|
Taharoa, Waikato North Head |
|
|
North Island, New Zealand |
| Main commodities:
Fe Ti
|
|
 |
|
|
 |
Super Porphyry Cu and Au
|
IOCG Deposits - 70 papers
|
All papers now Open Access.
Available as Full Text for direct download or on request. |
|
|
The Taharoa and Waikato North Head iron sand deposits on the west coast of the North Island of New Zealand. Taharoa is located 144 km south of Auckland, whilst Waikato North Head is 90 km to the north at the mouth of the Waikato River.
Titanomagnetite iron sand placer deposits are found along 480 km of the coastline between Kaipara Harbour and Wanganui on the west coast of the North Island, occurring as Quaternary beach and dune deposits, and offshore marine deposits. The provenance of the titanomagnetite is uncertain, but was presumably derived from eroded Quaternary andesitic volcanic rocks of western Taranaki, and the rhyolitic volcanic rocks of the Taupo Volcanic Zone, transported to the coast by rivers, and along the coast by shallow marine longshore currents, and subsequently concentrated by wave and wind action. Over the last 1 to 2 m.y.,
New Zealand has undergone at least 50 sea-level oscillations as a result of tectonic activity and the influence of the glacio-eustatic fluctuations.
These coastal sands represent a variety of sedimentary environments including sand spits with shallow marine characteristics, aeolian dunes, and lacustrine deposits, characterised by clay rich horizons, which can be attributed to tephras and geosols from various North Island volcanic eruptions.
The Taharoa deposit covers an area of approximately 16 km2 and is ~8 x 5 km, reaching a maximum depth of up to 120 m below sea level and has been extensively mined from 1971 to the present. The iron sands are mined by dredging beach and dune sand to produce a concentrate averaging 97% titanomagnetite, which is slurried via a 3 km pipeline to an offshore loading facility for export.
The North Island of New Zealand comprises sedimentary and volcanic rocks underlain by sedimentary, metamorphic and volcanic rocks. The Taharoa deposit occurs within the Murihiku Terrane. West of the deposit, the Brook Street Terrane and Median Batholith form offshore basement. The Dun Mountain-Matai Terrane and the Waipapa and Torlesse composite Terranes form the basement to the east of the deposit.
The Taharoa iron sand deposit fills an elongate, north-south trending depression, flanked by fault-bounded ranges between the headlands of Parahaki Point and Paparoa Point, cut into and overlying eastward-dipping Mesozoic greywacke which forms the coastal cliffs to the north and south. The depression was filled by the Kaihu Group, which includes the Nukumiti/Paparoa Sand Members and the Te Akeake Sands. The Nukumiti/Paparoa unit is unconsolidated and forms the youngest unit at Taharoa with a higher magnetic mineral content (average 55%). The Te Akeake Sands Member lies beneath the Nukumiti and the Paparoa Sands Members and has a very low in magnetic mineral content (<30%). The coastal ranges to the north and west are composed of the late Cenozoic Orangiwhao Volcanic Complex, interrupted by the basaltic andesitic cones of Mount Pirongia and Mount Karioi and by several northeast to southwest cross faults, active periodically throughout much of the late Neogene, to the late Pleistocene.
The deposit is estimated to have originally contained 565 Mt of titanomagnetite, of which 200 Mt occur below sea level. The heavy mineral-rich sands predominantly contain titanomagnetite and ilmenite, along with lesser amounts of hematite, amphiboles and pyroxenes. Mineralogical and petrographic analyses confirmed the high abundance of homogeneous magnetite and magnetite containing ilmenite exsolution lamellae which have been oxidised to hematite.
