Compilation of Regional Geochemical Survey Data from the Bella Coola Area (NTS 93D/01, /02, /06, /07, /08, /09 /10/11/12/14/15, 93C/04, /05, 93E/02 /03) Ray Lett, BC Geological Survey
introductionReconnaissance scale stream sediment and water geochemical surveys undertaken in British Columbia presently cover approximately 500 000 square kilometers of the province. Standard sample collection, preparation, and analytical methods established by the Geological Survey of Canada have been maintained since the start of the survey in 1976. Analytical results are carefully monitored to ensure the production of consistent and reliable survey data regardless of the area, year or analytical laboratory. Information compiled by the National Geochemical Reconnaissance Program (NGR) and BC Regional Geochemical Survey (RGS) has created a high-quality geochemical database suitable for mineral exploration, resource assessment, geological mapping, land management and environmental monitoring. In 2001 a regional geochemical survey was carried out in the Bella Coola and Bella Bella (NTS 93D, 103A) map sheets (Lett, 2002). A total of 1180 stream sediment and water samples were collected from 1003 sites. Survey results include 47 metals in stream sediments, fluorine and loss-on-ignition in sediments, and pH, uranium, fluoride and sulphate in stream waters. In addition, 213 stream water samples were analyzed for major and trace elements. Average sample site density was 1 site per 12.2 square kilometres over a 13,345 square kilometre survey area. In addition, 112 samples collected by Jackaman et al. (2000) from 94 sites in the area were processed and analysed with the samples from the 2001 survey. Samples were not collected in Tweedsmuir Park and the Fiordland-Kitlope Recreation area. Field duplicate sediment and water samples were routinely collected in each analytical block of twenty samples. The information presented here is a subset of stream sediment geochemical data from the area covered by the compilation. The file comprises analytical results for 17 selected elements and loss on ignition (LOI) for 656 samples from RGS 56 (Lett, 2002) and 135 samples from the adjacent NTS 93E map sheet (BC Energy, Mines and Petroleum Resources, 1987) sampling and analytical methodsFor both 2001, 2000 and 1986 stream sediment surveys, samples weighing 1 to 2 kilograms were obtained from active (subject to annual flooding) stream channels and placed in kraft paper bags. Samples are primarily composed of fine-grained sediment mixed with varying amounts of coarse sand, gravel and organic material. Contaminated or poor-quality sample sites were avoided by selecting alternate streams or moving sample sites a minimum of 60 metres upstream from the source of contamination. Surface water samples were collected in 250 millilitre bottles and precautions were taken to exclude suspended solids. Observations on sediment characteristics (e.g. texture, colour), sample site and local terrain were recorded on standard BC Geological Survey field forms. Sediment samples, dried at 30-40°C, are screened to - 80 mesh (< 0.177 mm) fraction. Analytical and quality control techniques for each survey are described by the BC Energy, Mines and Petroleum Resources (1987) and by Lett (2002). While a seamless data file can be created from the results of separate historical regional surveys the content of the file is limited to those elements where analytical techniques are similar. For example, aqua regia has been used for sample decomposition in both surveys, but inductively coupled plasma mass spectrometry (ICP-MS) was used to measure element concentrations in 2001 whereas less sensitive atomic absorption spectrophotometry was employed in 1986. Water samples from both surveys were analysed for U, F, and pH, but not all of the samples were analysed for U and F and so only pH values have been incorporated into the data file. The different methods have been coded in the combined data file and are summarized below.
· AR_ICPMS – Aqua regia digestion followed by inductively coupled plasma mass spectrometry. · AR_AAS - Aqua regia digestion followed by flame atomic absorption spectrophotometry. · AR_HAAS - Aqua regia digestion followed by hydride generation atomic absorption spectrophotometry. · AR_CAAS - Aqua regia digestion followed by cold vapour atomic absorption spectrophotometry. · INAA – Instrumental neutron activation. · FA_AAS – Lead collection fire assay followed by flame atomic absorption spectrophotometry. · GRAV – Loss on ignition at 500°C. · HF_AAS – Hydrofluoric-perchloric-nitric acid digestion followed by flame atomic absorption spectrophotometry. · ELEC – Water pH by a combination glass-calomel electrode. · SPEC – Potassium bisulphate fusion followed by solvent extraction and spectrophotometric analysis. Detection limits for elements determined by the different methods are listed in Table 1.
Table 1.
|
|
Units |
ICP/MS |
AAS |
INAA |
Other |
Ag |
ppb |
2 |
100 |
|
|
As |
ppm |
0.1 |
1 |
|
|
Au |
ppb |
|
1 |
2 |
|
Ba |
ppm |
|
|
50 |
40 |
Cd |
ppm |
0.01 |
0.1 |
|
|
Co |
ppm |
0.1 |
2 |
|
|
Cu |
ppm |
0.01 |
2 |
|
|
Fe |
% |
0.01 |
0.01 |
|
|
Hg |
ppb |
5 |
10 |
|
|
LOI |
% |
|
|
|
0.01 |
Mn |
ppm |
1 |
5 |
|
|
Mo |
ppm |
0.01 |
1 |
|
|
Ni |
ppm |
0.1 |
2 |
|
|
Pb |
ppm |
0.01 |
2 |
|
|
Sb |
ppm |
0.02 |
1 |
|
|
U |
ppm |
|
|
0.2 |
|
W |
ppm |
|
|
1 |
2 |
Zn |
ppm |
0.1 |
2 |
|
|
British Columbia Ministry of Energy, Mines and Petroleum Resources (1987): National Geochemical Reconnaissance 1:250 000 Map Series, Whitesale Lake (NTS 93E). BC RGS 16 – Geological Survey of Canada Open File 1360, 145 pages http://www.em.gov.bc.ca/Mining/Geolsurv/Geochinv/rgs/sheets/93j.htm
Jackaman, W., Cook, S.Day, S.J., Pinsent, R., and Ferbey, T. (2000): Stream sediment and water geochemistry of the Bella Coola area, NTS 93D1,2,7,8 BC. Ministry of Energy, Mines and Petroleum Resources Open File 2000-13.
Lett (2002): Regional stream sediment and water data: Bella Coola area (NTS 93C, 93D, 103A) BC. Ministry of Energy, Mines and Petroleum Resources RGS 56, Geological Survey of Canada Open File 4414.