Syntectonic vein and fibre growth associated with multiple slaty cleavage development in the Lake Moondarra area, Mount Isa, Australia

Winsor, C.N.

doi:10.1016/0040-1951(83)90090-2

Cited by 21 publications

(8 citation statements)

References 19 publications

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“…Deflection of micas of the Sn direction into Sn+l is restricted to a fraction of a millimeter width adjacent to the overprinting fabric and this tends to obscure the fact that it is a crenulation cleavage. The limited microfolding of Sn is attributed to the dominance of mass transfer processes in the formation of S,+i (e.g., Winsor, 1983). Average attitudes for S,+i in each of the ductile shear zone types are almost constant supporting the inference that S,+• relates to a regional superposition event which only developed in previously foliated rocks.…”

Section: Three-dimensional Lode Geometrymentioning

confidence: 82%

The Golden Mile, Kalgoorlie; a giant gold deposit localized in ductile shear zones by structurally induced infiltration of an auriferous metamorphic fluid

Boulter¹,

Fotios²

1987

Economic Geology

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Mesoscopic and microscopic analysis of the structurally controlled gold mineralization of the Golden Mile, Kalgoorlie, has demonstrated that the mineralogically simple gold pyrite mineralization style (70% of production) is restricted to an anastomosing system of narrow high strain zones (ductile shear zones) and to related tension fractures in the intervening unstrained rock. Virtually all ductile shear zone lode structures occur in the Golden Mile Dolerite because it was essentially mechanically isotropic prior to deformation. It is proposed that during the near-upright regional-folding event numerous ductile shear zones were established in an approximately axial planar relationship to the folds, with synchronous conjugate shear zones developed at low angles to this direction. A dynamic analysis shows that the tensional cross lodes can be related geometrically to the three ductile shear zones. Golden Mile-style mineralization is syntectonic and was not deposited posttectonically in structurally prepared sites. Microtextural analysis demonstrates that minerals associated with gold emplacement are strongly modified during strain within the ductile shear zones by ductile deformation dominated by mass transfer processes. In particular there is abundant evidence of crack-seal-type microfracturing within and marginal to grains and in microscopic transgranular sites; this deformation style contributed prominently to the bulk plastic flow of the shear zones. It is proposed that high fluid pressure gradients were established at each crack-seal cycle leading to much enhanced permeability and to considerable focusing of fluid flow through the narrow foliated zones. This structurally induced infiltration mechanism allowed the ore fluid to pervade the deforming zones and also controlled the straining process by moving dissolved mineral components from highly stressed contacts to sites of deposition. Thus the mineralization was introduced during the ductile phase of shear zone evolution, and though mesoscopic veins are present in the ductile shear zones, they are not a necessary part of the gold emplacement event: the majority of veins formed late in the tectonic history. Gold emplacement in the ductile shear zones was controlled by microscopic deformation processes and ductile shear zones are good exploration targets even in the absence of macro-to mesoscopic dilation sites.

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Section: Three-dimensional Lode Geometrymentioning

confidence: 82%

The Golden Mile, Kalgoorlie; a giant gold deposit localized in ductile shear zones by structurally induced infiltration of an auriferous metamorphic fluid

Boulter¹,

Fotios²

1987

Economic Geology

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“…Thus, Plumb et al (1980), although stating that: 'Relationships between metamorphism, granite intrusion, and deformation are not yet established', proposed a complex five-stage metamorphic history, much of which they related to granitoids now known to be much older than the low-Plhigh-T metamorphic event. The structural studies of Bell (1983) and Windsor (1983Windsor ( , 1986 provide such a structural framework, whilst Page (1983Page ( , 1988Page ( , 1990, Page & Williams (1981) and Page & Bell (1986) report on age determinations for some critical igneous and metamorphic events in the Mount Isa Inlier.…”

Section: Regional Geologymentioning

confidence: 99%

“…Unconformities occur between them, but the widespread ductile deformation/regional metamorphism post-dated deposition of cover sequence 3. For the western part of the Mount Isa Inlier, Bell (1983Bell ( , 1991 and Windsor (1986) have concluded that there are three major regional events, namely D1, D2 and D3 (Table 1). These have been Rb-Sr dated from samples of Sybella Granite, which occurs immediately NW and SW of the Hazeldene area, from localities where only one of the three foliations (Sl, S2, S3) was dominant (Page 8~ Bell, 1986).…”

