57 Geocarto International, Vol. 14, No. 3, September 1999 Published by Geocarto International Centre, G.P.O. Box 4122, Hong Kong. Space-based Synthetic Aperture Radar for Geological Mapping in the Central Coromandel Peninsula, South Auckland, New Zealand S.E. Belliss Landcare Research Box 69, Lincoln 8152, Canterbury, New Zealand A.B. Christie Resources Group, Institute of Geological and Nuclear Science Box 31312, Lower Hutt, New Zealand D.W. Burgess, S.J. McNeill and D. Pairman Landcare Research Box 69, Lincoln 8152, Canterbury, New Zealand A.D.W. Fowler 103 Pinehaven Road, Upper Hutt, New Zealand Abstract Synthetic aperture radar (SAR) data taken by the Japan Earth Resources Satellite-1 (JERS-1) was used to aid geological mapping in the Coromandel-Hauraki region, North Island, New Zealand, where volcanic terrain hosts more than 20 epithermal, gold-silver vein deposits. The JERS-1 SAR L-band, horizontal-send, horizontal-receive data were considered potentially useful for both structural and textural investigations. Linear features identified typically corresponded to topographic expressions in the field and are a useful aid to mapping the structural trends in the region. Several linear features coincide with rock unit boundaries identified in published geological maps, and some were used to help define rock unit boundaries in the new 1:50000 geological map of the Waihi area. Some trends in strike directions of the mapped linear features correspond to the location of gold-silver veins but in many cases veins generally strike in a different direction to the linear features. Only one of the many outcropping quartz-veins was visible on the SAR data. Mapping of different textures in the radar image failed to show any consistent relationship to mapped rock type. This was due to both the complexity of the volcanic deposits, and erosion, and hydrothermal alteration. map sheet, currently being mapped by the Institute of Geological and Nuclear Sciences (Rattenbury et al., 1994; Edbrook, S.W. & Brathwaite, R.L. in prep.). In previous work with L-HH SAR of the Ruahine Ranges taken by the Shuttle Imaging Radar-B sensor from Space Shuttle Columbia in October 1984, textural variations in the data corresponded well to lithological variations. These included Tertiary outliers on Mesozoic basement, some of which had not been recognised before. As well, major faults that had significant topographic expression were identified (Belliss & Oliver, 1988). Before this study satellite-based remote sensing data had not been used to aid geological mapping of this region in any routine operational sense, although a caldera noted on the recent T11 geological maps by Skinner (1993, 1995) was identified first from its strong semi-circular depiction on low sun angle, Landsat 3, multispectral scanner data (Skinner, 1983). Also from the Landsat data, Skinner (1983) recognised another circular Introduction Synthetic aperture radar (SAR) data for the Coromandel- Hauraki region, (Figs. 1 and 2), was taken by the Japan Earth Resources Satellite-1 (JERS-1) and made available in late 1993 for our research work. SAR remote sensing data can provide valuable information for geological mapping, especially in areas with poor outcrop and accessibility, such as the Coromandel-Hauraki region. The northernmost part of this area was recently geologically mapped at 1:50,000 by Skinner (1993, 1995), whereas the southernmost area was mapped by Houghton & Cuthbertson (1989). Work on the intervening area was progressing at the time of this study and included final field work and compilation for the New Zealand 1:50,000 metric map sheets T13 and U13 (Fig. 3) (Brathwaite & Christie, 1996), and some initial reconnaissance mapping for sheet T12. Most of the area will be included in a new 1:250,000 Auckland geological