CONTENT

Sampling
Sample Preparation
Analytical Methods

Atomic Absorption Spectroscopy (AAS)
Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES)
Instrumental Neutron Activation Analysis (INAA)
Fire Assay Inductively Coupled Plasma Mass Spectrometry (FA ICP-MS)
Gravimetric Analysis (LOI)

Quality Control

This help file contains documentation for the field and geochemical data for till samples of Newfoundland and Labrador. Surveys of till geochemistry have been carried out since the late 1970s. These surveys combine surficial mapping (a combination of aerial photograph analysis and field verification), paleo ice-flow mapping and sampling of till to be analyzed for geochemistry. Open-file releases (see Sources below) of the till geochemistry data from these surveys have been successful in generating exploration activity (e.g. following the Grand Falls release in 1998, 2357 new claims were staked having a value of $140 520).

The till field and geochemical data have been compiled in one large database and presented digitally on the Geoscience Atlas in the Geochemistry group. Earlier surveys analysed for a restricted suite of elements but many of these samples have been re-analysed to a standard modern analytical suite. Included in this digital database is data from more than 800 till samples collected in the early 1990's as part of a collaborative project with the Geological Survey of Canada (GSC). The analytical methods were not exactly the same as the NL Geological Survey Laboratory so some levelling of the GSC data to the NLGS data was performed (see Methods > Geological Survey of Canada).

The digital till geochemical dataset can be displayed in several ways in the Geoscience Atlas, including viewing just the site locations, turning on the incrementally sized dot plots representing geochemical values for selected elements, as well as listing the tabular data of the field and geochemical values for selected sites. The incremental size of the dots were determined using the Jenks optimization method, found within the ArcMap GIS application. This method examines the frequency distributions of the geochemical data and determines its goodness of variance fit (Jenks, 1967). Breaks in slope of the curves were used to subdivide the element values into four to six natural population groups. These groups are represented by symbols (dots) that increase in size with increasing element values.

This database will be updated as new data is released. Fluoride analyses for the Newfoundland samples have been completed and those for Labrador will be provided in the future. To help with analysis, the regional or detailed surficial geology map layers as well as the striation database layer can be turned on through the Surficial Geology group of the Geoscience Atlas. In future (post 2020) open file reports will contain

The sample target in these surveys is the C soil horizon (unaltered till). The majority of samples were taken from test pits at 40-60 cm depths and from road cuts. Mudboils were sampled at shallower depths (average 25 cm), and, in areas of thin till, samples were taken near the bedrock-till interface. B- and BC-horizon samples were taken in areas where the soil was too thin for a C-horizon to be present or where till was too bouldery to penetrate to greater depths. Approximately 0.5 kg of till matrix was sampled at each site, with larger grain-sizes discarded. Sample spacing was controlled by access as well as surficial geology, but was generally about 1 sample per 1 km2 in areas of good access to 1 sample per 4 km2 in areas where helicopter support was required. Duplicate field samples were collected to determine data reproducibility (see Quality Control section).

In the field, samples were placed in kraft-paper sample bags, and sent to the NL Geological Survey's Geochemical Laboratory in St. John's, where they were air-dried in ovens at 40° C and dry-sieved through 180 µm or 63 µm stainless-steel sieves. The <180 µm or <63 µm silt-clay fraction was analyzed for trace elements. Which fraction was used is indicated in the Fraction_u field.

The analytical methods used vary according to the date of survey; more modern surveys have a more complete range of elements. Re-analysis to modern standards has been completed for most surveys. The Open File report NFLD/3316 describes the latest analytical methods as of January 2018.

