Metamorphogenic Au‐W veins and regional tectonics: Mineralisation throughout the uplift history of the Haast Schist, New Zealand

Craw, Dave; Norris, Richard J.

doi:10.1080/00288306.1991.9514476

Cited by 79 publications

(51 citation statements)

References 37 publications

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“…Uplift and resultant tensional fracturing would have enabled the release of trapped fluids such as those derived from the breakdown of the hydrous mineral phases chlorite and micas during transition to higher grade metamorphic facies at depth. Such a derivation of the hydrothermal fluids in Otago from underlying higher grade schists has been argued by several authors (e.g., Henley et al 1976;McKeag et al 1989;Craw & Norris 1991;Craw 1992). However, the similar oxygen isotope values obtained for the quartz lodes and the country rocks simply show that the hydrothermal fluids equilibrated with the host schists, and cannot distinguish other fluid sources such as deeply circulating meteoric water.…”

Section: Ages Of Metamorphism Mylonite and Hydrothermal Alterationmentioning

confidence: 75%

“…A distinct Cr enrichment in and about the Otago lode> (McKeag et al 1989;Ashley & Craw 1995), has been related to leaching of Cr from the underlying metabasite-rich chloritic schists (Craw & Norris 1991 ;Craw 1992). Although the schist country rocks at Wakamarina are not enriched in Cr, the lodes themselves are enriched close to Cr-depleteo metabasites in the hanging wall, and metabasites with up to 411^70 ppm Cr are not uncommon in the Marlborough Schist (Johnston 1994;Skinner & Brathwaite 1998) Therefore, potential sources for the Cr-enrichment at Wakamarina are metabasites in underlying schist-hosted fluid reservoirs as well as from the Cr-leached hanging wall metabasites.…”

Section: Metal Deposition and Sourcesmentioning

confidence: 99%

“…IIA-IIB prehnite-pumpellyite to pumpellyite-actinolite facies at Wakamarina. From limited isotopic and fluid inclusion data, Craw & Norris (1991) estimated that vein deposition at Glenorchy was in the vicinity of 300°C and 1.5-3.5 kbar, at the low temperature end of BDT conditions. On the basis of their physical similarities to the Glenorchy lodes, similar pressure and temperature conditions are inferred for the Wakamarina lodes.…”

Section: Lode Structure and Pt Conditionsmentioning

confidence: 99%

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Mesozoic mesothermal quartz‐gold‐scheelite lodes, Wakamarina, Marlborough, New Zealand

Skinner

Brathwaite

1999

New Zealand Journal of Geology and Geophysics

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In the Wakamarina valley, Marlborough, ribbonbanded quartz lodes fill tensional faults in Caples Terranederived, Marlborough Schist and Wakamarina Quartzite. The largest of the lodes, the Golden Bar, has a strike length of at least 1.8 km and an average width of 2 m. It fills a steeply dipping normal fault which separates pumpellyite-actinolite fades psammitic schists on the footwall from stilpnomelanepumpellyite-spessartine quartzite (Wakamarina Quartzite) and metabasites on the hanging wall. The lode consists of bands of buck quartz separated by thin chlorite-sericite-rich laminae that have been split off the wall-rock schist.Five deformation events are recognised. The first two are linked with early Jurassic metamorphism, the younger event producing the earliest scheelite, whereas in early Mid Jurassic (illite/sericite K-Ar age of c. 175 Ma), the third event produced late metamorphic transtensional mylonites with minor quartz-scheelite veining. As uplift of the schist belt continued through the brittle-ductile transition zone, the fourth deformation created tensional faults across the mylonites which localised deposition of the quartzscheelite ± gold lodes (Golden Bar and Alfords). Internal lode structures indicate that internal pulsed fluid inflow and ductile vein deformation continued during this deformation. The fifth deformation, again with minor quartz-scheelite veining, created late brittle fracturing and compressional deformation of the lodes and country rocks.Fluid P-T conditions are probably comparable to those in similar mesothermal quartz-scheelite lodes at Glenorchy in Otago (1.5-3.5 kbar and 275-330°C), but co-existing albite and calcic plagioclase in Alfords lode implies that fluid temperatures at Wakamarina may have been locally higher. An extensive zone of sericitic hydrothermal alteration characterised by sericite and K-feldspar (sericite K-Ar age of c. 140 Ma -earliest Cretaceous) and loss of pumpellyite, stilpnomelane, and actinolitic amphibole surrounds the Golden Bar lode. The potassic enrichment, the stability of albite and chlorite in both wall rocks and the lodes, and a low sulphide content indicate that the fluids at Wakamarina had a higher aK + /aH + than in the Otago lodes, and a more neutral pH with a low capacity to carry gold in solution.

