Chemical compositions of selected sinter samples from Rotorua Museum

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Reyes, A.G. 2017 Chemical compositions of selected sinter samples from Rotorua Museum. Lower Hutt, N.Z.: GNS Science. GNS Science report 2017/45 11 p.; doi: 10.21420/G26Q06

Abstract: Eight sinter samples, purportedly from the Pink and White Terraces, were geochemically analysed using neutron activation analysis (NAA). The selection represents a range of colours: violet to red to yellowish red, orangish yellow, nearly white but with faint brownish tints and brownish. Seven of the samples are from the Rotorua Museum collection acquired in 2013 and one is from Mr Blair Polly. Gold and Ag show positive correlation, as do As and Sb. However high concentrations of Au and Ag occur where As and Sb are low. There is no correlation with colour and elevated concentrations of Au and Ag e.g., Au contents are highest in greyish red/violet (0.97 ppm) and nearly white samples (1.06 ppm). However, samples with reddish to reddish yellow to orange yellow hues (Munsell 7.5 YR and 2.5 YR) correlate with high concentrations of As and Sb e.g., 44 to 190 ppm As and 104 to 158 ppm Sb. Concentrations of Cs, Na, Rb, Sc and Br are high where As and Sb are also high. The small sample amounts (<4 g) limits the capacity of NAA to analyse for crucial elements, e.g., Hg, Mn and Fe which could contribute to red hues in the sinters, and also base metal elements such as Cu, Pb and Zn. Thus the plan is to sample at least 8 g of sinter from museum-authenticated Pink and White Terraces sinters at the Auckland Museum and the Natural History Museum in London and if warranted and allowed, resample crucial sinter specimens at the Rotorua Museum. The larger amount of samples would ensure analyses of a wider range of elements and lower limits of detection. (auth)