| Summary: | Thesis (M.S.) University of Alaska Fairbanks, 2024 The study uses data and samples from a 2009 and 2012 stream sediment sampling program, conducted in part by the author. With the aim to identify gold-bearing prospects, a data set of 417 samples was digested with aqua regia and analyzed using inductively coupled plasma mass spectrometry (ICP-MS). I had leftover material from the original samples reanalyzed by ICP-MS after 4 acid (nitric + hydrochloric + hydrofluoric + perchloric) digestion. I compared the compositional data for the two sample sets (308 samples, 45 elements). Accuracy and precision (reproducibility) for all elements of the aqua regia sample set is noticeable lower than that of the 4 acid digestion set. Accuracy is computed by the relative error that compares the assay of the standard sample to the known concentration of the standard. Precision is an estimate of the reproducibility of the sampling and analytical system. Precision is calculated by fractional uncertainty. Field duplicates are produced by splitting samples in two. Fractional uncertainty is calculated for each pair of original sample and field duplicate. Gold shows the lowest precision of all elements for both data sets, most likely due to the nugget effect. Using a paired sample T-Test I concluded that the mean concentrations of 42 elements are different for aqua regia versus 4 acid digestions. Only for three elements (sulphur, bismuth and copper) were non-distinguishable average element concentrations found for both digestion methods. A negative t-statistic (based on aqua regia vs. 4 acid digestion-based compositions) implies higher elemental recovery by 4 acid digestion. The aqua regia data set record only a portion (presented in brackets) of the values for 4 acid digestions for these elements: Na (1%), Hf (2%), Zr (3%), K (4%), Nb (5%), Sr (7%), Al (11%), Ti (12%), Rb (14%), Ba (16%) and Ca (19%). The digestion method determines the degree of element recovery from the solids (i.e., dissolution into solution) and consequently ...
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