Two geochemical surveys were undertaken in the Solomon Islands between 1976 and 1983 as part of a combined geological mapping and mineral exploration project.
The survey of Choiseul and the Shortland Islands was carried out between 1976 and 1979 by the Institute of Geological Sciences (now the British Geological Survey) with support from staff of the Geology Division of the Ministry of Land, Energy and Natural Resources, Solomon Islands. The project produced 12 geological maps at 1:50 000 scale as well as a series of unpublished reports which are listed in Section 6 of this note. The geochemical results are summarised in Ridgway (1984).
The survey of the New Georgia Group of islands was undertaken between 1979 and 1983. The project produced seven geological maps at a scale of 1:100 000 and a regional map of the entire island group at a scale of 1:250 000. The geology of the islands is described in a report by Dunkley (1986), that includes a summary of the results of the geochemical survey. A series of multielement geochemical anomaly maps were produced at a scale of 1:100 000 to accompany each of the published geological maps. Master copies of these are held at the Geological Survey in Honiara. Anomalies were standardised for background lithology by partitioning the data prior to interpretation using the rock codes and informal lithostratigraphic codes included in the dataset and summarised in the tables below. Full descriptions of the methods used are described in the margins of the anomaly maps.
A total of 8848 stream sediment samples were collected from Choiseul and 7441 from the New Georgia Group, resulting in an average sampling density for the two areas of 2.68 samples per km² and 1.47 samples per km² respectively. Sampling in the Shortland Islands was confined to the larger islands, 187 were collected from the Fauro Island group, 148 from Alu and 69 from Mono.
Field data was recorded on field cards, which were described in Ridgway (1980). A sample preparation and analytical laboratory was set up in Honiara. The samples were dry sieved and the fraction passing -80 mesh B.S. (177 microns) was analysed. A hot concentrated nitric acid digestion was used prior to analysis by atomic absorbtion spectrophotometry (AAS) for Co, Cu, Pb, Zn, Ni, Ag, and Mn. Samples from the vicinity of the Siruka Ultramafic Complex were determined for Cr by AAS after digestion by a bisulphate fusion technique. In the New Georgia survey Mo was also determined routinely by the zinc dithiol colorimetric method. Molybdenum analyses were not included in the digital database as almost all were below the detection limit (approximately 2 ppm) for the analytical method, except at the Kele River Prospect of Vangunu.
Samples from the Shortland Islands group were analysed colorimetricly for Mo, As, W and Sn, as well as for Co, Cu, Pb, Zn, Ni, Ag and Mn by AAS, and an interpretation of the results was published in Ridgway (1984). BGS does not hold a copy of this small dataset.
Two standard samples were prepared from locally collected stream sediment, and were used to monitor analytical precision. These samples were subjected to confirmatory analysis by the BGS analytical laboratories in London. The standard samples were analysed routinely in each analytical batch, and time series control charts were plotted to monitor between-batch variation and precision. Analyses of control samples outside the range mean ± 2 standard deviations indicated departure from the control and the batches in question were reanalysed. One sample in twelve was reanalysed, as were all apparently anomalous samples. Analytical precision was estimated from the duplicate analyses using the method of Thompson & Howarth (1978) (J. Geochemical Exploration. 9, 23–30). Precision was arbitrarily set at 20 per cent, which was deemed sufficient for exploration, although for most elements (except Ag) better precision was actually obtained.
2.1.1 Explanation of lithological and Geological unit codes used for Choiseul
|Clastic sediment||S||Mole Formation||M|
|Andesite||A||Nukiki Limestone Formation||N|
The AreaCode is a number series code that must be used with the SampNo (Sample Number) to give a unique ID.
A local code used by fieldworkers to identify which map they were working on. Code translation not available.
