Gold, silver, and base-metal bearing veins in the Maratoto—Wentworth region of the Hauraki Goldfield have many similarities: Host rocks are hydrothermally altered andesites (propylites) of the Beesons Island Group; all have sub-parallel strike directions and dip steeply; all are composed predominantly of quartz and carbonates. Within some veins, rich bonanza mineralisation occurs in fan-shaped bodies that taper with depth. This is associated with marked thickening of the vein and a change in strike direction. Very little mineralisation is present outside of these bodies. In fact, beyond the bonanza, the vein itself is often only weakly developed and passes into an intensely sheared zone. Near the bonanza, reverse faults, or well-defined veinlets, may transect the vein at near right angles.