The modern standard methods are as follows. At the Geological Survey laboratory, Ag and Rb were analyzed using atomic absorption spectroscopy (AAS; prior to 2005; from 2005 onwards these elements were analysed by ICP-OES), while Al, As, Ba, Be, Ca, Cd, Ce, Co, Cr, Cu, Dy, Fe, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, P, Pb, Sc, Sr, Ti, V, Y, Zn and Zr were analyzed with inductively coupled plasma emission spectroscopy (ICP-OES). Instrumental neutron activation analysis (INAA) was conducted by commercial laboratories for the following elements: As, Au, Ba, Br, Ca, Ce, Co, Cr, Cs, Eu, Fe, Hf, Hg, Ir, La, Lu, Mo, Na, Nd, Ni, Rb, Sb, Sc, Se, Sm, Sn, Sr, Ta, Tb, Th, U, W, Yb, Zn, Zr. In some surveys additional analysis of selected samples for platinum group elements has been undertaken.  F^- is analyzed by ion-selective electrode.

Field duplicates, laboratory duplicates and control reference materials are included incognito in all internal and external analyses (see Quality Control section). The trace elements are labeled with their elemental abbreviation (Table 1), a numeric code to distinguish the analysis type (Table 2) and the applicable unit of measurement. Missing data or insufficient sample for analysis is designated by a value of -9 in the data set. Values below the detection limit are indicated by half the detection limit. Note that post 2020, till geochemistry open file databases will report values below the detection limit as negative the detection limit but when compiled in the Geoscience Atlas these will be converted to half the detection limit.

Silver (Ag6) and Rubidium (Rb6) were determined on 0.5 g aliquots of sample following digestion in 2 ml of concentrated nitric acid overnight at room temperature, and then in a water bath at 90° C for 2 hours (Wagenbauer et al., 1983). Ag6 (referred to as Ag28 in other databases) was more recently analyzed by ICP-OES using a similar digestion method as described above (see Finch et al., 2018 (Lichte et al., 1987)).

For these analyses, the residue of the 1g aliquot of sample remaining from the LOI determination was digested in a mixture of 15 ml of concentrated hydrofluoric acid, 5 ml of concentrated hydrochloric acid, and 5 ml of 50 volume percent HClO4 in a 100 ml teflon beaker, and was allowed to stand overnight before being heated to dryness on a hot plate. The residue was taken up in 10 volume percent hydrochloric acid by gentle heating on a hot plate, was allowed to cool and was made up to 50 ml with 10 percent volume hydrochloric acid (Wagenbauer et al., 1983). For most elements dissolution is total with the exception of Cr from chromite, Ba from barite and Zr from zircon.

An approximately 30 g aliquot is encapsulated and weighed in a polyethylene vial and irradiated with flux wires and an internal standard (1 for 11 samples) at a thermal neutron flux of 7 x 1011 n/cm²s. After seven days (to allow Na24 to decay), the samples are counted on a high purity Ge detector with a resolution of better than 1.7 KeV. Using the flux wires, the decay-corrected activities are compared to a calibration developed from multiple certified international reference materials. The standard present is only a check on accuracy of the analysis and is not used for calibration purposes. 10-30% of the samples are checked by re-measurement.

Platinum, palladium and gold contents were evaluated by Activation Laboratories Ltd. (Ontario) using fire assay inductively coupled plasma mass spectrometry (FA-ICP-MS). A 30 g split of the sample is mixed with fire assay fluxes, and fused at 1050° C for one hour. After cooling the lead button is separated from the slag and cupelled at 1000° C to recover the Ag (doré bead) and Au, Pt, and Pd. The bead is digested in hot nitric plus hydrochloric acids. After cooling for two hours the sample solution is analyzed for Au, Pt and Pd by ICP-MS using a Perkin Elmer Sciex ELAN 6000 or 6100 ICP-MS.

Organic carbon content was estimated from weight loss on ignition (LOI) during a controlled combustion, in which 1 g aliquots of sample were gradually heated to 500° C in air, over a 3-hour period.

