Golden Bar gold deposit as an extension of the Hyde‐Macraes Shear Zone, east Otago, New Zealand

Jones, Philip; Craw, D.; Norris, R. J.

doi:10.1080/00288300709509837

Cited by 13 publications

(8 citation statements)

References 16 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The inferred directions of movement are at a high angle to the strike of the Hyde-Macraes Shear Zone (Teagle et al 1990). Jones et al (2007) reported a top-to-the-west-northwest direction of thrusting. They inferred the thrusting direction to be perpendicular to the line of intersection of steeply dipping duplex shears with the bounding duplex shears.…”

Section: Footwall Fault and Hyde-macraes Shear Zonementioning

confidence: 99%

Extensional deformation along the Footwall Fault below the Hyde-Macraes Shear Zone, Otago Schist, New Zealand

Ring

Mortimer

Butz³

et al. 2018

New Zealand Journal of Geology and Geophysics

View full text Add to dashboard Cite

We describe ductile-to-brittle structures across the Footwall Fault directly below the Hyde-Macraes Shear Zone in the Otago Schist. These indicate that pervasive deformation along the Footwall Fault was due to northeast-southwest crustal extension. Structures below the Footwall Fault are ductile top-to-the-northeast extensional shear bands that formed in a penetrative lower greenschist facies foliation. With progressive deformation, shear bands formed at higher angles to the foliation, culminating in the shear bands being cut by lowand high-angle normal faults. In the hanging wall, extensional structures are much less pervasive and comprise a few high-angle normal faults. This sharp contrast in structural evolution of footwall and hanging wall resembles the tectonic evolution of major extensional shear zones worldwide. We propose that mid Cretaceous normal movement on the lowangle Footwall Fault accompanied the formation of the steeper Waihemo Fault further north. On a regional scale, much of the boundary between the Otago Schist core and its northern flank is cut by mid Cretaceous normal faults. Zircon fission-track ages from the footwall range from 79 ± 13.7 to 46.1 ± 6.2 Ma (2σ uncertainties) and young in the direction of hanging wall transport. One sample from the hanging wall yielded a zircon fission-track age of 76 ± 12.9 Ma. The fission-track ages are hard to interpret as zircon across the fault zone was affected by partial or full annealing. In part, the ages confirm mid Cretaceous movement but may also be interpreted to suggest additional reactivation of the Footwall Fault at slow inferred slip rates. ARTICLE HISTORY

show abstract

Section: Footwall Fault and Hyde-macraes Shear Zonementioning

confidence: 99%

Extensional deformation along the Footwall Fault below the Hyde-Macraes Shear Zone, Otago Schist, New Zealand

Ring

Mortimer

Butz³

et al. 2018

New Zealand Journal of Geology and Geophysics

View full text Add to dashboard Cite

show abstract

“…Hence, the Otago Schist is a wellendowed gold province, and is considered to be prospective, particularly for new orogenic deposits. Recent and on-going gold exploration in the province has targeted the Macraes type of deposit, which is characterised by a shear zone containing large volumes of mineralised rock containing disseminated gold in association with sulphide minerals (Teagle, Norris and Craw, 1990;Craw, 2002;Mitchell et al, 2006;Jones, Craw and Norris, 2007).…”

Section: Introductionmentioning

confidence: 99%

Cretaceous tectonics and gold mineralisation in the Otago Schist, New Zealand

Mortimer¹,

Craw²,

MacKenzie³

et al. 2019

Preprint

View full text Add to dashboard Cite

This paper provides a regional-scale background for understanding gold-mineralising processes in the Otago Schist during the Cretaceous. At this time the schist belt was in the latter stages of formation as an accretionary complex with 2000 km strike length on the Pacific margin of Gondwana. The Otago Schist is interpreted as an exhumed accretionary wedge of structurally stacked clastic metasedimentary rocks with minor metabasic rocks. Metamorphic grade reached upper greenschist facies. Gold and other related elements were mobilised from the metasedimentary rocks during metamorphism, and these elements contributed to the high levels of orogenic gold endowment (>18 million ounces in the schist belt. Mesozoic Gold deposits were emplaced in two distinct pulses, one at the beginning of the Early Cretaceous (~140-135 Ma) and the other at the end of the Early Cretaceous (~112-100 Ma). These mineralising pulses were driven by regional tectonic events that may have involved episodic underplating of subducting material, and/or subduction of spreading ridges. The earlier event was most closely associated with metamorphic processes that mobilised gold from the accreted metasediments during convergent tectonics, and appears to have been the more economically significant. The later event took place as accretionary processes ceased and the Zealandia portion of Gondwana began to undergo intracontinental rifting.

