Pounamu in the Sugar Loaf Stream - Route Burn catchment, Wakatipu, New Zealand

Author:

Todd, Andrea Jane.

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Abstract:

Pounamu, the Maori name for nephrite and semi-nephrite stone, occurs in the Wakatipu region of Aotearoa/New Zealand in association with the Greenstone Melange. Tremolite-actinolite formed and developed into pounamu within these rocks, under regional greenschist facies metamorphism during the Mesozoic, and were uplifted and eroded during the late Cenozioc. In situ pounamu accounts for about 1% of melange source rocks. Distribution of melange material was assessed in the Sugar Loaf Stream - Route Bum catchment to quantify how pounamu changes downstream, and to allow for resource assessment of both in situ and transported alluvial occurrences. Stream clast size and composition were recorded every 50 cm along 3-30 m transects at seven localities. Pounamu is initially concentrated to 4% in the Sugar Loaf- Route Bum alluvial system, with proportions decreasing to 1% at 4.8 km downstream from the melange source rocks. Approximately 15 general areas of active erosion have been identified where there is high potential for new pounamu to be exposed and carried into the active alluvial system. These areas should be prioritised by resource managers for future monitoring after earthquakes, storms and floods. The highest concentration (4%) and largest clast (36 x 21.5 x 20 cm) of pounamu was found at the Sugar Loaf Stream site, within an alluvial fan. No pounamu clasts were intersected by transects >5.5 km downstream from the source. Although some clasts were observed in the stream bed significant resource is unlikely to be present at this distance. Metavolcanic material, also derived from the Greenstone Melange, shows similar downstream dilution patterns as pounamu, but at higher proportions and lower uncertainties, giving potential for use as a proxy for pounamu distribution. Total pounamu within the Sugar Loaf Stream- Route Bum catchment is estimated at 33,000 ± 5000 t, 23 ± 7% of provisional estimates of the total Wakatipu resource. In situ source rock pounamu is estimated at 11,000 ± 4000 t, compared with 23,000 ± 2000 t of transported pounamu in alluvial fans, river alluvium and till deposits. Surface resource associated with active deposits is approximately 5000 t, or 15% of the total catchment resource. This is the maximum amount of resource expected to change within human time scales and forms a basis for setting maximum sustainable extraction/collection volumes.

Thesis description:

63, A16 leaves : ill.(some col.), maps (some col.) ; 30 cm.

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OU geology Identifier:

2003Todd

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POLYGON ((168.259074584233588 -44.690733246295466,168.334748158351573 -44.694158331284314,168.330421735394424 -44.734727143439834,168.256383684578481 -44.731367243019598,168.259074584233588 -44.690733246295466))

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http://download.otagogeology.org.nz/temp/Abstracts/2003Todd.pdf

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Citation

Todd, Andrea Jane., “Pounamu in the Sugar Loaf Stream - Route Burn catchment, Wakatipu, New Zealand ,” Otago Geology Theses, accessed February 7, 2025, https://theses.otagogeology.org.nz/items/show/420.

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