Exploration Potential, page-125

Preliminary Considerations: Seismic Influence and Electrochemical Reworking of Gold

1. Seismic Influence on Gold Redistribution at Hill End

Hypothesis:

o Repeated fault reactivation and seismic activity along the Hill End Anticline may have led to physical redistribution of gold within existing vein systems.

o Seismic pumping, a well-documented phenomenon in orogenic systems, involves the repeated opening and closing of fractures during earthquakes, driving high-pressure fluids along vein systems.

Mechanism:

o During fault slip and earthquake activity, transient low-pressure zones form along reactivated faults and bedding-plane shears.

o These sudden pressure drops allow for episodic fluid expulsion and gold mobilization, potentially re-precipitating gold in structural traps (e.g., bends, intersections, or fault jogs).

o This process could explain the formation of steeply plunging high-grade ore shoots in reactivated faults intersecting Hill End’s bedding-parallel veins.

Significance:

o This mechanism could enhance pre-existing gold grades by redistributing gold and creating localized zones of enrichment.

o Seismic reactivation postdates the main gold pulses at ~356 Ma and ~343 Ma, implying that later fault activity may have “reworked” the primary mineralization, upgrading specific zones along fault intersections.

2. Electrochemical Charging and Gold Mobilization During Seismic Events

Hypothesis:

o Recent research suggests that electrochemical processes triggered by seismic activity may have mobilized gold during fault movements.

o Earthquake-induced stress can generate piezoelectric effects in quartz-rich host rocks, creating transient electrical currents that interact with gold-bearing fluids.

Electrochemical Mechanism:

o Piezoelectric Effect: Quartz crystals in the veins undergo deformation during seismic events, generating electrical charges.

o Electrokinetic Fluids: Movement of charged fluids along the faults creates an electrochemical gradient that can dissolve and transport gold as ionic complexes.

o Re-Precipitation of Gold: As the fluids encounter reducing conditions (e.g., carbonaceous shales or Fe-rich host rocks), gold is re-precipitated, often forming high-grade pockets or bonanza zones in fault intersections or dilation zones.

Significance:

• This hypothesis suggests that gold reworking and upgrading occurred after the initial mineralization via electrically driven fluid migration during seismic activity.

• Temporal Context:

o The electrochemical reworking likely occurred post-Devonian, during post-orogenic fault reactivation, potentially linked to continued tectonic activity along the Great Dividing Range.

o This timeframe aligns with episodic fault reactivation and renewed fluid movement in the Hill End area, which may have redistributed earlier gold accumulations.

3. Timing and Relevance – How This Fits Into Hill End’s Paragenesis

Post-Peak Gold Reworking:

o The primary gold pulses (~356 Ma and ~343 Ma) deposited most of Hill End’s gold during late-stage deformation in the Devonian.

o However, subsequent faulting and seismic activity likely occurred during ongoing deformation and uplift along the Great Dividing Range, potentially extending from the Carboniferous into the Permian and beyond.

Electrochemical Reworking Timing:

o This late-stage reworking of gold via electrochemical processes would have taken place after Stage V of Hill End’s paragenesis, likely occurring during periods of fault reactivation along the Hill End Anticline.

4. Global and Australian Analogues – Similar Processes Elsewhere

Several other gold deposits in Australia and globally provide analogues for seismic reworking and electrochemical upgrading of gold deposits:

• Fosterville (Victoria):

o Post-mineralization faulting and reactivation resulted in the formation of high-grade shoots (e.g., Swan Zone) at depth.

o Visible gold and stibnite were deposited along fault intersections, suggesting late-stage structural and fluid reworking postdating primary mineralization.

• Bendigo (Victoria):

o Multiple phases of reactivation along the Bendigo lines of reef led to remobilization and enrichment of gold in fold hinges and fault intersections.

o The inferred seismic history at Bendigo contributed to episodic fluid expulsion and re-precipitation of gold in structural traps.

• Hauraki Goldfield (New Zealand):

o Studies in the Hauraki Goldfield demonstrated that seismic-induced electrochemical reworking enriched gold in steep vein arrays.

o Piezoelectric effects in quartz-rich host rocks led to localized high-grade zones along fault intersections.

• Tanami (Northern Territory):

o At Callie and Dead Bullock Soak, repeated fault reactivation during post-peak metamorphism redistributed gold into higher-grade structural sites.

o These deposits show evidence of multi-phase fluid movement and gold enrichment similar to Hill End.

Conclusions and Implications for Hill End Exploration

1. Potential for Deeper High-Grade Shoots

• Seismic reactivation and electrochemical mobilization may have upgraded zones of primary gold along fault intersections and vein intersections at Hill End.

• Exploration Target: Deep-plunging ore shoots along reactivated fault zones or intersections of bedding-parallel veins with steep faults should be prime targets for deeper exploration.

2. Timing and Structural Traps

• If electrochemical reworking occurred after the main gold pulses (~356 Ma and ~343 Ma), it suggests that exploration should target fault zones that were reactivated during post-orogenic deformation along the Great Dividing Range.

• Exploration Target:

• Focus on fault jogs, dilational bends, and vein-fault intersections where electrochemical reworking may have created enriched gold zones.

3. Potential for New Discovery Models

• Understanding this late-stage electrochemical process can guide future exploration by emphasizing zones where fluid flow, stress, and electrical currents would have interacted to mobilize and re-precipitate gold.

• Exploration Strategy:

• Consider deeper, structurally complex zones for potential high-grade discoveries beyond known workings.

• Geophysical methods (e.g., induced polarization and resistivity surveys) could help identify areas with higher piezoelectric potential.

Next Steps:

• Integrate Seismic Impact into Hill End Exploration Model:

• Incorporate the possibility of post-mineralization gold reworking into the current exploration model.

• Prioritize deep-plunging intersections of bedding-parallel veins and steep reverse faults as prime targets for new high-grade zones.

• Geophysical Surveying:

o Conduct geophysical surveys (e.g., induced polarization, resistivity) to identify zones with high electrochemical potential for gold enrichment.

o Deep Drilling of Structural Intersections:

o Target structural intersections where late-stage fault reactivation and electrochemical processes may have upgraded gold grades.

This hypothesis of seismic-induced electrochemical reworking provides a compelling new exploration dimension for Hill End, significantly enhancing the case for deeper, high-grade gold potential.