At Waikato North Head, an 80 m, and locally up to 120 m, thick sequence of coastal and river sands at the mouth of the Waikato River occupies a depression on the north head of the Waikato River mouth and the southern end of the Awhitu Peninsula, a 40 km long coastal sand barrier. This depression occurs where the ENE striking Waikato Fault, which is normal to the coastline and controls the course of the Waikato River mouth, is shown by gravity data modelling to down-fault the greywacke basement of the Murihiku Terrane exposed to the south, by ~2.7 km (Hochstein and Nunns, 1976). Two 14C dates, limited palynology and regional stratigraphic correlations indicate an early Pleistocene to Recent age for the sands (Brathwaite et al., 2018). The sequence is composed of four formations, as follows, from the base:
• Awhitu Sands - which to the south of the Waikato River mouth, unconformably overlies the late Pliocene (2.5 to 1.7 Ma) Oruarangi pumiceous beds. It is composed of a lower sand member overlain by a white clay, the Awhitu Clay, representing a weathered tephra (Christie, 1979; Dingley, 2002) and then by a fluvial quartz-rich sand with minor pumice clasts, the River Sand Member;
• Hood Sands, which are predominantly dune sands with local interdune swamp or lake beds. It comprises the Lower Hood and Upper Hood sands, bracketing the Waiuku Black Sand Member. This latter member is up to 20 m thick at the mine site and is variably oxidised to limonite with a reddish-brown colour. It is composed of well consolidated, cross-bedded to laminated, titanomagnetite-rich (up to 70% magnetics and seldom <30%) dune sands, with thin mud layers and a tephra bed (Christie, 1979). The richer sands are very clayey, while the oxidation to limonite has led to some lithification. Sand from unweathered and undeformed foresets of the Waiuku Black Sand Member is fine, moderately well sorted, near symmetrically skewed and texturally very similar to dune sand from foresets of the mineralised Entrican Dune Member higher in the sequence, as described below (Christie, 1979). A sample of peat at the base of the Lower Hood Sand, contains a pollen assemblage that indicates a warm, interglacial climate and an age of <1 Ma (Brathwaite et al., 2018).
• Bothwell Sands, which are <10 m thick and comprise well compacted orange to brown-grey sands overlain by a distinct brown oxidised paleosol referred to as C1. The top of C1 is marked by an ash unit consisting of a 1 to 4 m thick, paleosol of orange clay and clayey sand.
• Mitiwai Sands, which are subdivided into the Alder and Entrican Sand members of late Holocene to Recent age. Both are grey dune sands with the Entrican Sand having a higher titanomagnetite content. The Entrican Dune Member comprises up to 50 m of recent wind-blown dune sand. Unweathered and
unconsolidated sand contains up to 20% titanomagnetite. Texturally, sand from the dune foresets is fine, well sorted, near symmetrically skewed and mesokurtic. Stratification is marked by alternating light (titanornagnetite poor) and dark (titanomagnetite rich) laminae, averaging 2 mm and 0.5 mm thick respectively (Christie, 1979).
An in situ resources have been estimated at Waikato North Head of 780 Mt of raw sand @ 18% magnetics grade, for 140 Mt of concentrate (Waterhouse and MacArthur, 1989). Mining commenced in 1969, and is currently being exploited at a rate of ~1.2 Mt per annum and contains >150 Mt of iron sand resources (New Zealand Steel website, viewed 2021).
The most recent source geological information used to prepare this decription was dated: 2021.
Record last updated: 26/1/2021
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
|
|
|
|
Brathwaite, R.L., Christie, A.B., and Gazley, M.F., 2021 - Stratigraphy, provenance and localisation of the titanomagnetite placer at Waikato North Head, South Auckland, New Zealand: in Mineralium Deposita v.56, pp. 343-362.
|
Brathwaite, R.L., Gazley, M.F. and Christie, A.B., 2018 - Stratigraphy, mineralogy and provenance of the sand sequence at Waikato North Head, south Auckland: in NZ Branch AusIMM Conference 2018, Tauranga, New Zealand Proceedings, pp. 71-78.
|
Christie, A.B., 1979 - Sedimentary structures in Quaternary ironsands at Waikato North Head, New Zealand: in NZ Journal of Geology and Geophysics, v.22, pp. 213-226
|
Macorison, K.T., Mauk, J.L. and Jokanovic, S., 2002 - Mineralogical and geochemical analysis of ironsand at Taharoa, New Zealand: in The AusIMM Annual Conference, 2002, 150 Years of Mining, Auckland, New Zealand, The Australasian Institute of Mining and Metallurgy, Melbourne, 10p
|
|
Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
|
Top | Search Again | PGC Home | Terms & Conditions
|
|