F = Fluvatile (i.e. drainage sediment)
S = Soil
2.2 New Georgia Group
2.2.1 Island codes (Iscode) for the New Georgia Group
- VL Vella Lavella
- RA Ranongga
- GZ Ghizo (no stream samples taken)
- KB Kolombangara
- NG New Georgia
- RE Rendova
- TP Tetepare
- VA Vangunu
- NK Nggatokae
2.2.2 Lithology codes (Lithcode) used in the New Georgia Group data
- A Hornblende andesite, plus minor basaltic andesite and rare dacite
- AH Hypersthene andesite and basaltic andesite
- B Olivine basalt, in places with picritic and ankaramitic flows
- BA Basaltic andesite
- BF Feldsparphyric basalt with minor felsparphyric trachybasaltic andesite
- DG Diorite – Gabbro, Choe intrusion complex, South New Georgia
- G Gabbro
- L Coralline limestone
- S Superficial deposits (largely volcanogenic)
2.2.3 Informal lithostratigraphic codes (Geolcode) used in the New Georgia Group data
- CD Choe intrusion complex, South New Georgia (gabbro – diorite – tonalite))
- H Kolo Volcanic Centre, South New Georgia (picrites, olivine basalts ankaramitic basalts
- IG Gabbro, Iana Hill, South-west New Georgia
- K Kela Volcanic Formation, Ranongga
- KB Kolombangara volcanics (olivine basalt lavas and breccias, rare andesite)
- L Coralline Limestone, mostly coastal areas. Stream sediment geochemistry contolled by dominant volcanic lithology in hinterland
- MA Mase Volcanic Centre, North New Georgia (olivine basalt lavas and breccias, minor feldsparphyric basalts)
- MB Mbareke Volcanic Centre, Vangunu
- N Nondo Volcanics, North Vella Lavella (mainly hornblende andesite basalt lavas and breccias with minor basaltic andesites and dacites.
- NK Nggatokae Volcanic Centre (hypersthene andesite and basaltic andesite lavas and breccias
- O Oula Formation, South Vella Lavella (calcareous clastic sediments)
- P Pilipilo Volcanics, Central Vella Lavella (olivine basalt lavas and breccias)
- R Feldsparphyric basalts and volcanogenic sediments
- RF Rendova formation, informal grouping of olivine basalts and feldsparphyric basalts
- RV Ravete Volcanic Centre, central-northern New Georgia (olivine basalt lavas and breccias)
- S Superficial deposits, sediments and alluvium with volcanogenic detritus
- SM Sumbulo lavas, North Vangunu (feldsparphyric basalts)
- SV Sakambare lavas, northern and central New Georgia (feldsparphyric basalts)
- Tv Tuara Formation, Ranongga
- TF Tetepare Formation, Tetepare and southern Rendova (uplifted forearc sedimentary sequence of hemipelagic limestones, and turbiditic sandstones, siltstones and debris flow deposits)
- TV Tita volcanics, central New Georgia (olivine basalt lavas and breccias)
- Uv Urmangge volcanics, southern Vella Lavella (mainly hornblende andesite and basaltic andesite lavas and breccias
- VA Vangunu Volcanic Centre (hornblende andesite lavas and breccias)
Values in ppm assigned to samples below the limit of detection are:
The grid co-ordinates were derived from 1:100 000 scale maps published (largely from photogrammetric data) by the U.K. Directorate of Overseas Surveys in the 1960s. The UTM projection and the Hayford (=International) spheroid were used. The area falls within UTM Zone 57.
|Choiseul||New Georgia Group|
|Number of Sites||8,848||7,441|
|Area||3300 km²||5060 km²|
|Average sample density||2.68 samples per km²||1.47 samples per km²|
|Fraction used||-80 mesh B.S.||-80 mesh B.S.|
|Elements by AAS||Cu, Pb, Zn, Ag, Co, Ni, Mn, (Cr)*||Cu, Pb, Zn, Ag, Co, Ni & Mn|
|Elements by colorimetry||(Mo )*|
*elements not reported in digital database (see Section 1)
The CD-ROM should be referenced as:
BGS (2007). Solomon Islands Regional Geochemical Survey CD-ROM: Choisuel and New Georgia. Version 2.0. BGS International Regional Geochemistry CD-ROM Series, No. 6 Solomon Islands. British Geological Survey, Keyworth, Nottingham, UK
Other reports include:
Arthurs J.W. 1977. A heavy mineral orientation survey, Siruka Ultramafic Complex, Choiseul. Geological Survey of the Solomon Islands, unpub.
Dunkley, P. N. 1986. Geology of the New Georgia group, Solomon Islands. British Geological Survey Overseas Geology Series WC/MP/86/6, 83pp. unpub. Contributors: D.A.Abraham, S.J. Booth, G.W. Hughes, R.L. Langford, P.R. Philip, J. Ridgway, A. Smith and P.J. Strange. – Held in box with 8 folded maps.
Edridge, S. 1985. Solomon Islands bibliography to 1980. pub. Suva, Fiji: Institute of Pacific Studies, the University of the South Pacific, 476 pp.
Grover, J. C. 1955. Geology, mineral deposits and prospects of mining development in the British Solomon Islands Protectorate (Interim Geological Survey of the British Solomon Islands. Memoir ; No.l pub. Honiara : Western Pacific Commission, 108 pp.
