Exploration Potential, page-55

Geology of Hill End

The Hill End Goldfield in central-western New South Wales lies within the Hill End Trough, a 7 km thick succession of late Middle Silurian to Middle Devonian (~425-385 Ma) deep-water epiclastic and volcaniclastic sedimentary rocks. This deep marine basin, around 70 km wide and over 200 km long, is underlain by Ordovician volcanic rocks, situated between the Molong and Rockley-Gulgong Volcanic Belts, both part of the Ordovician Macquarie Arc in the Lachlan Fold Belt .

The local geology is dominated by the Hill End Anticline, where gold-bearing, bedding-parallel laminated quartz veins are hosted within the late Silurian Chesleigh Formation. This formation consists of interbedded sandstones, siltstones, and slates, deposited from deep-water turbidity currents in a submarine fan environment . Gold mineralization primarily occurs along bedding-parallel veins and associated structures, with mineralization events linked to high-angle reverse faults .

Key structural controls include:

- N-S trending folds (formed during the Tabberabberan Orogeny).

- Late-stage, W-dipping reverse faults intersecting E-dipping bedding-parallel veins, forming high-grade gold shoots .

Geology of Fosterville

The Fosterville Gold Mine, located in Victoria, shares similarities with Hill End in terms of structural controls. Fosterville’s geology is characterized by:

- Orogenic gold deposits hosted within turbidite sequences of sandstones, siltstones, and shales/black shales.

- E-W compression faults that formed upright fold sets and late brittle faults .

- High-grade gold mineralization controlled by reverse faults and laminated quartz veins, often bedding-parallel and located along sandstone contacts.

Comparison of Hill End and Fosterville

Both deposits are orogenic gold systems with strong structural controls:

1. Structural Similarities:

- High-grade mineralization is controlled by reverse faults intersecting bedding-parallel quartz veins in both locations.

- Both experienced significant deformation during the Tabberabberan Orogeny.

2. Geological Setting:

- Hill End is part of the eastern Lachlan Orogen, while Fosterville lies in the western Lachlan Orogen.

- Hill End’s mineralization continued into the Kanimblan Orogeny, whereas Fosterville’s mineralization is more closely tied to earlier deformation phases.

3. Mineralization Style:

- Hill End features stacked, bedding-parallel veins with high-angle reverse faulting leading to repeated high-grade shoots .

- Fosterville exhibits more consistent mineralization along fault intersections, with deeper zones showing bonanza-grade gold associated with visible gold and arsenopyrite.

Conclusion

While Hill End and Fosterville share structural styles and orogenic gold characteristics, Hill End shows more episodic mineralization events tied to different deformation phases, whereas Fosterville’s mineralization is more continuous with depth. The similarities in reverse fault control and bedding-parallel vein systems highlight their comparable geological evolution within the Lachlan Fold Belt.