnage and
grade above the adit and confirm the continuation of the vein down plunge.
Historical core recovery was very poor as only EX core was drilled.

The main upper orebody should be filled in with four to six NQ sized holes. Four
to six deeper holes should be drilled targeting the down plunge extension of #10
vein to about 1000 ft (300 m) below the adit. The higher grade mineralization
appears to plunge at 30 degrees to the north.

Заранее спасибо

Это в Гугле добыто, EX там тоже полно, но в миллиметрах
мне найти пока не удалось.