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Section: Ages Of Metamorphism Mylonite and Hydrothermal Alterationmentioning

confidence: 75%

Section: Metal Deposition and Sourcesmentioning

confidence: 99%

Section: Lode Structure and Pt Conditionsmentioning

confidence: 99%

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Mesozoic mesothermal quartz‐gold‐scheelite lodes, Wakamarina, Marlborough, New Zealand

Skinner

Brathwaite

1999

New Zealand Journal of Geology and Geophysics

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“…The Oturehua mineralised faults more closely resemble mineralised faults at Nenthorn (Fig. 1), where steeply dipping northwest-striking normal faults host veins with abundant open cavities and prismatic quartz that formed at relatively shallow crustal levels (<2 km; Mckeag & Craw 1989;Craw & Norris 1991). The Oturehua mineralised faults also resemble those at Barewood (Fig.…”

Section: Comparison To Other Otago Mineralised Structuresmentioning

confidence: 79%

“…6B) may represent an intermediate stage in development of more through-going structures. However, the mineralogy and style of mineralisation at Glenorchy are distinctly different from North Rough Ridge, and the Glenorchy mineralised faults probably formed at a greater depth within the metamorphic pile than the Oturehua mineralised faults (Paterson 1986;Mckeag & Craw 1989;Craw & Norris 1991). Further, the North Rough Ridge mineralised system resulted from northeast-southwest-directed extension, rather than east-west as at Glenorchy.…”

Section: Relationships Between Extensional Veins and Mineralised Faultsmentioning

confidence: 99%

Structural and lithological controls on gold mineralisation at Oturehua on the northeastern margin of the Otago Schist, New Zealand

Mackie

MacKenzie

Craw³

2009

New Zealand Journal of Geology and Geophysics

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A set of more than 50 mineralised normal faults cuts lower greenschist facies rocks at the northeastern margin of the Otago Schist belt near Oturehua, central Otago. The faults strike northwest and dip steeply (>60°) northeast, and individual mineralised zones are traceable for up to 700 m along strike. The mineralised faults are closely associated with, and are generally parallel to, a swarm of northwest striking, steeply dipping extensional quartz ± ankerite veins (centimetre scale) that occur over an area of at least 25 km 2 in the host schist. Mineralised faults contain 10-100 cm thick quartz veins that are traceable as interlinked structures for tens of metres along strike. where faults cut massive quartz-feldspar-rich schist, the veins are planar, contain scattered sulfide minerals and visible gold, and there has been little alteration of essentially undeformed adjacent wall rock (centimetre scale). in contrast, muscovite-rich laminated schist host rock is extensively deformed and altered adjacent to mineralised faults (metre scale), with addition of quartz (silicification) and ankeritic replacement of metamorphic chlorite by kaolinite and/or sericitic muscovite. Veins adjacent to laminated (micaceous) schist contain abundant breccias with variably altered clasts. widespread addition of auriferous sulfide minerals, mainly arsenopyrite, has occurred in the laminated schist alteration zones and breccias. The mineralised faults formed in the hinge of a northwest-trending post-metamorphic antiform, and the faults may have been localised by zones of weakness associated with kink folding in the hinge of the antiform. Hydrothermal fluids responsible for mineralisation were channelled by the normal faults. These faults developed by coalescence of extensional fractures in the schist rock mass during middle Cretaceous regional extensional unroofing of the Otago Schist belt. The location of these mineralised faults near the margin of the Otago Schist belt suggests a genetic relationship between mineralisation and the regional northwest-striking normal fault systems that cut and define the schist margin.

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Mineralogy and Paragenesis

Craw

MacKenzie

2016

SpringerBriefs in World Mineral Deposits

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Metamorphogenic Au‐W veins and regional tectonics: Mineralisation throughout the uplift history of the Haast Schist, New Zealand

Cited by 79 publications

References 37 publications

Mesozoic mesothermal quartz‐gold‐scheelite lodes, Wakamarina, Marlborough, New Zealand

Mesozoic mesothermal quartz‐gold‐scheelite lodes, Wakamarina, Marlborough, New Zealand

Structural and lithological controls on gold mineralisation at Oturehua on the northeastern margin of the Otago Schist, New Zealand

Mineralogy and Paragenesis

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