Structural, mineralogical, and textural data from the
Tarnagulla Goldfield demonstrate that the area has undergone three significant
phases of deformation. The first phase of deformation (D1) predates
the intrusion of the Tarnagulla pluton, which has been dated using K/Ar as 391
5MY. We regard this pre-granite deformational event as the major regional
deformation. Gold-bearing quartz veins have been deposited in dilational sites
on west-dipping reverse faults. These sites demonstrate a geometry related both
to faulting associated with D1 and the plunge of the F1
fold axes. This evidence, together with chronology of unmineralised ?
D2 and D3 faults, the absence of quartz veining associated
with D3 events, and the deformation of
carbonate-quartz-biotite-sulphide aggregates within Sl by later
S2, lead us to conclude that the bulk of the mineralisation was
essentially syn- or late D1 . 18O values for fluids in
equilibrium with vein quartz from Central
Victoria
have indicated equivocal support for either a magmatic or metamorphic origin.
Our evidence supports a pre-magmatic origin for mineralisation at Tarnagulla and
hence tends to favour a metamorphic fluid source.