I'm not an expert on geology but two things:1. The samples were...

I'm not an expert on geology but two things:

1. The samples were homogenised in 4-metre sections and then sub-sampled for chemical assays, so actual anomalies would be dampened.

2. I refer to this paper, to review the background ppm of 50+ elements in topsoil which is consistent across Australia as per the paper results.

Clemens Reimann, Patrice de Caritat,Establishing geochemical background variation and threshold values for 59 elements in Australian surface soil,Science of The Total Environment,Volume 578,2017,Pages 633-648,ISSN 0048-9697,https://doi.org/10.1016/j.scitotenv.2016.11.010.

https://www.sciencedirect.com/science/article/pii/S004896971632441X

(Now forgive me if I am wrong)

In Table 1, there are two results for each section of soil sampling, for coarse and fine grit.

For A fines, minimum, 25% percentile, 50%, 75% and maximum Arsenic (As) ppm are: < 0.1, 0.9, 1.6, 2.9 and 218

For coarse, minimum, 25% percentile, 50%, 75% and maximum As ppm are: < 0.1, 1.1, 2, 3.4 & 79

Hence all but one result* for As reported in Table 1 of the announcement from MTL today are therefore definitely anomalous unless the established background As levels in ultramafic rock and topsoil is known to be higher or higher in the Pilbara, or specifically the Mt Berghaus/Mallina or Hemo regions/deposit overburden.

*Still likely anomalous without a survey of Pilbara overburden varying significantly from other catchments in the continent-wide sampling from the 2017 paper.