Rare Earth Element Distribution Patterns in Shetland Steatite ‐ Consequences for Artifact Provenancing Studies

Abstract

An attempt has been made to relate steatite artifacts to the source of rock from which they were manufactured, using the distribution patterns of rare earth elements. Radiochemical‐ and instrumental‐neutron activation analyses of Shetland steatites suggest that the use of rare earth elements in artifact provenancing may be unreliable. Concentrations of rare earth elements in many Shetland steatites are too low to be measured reliably by a cost effective method. The relative importance of primary igneous and secondary metasomatic processes in controlling steatite rare earth element geochemistry is discussed and geological arguments against the existence of unique rare earth ‘fingerprints’ for steatite are presented.

A new protocol for the chemical characterisation of steatite – two case studies in Europe: the Shetland Islands and Crete

“…However, the data presented here suggest that there may have been some artefacts due to pre-concentration steps adopted by Bray, potentially due to variable recovery yields, or perhaps (as suggested by Bray (1994)) to blank levels associated with the exchange process. Nonetheless, both sets of ICP-MS-REE determinations show strongly source-specific patterns, which contrast favourably with the earlier INAA data from Moffat and Buttler (1986).…”

“…At Cunningsburgh (Fig. 3), the element concentration ranges (Table 4a) are low and vary considerably, as Moffat and Buttler (1986) found. However, Moffat and Buttler's determinations of Sm, Eu, Gd and Tb, for four of their samples from Cunningsburgh and Catpund Burn appear significantly over-estimated by comparison with samples in the present data set from similar localities (Fig.…”

“…Also sampled were smaller steatite outcrops whose significance was regarded as more geological than archaeological. All three of these quarries were described and analysed by Moffat and Buttler (1986) and Bray (1994), who also documented earlier analytical work. To this should be added the work reported by Turner (1998) The critical issue for this island is that, as a result of its tectono-metamorphic history, any previously existing chemical uniformity of petrologically similar formations, such as the ophiolitic bodies, will have been altered.…”

“…Despite the considerable progress made by Allen and co-workers on the geochemical characterisation of steatite from eastern North America (Allen and Pennell, 1978;Allen et al, 1975), efforts elsewhere have met with less success: transition metal and rare earth element (REE) determinations by neutron activation analysis carried out in different laboratories during 1970s and 1980s largely failed to differentiate the sources for a number of reasons, including wide intra-source variation and thus small or overlapping inter-source composition ranges, and low elemental concentrations that challenged analytical detection limits. Moffat and Buttler's (1986) study of REEs in steatite from five major quarries on the Shetland Islands employed both instrumental (INAA) and radiochemical (RNAA) neutron activation, while Allen and Pennell (1978) and Allen et al (1984) published summary INAA data for 20 (transition and rare earth) elements from some 10 geological sources on Crete. Similar problems have confronted those investigations of steatite and related softstone which have utilised other analytical techniques commonly in conjunction with mineralogical characterisation with X-ray diffraction: on Shetland (Buttler, 1984), Scandinavia (Resi, 1979), Crete (M Becker, pers.…”

“…Comparison between REE determinations in parts per million determined by ICP-MS (CUN, CAT) and RNAA(Moffat and Buttler, 1986) in steatite from Cunningsburgh (and Catpund).…”