New Zealand Journal of Geology and Geophysics abstracts
Coal rank, coal type, and marine influence in the north Taranaki coalfields, New Zealand
R. P. Suggate
GNS Science
P.O. Box 30 368
Lower Hutt, New Zealand
p.suggate@gns.cri.nz
Abstract A few coal seams in the thin early
Miocene Maryville Coal Measures have been mined in the relatively minor
north Taranaki coalfields: Mokau, Ohura, Tangarakau, Waitewhena, and
Aria. Generally accepted as sub-bituminous, the coals are discussed in
terms of the Rank(Sr) classification to identify more
closely the variations of coal type and coal rank. The use of a
mineral-matter- and sulphur-free basis for the analyses is made
necessary by the generally moderate to high sulphur contents. The range
of volatile matter is 15%, and of calorific value is 1500 Btu/lb (=
3.5 MJ/kg specific energy). In the most closely explored
coalfield, Mokau, c. 450 coal analyses from up to 5 seams in 130
drillholes over an area of c. 65 km2 have been used. Analyses from 27 seam sections in Tatu Mine (Tangarakau Coalfield) come from an area of c. 2.5 km2.
Analyses from a few mines in Waitewhena and Aria Coalfields, and from
widely spaced drillholes in Waitewhena, Ohura, and Tangarakau
Coalfields, provide additional data. In Mokau Coalfield, a detailed
pattern of lateral rank variation is demonstrated within a Rank(Sr) range from 6.6 to 8.1. The rate of lateral rank variation, up to 1.5 Rank(Sr)/km,
is too rapid to result from depth of burial variation. The rank
variation is tentatively ascribed to localised differential heating as
a result of fluid movement up faults during minor disruption of the
downwarping basin at the end of Miocene sedimentation when the coal
ranks were imprinted. Such disruption may have produced the older
north-trending faults; the dominant younger
east–northeast-trending faults are likely to have formed during
uplift after the rank pattern was established. The lower ranks over
most of the region are considered to indicate the general depth of
burial, c. 1.7 km, but a regional decrease in rank along the
eastern margin and in the northeast at Aria indicates a probable
regional decrease in thickness of the former cover to
c. 1.25 km.
Keywords north Taranaki; Mokau Coalfield; Waitewhena Coalfield; Tatu Mine; coal rank; Rank(Sr); sub-bituminous coal; coal type; sulphur; marine influence
G05035; Received 21 July 2005; accepted 23 February 2006; Online publication date 17 May 2006
New Zealand Journal of Geology & Geophysics, 2006, Vol. 49: 255–268
0028–8306/06/4902–0255 © The Royal Society of New Zealand 2006
PDF file of entire paper: Print-quality (1227K) | screen-quality (1314K)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
