ore-roasting furnace
ore-roasting kiln
ore-roasting oven

In their academic report on ore-roasting kilns of the Hauraki goldfield, Moore and Richie conclude:

Dug into the hill are 10 in-ground ore-roasting kilns, the historic 110-year-old remnants of 13 recorded kilns, and part of a series of similar structures found throughout the Hauraki goldfield which extends north towards the Coromandel.