Section: Deformation and Metamorphic History Of The Western And Centrmentioning

confidence: 99%

Proterozoic low‐pressure/high‐temperature metamorphism and an anticlockwise P–T–t path for the Hazeldene area, Mount Isa Inlier, Queensland, Australia

Rubenach

1992

Journal Metamorphic Geology

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In the Hazeldene area, situated in the Mount Isa Inlier, Queensland, the metamorphic grade changes from chlorite zone, through biotite and cordierite zones, to sillimanite/K-feldspar zone.Microstructural studies of rocks near the sillimanite isograd demonstrate that cordierite grew early during the development of a steep foliation (S2), was replaced by biotite, andalusite and sillimanite at the metamorphic peak late in S2, and in turn by kyanite + chlorite adjacent to localized small post-D2 shear zones. Although the anticlockwise P-T-t path is well defined, the precise P-T conditions are uncertain because of problems with experimental and thermodynamic data. The best estimate for the metamorphic peak for rocks close to the sillimanite isograd is around 600" C at 4 kbar.The metamorphism has been dated at 1544 Ma, and was synchronous with a major crustal shortening event. Because proposed extensional events occurred more than 60 Ma earlier, their contribution to the peak metamorphic thermal perturbation would have been insignificant. The syn-metamorphic Mica Creek Pegmatites, the abundance of high heat-producing elements in the nearby pre-D2 Sybella Granite, and advective heat by fluids which caused considerable metasomatism in the Hazeldene area, may have each contributed to the thermal budget. However, the metamorphic thermal gradient may be 80" C km-' or higher, strongly suggesting a local magmatic control. As none are known in the area, such synmetamorphic plutons would have to lie beneath the exposed high-grade rocks.

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“…These four deposits, Mammoth-Esperanza, Mount Oxide, Mount Kelly, and Lady Annie, have been classified as brecciated sediment-hosted copper deposits (Williams, 1980;Kay, 1985), although Mount Kelly was regarded as stratiform by Guy (1975). A comparison of these four copper oc- the Western Succession of the Mount Isa block (Bell, 1983;Winsor, 1983Winsor, , 1986Bell et al, 1988). These have been dated at 1,610, 1,544, and 1,510 Ma, respectively (Rb/Sr whole rock, Page and Bell, 1986).…”

Section: Presented a Complementary Fluid Inclusion And Stable Isotopementioning

confidence: 97%

Regional syndeformational copper mineralization in the western Mount Isa Block, Australia

Dijk

1991

Economic Geology

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The recently proposed syndeformational model for copper mineralization at Mount Isa has tremendous implications for metallogenesis and exploration, and hence, a regional assessment of its validity was made. Detailed studies on the structural setting, timing, and microstructural development of four brecciated sediment-hosted copper deposits situated northwest of Mount Isa, plus the assessment of many small prospects in the same area, reveal that all primary copper mineralization is strikingly similar and involves syndeformational (syn-Da) veining and alteration. Variation in and between deposits can be attributed to their host-rock lithologies and local structural relationships. "Silica dolomite" replacement as recognized at Mount Isa mine is associated with all copper mineralization in dolomitic host rock. Sulfide (+ chlorite) replacement in arenaceous host rock, for example at the Mammoth deposit, occurs concomitantly with silica dolomite alteration in other deposits that comprise both host-rock types. The matching alteration history of the deposits indicates a common origin for the mineralization, and together with a large number of similar small-sized copper occurrences, suggests that a major regional copper mineralizing event occurred during the third deformation phase throughout the western Mount Isa block. Local structural relationships, common to several deposits, such as the presence and degree of bedding discordance across low-angle (D1) faults together with later (D2) folding, may constitute suitable structural traps for subsequent (D3) mineralization. Therefore, the structural geometry, together with the alteration features, is essential in exploration and assessment of prospects.

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Syntectonic vein and fibre growth associated with multiple slaty cleavage development in the Lake Moondarra area, Mount Isa, Australia

Cited by 21 publications

References 19 publications

The Golden Mile, Kalgoorlie; a giant gold deposit localized in ductile shear zones by structurally induced infiltration of an auriferous metamorphic fluid

The Golden Mile, Kalgoorlie; a giant gold deposit localized in ductile shear zones by structurally induced infiltration of an auriferous metamorphic fluid

Proterozoic low‐pressure/high‐temperature metamorphism and an anticlockwise P–T–t path for the Hazeldene area, Mount Isa Inlier, Queensland, Australia

Regional syndeformational copper mineralization in the western Mount Isa Block, Australia

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