Geochemical signature of orogenic hydrothermal activity in an active tectonic intersection zone, Alpine Fault, New Zealand

Campbell, J.; Craw, D.; Frew, Russell; Horton, Travis W.; Chamberlain, C. Page

doi:10.1007/s00126-004-0421-4

Cited by 12 publications

(9 citation statements)

References 29 publications

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“…Arsenic displays an abrupt decrease in bulk As content from ~10 ppm at greenschist facies and below, to <1 ppm As in amphibolite facies (Fig. 12;Campbell et al 2004, Pitcairn et al 2006a. The decrease in the abundance of pyrite and cobaltite, which are important host minerals for As, is more gradual, and begins at lower metamorphic grade than the large depletion in wholerock As concentrations at between the greenschist and amphibolite facies.…”

Section: Metal Mobility At Middle To High Metamorphic Gradesmentioning

confidence: 93%

Sulfide Evolution During Prograde Metamorphism of the Otago and Alpine Schists, New Zealand

Pitcairn

Olivo

Teagle

et al. 2010

The Canadian Mineralogist

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Sulfide minerals in the Otago and Alpine schists, New Zealand, a metasedimentary belt exposed from unmetamorphosed greywackes up to amphibolite facies, underwent systematic changes in abundance, composition and texture during prograde metamorphism. In unmetamorphosed rocks, the most common sulfide mineral is framboidal pyrite, which contains abundant As (up to 14000 ppm), Co (up to 4000 ppm), Cu (up to 14000 ppm), Ni (up to 1100 ppm) and, locally, Ag (up to 270 ppm), Au (up to 90 ppm), and Sb (up to 240 ppm). Chalcopyrite, sphalerite, and galena also occur as isolated grains. Chalcopyrite and sphalerite contain few trace elements, whereas galena contains significant Se (up to 1600 ppm) and locally abundant Hg (up to 600 ppm). The distribution of these trace and minor elements is extremely heterogeneous. In subgreenschist-facies rocks, pyrrhotite replaces pyrite, and there is a clear textural change from framboidal pyrite to composite grains of pyrrhotite, sphalerite, chalcopyrite, galena and cobaltite. Pyrrhotite contains Co (average values 1100 ± 490 ppm), Cu (up to 17000 ppm), and Ni (up to 11000 ppm). Antimony and Hg are above detection in rare individual grains, but none of the other trace and minor elements sought are detectable. Sphalerite, galena and cobaltite increase in proportion in subgreenschist-facies rocks, and also contain higher concentrations of Ag (up to 1480 ppm in galena), Au (up to 230 ppm in galena and 110 ppm in cobaltite), As (38 ± 6 wt. % in cobaltite), Co (26 ± 4 wt. % in cobaltite), Hg (up to 4500 ppm in galena and 1100 ppm in sphalerite), and Sb (up to 1280 ppm in cobaltite and 770 ppm in galena). Pyrite, sphalerite, galena, and cobaltite become less abundant from subgreenschist-to amphibolite-facies rocks. In amphibolite-facies rocks, only pyrrhotite, chalcopyrite and trace amounts of galena and molybdenite occur, and none of these minerals contain detectable levels of Ag, Au, As, or Hg. Mass-balance calculations between sulfide minerals and whole rocks show that sulfides are important host minerals for S, Cu, and As, but host a minor proportion of Fe, Zn, and Pb. As pyrite, sphalerite, galena, and cobaltite become less abundant at higher metamorphic grade, Pb, Zn and Co are retained in the rock incorporated in other minerals, whereas As, Sb, Hg, Au, and Ag are removed from the rock, most likely by metamorphic devolatilization.

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Section: Metal Mobility At Middle To High Metamorphic Gradesmentioning

confidence: 93%

Sulfide Evolution During Prograde Metamorphism of the Otago and Alpine Schists, New Zealand

Pitcairn

Olivo

Teagle

et al. 2010

The Canadian Mineralogist

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“…The background As content of the metaturbidites is broadly consistent up to greenschist facies, and then drops to below 1 ppm in amphibolite facies metaturbidites ( Fig. 6A; Campbell et al 2004;Pitcairn et al 2006). This drop in background As content of the metaturbidites has been attributed to bulk synmetamorphic As mobilization into a metamorphic fluid, with subsequent expulsion from the rocks (Pitcairn et al 2006;Large et al 2012).…”

Section: Arsenic and Antimonymentioning

confidence: 94%

“…6A; Campbell et al 2004;Pitcairn et al 2006). This As is strongly partitioned into pyrite in lowgrade rocks, where pyrite As contents can exceed 1000 ppm (Fig.…”

Section: Arsenic and Antimonymentioning

confidence: 97%

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Contrasting geochemistry of orogenic gold deposits in Yukon, Canada and Otago, New Zealand

