Strain and displacement in the Middle Vale Reef at Telfer, Western Australia

Vearncombe, J.R.; Hill, A

doi:10.1016/0169-1368(93)90034-v

Cited by 8 publications

(4 citation statements)

References 4 publications

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“…In Victoria, deposits that are considered to have formed late during orogenesis include the Bendigo, St Arnaud, Ballarat and Inglewood deposits (Forde & Bell 1994). Other examples in older rocks elsewhere include the Sigma Mine in the Abitibi Greenstone belt in Quebec (Robert & Brown 1986), and the Telfer (Vearncombe & Hill 1993), Mt Charlotte (Ridley & Mengler 2000), Sunrise Dam and Granny Smith (Mair et al . 2000) deposits in Western Australia.…”

Section: Discussionmentioning

confidence: 99%

Formation of lode‐style gold mineralisation during Tabberabberan wrench faulting at Lefroy, eastern Tasmania

Reed

2002

Australian Journal of Earth Sciences

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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 (D 3 ), 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 D 1 /D 2 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-D 3 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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Section: Discussionmentioning

confidence: 99%

Formation of lode‐style gold mineralisation during Tabberabberan wrench faulting at Lefroy, eastern Tasmania

Reed

2002

Australian Journal of Earth Sciences

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“…It has been called a Paleoproterozoic RIRGD gold deposit due to reduced sulfide phases in the ores such as pyrrhotite and loellingite (McFarlane et al 2011) but such classification given the structural setting and nature of the magmatism seems very challenging (Goldfarb et al 2017). Early structural studies of the Neoproterozoic Telfer deposit in Western Australia described features typical of shear zone-related orogenic gold ores (Vearncombe and Hill 1993;Hewson 1996) leading to a genetic model that involved contact metamorphism producing a highly saline metamorphic fluid capable of transporting the Au and Cu in the deposit (Rowins et al 1997). The local geology includes shelf sequences and, as stressed by Yardley and Graham (2002), metamorphism of such units may produce a fluid that is quite saline.…”

Section: Giant Deposits In Metamorphic Terranes Sometimes Argued To B...mentioning

confidence: 99%

Orogenic gold: is a genetic association with magmatism realistic?

Goldfarb

Pitcairn

2022

Miner Deposita

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Many workers accept a metamorphic model for orogenic gold ore formation, where a gold-bearing aqueous-carbonic fluid is an inherent product of devolatilization across the greenschist-amphibolite boundary with the majority of deposits formed within the seismogenic zone at depths of 6–12 km. Fertile oceanic rocks that source fluid and metal may be heated through varied tectonic scenarios affecting the deforming upper crust (≤ 20–25 km depth). Less commonly, oceanic cover and crust on a downgoing slab may release an aqueous-carbonic metamorphic fluid at depths of 25–50 km that travels up-dip along a sealed plate boundary until intersecting near-vertical structures that facilitate fluid migration and gold deposition in an upper crustal environment. Nevertheless, numerous world-class orogenic gold deposits are alternatively argued to be products of magmatic-hydrothermal processes based upon equivocal geochemical and mineralogical data or simply a spatial association with an exposed or hypothesized intrusion. Oxidized intrusions may form gold-bearing porphyry and epithermal ores in the upper 3–4 km of the crust, but their ability to form economic gold resources at mesozonal (≈ 6–12 km) and hypozonal (≈ > 12 km) depths is limited. Although volatile saturation may be reached in magmatic systems at depths as deep as 10–15 km, such saturation doesn’t indicate magmatic-hydrothermal fluid release. Volatiles typically will be channeled upward in magma and mush to brittle apical roof zones at epizonal levels (≈ < 6 km) before large pressure gradients are reached to rapidly release a focused fluid. Furthermore, gold and sulfur solubility relationships favor relatively shallow formation of magmatic-hydrothermal gold systems; although aqueous-carbonic fluid release from a magmatic system below 6 km would generally be diffuse, even if in cases where it was somehow better focused, it is unlikely to contain substantial gold. Where reduced intrusions form through assimilation of carbonaceous crustal material, subsequent high fluid pressures and hydrofracturing have been shown to lead to development of sheeted veins and greisens at depths of 3–6 km. These products of reduced magmatic-hydrothermal systems, however, typically form Sn and or W ores, with economic low grade gold occurrences (< 1 g/t Au) being formed in rare cases. Thus, whereas most moderate- to high-T orogens host orogenic gold and intrusions, there is no genetic association.

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“…The northeast-dipping shears at Mount Charlotte were formed in an earlier deformation phase and became included in the deposit essentially by chance. In many fault or shear zone-hosted deposits in the Yilgarn craton and elsewhere, there is evidence that veins formed late in the deformation history of the host structures (e.g., Andrews et al, 1986;Robert and Brown, 1986;Vearncombe and Hill, 1993), implying fluid flow into preexisting structures. By analogy with the model here for Mount Charlotte, some of these shear and fault zones could have formed in an earlier phase of deformation, have been favorably oriented for reactivation, and give limited direct information about the tectonic regime during mineralization.…”

Section: Implications For Models Of Fluid Flow In Lode Gold Systemsmentioning

confidence: 99%

Lithological and Structural Controls on the Form and Setting of VeinStockwork Orebodies at the Mount Charlotte Gold Deposit, Kalgoorlie

Ridley

Mengler

2000

Economic Geology

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The Mount Charlotte quartz vein gold deposit comprises a series of steeply plunging, pipelike vein stockwork orebodies in massive metagabbro. The orebodies are strata bound to the most differentiated unit of the host sill and are typically adjacent to major steeply dipping faults that cut the sill. The stockworks have two sets of veins with a dihedral angle of about 50°that developed as hydraulic fractures, filled simultaneously, and are generally approximately equally developed. Veins crosscut major faults and parallel minor faults of two sets but are cut along reactivated fault surfaces. The fault sets were inactive during mineralization and are neither veined nor are loci of zones of intense alteration. Rare faults of a third set are in part veined and are loci of zones of mineralization. Two interpretations of the stress regime during vein formation are based on different models of fracture formation. For both stress regimes, the major fault sets are relatively unfavorably oriented for slip or dilation, and predicted movement vectors do not fit fault-plane lineations. The lack of fault activity during ore fluid flow promoted formation of vein stockworks at Mount Charlotte rather than shear zone or fault-hosted veins. Fluid flow paths and orebody siting are controlled by stress-guide effects due to the rheology of the host gabbro, and by the three-dimensional geometry of impermeable faults and of fault-bounded blocks of rock.

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Strain and displacement in the Middle Vale Reef at Telfer, Western Australia

Cited by 8 publications

References 4 publications

Formation of lode‐style gold mineralisation during Tabberabberan wrench faulting at Lefroy, eastern Tasmania

Formation of lode‐style gold mineralisation during Tabberabberan wrench faulting at Lefroy, eastern Tasmania

Orogenic gold: is a genetic association with magmatism realistic?

Lithological and Structural Controls on the Form and Setting of VeinStockwork Orebodies at the Mount Charlotte Gold Deposit, Kalgoorlie

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