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Macraes Mine, Macraes (Macraes Flat), Waitaki District, Otago Region, South Island, New Zealand

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Latitude & Longitude (WGS84): 45° 22' 34'' South , 170° 27' 1'' East
Latitude & Longitude (decimal): -45.37620,170.45040
GeoHash:G#: pzcjyew0q
Locality type:Mine
Köppen climate type:Cfb : Temperate oceanic climate


Open-cast gold mine working gold-scheelite deposits in lode shears, stockworks and disseminated stockworks within the gently dipping Hyde-Macraes Shear Zone (although scheelite is not being currently extracted due to metallurgical difficulties). Mined from a series of open pits extending 6km.

Located close to the settlement of Macraes Flat, 40 kilometres west north-west of Palmerston, and 80 km north of Dunedin, eastern Otago. A heritage precinct, art park, and trout hatchery are planned for the site once the mine closes.

The Macraes Mine started in 1990, and in 2003 produced about 5,000 kilograms of gold. Production from 1990-2013 ~3 Moz of gold.

Owned by Oceana Gold Corporation. The Frasers underground mine was commissioned in January 2008. Oceana Gold Corporation states in 2016 that the mine was 740 metre below the surface and 200 metres below sea level, with over 48 kilometres of developed tunnel drives.

Mineralisation is part of a duplex thrust system called the Hyde-Macraes Shear Zone, around 25 kilometres long, north-west to south-east trending, dipping 10-20 degrees north-east, of variable thickness up to 150 metres, hosted by the Otago schist.

The duplex system is dominated by steep dipping thrust faults, below well defined shallow upper and lower bounding thrusts. Mineralisation forms mainly in dilational jogs, or local extension zones. This occurs in relatively shallow parts of the intrashear thrust faults, cross-cut by late stage shallow, south dipping extensional veins. Gold was deposited about 130-140 million years ago, when the site was part of a thrust fault. The site is unusual as most gold deposits in Otago are found in steeper locations, in well defined quartz veins.

There are four types of gold and scheelite mineralisation 1) schist with disseminated sulphides; 2) black sheared schist consisting of fine grained graphite and sulphide bearing shears, proximal to the Hanging Wall; 3) sub-parallel quartz veins within and/or adjacent to the black sheared schist, locally cross-cutting schist foliation, containing disseminated sulphides in quartz veins; 4) local swarms of stockwork 100-2000 metre square, containing 10-100 sub-parallel quartz veins each, filling fractures, dipping almost vertical to the shallow east dipping schist.

The shear zone has a complex history from overprinting of numerous alteration and deformation episodes. It contains micaceous and feldspathic schist. The micaceous schist contains abundant muscovite, chlorite, abundant pyrite cubes up to 5mms in diameter, massive pyrite, arsenopyrite and gold. The feldspathic schist contains abundant albite, with thin black microshears, contain graphite, pyrite, arsenopyrite, gold, and rutile.

White massive quartz veins form a stockwork, discontinuous shallow dipping 10-20 degrees, and steeper veins 50-80 degrees. The quartz veins contain pyrite, arsenopyrite, and scheelite. Some native gold can be seen as free in quartz veins, but over 90% is microscopic enclosed within pyrite and arsenopyrite. Late pyrite veinlets contain microscopic sphalerite, chalcopyrite, and galena. Pyrite is the most dominant sulphide, formed and recrystallised throughout the deposit's history. Arsenopyrite may be found intergrown with boulangerite.

Some hydrothermal alteration has occurred in the shear rocks, with albite partial altered to muscovite and titanite, and epidote to rutile, quartz, calcite, kaolinite, chlorite and widespread siderite (Craw et. al., 1995). Titanite is replaced by rutile, and epidote by siderite, chlorite, muscovite, and calcite (Craw et. al., 1999).

This alteration is most evident in the black micro shears. These shears also contain very fine hydrothermal graphite, with pyrite, arsenopyrite, and widespread rutile. Gold is found here without quartz veins, precipitated during the reduction of the fluids by hydrothermal graphite. The sequence was later cut by mesothermal quartz veins, containing gold, scheelite, rutile, pyrite, and arsenopyrite.

Oxidation is up to 50 metres below the surface, and some coarse gold that was able to escape from the sulphides was found here, in the initial alluvial mining of the 1860's to 1940's.

