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Abstract

We propose that zones of transient high permeability around
ancient fault systems can be predicted if fault segments and likely
locations for paleo-rupture arrest are identified. Lode gold deposits
in the Kalgoorlie terrane, Western Australia, are the products of
focused fluid flow through faulted crust. Deposits in the Mount
Pleasant area are clustered on small-displacement structures over
;10 km of the .50-km-long Black Flag fault. Field relationships
and net slip distribution along the fault indicate that the deposits
are adjacent to, but not within, a kilometer-scale dilatant jog,
where two segments of the fault are linked. On this basis we infer
that the dilatant jog was a long-term rupture-arrest site. The observations
are compatible with rupture on segments of the Black
Flag fault changing stress in the surrounding crust and bringing
specific zones closer to failure. By analogy with active seismogenic
fault systems, those zones correspond to regions where aftershocks
occur preferentially after failure. Stress-transfer modeling of
the system helps explain the location of mineralized smalldisplacement
structures around the Black Flag fault and indicates
that gold deposits in the area are located on structures that became
transiently permeable and localized fluid flow during repeated aftershock
ruptures. Thus, localized through-flow, or mixing of fluids
within fault systems, is likely to be controlled by the distribution
of aftershocks following rupture events; this distribution is
predictable.

Item Type:	Article
Authors/Creators:	Micklethwaite, S and Cox, SF
Keywords:	fault zones, aftershocks, fluids, mineral deposits, genesis, permeability, segmentation
Journal or Publication Title:	Geology
ISSN:	0091-7613
DOI / ID Number:	https://doi.org/10.1130/G20559.1
Additional Information:	© 2004 Geological Society of America
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