ON-IV

Production 1927 - 1966: 13.754.000 tonnes.
Number of shafts: 1.
Location of the mine site: Heksenberg, Heerlen

In 1910 the construction of the shaft was started, which originally was intended to be a ventilation shaft for ON-III. However, finally it became a mine of its own, but it took until 1927 before it came into production. The ON-IV was the smallest of all the four ON-mines

In 1966 the subsurface works were joined to those of the neighbouring mine ON-III, and the surface works of ON-IV were abadoned and later demolished (with exclusion of the shaft, which became the second shaft of the ON-III mine). In later years at the mine site a quarry for quartz-sand (locally called "zilverzand") was opened, which is in production until today (Sigrano). Quartzsansd was already mined in quarries in the neighbouhood for a long time. Most were privately owned, but one smaller one near the ON-IV was owned by Oranje Nassau Mines.