The Bulolo Graben represents an intra-arc rift formed by activa- tion of transfer structures in an extensional setting formed be- tween the eastern and western sectors of the New Guinea Origin.
Crustal thinning has facilitated the emplacement of dacitic Edie
porphyry intrusions, locally as flow dome complexes,
phreatomagmatic (diatreme) breccias and the Bulolo ignimbrite/
agglomerate as an extrusive equivalent of the Edie Porphyry. Gold
mineralization is localized along intra-graben structures, com- monly at the intersection with cross structures and occurs in sub- sidiary dilational fractures and not the localizing major structures. Gradations are apparent in the styles of mineralization according
to the degree of erosion of the hydrothermal system. Hamata occurs as the deepest mineralization of the quartz-sul- phide style Wau, Hidden Valley, and Edie Creek are dominated
by carbonate-base metal styles. Kerimenge grades from quartz
sulphide through carbonate-base metal to epithermal mineraliza- tion, the latter style also being present in the periphery of Edie
Creek. Here, pre-existing fractures of the Edie Creek Structural
Corridor have been reactivated by movement on NS structures to
form the ore-hosting dilatant lodes. Fluid flow may have been
from the vicinity of the Nauti diatreme margin and along the vein
System.