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New Zealand journal of geology and geophysics
Dept. of Scientific and Industrial Research
New Zealand journal of geology and geophysics

Dept. of Scientific and Industrial Research

0028-8306

New Zealand journal of geology and geophysics/Journal New Zealand journal of geology and geophysicsSCI
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    Introduction to the Special Issue on South Island detrital gold, from sources to mines

    Anthony B. Christie
    241-244页
    查看更多>>摘要：Giant placer gold fields are present in Cenozoic gravel and sand in Westland and Otago-Southland, and smaller placers are found in west Nelson and Marlbor-ough (Figure 1; Christie 2016). The West Coast placers also extend offshore (Youngson and Stevenson 2016). Mining of the onshore placer gold deposits has been an important contributor to New Zealand's economy, especially in the early gold rushes of the 1860s-1870s that resulted in a substantial increase in the European population, a diversity of culture and the development of industry. New Zealand's total production from the 1850s to present day is c. 20 million oz of gold and the current annual production is c. 34,000 oz of gold with c. 90% from the West Coast. New Zealand has been a World-leader in many aspects of placer gold mining and processing technology, and geological research.
      原文链接:
    • NETL
    • NSTL
    • Taylor & Francis

    Detrital gold morphology and recycling around the early Miocene St Bathans paleovalley, Central Otago, New Zealand

    Marshall PalmerDave Craw
    245-259页
    查看更多>>摘要：The St Bathans paleovalley developed as a major southwest-draining fluvial system during early Miocene rejuvenation of the Central Otago landscape. Rounded quartz pebbles and detrital gold were recycled from Eocene quartz pebble conglomerates into the headwaters of this Miocene paleodrainage system on the northern margin of the Otago Schist belt. Gold particle morphology is mostly irregular and rough, locally with relict gold crystal shapes, plus a minor component of well-defined flakes. Incremental rounding and surface deformation at the 10 μm scale has occurred through several recycling events in Central Otago, hindering linkage of Miocene and younger placer gold to ultimate basement sources. More intense deformation of the gold, forming thin flakes, occurred in the lower reaches of the Miocene paleodrainage system as gold was transported >100 km to eastern Southland. Hence, the St Bathans paleovalley has been an important source of gold for historic mining in Central Otago and Southland.
      原文链接:
    • NETL
    • NSTL
    • Taylor & Francis

    Contrasting evolution of beach gold on two sides of an active orogen, Southern Alps, New Zealand

    Marshall PalmerTom RitchieDave Craw
    260-281页
    查看更多>>摘要：Placer gold on beaches on either side of a major active mountain belt has strongly contrasting compositions and morphologies. Pleistocene-Holocene beach gold placers have formed along the West Coast where silver (Ag)-bearing gold has been eroded from mountains via steep rivers and glaciers, followed by rapid burial in the abundant associated coastal sediments. Deformation along transport pathways has produced flattened gold flakes, but some primary crystalline shapes are preserved. Internal deformation of particles has caused recrystallisation to fine-grained (urn scale) grain structures including mylonitic banding. However, only minor localised (urn scale) Ag leaching has occurred on some particle margins. In contrast, Pleistocene beach placers formed on the southern side of the mountains contain flattened gold particles with a complex transport history involving longdistance (hundreds of km) fluvial transport since Cretaceous. Most primary Ag has been leached from this gold during transport-related recrystallisation to fine (5-20 urn) internal grains. Sand-blasting on the southern beaches with low sediment supply has resulted in further deformation and leaching of Ag to form toroidal shapes with Ag-free delicate extremities. Placer gold which has undergone rapid transport and deposition is useful as a prospecting tool for bedrock deposits in glaciated terranes around the world.
      原文链接:
    • NETL
    • NSTL
    • Taylor & Francis

    Redistribution of fine gold from hydrothermal sources to sedimentary sinks, Rakaia River, Canterbury, New Zealand

    Marshall PalmerDave Craw
    282-303页
    查看更多>>摘要：The Rakaia River in the South Island of New Zealand is a unique catchment in which to trace active detrital gold transport, deformation and concentration from near-coeval orogenic sources. The catchment hosts widespread small late Cenozoic hydrothermal alteration zones, some of which are gold-bearing, in actively rising and eroding mountain headwaters. Detrital gold liberated from the sources is distinctively porous with abundant micron-scale silicate inclusions, especially albite. Fine gold (～200-100 μm) has been transported >100 km downstream, but coarse gold remains highly diluted in proximal fluvial sediments. Fine gold is also diluted by coarse fluvial sediments that form the upper kilometre of the Canterbury sedimentary basin southeast of the mountain front. Minor re-concentration of fine gold occurs in a bedrock gorge at the mountain front, and on steep ocean beaches beyond the river mouth. Despite the long-distance transport, the fine gold particles have been only superficially modified by surface smearing and minor flattening. The gold may have travelled in suspension in the river, buoyed by electrostatically adhering fine micas, in contrast to detrital garnets that were rounded in bed-load. In contrast, detrital gold on the western side of the mountains has been flattened to thin flakes during bed-load transport.
      原文链接:
    • NETL
    • NSTL
    • Taylor & Francis

