Using the Rock Canyon Creek carbonate-hosted rare earth element (REE)–F–Ba deposit as an example, we demonstrate the need for verifying inherited geochemical data prior to reinterpretation. Inherited La, Ce, Nd and Sm data obtained by pressed pellet X-ray fluorescence (XRF), and La and Y data obtained by aqua regia digestion inductively coupled plasma atomic emission spectroscopy (ICP-AES) for more than 300 drill-core samples were analysed in 2009 and were subsequently compared to sample subsets re-analysed using lithium metaborate-tetraborate (LMB) fusion ICP mass spectroscopy (ICP-MS), Na
2
O
2
fusion ICP-MS, and LMB fusion-XRF. We determine that LMB ICP-MS and Na
2
O
2
ICP-MS accurately determined REE concentrations in control reference materials (CRM) SY-2 and SY-4, and provided precision of about 10%. Fusion-XRF was precise for La, Ce and Nd at concentrations greater than ten times the lower detection limit; however, accuracy of this method was not established because REE concentrations in SY-4 were below the lower detection limit. Analysis of the sample subset revealed substantial discrepancies for Ce concentrations determined by pressed pellet XRF in comparison to those determined by other methods due to Ba spectral interference. Samarium, present in lower concentrations than other REE that were determined, was consistently underestimated by XRF methods relative to ICP-MS methods. This may be the result of Sm concentrations approaching the lower detection limits of XRF methods, elemental interference or inadequate background corrections. Aqua regia dissolution results, reporting only for La and Y, are underestimated relative to the other methods. We highlight the importance of selecting the most appropriate analytical method and reference materials for determining the REE content of mineralized rock which may be several orders of magnitude higher than that of typical host rock.
An on-site procedure involving filtration and ion exchange has been developed to study aluminium speciation in water samples from shallow wells. Immediately following collection samples are mixed continuously with Chelex 100 ion-exchange resin for eight hours. At
intervals during the mixing cycle subsamples of the water are taken, filtered, preserved, and later analyzed for aluminium by graphite furnace atomic absorption spectrophotometry. The method has been applied to examine aluminium chemistry in water from selected shallow wells in rural areas of
eastern Canada exposed to acid rain. Results show that in weakly acid water much of the aluminium remains in polymeric forms whereas more strongly acid (pH below 5.5) well waters contain predominantly monomeric, labile aluminium.
This paper demonstrates the application of geochemical exploration for sulphide mineralization in glaciated areas by a case history illustrating the discovery of Cu-Pb-Zn-Ag-Au massive sulphide deposits in southern British Columbia, Canada. These deposits, hosted by Palaeozoic metasedimentary and metavolcanic rocks of the Kootenay Terrane, were first detected by weakly anomalous Cu and Au values in regional stream sediment samples and subsequently confirmed by more detailed stream and soil geochemical surveys, prospecting and diamond drilling.Till geochemistry is a very effective exploration method because there is a well developed dispersal plume of mineralized bedrock down-ice from the massive sulphide deposits. Elevated Au, Pb, Cu and As levels in till samples collected up to 8 km down-ice from the deposits are direct indicators for sulphide mineralization. Barium, Cr and Ni are pathfinders for distinguishing different types of sulphide mineralization. The relationship between the bedrock, stream sediment, stream water and till geochemistry is shown more clearly in a conceptual model. This model has a practical application to future exploration for massive sulphides in southern British Columbia by establishing criteria such as geochemical anomaly size and contrast for different sample media.
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