Rahu prospect, Karangahake, Hauraki District, Waikato Region, North Island, New Zealand

Latitude & Longitude (WGS84):	37° 24' 52'' South , 175° 43' 18'' East
Latitude & Longitude (decimal):	-37.41465,175.72192
Köppen climate type:	Cfb : Temperate oceanic climate

Gold-silver prospect.

Located approximately two kilometres north of the Talisman Mine, and north both of the Ohinemuri River and Karangahake town site.

In 2017, New Talisman Gold Mines, which owns the Talisman leases to the south of the Ohinemuri River, purchased an 80% stake in the Rahu prospect, through its acquisition of Newcrest Mining's subsidiary, Newcrest New Zealand Exploration.

While gold-silver is found south of the river in epithermal veins, mineralisation at Rahu is found in collapse and tumbling breccia. The Rahu prospect shows a complex structural history, with a main phase right-lateral extensional faulting associated with the mineralisation, and final normal faulting stage with structural blocks downthrown to the north.

The main faults strike north-east, sub-vertical, with oblique displacement and strike slip. These are crossed by east-west faults. A horst and graben structure delineates the prospect.

The host rock is the Waipupu Formation andesite, overlain by the localised Rahu Formation, then the Whakamoehau Formation, all late Miocene. The Waipupu and Whakameohau formations contain interbedded sandstone and mudstone. The Rahu Formation contains acid to intermediate tuffs, fine grained sedimentary rocks, dacite, lapilli tuffs, and pyrite rich lake bed sediments. This formation hosts the hydrothermal breccia and mineralisation.

There are three mineralised anomalies, called Eunice, Barbara, and Hodgson, found on the edges of the zone. The intervening rocks are not silicified, but are intensely hydrothermally altered. The anomalies contain polymictic hydrothermal and collapse breccia, silicified cataclasites, jigsaw breccia, and rounded clasts of andesite and minor black mudstone. This is set in a matrix of quartz and opaline silica with varying amounts of un-named sulphides.

There is a main north north-east trending vein, and subsidiary east north-east or east south-east vein, both with similar geology. The veins are filled with massive white microcrystalline quartz, and clear comb quartz, with some colloform and crustiform banding, and replacement of platy calcite with quartz. Cavities are common, caused by acidic hydrothermal fluids, and are commonly filled with clear quartz prisims to 3 cms long as comb quartz. The veins are cross-cut by light grey microcrystalline quartz, and opaline silica veinlets.

Mineral List

4 valid minerals.

Rock Types Recorded

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: 3187411	Cenozoic volcanic rocks Age: Pleistocene (0 - 2.588 Ma) Lithology: Ignimbrite(s); felsic volcanic rocks; rhyolite 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]
Pliocene - Late Miocene 2.588 - 11.62 Ma ID: 1309470	Whitianga Group rhyolite lava and related deposits Age: Neogene (2.588 - 11.62 Ma) Stratigraphic Name: Whitianga Group Description: Rhyolite lavas and dome complexes with associated breccia and tuff; minor obsidian and intense hydrothermal alteration locally. Comments: Zealandia Megasequence Extrusive and Intrusive Rocks (Neogene) Lithology: Rhyolite, breccia, tuffite 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]
Messinian - Tortonian 5.333 - 11.62 Ma ID: 1335722	Waiwawa Subgroup andesite and dacite (Coromandel Group) of Coromandel Volcanic Zone Age: Miocene (5.333 - 11.62 Ma) Stratigraphic Name: Waiwawa Subgroup Description: Andesite, dacite and rhyodacite flows and domes with intercalated tuff, tuff breccia and volcaniclastic sediments. Local, non--welded, dacitic, pumice-rich ignimbrite. Comments: Neogene igneous rocks. Age based on K-Ar Lithology: Major:: {andesite},Minor:: {dacite, rhyodacite, tuff, breccia} Reference: Heron, D.W. . Geology Map of New Zealand 1:250 000. GNS Science Geological Map 1. [13]

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

References

External Links