Manganese mineralisation in the Otago schist, Mount Patriarch, northwest Otago, New Zealand
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Abstract:
Manganiferous metachert outcrops in several localities on Mount Patriarch, northwest Otago New Zealand. The Otago Schist in the Mount Patriarch region grades from TZIIA in the east of the field area to TZIII in the west (Map 1). The metamorphic grade of the rocks in the study area grades from pumpellyite-actinolite facies in the east to lower greenschist facies in the west. The pumpellyite-out isograd is mapped lkm to the west of Mount Patriarch. Lithologies in the area are interbedded turbidite sequences comprising pelite and psammite rich schists together with metaconglomerate, greenschist, metachert and manganiferous chert horizons. The mineral assemblage of the schist is typically quartz-albite-epidote-actinolitepumpellyite- chlorite-stilpnomelane-calcite. Bedding is well preserved in the area and defines a large 12km wide syncline plunging steeply to the southwest at ea. 60-70°. A strong axial planar cleavage is developed in the hinge area of the syncline, which is situated on Mount Patriarch. Bedding is intensely transposed in the hinges of common, mesoscopic, isoclinal folds. Kink folding and dextral strike-slip faulting in the area postdates the ductile phase of deformation. The schists in the area were geochemically determined to belong to the Rakaia subterrane of the Torlesse terrane. The greenschists showed an ocean-island/island-arc geochemical signature. The mineral assemblage and geochemistry of two manganese associations sampled on Mount Patriarch was determined. The massive manganese association has a mineral assemblage of rhodochrosite, rhodonite, quartz and spessartine. The mineral assemblage of the nodular manganese association is Mn-calcite, rhodochrosite, kutnohorite, rhodonite, spessartine, caryopilite, coombsite, Mn-stilpnomelane?, quartz, pyrite, sphalerite, Ni-Cu-Co-Zn-As sulfides and Fe-sulfates. The coombsite occurrence is the third observation worldwide. The nodular manganese association shows many similarities to modern and fossil manganese nodules. The geochemical signature of the two manganese associations shows a submarinehydrothermal signature. A combination of the submarine-hydrothermal signature and the manganese associations stratigraphic sequence points to a tectonic setting involving an island arc or ocean island setting, near an active continental margin.
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156 leaves : ill. (some col.), maps (some col., some folded) ; 30 cm.
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2003Morton
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Citation
Morton, John (Jonathon Peter), “Manganese mineralisation in the Otago schist, Mount Patriarch, northwest Otago, New Zealand,” Otago Geology Theses, accessed February 7, 2025, https://theses.otagogeology.org.nz/items/show/416.