Geology of the Macraes Flat area.
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Abstract:
The area mapped covers 145 square kilometres in the Macraes Flat district and consists of rocks of the Haast Schist Zone, Tertiary volcanics, Tertiary to Recent sediments and mineralised quartz lodes.
Segregated quartzofeldspathic schist is the most common metamorphic lithology with greenschist, massive schist, phyllite and metachert also represented. All these lithologies are assigned to the Biotite Zone of the Greenschist Facies of metamorphism. Four phases of deformation have been recognised from mesoscopic and microsconic structures within the schist.
Tertiary volcanics of the Waipiata Volcanic Formation have basanitic mineralogy and contain four-phase (olivine - orthopyroxene - clinopyroxene - spinel) lherzolite nodules.
Tertiary sediments are described in terms of three broad facies which are correlated with rocks of the Stranraer Group and the Maori Bottom Formation.
Quartz lodes described are of two types:
(a.) Gold lodes
(b.) Gold-scheelite lodes
Gold lodes are located in quartzofeldspathic schist. Gold-scheelite lodes are restricted to a distinctive phyllite (pelitic) schist and appear to be of greater vertical and lateral extent than gold lodes. The strike of gold lodes and gold-scheelite lodes parallels the strike of penetrative foliation in the schist and gold-scheelite lodes of Golden Point and Round Hill tend to parallel the trend of fold axes. It is tentatively proposed that phyllite horizons have acted as source rocks for tungsten trace elements.
Segregated quartzofeldspathic schist is the most common metamorphic lithology with greenschist, massive schist, phyllite and metachert also represented. All these lithologies are assigned to the Biotite Zone of the Greenschist Facies of metamorphism. Four phases of deformation have been recognised from mesoscopic and microsconic structures within the schist.
Tertiary volcanics of the Waipiata Volcanic Formation have basanitic mineralogy and contain four-phase (olivine - orthopyroxene - clinopyroxene - spinel) lherzolite nodules.
Tertiary sediments are described in terms of three broad facies which are correlated with rocks of the Stranraer Group and the Maori Bottom Formation.
Quartz lodes described are of two types:
(a.) Gold lodes
(b.) Gold-scheelite lodes
Gold lodes are located in quartzofeldspathic schist. Gold-scheelite lodes are restricted to a distinctive phyllite (pelitic) schist and appear to be of greater vertical and lateral extent than gold lodes. The strike of gold lodes and gold-scheelite lodes parallels the strike of penetrative foliation in the schist and gold-scheelite lodes of Golden Point and Round Hill tend to parallel the trend of fold axes. It is tentatively proposed that phyllite horizons have acted as source rocks for tungsten trace elements.
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103 leaves : illus. (part col.), maps (in pocket at back) ; 30 cm.
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OU geology Identifier:
1975Sampson
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Location (WKT, WGS84):
POLYGON ((170.440055961295116 -45.379923602804681,170.401537248852264 -45.379767724754117,170.404041833898731 -45.325046893333813,170.469442649083163 -45.327230080040245,170.466073146955154 -45.380027795330363,170.440055961295116 -45.379923602804681))
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Sampson, Peter Goodwin., “Geology of the Macraes Flat area.,” Otago Geology Theses, accessed September 5, 2026, https://theses.otagogeology.org.nz/items/show/89.