• Lake sediment data
• Stream sediment data
• Lake water data
• Stream water data

Mineral exploration in Canada is a challenging occupation requiring considerable amounts of money and luck. There is no guarantee of success. Nevertheless, in addition to diamonds, companies continue to search for base metals, gold, platinum-group elements (PGE's) and other commodities. Given the vast areas of land and limited exploration funds, an important source of information for an exploration program is a regional reconnaissance survey, usually carried out by federal or provincial government agencies, designed to delineate areas favourable for further detailed exploration. Regional surveys are typically lake or stream sediment surveys, geophysical surveys, or till surveys. All attempt to 'see through' cover to the bedrock beneath, and all require some special interpretative skills.

Canada's National Geochemical Reconnaissance (NGR) Program is an ongoing reconnaissance-scale drainage sediment and water sampling program that began in 1975 with lake sediment surveys in Saskatchewan and Manitoba. Areas of coverage have been incrementally increased across the country so that today geochemical data are available for over 83,000 lakes and 78,000 streams in an area equivalent to one-fifth of the country. Early surveys included atomic absorption spectrophotometry and colorimetric data for 12 or 13 elements in sediments, along with uranium, pH and fluoride values in waters. The most recent open files contain data for 50 or more variables in both sediments and waters from a combination of ICP-MS, ICP-ES, ion chromatography, INAA and specific methods. The reports were originally used by the mineral exploration industry to search for uranium and base metals, but as analytical techniques evolved, data became available for gold and other precious metals, rare earths, and now, with the most recent release, diamonds.

Collection and analysis of drainage sediments and waters is an established method of mineral exploration in Canada. Large areas of the country can be surveyed rapidly and at a relatively low cost. Stream sediments are the most widely used media for exploration at intermediate to regional scales and suitable drainage systems exist in many areas of the country. Lake sediments are suited to glaciated basement terrains such as found over much of the Canadian Shield. The importance of waters has increased as the understanding of the chemistry of natural waters has increased along with the improvement in the sensitivity of analytical techniques, particularly ICP-MS.

For details on sampling methods, refer to Methodology (National Geochemical Reconnaissance)

One of the most important characteristics of NGR surveys is the structure of the sampling routine. Each block of 20 consecutive field numbers consists of 17 routine field samples, a field duplicate sample, a blind (analytical) duplicate sample and a control reference sample. The field duplicate sample is a separate sample collected at one of the 17 routine sites, at the discretion of the sampling team. One number, always the first in a block of 20 (i.e. 001, 021, 041, etc.) is reserved for a blind duplicate. The sample preparation laboratory splits a sample in the block, preferably one of the field duplicate samples, and places one of the splits into the blind duplicate position. A randomly pre-selected number within a block of 20 is reserved for a control reference sample. Control reference samples are lake or stream sediments with well-established analytical values.

Field duplicates, blind duplicates and control reference samples are incorporated in every block of 20 samples, and are used to monitor and control sampling and analytical variance. As a result of stringent quality control and consistency of analytical methods over time, it is possible to generate a regional compilation for an element with minimal boundary effects between different surveys using the same analytical method.

Data are stored in files consisting of one record (or row) for each site, with fields for sample number, geographic coordinates (NAD27), field observations, and analytical data. Occasional missing items in any field may be the result of observations not made at the time, in the case of site observations, or, in the case of analytical data, samples with insufficient material for analysis.

Each analytical data field is populated by results derived from identical or similar analytical methods. In cases where analytical methods are significantly different, analytical results are shown in separate fields. For example, results from two different analytical procedures are listed for elemental concentrations of gold in sediments. Until 1989, samples were analyzed using a combination of fire assay and neutron activation (FA-NA) techniques. In 1990, a new method, non-destructive instrumental neutron activation analysis (INAA) replaced the fire assay-neutron activation method. In time, thousands of samples not originally analyzed for gold were reanalyzed by INAA.

In some cases, for some elements, analytical results obtained by two methods are shown for the same sample. Before attempting to compare these data, some caution should be exercised. Generally, analytical results for elements such as As, Co, Fe, Sb, U and W in sediments are either 'partial' or 'total.' An example of a partial extraction method is an HNO₃ - HCl (aqua regia) digestion. Silicates such as zircon and pyroxene remain relatively unaffected by this digestion. However, data for these elements obtained by INAA are 'total' data. Hence, median values for sediments determined with a partial extraction method will usually be somewhat lower than those for INAA data.

Original observations for stream width, stream depth and lake depth were in feet. Although every attempt has been made to convert all data to metres, there may be cases, particularly in earlier data, of measurements in the original imperial form.

Coordinate data are given as geographic coordinates (latitude/longitudes), in decimal degrees, using a NAD27 (Clarke 1866 spheroid) datum.

• National Geochemical Reconnaissance
• Geochemistry