Gold nuggets: supergene or hypogene?
Native gold in placers and intensely weathered rocks commonly occurs as grains (less than 500 μm) and, more rarely, as large (greater than 4 mm or 1 g) nuggets. There has long been speculation about whether gold nuggets, especially those found in deeply weathered regolith environments, are supergene...
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| Format: | Journal Article |
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2007
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| Online Access: | http://hdl.handle.net/20.500.11937/33276 |
| _version_ | 1848753900316786688 |
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| author | Hough, R. Butt, C. Reddy, Steven Verrall, M. |
| author_facet | Hough, R. Butt, C. Reddy, Steven Verrall, M. |
| author_sort | Hough, R. |
| building | Curtin Institutional Repository |
| collection | Online Access |
| description | Native gold in placers and intensely weathered rocks commonly occurs as grains (less than 500 μm) and, more rarely, as large (greater than 4 mm or 1 g) nuggets. There has long been speculation about whether gold nuggets, especially those found in deeply weathered regolith environments, are supergene or hypogene in origin. An examination of the external and internal characteristics of more than 30 nuggets from different locations in Western Australia, Queensland and Victoria, ranging from 1 g to greater than 8 kg, was carried out. All of these nuggets are composed of gold - silver alloys, typical of hypogene gold. Furthermore, each has a polycrystalline internal structure that is characteristic of high temperature (greater than 250C) thermal annealing. All of the nuggets also exhibit corrosion features, including pits, voids and silver depletion that are due to weathering. The silver depletion is strongly controlled by the crystal structure and proceeds along crystallographic grain boundaries by a selective solution process equivalent to depletion gilding. Polycrystalline Au - Ag nuggets with the characteristics presented here are hypogene in origin, concentrated at the surface as the residue of prolonged exposure, weathering and erosion of gold deposits, not by supergene growth. |
| first_indexed | 2025-11-14T08:31:52Z |
| format | Journal Article |
| id | curtin-20.500.11937-33276 |
| institution | Curtin University Malaysia |
| institution_category | Local University |
| last_indexed | 2025-11-14T08:31:52Z |
| publishDate | 2007 |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | curtin-20.500.11937-332762019-02-19T05:36:13Z Gold nuggets: supergene or hypogene? Hough, R. Butt, C. Reddy, Steven Verrall, M. gold nuggets hypogene supergene silver depletion crystallography annealing Native gold in placers and intensely weathered rocks commonly occurs as grains (less than 500 μm) and, more rarely, as large (greater than 4 mm or 1 g) nuggets. There has long been speculation about whether gold nuggets, especially those found in deeply weathered regolith environments, are supergene or hypogene in origin. An examination of the external and internal characteristics of more than 30 nuggets from different locations in Western Australia, Queensland and Victoria, ranging from 1 g to greater than 8 kg, was carried out. All of these nuggets are composed of gold - silver alloys, typical of hypogene gold. Furthermore, each has a polycrystalline internal structure that is characteristic of high temperature (greater than 250C) thermal annealing. All of the nuggets also exhibit corrosion features, including pits, voids and silver depletion that are due to weathering. The silver depletion is strongly controlled by the crystal structure and proceeds along crystallographic grain boundaries by a selective solution process equivalent to depletion gilding. Polycrystalline Au - Ag nuggets with the characteristics presented here are hypogene in origin, concentrated at the surface as the residue of prolonged exposure, weathering and erosion of gold deposits, not by supergene growth. 2007 Journal Article http://hdl.handle.net/20.500.11937/33276 10.1080/08120090701488289 fulltext |
| spellingShingle | gold nuggets hypogene supergene silver depletion crystallography annealing Hough, R. Butt, C. Reddy, Steven Verrall, M. Gold nuggets: supergene or hypogene? |
| title | Gold nuggets: supergene or hypogene? |
| title_full | Gold nuggets: supergene or hypogene? |
| title_fullStr | Gold nuggets: supergene or hypogene? |
| title_full_unstemmed | Gold nuggets: supergene or hypogene? |
| title_short | Gold nuggets: supergene or hypogene? |
| title_sort | gold nuggets: supergene or hypogene? |
| topic | gold nuggets hypogene supergene silver depletion crystallography annealing |
| url | http://hdl.handle.net/20.500.11937/33276 |