Regional structural controls of gold mineralisation, Bendigo and Castlemaine goldfields, Central Victoria, Australia

Willman, C. E.

doi:10.1007/s00126-006-0072-8

Cited by 47 publications

(20 citation statements)

References 36 publications

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“…The seismic survey confirms the presence of a series of steep west‐dipping reverse faults with most major goldfields in the hangingwall of the faults and offset by a few kilometres (Cox et al. , 1995; Willman, 1995). These faults may flatten with depth.…”

Section: Where Might Gold Deposits Not Be Expected?mentioning

confidence: 53%

Formation of gold deposits: a metamorphic devolatilization model

Phillips

Powell

2010

Journal Metamorphic Geology

494

177

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A metamorphic devolatilization model can explain the enrichment, segregation, timing, distribution and character of many goldfields such as those found in Archean greenstone belts, slate-belts and other goldonly provinces. In this genetic model, hydrated and carbonated greenschist facies rocks, particularly metabasic rocks, are devolatilized primarily across the greenschist-amphibolite facies boundary in an orogenic setting. Devolatilization operates on the scale of individual mineral grains, extracting not just H 2 O and CO 2 but also S and, in turn, Au. Elevated gold in solution is achieved by complexing with reduced S, and by H 2 CO 3 weak acid buffering near the optimal fluid pH for gold solubility (the buffering is more important than being at the point of maximum gold solubility). Low salinity ensures low base metal concentrations in the auriferous metamorphic fluid. Migration of this fluid upwards is via shear zones and ⁄ or into hydraulic fracture zones in rocks of low tensile strength. The geometry of the shear zones dictates the kilometre-scale fluid migration paths and the degree of fluid focusing into small enough volumes to form economic accumulations of gold. Deposition of gold from solution necessitates breakdown of the gold-thiosulphide complex and is especially facilitated by fluid reduction in contact with reduced carbon-bearing host rocks and ⁄ or by sulphidation of wallrocks to generate iron-bearing sulphide and precipitated gold. As such, black slate, carbon seams, banded iron formation, tholeiitic basalt, magnetite-bearing diorite and differentiated tholeiitic dolerite sills are some of the important hosts to major goldfields. Gold deposition is accompanied by carbonation, sulphidation and muscovite ⁄ biotite alteration where the host rock is of suitable bulk composition. The correlation of major gold deposits with rock type, even when the gold is primarily in veins, argues for rock-dominated depositional systems, not fluid-dominated ones. As a consequence, a general role in gold deposition for fluid mixing, temperature decrease and ⁄ or fluid pressure decrease and boiling is unlikely, although such effects may be involved locally. Several geological features that are recorded at gold-only deposits today reflect subsequent modifications superimposed upon the products of this generic metamorphic devolatilization process. Overprinting by higher-grade metamorphism and deformation, and ⁄ or (palaeo)-weathering may provide many of the most-obvious features of goldfields including their mineralogy, geochemistry, geometry, small-scale timing features, geophysical response and even mesoscopic gold distribution.

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Section: Where Might Gold Deposits Not Be Expected?mentioning

confidence: 53%

Formation of gold deposits: a metamorphic devolatilization model

Phillips

Powell

2010

Journal Metamorphic Geology

494

177

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“…For example in Otago the Macraes deposit that occurs in a shear zone within carbonaceous schists, which represents a very efficient focussing and trapping structure (McKeag et al, 1989;Teagle et al, 1990). In the Victoria goldfields, the Au mineralisation is hosted in carbonaceous black shales or Fe-rich rocks that are very efficient chemical traps, and the syn-mineralisation folding and faulting of interlayered sand and mudstones creates efficient structural trapping mechanisms (e.g., Willman, 2007). Gold anomalies in stream sediments in the Dalradian of Scotland, particularly in the SW Highlands (Gunn et al, 1996), indicate that there is potential for undiscovered mineralisation in this area.…”

Section: Implications For Formation Of Orogenic Au Depositsmentioning

confidence: 99%

Mobility of gold during metamorphism of the Dalradian in Scotland

Pitcairn

Skelton

Wohlgemuth‐Ueberwasser

2015

Lithos

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“…Since it is likely that the most highly mineralised zones occur at the brittle-ductile transition in the hangingwalls of the major intrazone faults (e.g. Willman 2007;Willman et al 2010), a method to identify the major faults and any associated brittle-ductile transitions is a key step in determining new targets for gold exploration. Willman et al (2010) also suggested that the points of inflexion of major faults may be important in determining the locations of gold deposits, since they determine the places where the faults become impermeable to fluids that were rising along them.…”

Section: Discussionmentioning

confidence: 99%

“…The lack of any currently known major gold deposits in the area is hence more likely to be the result of limited effective exploration as opposed to the absence of economic mineralisation (Lisitsin et al 2007). Models suggesting that the geometry and distribution of the groups of goldfields are the surface expressions of fluid flows related to the major faults (Cox et al 1991;Willman 2007;Willman et al 2010) may encourage the use of MT methods as a tool for further exploration. Previous comparisons with deep seismic data (Dennis et al 2011) also demonstrate the merits of the MT method for the mapping of major faults.…”

Section: Introductionmentioning

confidence: 97%

A geological interpretation of the Echuca magnetotelluric survey, Victoria

Dennis¹,

Moore²,

Cull³

2011

Australian Journal of Earth Sciences

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The northern part of the auriferous Bendigo Zone is obscured by thick Cenozoic sediments of the Murray Basin, and as such remains poorly explored. Consequently, in addition to the 2006 deep seismic line obtained in Central Victoria, a magnetotelluric (MT) survey was completed to provide a signature for the major structures previously defined in the Bendigo area. Based on these correlations a second MT line, which we present here, was completed some 50 km to the north of the original line in an attempt to trace the deep structural trends extending north to the Victorian/NSW border. Extending some 155 km across the central north of the state, data were collected at 52 sites along an east-west profile. The new electrical conductivity model generated correlates well with the results from the southern transect; it confirms previously identified structural trends to the north and identifies additional unknown deep structures, thus adding to the understanding of the geology of the covered region and to its goldbearing potential.

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Regional structural controls of gold mineralisation, Bendigo and Castlemaine goldfields, Central Victoria, Australia

Cited by 47 publications

References 36 publications

Formation of gold deposits: a metamorphic devolatilization model

Formation of gold deposits: a metamorphic devolatilization model

Mobility of gold during metamorphism of the Dalradian in Scotland

A geological interpretation of the Echuca magnetotelluric survey, Victoria

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