Compilation of data sets for a geochemical atlas of West and South Greenland based on stream sediment surveys 1977 to 1997

The stream sediment data compiled to form the basis for producing a geochemical atlas of the Precambrian part of West and South Greenland between 59° and 70°30’N comprises results obtained in 16 individual surveys carried out in the period 1977 to 1993. A comprehensive bibliography provides an overview of the geochemical exploration and mapping activities within this area. Samples were analysed using analytical facilities existing at the time they were collected and many sample batches have been reanalysed at a later date with more modern equipment. Thus, for each sample batch there exists a number of analytical data sets derived from analysis at two to three different laboratories and three to four different methods.

The compilation of data has involved the selection of suitable samples from detailed surveys to match the general density of one sample per 25 to 30 km² for West Greenland and one sample per 5-6 km² for South Greenland. In addition, a selection of analytical data sets for each element was made to ensure that the most reliable data set is used where samples have been analysed for the same element by different methods. The reliability of analytical results has been monitored by internal standards since 1990. The compatibility of element determinations by various methods has also been investigated using correlation diagrams for whole sample batches.

Analytical bias was found to exist between batches analysed by different methods and between batches analysed by the same method at different times. A calibration, i.e. a correction of the obtained analytical values was applied to eliminate the bias. For batches monitored by internal standards the correction was done by linear regression of values measured in the standards against reference values. For batches analysed without accompanying internal standards a small subset of samples were analysed together with internal standards, and the correction parameters were found by regression of measured original values against the calibrated values. The correction was then applied to the entire analytical batch.

The calibration applied to the measured analytical values ensures that the whole data set for each element is internally consistent. The analysis of a set of eight international standards together with the internal standards enables the data from Greenland to be made directly comparable with geochemical data sets from other parts of the world.

The compilation and calibration efforts have resulted in the production of reliable data sets for 10 major and 32 trace elements.