Craw

Mortensen

MacKenzie

et al. 2015

GEEA

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The YTT and OSB both formed and were mineralized during convergent tectonism that spanned Palaeozoic, Mesozoic and Cenozoic (Fig. 1). Initial Palaeozoic accretion and construction of the basement of both regions were followed by distinct collisional events that produced the main orogenic gold deposits in the Abstract: The Yukon-Tanana Terrane (YTT) of western Yukon Territory in NW Canada and Otago Schist belt (OSB) of South Island, New Zealand share similar geological evolutionary histories as convergent orogenic belts. Both belts host orogenic gold deposits of mainly Jurassic to Early Cretaceous age. Jurassic mineralization in the YTT occurred during convergent orogenesis and stacking of previously-metamorphosed (Palaeozoic) greenschist-amphibolite facies metasediments, metavolcanic rocks, and metagranitoids. Early Cretaceous OSB mineralization occurred in the latter stages of terrane accretion of un-metamorphosed turbidites with minor basaltic rocks. Metamorphism of the OSB turbidites mobilised background levels of Au (0.6-1.3 ppb), As (2-20 ppm), Sb (0.1-1 ppm), and W (< 10 ppm), primarily under greenschist to lower amphibolite facies conditions when diagenetic pyrite (Au c. 0.5-2 ppm; As c. 500-10 000 ppm) transformed to pyrrhotite on a regional scale. In contrast, the previously-metamorphosed YTT rocks had generally low background As contents (1-2 ppm) apart from some As-rich quartzites (up to 100 ppm As). Consequently, there was less As available for orogenic mobilisation, and YTT Au deposits generally have lower concentrations of this pathfinder element compared to the OSB. YTT host rocks, especially metagranitoids, have anomalous levels of Mo (10-300 ppm), and many orogenic deposits contain elevated Mo, locally including molybdenite. OSB turbidites have elevated Mo (2-200 ppm), along with elevated Au and As, in diagenetic pyrite, but this Mo became largely dispersed through the metamorphic pile as metamorphic grade increased and pyrite transformed to pyrrhotite. OSB orogenic deposits have only marginally elevated Mo (c. 1 ppm), no molybdenite, and accessory scheelite in these deposits is distinctly Mo-poor. Only minor mobilisation of base metals occurred in these orogenic belts, and orogenic Au deposits contain sparse base metal sulphides. Orogenic deposits in the YTT and OSB differ in that Au (and other associated elements) in many of the orogenic deposits in the YTT was remobilised from relatively local sources (e.g. pre-existing Cu-Mo-Au porphyry or volcanogenic sulphide mineralization) whereas Au in the OSB was mobilised from larger volumes of homogeneous rock at depth.

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“…6 km. Deep-sourced crustally exchanged fluids are an important component of gold-bearing fluids in this hydrothermal system (Cox et al 1997;Craw et al 2002;Campbell et al 2004;Craw 2006).…”

Section: Alpine Schistmentioning

confidence: 99%

Lead isotope constraints on the origin of Cenozoic orogenic gold systems in the Southern Alps and northwestern Otago, South Island, New Zealand

Mortensen

Craw

MacKenzie

et al. 2010

New Zealand Journal of Geology and Geophysics

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Lead isotopic compositions were determined for sulphides from Pliocene-Pleistocene gold-bearing veins in the Alpine Schist and from Miocene gold-bearing veins and vein breccias from the Shotover-Macetown area in the northwest Otago Schist belt. The lead isotopic signatures are consistent with derivation of Pb in the vein minerals predominantly from metasedimentary rocks that underlie the region. Differences in Pb isotopic signatures between deposits are interpreted to result from lateral and vertical lithological variability within the source rock mass. The host rocks also contain metabasic rocks with N-MORB, E-MORB or within-plate basalt chemistry. However, the observed Pb isotopic signatures in the gold-bearing veins preclude incorporation of significant amounts of Pb from the metabasites. The Pb isotopic signatures of lamprophyre dikes that were intruded into the Otago Schist coeval with Miocene gold mineralisation are distinctly more radiogenic than those of the hydrothermal veins. Thus, although the lamprophyre dikes were emplaced into similar extensional structural sites to the gold-bearing veins, there was no genetic relationship between lamprophyre dikes and gold mineralisation.

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Geochemical signature of orogenic hydrothermal activity in an active tectonic intersection zone, Alpine Fault, New Zealand

Cited by 12 publications

References 29 publications

Sulfide Evolution During Prograde Metamorphism of the Otago and Alpine Schists, New Zealand

Sulfide Evolution During Prograde Metamorphism of the Otago and Alpine Schists, New Zealand

Contrasting geochemistry of orogenic gold deposits in Yukon, Canada and Otago, New Zealand

Lead isotope constraints on the origin of Cenozoic orogenic gold systems in the Southern Alps and northwestern Otago, South Island, New Zealand

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