Structure, metamorphism and mineralisation in the Haast Schist at Bendigo, Central Otago.
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Abstract:
Thirty square miles of the Haast Schist within The Bendigo area, including the quartz-gold lodes of the Bendigo mining area, were investigated. Although previously mapped as Chlorite IV Subzone of the Greenschist Facies, this area is now considered to be in the Biotite Zone.
Three principal phases of deformation were recognised on the basis of mesoscopic structures. The dominant structures on a mesoscopic scale were produced during the second phase, and are related to a macroscopic Phase II recumbent isocline or nappe facing north-east, with a hinge zone west of the Rise and Shine Shear Zone. This hinge zone is mapped throughout the area. Tectonic profiles indicate that the axial surface of this structure is flexured, although no mesoscopic evidence of this was found.
Two major faults are mapped. The already documented, mineralised Rise and Shine Shear Zone separates schist which has suffered extreme flattening perpendicular to S2 in the northeast, from schist characterised by abundant tight F2 folds in the southwest. The Green Valley Fault is here proposed for structural discontinuity in the southwest corner of the Bendigo area. It separates a zone of abundant greenschist and piemontite schist horizons in the southwest, from the more common coarsely laminated, quartzofeldspathic schist in the northeast.
As far as exposure allows, the quartz-gold and quartz-scheelite-gold lodes in the area are described. Fluid inclusions in the lode quartz are studied with a view to elucidating the origin of the mineralised quartz lodes. The undeformed nature of the quartz lodes suggests lode formation occurred after the peak of deformation and metamorphism, i.e. at temperatures and pressures below Biotite Zone metamorphism conditions of 440
Three principal phases of deformation were recognised on the basis of mesoscopic structures. The dominant structures on a mesoscopic scale were produced during the second phase, and are related to a macroscopic Phase II recumbent isocline or nappe facing north-east, with a hinge zone west of the Rise and Shine Shear Zone. This hinge zone is mapped throughout the area. Tectonic profiles indicate that the axial surface of this structure is flexured, although no mesoscopic evidence of this was found.
Two major faults are mapped. The already documented, mineralised Rise and Shine Shear Zone separates schist which has suffered extreme flattening perpendicular to S2 in the northeast, from schist characterised by abundant tight F2 folds in the southwest. The Green Valley Fault is here proposed for structural discontinuity in the southwest corner of the Bendigo area. It separates a zone of abundant greenschist and piemontite schist horizons in the southwest, from the more common coarsely laminated, quartzofeldspathic schist in the northeast.
As far as exposure allows, the quartz-gold and quartz-scheelite-gold lodes in the area are described. Fluid inclusions in the lode quartz are studied with a view to elucidating the origin of the mineralised quartz lodes. The undeformed nature of the quartz lodes suggests lode formation occurred after the peak of deformation and metamorphism, i.e. at temperatures and pressures below Biotite Zone metamorphism conditions of 440
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142 leaves : ill, photos, map (folded in pocket); 27 cm.
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1971Paterson
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POLYGON ((169.465968833000034 -44.979481206999935,169.464040016000013 -45.020740222999962,169.415240285000095 -45.020082112999944,169.408048343000019 -45.019982162999952,169.270741612000052 -45.018011699999931,169.237401509000051 -45.017505959999937,169.23902492000002 -44.963132512999948,169.240499027000055 -44.913758276999943,169.272723363000068 -44.914265306999937,169.369780085000116 -44.915730030999953,169.411927831000071 -44.916340437999963,169.414306060000058 -44.91637327199993,169.438955300000089 -44.916725422999946,169.468877621000047 -44.917142372999933,169.466858546000026 -44.960443694999981,169.466586572000097 -44.966276852999954,169.465968833000034 -44.979481206999935))
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Citation
Paterson, CJ, “Structure, metamorphism and mineralisation in the Haast Schist at Bendigo, Central Otago.,” Otago Geology Theses, accessed April 25, 2024, http://theses.otagogeology.org.nz/items/show/55.