Publication abstracts
With the exception of some of the deposits in the 1982 paper, virtually all the deposits cited are recognised as type for their class and are of major magnitude.
Some ore deposits coincide with large necking structures that are probably related to boudinage. The neck locating an individual orebody is usually part of a more regional necking environment, which in a generalised way is associated with the greatest amount and diversity of mineral occurrences in the district. These regional necking structures have close similarities with each other, and are broadly analogous to the smaller scale necks immediately hosting the mineralisation. Necking thus seems to locate ore deposits. The illustrations are chosen from the gold and nickel deposits of the Kalgoorlie - Norseman belt and the Agnew belt of Western Australia, the lead-zinc-silver deposits of Broken Hill in New South Wales, the copper-lead-zinc deposits of Mt Isa in Queensland, the Mt Lyell* copper deposits in Tasmania, and the Mt Painter copper - uranium occurrences in South Australia. However, many other metallifierous ore deposits are also probably related to large-scale necking structures.1982:- Necking, a structural control in the location of ore deposits. Global tectonics and Metallogeny, v.1, p. 304-324. *See also Domingo Aerden's 1991 description of Roseberry (and 1995 for Hercules), Tasmania 1994:- Boudinage control on the emplacement of lodes of the Kalgoorlie Goldfield. Australian Journal of Earth Sciences, v. 41, 105-113. (References)
Recognising Broken Hill geology as a large scale boudinage structure provides an aspect of the geology that has been missing from the previous controversial debate, and a possible explanation for the orebody which has been previously overlooked. Although the interpretation implies that the orebody is epigenetic in its location and configuration, and is largely post-F2 deformation, it allows that the ore constituents may have been syngenetic, possibly as dewatering of metal-rich brines. If true, this would easily reconcile opposing epigenetic and syngenetic views.1994:- Boudinage, a reinterpretation of the structural control on the mineralisation at Broken Hill. Australian Journal of Earth Sciences, v.41, p.387-390. A prima facie comparison is made between diagenetic 'sedimentary' boudinage structures at outcrop scales (scales of centimetres to tens of centimetres), and zones of localised stratigraphic thinning (on scales of tens of metres) in beds of Marra Mamba and Brockman Iron Formations of the Hamersley Iron Province of Western Australia. If the comparison is valid, it suggests that some of the hematite enrichment ores of the province may be diagnetic ores located in necks of diagenetic boudinage structures related to extensional disturbance of the basin when the sequence was only partly consolidated. This interpretation is seen as similar to the consensual supergene metasomatic replacement hypothesis for the origin of the ores in respect of mineral solution-precipitation mechanisms, but differs in respect of important aspects of bulk process, and in their implications for iron ore exploration. A prima facie comparison is also made with the structure locating some ores of the Krivoi Rog region of Ukraine for which a boudinage control has been explicitly described, and with the structure controlling the Nimba Range deposit, Liberia. If such a comparison is valid, then boudinage could account simultaneously for the Proterozoic age of the deposits, the localised stratigraphic thinning, the influx of iron and the 'removal' of silica. Further, on the basis of self-similarity of boudinage structure across scale, region, and tectonic regime, and in conjunction with the recognition by others on different grounds that the examples described in the paper may be extrapolated world-wide, boudinage may provide a partial framework within which existing models for the formation of enriched hematite ores of Proterozoic banded iron formations can be adapted. The paper is conceptual and provides no new data.1994:- Diagenetic boudinage, an analogue model for the control on hematite enrichment iron ores of the Hamersley iron province of Western Australia, and a comparison with Krivoi Rog of Ukraine, and Nimba Range, Liberia. Ore Geology Reviews, v.9, p. 311-324. A boudinage analogue may provide a framework for linking basin formation, inversion, and the formation of some ore deposits. Domains of basin formation (subsidence) and basin deformation (inversion) can be regarded as paired phenomena lying on opposide sides of a crustal-scale neck. Pull-apart initiates basin formation, and, simultanteously, mantle rise. Gravity aids basin subsidence but hinders mantle rise, resulting in the characteristic progression of structural sequence from basin formation to inversion. Basin formation and deformation may