Hackman, B.D. 1980. The geology of Guadacanal, Solomon Islands. (Overseas Memoir Institute of Geological Sciences No. 6) pub. London : HMSO, 115pp
Ridgway J and Coulson F.I.E. 1987. The geology of Choiseul and the Shortland Islands, Solomon Islands (Overseas Memoir British Geological Survey ; No.8) pub. London : HMSO, 134pp
Contributors include: B.D.Hackman, P.R.Philip, A.Smith, P.J.Strange. – Accompanied by 5 folded maps (scale 1:100000 & 1:200000) in endpocket.
Ridgway, J. and Midobatu C. 1991. Temporal variations in the trace element content of stream sediments: an example from a tropical rain forest regime, Solomon Islands. Applied Geochemistry Vol 6, pp185-193
Western Solomons Mapping Project Report series (unpublished), copies of which are available at the British Geological Survey Library at Keyworth, U.K. and at the Geology Division, Ministry of Energy,Water & Mineral Resources, Honiara, Solomon Islands.
Strange P.J. 1978. Report No. 1/2. The geology of the Choiseul Bay and Chörovanga areas, Choiseul. (Unpublished Report available BGS Library).
Danitofea S. 1979. Report No. 3. The geology of the Voza area, Choiseul. (Unpublished Report available BGS Library).
Hughes G.W. 1979. Report No. 4. The geology of the Ririo area, Choiseul. (Unpublished Report available BGS Library).
Arthurs J.W. 1979. Report No. 5. The geology of the Mbambatana area, Choiseul. (Unpublished Report available BGS Library).
Strange P.J. 1979. Report No. 6. The geology of the Katurasele area, Choiseul. (Unpublished Report available BGS Library).
Hughes G.W. 1979a. Report No. 7. The geology of the Panggoe area, Choiseul. (Unpublished Report available BGS Library).
Smith A. 1980. Report No. 8. The geology of the Nuatambu area, Choiseul. (Unpublished Report available BGS Library).
Philip P.R. 1981. Report No. 9. The geology of the Mt Sambe area, Choiseul. (Unpublished Report available BGS Library).
Hughes G.W. 1979b. Report No. 10. The geology of the Oaka and Siruka Bay area, Choiseul. (Unpublished Report available BGS Library).
Strange P.J. 1980. Report No. 11. The geology of the Kömboro and Rob Roy area, Choiseul. (Unpublished Report available BGS Library).
Hughes G.W. 1980. Report No. 12. The geology of Vanghena, Choiseul. (Unpublished Report available BGS Library).
Turner C.C. 1981. Report No. 13. The geology of the Shortland Islands, Solomon Islands.
Ridgway J. 1980. Report No. 14. Geochemical exploration methods used in Choiseul and the Shortland Islands. (Unpublished Report available BGS Library).
Ridgway J. 1981. Report No. 15. Analytical methods used in the laboratories of the Geology Division, Ministry of Natural Resources, Honiara. (Unpublished Report available BGS Library).
Arthurs J.W. 1980. Report No. 16. Micropetrography of the Voza Lavas and Choiseul Schists, Choiseul.
Hughes G.W. 1981. Report No. 17. The micropalaeontology of the Shortland Islands and Choiseul. (Unpublished Report available BGS Library).
Ridgway J. 1984. Report No. 19. Choiseul and the Shortland Islands: Summary of the geology and geochemical exploration results. (Unpublished Report available BGS Library).
BGS in the Solomon Islands
British Geological Survey,
Nottingham, NG12 5GG
Collaborating organisation: Ministry of Energy, Water and Mineral Resources
Director of Geology
Ministry of Mines, Energy and Rural Electrification
PO Box 619
Tel: +677 28 520
Fax: +677 24 272
|readme.doc||Information file (in MS Word 2003 format)|
|readme.pdf||Information file in PDF format|
|choiseul.csv||Choiseul Geochemical results and locational data for stream sediments and soils in comma separated variable format, first row contains field names|
|choiseul.xls||Choiseul Geochemical results and locational data for stream sediments and soils in MS Excel 2003 format, first row contains field names|
|choiseul.dbf||Choiseul Geochemical results and locational data for stream sediments and soils in dBase III+ format|
|NGeorgia.csv||New Georgia Group Geochemical results and locational data for stream sediments and soils in comma separated variable format, first row contains field names|
|NGeorgia.xls||New Georgia Group Geochemical results and locational data for stream sediments and soils in MS Excel 2003 format, first row contains field names|
|NGeorgia.dbf||New Georgia Group Geochemical results and locational data for stream sediments and soils in dBase III+ format|