Data quality was monitored through the collection of site-duplicate samples at a frequency of approximately 5% of the sites sampled, the splitting of 1 sample in 20 during sample preparation to give laboratory duplicates, and the inclusion of bulk controls (both internal and national reference materials) also at a frequency of 5% throughout the analytical program. The controls measure the consistency of the calibration throughout the extended period of analysis (1977 to present) and, from national reference materials, the accuracy of reported element levels. From the laboratory and site duplicates the analytical variance, and the combined sampling and analytical variance, respectively, can be estimated. It is the relative size of the combined sampling and analytical errors with respect to the overall data variance that is important in assessing data quality. Some elements whose quality is rated as "poor" are those where the analytical detection limit is close to or above the median level for the whole data set. In regions where these elements are locally above the overall background, however, their reproducibility is much better and their spatial distribution is adequately defined.

As part of the Buchans-Robert's Arm project in the early 1990's, both the GSC and the NLGS collected till samples within NTS sheets 2E/5, 2E/12, 12H/1, 12H/8, 12A/15, 12A/16 and also 12A/9 and 12A/10 to the south. More than 800 samples were collected by GSC personnel (defined in the till database by Geologist=RAK). The analytical methods were not exactly the same as the NL Geological Survey Laboratory so some levelling of the GSC data to the NLGS data was performed and the regressed GSC data is reported in the digital till database. A detailed description of the levelling procedure is provided in the Digital Geoscience Atlas of the Buchans - Robert's Arm Belt (Davenport et al., 1996, Nfld/2611).

Open File reports, maps and digital data issued by the Geological Survey Division of the Mining and Mineral Development Branch, Government of Newfoundland and Labrador, are made available for public use. They have not been formally edited or peer reviewed, and are based upon preliminary data and evaluation. The user agrees not to provide a digital reproduction or copy of this product to a third party. Derivative products should acknowledge the source of the data.

The Geological Survey (the "authors and publishers") retains the sole right to the original data and information found in any product produced. The authors and publishers assume no legal liability or responsibility for any alterations, changes or misrepresentations made by third parties with respect to these products or the original data. Furthermore, the Geological Survey assumes no liability with respect to digital reproductions or copies of original products or for derivative products made by third parties. Please consult with the Geological Survey in order to ensure originality and correctness of data and/or products.

(for downloaded database)

Newfoundland and Labrador Geological Survey. "Till Geochemistry." Newfoundland and Labrador GeoScience Atlas OnLine. Last update: (enter date from the What's New file). https://geoatlas.gov.nl.ca/ . [fill in date downloaded].

The original source should be referenced wherever possible. Please refer to the Source citations below, the Atlas Index of Till Geochemical Surveys or the Geofiles, to search for the pertinent reports and maps.

Finch, C., Roldan, R., Walsh, L., Kelly, J. and Amor, S.
2018: Analytical methods for chemical analysis of geological materials. Government of Newfoundland and Labrador, Department of Natural Resources, Geological Survey, Open File NFLD/3316, 67 pages.

Finch, C.
1998: Inductively coupled plasma-emission spectrometry [ICP-ES] at the geochemical laboratory. In Current Research, Department of Mines and Energy, Geological Survey, Report 98-01, pages 179-193.

Jenks, G.F.
1967: The Data Model Concept in Statistical Mapping. International Yearbook of Cartography 7, pages 186-190.

Wagenbauer, H.A., Riley, C.A. and Dawe, G.
1983: The Geochemical Laboratory. In Current Research, Newfoundland Department of Mines and Energy, Mineral Development Division Report 83-1, pages 133-137.

All open file reports contain full data listings or links to data listings, description of field and laboratory methods, and may discuss surficial geology and ice flow. All open file reports are published by the Geological Survey of Newfoundland and Labrador.

More recent publications are available on-line as pdf files with accompanying downloadable data files.  These are linked from the citations available through the Geofiles, through the Index of Surficial Geology Maps, through the List of Recent Publications, and through each point site location in the Geoscience Atlas (click on the site dot and in the Search Results window click on the left side of the record "Links").

Email: GeoscienceOnline@gov.nl.ca
 

(Help File updated March 2021)
(Database last updated: check the What's New file)