Formation of lode-style gold mineralisation during Tabberabberan wrench faulting at Lefroy, eastern Tasmania
Titel:
Formation of lode-style gold mineralisation during Tabberabberan wrench faulting at Lefroy, eastern Tasmania
Auteur:
Reed, A.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 49 (2002) nr. 5 pagina's 879-890
Jaar:
2002-10
Inhoud:
The Lefroy Goldfield in eastern Tasmania is anomalous in southeastern Australia because mineralised fault reefs (i.e. reefs that are also faults) strike in an easterly direction at a high angle to the predominantly northwest strike of bedding and folds. Gold mineralisation is of Early to Middle Devonian age, with reef formation coinciding with a third regionally compressive deformation event (D3), and a second phase of Tabberabberan orogenesis. Mineralised reefs are hosted by Mathinna Supergroup turbidites of Cambrian to Ordovician age and extend for up to 2 km across the boundary between the sandstone-dominated Stony Head Sandstone and the shale-dominated Turquoise Bluff Slate. Ore shoots in the reefs plunge moderately west and, in the Volunteer Mine, coincide with the intersection of the reef and a D1/D2 thrust contact. The subvertical orientation and discordant relationship of the mineralised reefs to bedding, as well as the lack of gold mineralisation along bedding and pre-D3 structures, indicate that the reefs formed during a period of wrench faulting. In contrast to lode-style deposits in Victoria, the far-field minimum compressive stress at Lefroy during reef formation was not vertical but, rather, occupied a subhorizontal orientation.
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