show abstract

“…The Hyde-Macraes Shear Zone is more than 250 m thick and has at least 30 km traceable strike length (Teagle et al 1990;Jones et al 2007). Mineralised rocks are typically highly micaceous schists, although some mineralisation of more feldspathic schists has occurred also (Petrie et al 2005).…”

Section: Macraes Mine Geologymentioning

confidence: 99%

“…3D). The structurally higher shear is a complex duplex structure that is focused in micaceous schists, but includes lenses of more feldspathic schist and silicified schist, with some mineralised quartz veining, that has been resheared after initial mineralisation (Jones et al 2007). The lower, graphitic micaceous shear (Fig.…”

Section: Pyrite In a Macraes Mine Shearmentioning

confidence: 99%

Diagenetic pyrite as a source for metals in orogenic gold deposits, Otago Schist, New Zealand

Large

Thomas

Craw

et al. 2012

New Zealand Journal of Geology and Geophysics

109

View full text Add to dashboard Cite

Framboidal diagenetic pyrite occurs in low-grade turbidites on the northeast margin of the Otago Schist. Laser ablation inductively coupled plasma mass spectrometry (ICP-MS) analyses of these framboids show that the main metals present, in addition to Fe, are As, Pb, Zn, Te, Ag and Mo; Au is present at between 0.5 and 2 ppm. Minor Au and As anomalies also occur sporadically in the turbidite matrix. Porphyroblastic pyrite at the nearby Macraes mine contains micron-scale native gold and solid solution gold up to 30 ppm. These pyrite porphyroblasts are also enriched in As, W, Ni, Co and Bi. Lead, Zn, Te and Mo contents are distinctly lower than in the low-grade framboids. These results show that low-grade turbidites were a fertile source for Au and As for orogenic gold deposits such as Macraes. The pyrite to pyrrhotite transition, which occurred mainly under greenschist facies conditions, was probably the most effective As and Au mobilisation reaction during Mesozoic metamorphism.Keywords: pyrite; framboid; gold; arsenic; tungsten; orogenic; Macraes mine IntroductionProgressive metamorphism of sedimentary rocks has been shown to mobilise elements that, when concentrated, make up orogenic gold deposits (Pitcairn et al. 2006(Pitcairn et al. , 2010Large et al. 2007Large et al. , 2009Large et al. , 2011. These elements, including gold, were present in trace concentrations in the original sedimentary rocks, and were released from those rocks in metamorphic fluids that are generated by metamorphic dehydration reactions (Pitcairn et al. 2006(Pitcairn et al. , 2010Large et al. 2011). At least some of these trace metals can be concentrated in the sediments by diagenetic processes on the sea floor, particularly into diagenetic pyrite (Large et al. 2007(Large et al. , 2009. Hence, recrystallisation and decomposition of this diagenetic pyrite during prograde metamorphism are potentially fertile sources for gold and other trace elements during orogenesis (Pitcairn et al. 2006;Scott et al. 2009;Large et al. 2011).In the Otago Schist of southern New Zealand, trace metals were released from the metasedimentary pile over a wide range of metamorphic conditions, from subgreenschist facies to amphibolite facies, but primarily within the greenschist facies (Pitcairn et al. 2010). The Macraes mine, a world-class orogenic gold deposit, formed under greenschist facies conditions in the same metamorphic pile, with mineralisation driven by metamorphic processes (Craw et al. 1999;Craw 2002). Pyrite is an important constituent of the mineralised rocks at the Macraes mine and hosts a significant proportion of the gold (Craw et al. 1999). Hence, pyrite is a key mineral throughout the metamorphicÁ hydrothermal mineralisation process in the Otago Schist, at the source of metals in low-grade rocks, during metamorphic mobilisation of metals from those rocks, and at the site of deposition under greenschist facies conditions.In this study, we focus on the trace element compositions of diagenetic pyrite in low-grade rocks, and on ore pyrite in the Mac...

show abstract

Golden Bar gold deposit as an extension of the Hyde‐Macraes Shear Zone, east Otago, New Zealand

Cited by 13 publications

References 16 publications

Extensional deformation along the Footwall Fault below the Hyde-Macraes Shear Zone, Otago Schist, New Zealand

Extensional deformation along the Footwall Fault below the Hyde-Macraes Shear Zone, Otago Schist, New Zealand

Cretaceous tectonics and gold mineralisation in the Otago Schist, New Zealand

Diagenetic pyrite as a source for metals in orogenic gold deposits, Otago Schist, New Zealand

Contact Info

Product

Resources

About