The mine is the largest gold producer in New Zealand. Most gold mines in New Zealand, accessed historically quartz veins of a limited extent, whereas the Hyde-Macaes Shear Zone contains a package up to 150 metres thick of gold found in quartz veins, and outside this within the zone, along a 25 kilometre front. Satellite pits have been developed at the richest points. However the gold grade is low, ranging usually 1 to 1.5 g/t, and is only economic due to the large scale at which it is mined.

Specimens are not usually seen from the location, common with industrial scale mines. However, these types of mine often contain a process yet to be explained by science, where rocks of a non-monetary value end up in boxes under the beds of geologists and mine workers, only to see the light of day years after the mine has closed.


Mineral List

Mineral list contains entries from the region specified including sub-localities

25 valid minerals.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Quaternary
0 - 2.588 Ma



ID: 1308963
Late Quaternary alluvium and colluvium

Age: Pleistocene (0 - 2.588 Ma)

Stratigraphic Name: Pakihi Supergroup

Description: Unconsolidated to poorly consolidated mud, sand, gravel and peat of alluvial and colluvial origin.

Comments: Zealandia Megasequence Terrestrial and Shallow Marine Sedimentary Rocks (Neogene)

Lithology: Mud, sand, gravel, peat

Reference: Edbrooke, S.W., Heron, D.W., Forsyth, P.J., Jongens, R. (compilers). Geology Map of New Zealand 1:1 000 000. GNS Science Geological Map 2. [12]

Late Pleistocene
0.0117 - 0.126 Ma



ID: 1358633
OIS2 (Late Pleistocene) river deposits

Age: Pleistocene (0.0117 - 0.126 Ma)

Description: Gravel, sand and silt of low river terraces.

Comments: Late Pleistocene river deposits. Age based on geomorphic estimate

Lithology: Major:: {gravel},Minor:: {sand, silt}

Reference: Heron, D.W. . Geology Map of New Zealand 1:250 000. GNS Science Geological Map 1. [13]

Triassic - Permian
201.3 - 298.9 Ma



ID: 3189657
Paleozoic-Mesozoic crystalline metamorphic rocks

Age: Phanerozoic (201.3 - 298.9 Ma)

Stratigraphic Name: Haast Schist

Comments: Caples Terrane

Lithology: Metawacke; greenschist/almandine amphibolite grade metasedimentary/metavolcanic schist

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License


Localities in this Region
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New Zealand
New Zealand

This page contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.

References

Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Teagle, D.A.H., Norris, R.J., Craw, D. (1990) Structural Controls on Gold Bearing Quartz Mineralisation in a Duplex Thrust System Hyde-Macraes Shear Zone Otago Schist New Zealand, Economic Geology, Vol. 85, 1711-1719.
Craw, D., Hull, A.J., Fallick, A.E., Boyce, A.J. (1995) Sulphur isotopes as a metamorphogenic gold deposit Macraes mine Otago schist New Zealand, New Zealand Journal of Geology and Geophysics, 38:2, 131-136.
Craw, D., Windle, S.J., Angus, P.V. (1999) Gold mineralization without quartz veins in a ductile-brittle shear zone, Macraes Mine, Otago Schist, New Zealand. Mineralium Deposita 34, 382-394.
Pitcairn, I.K., Roberts, S., Teagle, D.A.H., Craw, D. (2005) Detecting hydrothermal graphite deposition during metamorphism and gold mineralization, Journal of the Geological Society London, Vol. 162, 429-432.
Ryan, C., Petrie, B.S., Craw, D. (2005) Geological controls on refractory ore in an orogenic gold deposit Macraes Mine New Zealand, Mineralium Deposita, 40:1, 45-58, January 2005.
Reddan, R., Moore, J.G. (2010) OceanaGold Technical Report for the Macraes Project located in the province of Otago New Zealand, OceanaGold Corporation and Oceana Gold (New Zealand) Limited.
MacKenzie, D., Farmer, L., Craw, D. (2013) Multi-stage ore formation at the Macraes gold scheelite deposit Otago Schist, NZ. AusIMM New Zealand Branch Annual Conference 2013 pp 281-294.
MacKenzie, D., Craw, D. (2016) Macraes Orogenic Deposit (New Zealand): origin and development of a world class gold mine, Springer International Publishing.

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