A variety of cement raw materials occur within the
Cenozoic sequence in Northland. These form the basis of Golden Bay Cement's
cement manufacturing operation at Portland, Whangarei. High grade limestone is
taken from the Whangarei Limestone formation, which has been shown to have been
sub-aerially weathered and developed mature karst features prior to deposition
of the overlying allochthon sediments. In this instance, remobilisation of
allochthon sediments following uplift and erosion is inferred. At Portland
Quarry, argillaceous limestone is extracted from deformed thrust sheets in the
allochthon sequence. Quarry operations have been designed to handle the steep
asymmetric folds, thrust faults and fracture zones that affect the
resource.