Ruatapu Cave (Alum Cave), Orakeikorako Thermal Area (Orakei Korako; The Hidden Valley), Taupo District, Waikato Region, North Island, New Zealand
|Latitude & Longitude (WGS84):||38° 28' 32'' South , 176° 9' 3'' East|
|Latitude & Longitude (decimal):||-38.47556,176.15111|
|Köppen climate type:||Cfb : Temperate oceanic climate|
Ruatapu or "Alum" Cave is one of the few caves known to have developed within an active thermal field. The Orakei Korako thermal area is dominated by alkali-chloride alteration but the cave hosts a steaming acid-sulphate pool and a series of efflorescences and other minerals produced as a result of acid-sulphate alteration of the host rocks (tuff).
While some caves in Australiasia produces powdery minerals from the interaction of bat guano and the chemistry in the wall rocks, at Ruatapu Cave new minerals are formed from the interaction of steam condensate, heat, and the wall rock chemistry. Kaolinite, opal-A, cristobalite, alunite, alunogen dominate the assemblage near the cave mouth. As conditions change further into the cave, tamarugite and potash alum form efflorescences, with lesser alunogen, meta-alunogen, mirabilite, halotrichite, kalinite, gypsum and tschermigite. Jarosite crusts have developed where acid sulphate pools meet ignimbrite wall rock covered in once living microbial mats. Decreases in water levels causes the jarosite to alter to potash alum, akaganeite, and schwertmannite.
Sometimes marketed as Aladdins Cave.
19 valid minerals.
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
0 - 2.588 Ma
|Cenozoic volcanic rocks|
Age: Pleistocene (0 - 2.588 Ma)
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. 
0.0117 - 2.588 Ma
|Middle Quaternary lake deposits|
Age: Pleistocene (0.0117 - 2.588 Ma)
Stratigraphic Name: Pakihi Supergroup
Lithology: Silt, pyroclastic material
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. 
0.126 - 0.781 Ma
|Middle Pleistocene lake deposits|
Age: Pleistocene (0.126 - 0.781 Ma)
Comments: Middle Pleistocene lake deposits. Age based on mixed
Reference: Heron, D.W. . Geology Map of New Zealand 1:250 000. GNS Science Geological Map 1.