Overlying the upper pillow Lavas, the latest extrusives of the Troodos Massif, interpreted as Cretaceous ocean floor, there occur umbers; iron, manganese and trace-metal enriched mudstones of volcanic exhalative origin.
Umber deposits occur in hollows, underline by thin lava breccias, also by deeper zones of intensely veined and fragmented pillow lavas. Occasional thicker umber deposits are located in elongate fault-controlled depressions; within and above thick lava breccias, restricted to the south margin of the Troodos Massif; and also in depressoions inherited from earlier emplacement of stratiform cupriferous sulphides.
Umbers originated in the Campanian due to volcanism on an ocean ridge. The sub-umber veining and brecciation was produced by late-stage hydrothermal activity, associated initially, with a brief episode of violent volcanism, then with more quiescent discharge of submarine thermal springs from a geothermal system. Large volumes if dilute metalliferous brines were released into open marine waters whereupon umbers were rapidly precipitated.