thus be seen as nartural in-situ correlatives of each other, different expressions of the same dynamic system offset in time by the polar asymmtry of gravity. Crust - mantle detachments on conjugate shear analogues laterally offset the basin and the zone of inversion and help to maintain a balance between erosional and deposition regimes. Kalgoorlie (gold), Kambalda (nickel) Broken Hill (lead-zinc-silver), and the Nimba Range hematite enricnment ores are illustrated as examples of the way in which boudinage may provide a framework for describing the settings of some different types of ore deposits.1997 and Bowes, D.R.:- A boudinage perspective on basin formation, deformation and emplacment of ore deposits. Utkal University Special Publication in Geology 2, p. 283-307. Restoration of fault displacements on a section through the Lunnon shoot is made in accordance with the general importance, noted by others, of flexural slip and ductile flow in the growth of the Kambalda Anticline. Coupled with the interpretation here that 'normal' and 'reverse' faults at Kambalda may simply be opposite walls of the same dilated fracture (one movement instead of two) this restoration allows the prism of anomalous stratigraphic sequence confined by faults and hosting the ores to be interpreted structurally-metamorphically (/ metasomatically) rather than magmatically. The movement picture may be synoptically described as 'boudinage on radial fractures or axial-plane cleavage', the structure being close to that for which the term 'boudinage' was originally coined. A model is proposed whereby flattening and commensurate pull-apart due to tangential longitudinal strain between the footwall Lunnon Basalt and the overlying Upper (ultramafic) Sequence is focussed within the contact zone occupied by the Lower (ultramafic-sediment) Sequence (the ore sequence). Sulphur-halogen-rich volatiles expressed from the shales and ductile interlayered ultramafics are mobilised intraformationally commensurate with flattening, and are juxtaposed in the gaps created as the sediment units are pulled apart over the tightening anticline (the 'zones of missing sediments' = ore zones). A boudinage model that allows for the juxtaposition of ore constituents (sulphur-halogen-rich volatiles and silicate nickel) in the sites that are now ore, supports the view that metamorphism has been important in the formation of the orebody, and provides scope for interpreting the entire orebody as having been structurally- metamorphically/ metasomatically emplaced. A boudinage model is arguably simpler than magmatic models, accounting not only for all the features supporting magmatic models but also for features that magmatic models cannot explain adequately. As the Lunnon shoot is typical of Kambalda ores, and Kambalda is the type for stratiform ultramafic-hosted nickel deposits in Archaean greenstone belts worldwide, the currently widely accepted magmatic model could usefully be reappraised.1998:- Boudinage on radial fractures: an alternative to magmatic models for the emplacement of nickel ores, Lunnon shoot, Kambalda, Western Australia. Australian Journal of Earth sciences, v.45, 943-954. A number of ore deposits are juxtaposed to illustrate a common boudinage signature. Examples are (1) Kalgoorlie (an epigenetic vein-type gold deposit from the Eastern Goldfields of Western Australia; (2) Broken Hill ( a stratiform sediment-hosted lead-zinc-silver deposit from New South Wales, Australia); (3) three haematite enrichment iron ore deposits, one from the Hamersley region of Western Australia, one from the Krivoi Rog region of Ukraine, and one from Nimba Range, Liberia; (4) Kambalda (an Archaean stratiform and stratabound ultramafic-hosted nickel deposit in the Eastern Goldfields of Western Australia, with the same tectonic environment as Kalgoorlie); (5) the diamondiferous Argyle kimberlite pipe in the Kimberley region of Western Australia; and (6) typical oil and gas plays* of western Europe. The first four of these deposits are the type, or close to the type for their class, emphasising the importance of the linkage. A further boudinage emphasis lies in the historical perspective for these first enumerated deposits, for which a boudinage control was either explicitly or implicitly described by others. It is concluded that an important organising principle in ore emplacment is probably being addressed, one which operates regardless of mineralisation type or crustal level (tectonic environment), which remains unrecognised in the popular consensus on ore controls, which could usefully be a framework for other popular consensual models, and which could substantially advance understanding of controls on emplacment of mineralisation and related tectonics1998:- Boudinage, a key to an organising principle for the formation of ore deposits. Economic Geology, v 93, p.671-682. |