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Table 1 Subsurface lithology of Ngatamariki from wells NM1-7, as described by Bignall (2009)

From: Matrix permeability of reservoir rocks, Ngatamariki geothermal field, Taupo Volcanic Zone, New Zealand

Ngatamariki stratigraphy
Formation name Thickness (m) Lithological description
Orakonui Fm 0–10 Pumice breccia, with common volcanic lithics, quartz and minor feldspar
Orunanui Fm 15–85 Cream to pinkish vitric–lithic tuff, with vesicular pumice and lava lithics, plus quartz, feldspar and rare pyroxene crystal fragments
Huka falls Fm > 70–285 Coarse to medium grained sandstone, minor gravel (laminated lacustrine sediments)
Waiora Fm 0–10 An upper level interval of Waiora Formation, comprises pumice-rich vitric tuff, with volcanic lithics, quartz, rare biotite and pyroxene crystals
Rhyolite lava 115–315 Glassy rhyolite lava, with perlitic textures, phenocrysts are quartz, feldspar, pyroxene and magnetite
Waiora Fm 0–240 A lower interval of Waiora Formation, comprising pumice-rich vitreous tuff, intercalated with crystal tuff, tuffaceous coarse sandstone and tuffaceous siltstone
Wairakei ignimbrite 100–200 Crystal–lithic tuff/breccia, with abundant quartz, minor feldspar, rare biotite and pyroxene, minor volcanic lithics and pumice, in a fine ash
Rhyolite lava 0–285 Hard porphyritic quartz-rich rhyolite lava with phenocrysts of quartz, minor feldspar, and minor ferromagnesian minerals
Tahorakuri Fm 460–700 White to pale grey lithic tuff/breccia intercalated with fine sediments. In NM6 it is intercalated with 310 m of andesite lavas and breccias (tuffs and sediments)
Tahorakuri Fm > 200–840 Pale grey, lithic tuff/breccia containing dark grey/brown lava, rhyolite pumice greywacke–argillite and sandstone clasts in a silty matrix (Akaterewa ignimbrite)
Tahorakuri Fm > 830 Pale grey porphyritic feldspar, pyroxene and amphibole andesite lava and breccia (andesite lava, breccia)
Torlesse greywacke Undefined Pale grey to grey, massive meta-sandstone which lack obvious bedding, quartz veins