|Latitude & Longitude (WGS84):||37° 6' 4'' South , 175° 33' 20'' East|
|Latitude & Longitude (decimal):||-37.10127,175.55574|
|Köppen climate type:||Cfb : Temperate oceanic climate|
Centred on, and named after Ohio Stream, 3 kilometres north north-east of Thames. Geological speaking the area covered by the prospect is poorly constrained, with some of the references also describing neighbouring historic gold mines, which will be listed separately where enough information is found.
The prospect occupies a jog in the Hauraki graben fault, shared with other deposits in the Thames area. Dextral rotation with associated plate rotation, produced a series of dilational fractures hosting sulphidation alteration of the Ohio Stream porphyry, with more distal auriferous mesothermal veins.
There is progressive alteration zoning north-west to south east covering propylitic (epidote-chlorite); intermediate argillic (chlorite-sericite); phyllic (sericite-quartz); advanced argillic (pyrophyllite-diaspore-quartz); silicified ledges with progressively more abundant alunite; argillic (dickite, kaolinite, illite); and low grade propylitic (chlorite, carbonate, illite).
The porphyry deposit and intrusive breccia is altered to a core of potassic K feldspar-magnetite-biotite, with surrounding propylitic quartz-chlorite and epidote-pyrite calcite alteration, both overprinted by quartz-sericite-pyrite or chlorite-sericite alteration.
Lookout Rocks on the north-east border of the prospect contains a narrow core zone of quartz-alunite-dickite grading outwards to an extensive pyrophyllite-dickite-diaspore-kaolinite zone, that overlaps the upper part of the phyllic alteration zone of the Ohio Stream porphyry Cu-Au-Mo deposit.
The dacite porphyry and surrounding the intrusion contains thin quartz-anhydrite-carbonate stock work veins containing disseminated sulphides such as pyrite, molybdenite, galena, sphalerite, tetrahedrite, and chalcopyrite. Mineralisation is overall low grade with 0.12-0.20% Cu, and 0.23-0.4 g/t Au, with a vertical extent greater than 600 metres. Other minerals present which are noted are magnetite, rutile, hematite, bornite, covellite, enargite.
The veins trend sub-parallel north-east across 4 x 2 kilometres contain ore assemblages of (1) quartz-pyrite-electrum-pyrargyrite locally bonanza grades; (2) quartz-sulphides-tellurides (Au, Ag, Bi).
26 valid minerals.
Rock Types Recorded
Select Rock List TypeAlphabetical List Tree Diagram
Entries shown in red are rocks recorded for this region.
- Igneous rock
- Sedimentary rock and sediment
- Unclassifed rock
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. 
5.333 - 23.03 Ma
|Coromandel Group Miocene andesite and basaltic andesite lava|
Age: Miocene (5.333 - 23.03 Ma)
Stratigraphic Name: Coromandel Group
Comments: Zealandia Megasequence Extrusive and Intrusive Rocks (Neogene)
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. 
|Tortonian - Burdigalian|
7.246 - 20.44 Ma
|Kuaotunu Subgroup andesite and dacite (Coromandel Group) of Coromandel Volcanic Zone|
Age: Miocene (7.246 - 20.44 Ma)
Stratigraphic Name: Kuaotunu Subgroup
Reference: Heron, D.W. . Geology Map of New Zealand 1:250 000. GNS Science Geological Map 1.