There are four main types of base metal and gold mineralisation
recognised in the central Pine Creek Geosyncline. These are stratiform,
polymetallic veins, stockwork/concordant gold-quartz veins and
unconformity related uranium-gold-platinoid mineralisation. The stratigraphy of the central Palaeoproterozoic Pine Creek
Geosyncline has been simplified into three groups comprising the
Batchelor, Frances Creek and Finniss River Groups in ascending order. Stratiform mineralisation occurs within the Frances Creek Group. The
earliest mineralisation is found adjacent to circular faults ringing
basement highs. Higher in the stratigraphy, stratiform mineralisation is
often associated with zones of high compression in the vicinity of
basement highs. A synsedimentary-diagenetic origin for stratiform
mineralisation is proposed. Polymetallic vein mineralisation occurs within the Frances Creek and
Finniss River Groups. Its composition changes systematically through
the stratigraphy similar to the stratiform mineralisation. The
mineralisation is structurally controlled and usually occurs in the vicinity
of basement highs. Stockwork-concordant gold-quartz vein mineralisation is hosted by the
upper Frances Creek and Finniss River Groups. It occurs within
compressional zones and along the Pine Creek Structure corridor around,
above and particularly between basement highs. Mineable reserves occur
in thick continuous semi concordant quartz-sulphide veins and/or
stockworks. Unconformity related uranium-gold-platinoid mineralisation shows a
close spatial relationship with the Palaeoproterozoic/Mesoproterozoic
unconformity. The mineralisation is localised by structures formed during
Mesoproterozoic deposition and is commonly adjacent to Archaean
basement or its remobilised equivalents. The type of mineralisation (stratifom/polymetallic vein) is a reflection
of local stress regimes, structure and physio-chemical conditions. An
initial phase of stratiform mineralisation is postulated to have occurred
with the first significant marine transgression in a tensional regime. A
second phase occurred later during a compressive regime. "Ihermochemical sulphate reduction of mineralising fluids by
hydrocarbons is invoked as the precipitation mechanism for the
polymetallic vein type of mineralisation. Hydrocarbon generation is
postulated to have occurred within the Frances Creek Group, in many
places contemporaneously with the movement of mineralising fluids and
basin compression. Polymetallic veins formed from the interaction of
mineralising fluids and hydrocarbons which were trapped in suitable
structures. An abundant, continuing supply of hydrocarbons was
necessary to form significant deposits. Where these conditions were not
net, the mineralising fluids largely continued their ascent to the near
surface environment to form stratiform deposits. The stockwork/concordant gold-quartz vein mineralisation is a later
event and occurred during the relaxation of compressional defonnation
after deposition of the 1-inniss River Group.