    Beach gold transport and aeolian concentration, southern New Zealand

    Marshall PalmerDave Craw
    304-326页
    查看更多>>摘要：Aeolian concentration of iron-titanium oxides (black sand) is a common phenomenon on coasts around the world but associated aeolian detrital gold is relatively rare. In contrast, Holocene and active dunes at Waipapa beach on the coast of the southern South Island of New Zealand host aeolian black sand layers with locally abundant finely particulate (<200 μm) gold and platinum, some of which have been mined historically. Aeolian concentration of black sand, gold and platinum is driven by strong prevailing westerly winds (gusts >100km/h) on annual or decadal time scales. Holocene fluvial recycling of aeolian sands has been important in upgrading the black sand, gold, and platinum contents. Surf concentration of black sand on the beach is minor and merely feeds the aeolian system, and this differs from other beach gold deposits around the world, which are surf-dominated. Most of the Waipapa beach gold (>90%) has flaky morphology with abundant superficial transport-related deformation reflective of fluvial transport, probably down the nearby Mataura River (～200 km transport) between Miocene and Holocene. Minor distinctive wind-sculpted toroidal gold, and the platinum, arrived from the west (～300 km transport) via the Waiau River and Foveaux Strait.
      原文链接:
    • NETL
    • NSTL
    • Taylor & Francis

    Fine and super-fine gold in mine waste from a coastal placer in southern New Zealand

    Marshall PalmerDave Craw
    327-341页
    查看更多>>摘要：Reprocessing of mine wastes is a growing procedure around the world, in order to extract more resources from already-mined rocks. Mineralogical and geometallurgical investigations are useful for planned reprocessing, and in this study at Round Hill placer gold mine we characterise fine (<100μm) and super-fine (micron-scale) particulate gold that has passed through the mine separation stages without being extracted. The gold was discharged with water and suspended sediments to settling ponds, separate from the more voluminous gravel and sand tailings. Authigenic clay and pyrite are abundant in the placer deposit and the settled suspension, and oxidised pyrite yielded gypsum and ferric oxyhydroxide. These minerals coat surfaces of gold particles and are locally intergrown with micron-scale authigenic gold. Most of the gold has toroidal shapes characteristic of beach derivation, and many of these are hollow or clay-filled. Minor super-fine cinnabar and mercury-bearing gold occur with clay. Annealing of gold has liberated silver, and micron-scale authigenic native silver occurs in the settled sediment. Reconcentration of fine and super-fine gold used abundant clean water and slow reprocessing and may be currently uneconomic at this site. The observations on suspended gold loss are relevant to gold recovery at placer mines around the world.
      原文链接:
    • NETL
    • NSTL
    • Taylor & Francis

    Anthropogenic Hg-Au residues from placer mining compared to natural Au-Hg sources, South Island, New Zealand

    Dave CrawMarshall Palmer
    342-361页
    查看更多>>摘要：Amalgamation of gold (Au) with mercury (Hg) has been occurring around the world for thousands of years, and global modern uncontrolled use of the process for gold concentration is causing widespread Hg contamination. Despite the environmental significance of HgAu-amalgamation, there has been little characterisation of solid materials that escape the processes and contribute to the Hg contamination. We describe herein the morphological and compositional characteristics of solids sampled through amalgamation processes obtained from small modern active mines in New Zealand under well-confined conditions. Liquid Hg droplets resisted amalgamation because of clay coatings on gold, and finely particulate gold (especially <100 μm) was only superficially coated by HgAu-amalgam with relict liquid Hg droplets. Recovery of purified gold and liquid mercury after amalgamation was done at high temperature (>360℃) by retorting, and at room temperature with acid treatment. Acid treatment yielded variably crystalline bronze-coloured Au with ～10% Hg, whereas retorting yielded pale yellow porous amorphous ('sponge') Au with <1% Hg. Most anthropogenic products are distinguishable from natural Hg-bearing materials, but some micron-scale features of retorted gold are indistinguishable from natural authigenic gold. Materials from all stages of the amalgamation process can be discharged to the environment, contributing to elevated dissolved Hg.
      原文链接:
    • NETL
    • NSTL
    • Taylor & Francis

    Atlas of beach gold morphology variations around the South Island, New Zealand

    Dave CrawMarshall Palmer
    362-373页
    查看更多>>摘要：This atlas presents a set of typical detrital gold scanning electron microscope images for beach gold samples from around the South Island of New Zealand. Images are presented as general views of gold particles, and of detailed features on the surfaces of particles. The samples for the images were obtained from a wide variety of geological and coastal sedimentary settings. The aim of the atlas is to provide comparative imagery for workers on beach gold deposits elsewhere in New Zealand and around the world. This atlas is the first comprehensive set of images of beach gold published anywhere in the world. The beach gold is typically finely particulate (50-200 urn), but most beach gold retains morphology derived from deformation during fluvial transport to the beach from ultimate sources. However, wind-sculpted toroidal gold is distinctive and widespread along Foveaux Strait beaches.
      原文链接:
    • NETL
    • NSTL
    • Taylor & Francis