Characterisation of mineral deposition systems associated with rock art in the Kimberley region of northwest Australia

This data article contains mineralogical and chemical data from mineral accretions sampled from rock art shelters in the Kimberley region of north west Australia. The accretions were collected both on and off pigment and engraved rock art of varying styles observed in the Kimberley with an aim of providing a thorough understanding of the formation and preservation of such materials in the context of dating [1]. This contribution includes processed powder X-ray Diffraction data, Scanning Electron Microscopy energy dispersive spectroscopy data, and Laser Ablation ICP-MS trace element mapping data.


a b s t r a c t
This data article contains mineralogical and chemical data from mineral accretions sampled from rock art shelters in the Kimberley region of north west Australia. The accretions were collected both on and off pigment and engraved rock art of varying styles observed in the Kimberley with an aim of providing a thorough understanding of the formation and preservation of such materials in the context of dating [1]. This contribution includes processed powder X-ray Diffraction data, Scanning Electron Microscopy energy dispersive spectroscopy data, and Laser Ablation ICP-MS trace element mapping data.
& 2017 Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Subject area
Archaeological Science More specific subject area

Geochemistry of rock art shelters
Type of data

Value of the data
Data presented here will be useful to other researchers as a benchmark for X-ray diffraction analysis of the range of mineral accretion systems present in Kimberley rock art shelters Laser-Ablation trace element maps coupled with site and sample photographs of four distinct mineral systems present in shelters in the Kimberley region of Western Australia may be used to aid sampling strategies associated with future rock art dating programs 1. Data

Data from laser-ablation trace element mapping
Laser ablation trace element maps of cross sectioned mineral accretions collected at rock art shelters in the Kimberley display variations in the characteristics of their internal micro-stratigraphies dependent on the mineral system to which they have been assigned (Figs. 1-22) [1]. The accretions also display differing concentrations of particular elements, which is useful for the assessment of the suitability of each accretion, and in turn, mineral system to particular radiogenic dating techniques. The varying concentration of these different elements also provides information which aids the generation of hypotheses surrounding the formation mechanisms associated with the different mineral systems.

Data from X-ray diffraction analysis
Tables 1 and 2 display the occurrence of a range of sulphate, oxalate and phosphate minerals across the four different mineral systems from a range of sites across the Kimberley. This is a semi-quantitative analysis of the crystalline component of the sample as X-ray Diffraction does not detect any amorphous content that may be present. Table 1 includes data from 44 samples of Polychrome Fringes. Table 2

X-ray diffraction
Characterisation of accretion mineralogy was predominantly established using a Bruker D8 Advance x-ray powder diffractometer (XRD) with Ni-filtered Cu kα radiation (1.54 Å) at the University of Melbourne Materials Characterisation and Fabrication Platform. Data were collected between 5-85°2θ, with a step size of 0.02°and a scan rate of 1.0 s per step. An incident beam divergence of 0.26°w as used with a 2.5°soller slit in the diffracted beam. The sample was spun at 15 revolutions per minute. The background was fixed manually. Following measurement, phase identification was completed using Materials Data, Inc., Jade 9.3 and Bruker EVA software with the ICDD PDF-2 and PDF-4 databases with key mineral phases established for each sample using standard search-matching procedures. Several samples were also analysed at The Melbourne Museum using a Phillips X'Pert      PRO XRD system traversing a scattering angle of 75°, coupled to an X'Pert Data Collector with X'Pert HighScore search-match software. Data is presented in Tables 1 and 2.

Laser-ablation trace element mapping
Elemental distribution maps were used to analyse the internal structures of the accretion samples. Maps were produced using LA-ICP-MS analyses, performed on an Agilent 7700x quadrupole mass spectrometer, coupled to a Lambda Physik Compex UV 193 nm excimer laser system at the University of Melbourne employing a S-155 ablation cell. Samples were ablated under helium with an argon carrier gas. Prior to laser ablation analysis, samples were mounted in a 'freeform' sample holder and imaged at high resolution on a flatbed scanner. The resulting images, referenced to the coordinate system of the ablation cell, could then be used as a base layer upon which to overlay the laser ablation concentration 'maps'. The latter were produced by analysing the material liberated from a series of parallel ablation tracks across the sample surface, oriented perpendicular to the growth banding. The analysis protocol utilised a scan speed of 40 µm s -1 , with a spot size of 40 µm, pulse rate of 10 Hz, and laser fluence of~2.5 J/cm −2 . NIST SRM 612 was used as the primary calibration material. In all laser analyses reported herein, the elements for which data were acquired are Al, Ca, Ce, Fe, Mg, Mn, P, S, Sr, Si, Th and U with an estimated precision of elemental concentrations of ca o 5%. All data were reduced using Iolite software [2] with data deconvolution as described in [3]. Data are presented in Figs. 1-22.

Scanning electron microscopy
The distribution and morphology of minerals within accretions were established using both a Quanta FEG 200 ESEM and a Phillips FEI XL30 environmental scanning electron microscope (ESEM) equipped with an OXFORD INCA energy-dispersive x-ray spectrometer (EDS) at the University of Melbourne. The instrument has a tungsten filament electron source with a beam of 15 kV and spot size 6 and was operated in high vacuum mode with a gold coating used to render the samples conductive. The EDS system uses a liquid-nitrogen cooled Si-Li detector with an area of 10 mm 2 and an ATW2 thin detector window allowing collection of x-rays between B and U. Valuable information was obtained from the morphology of crystalline forms and the elemental composition of each constituent was determined using EDS spot analysis. Data are presented in Figs. 23-28.      Table 1 Semi-quantitative X-ray diffraction mineralogical data for 44 Polychrome Fringe accretion samples collected in the Kimberley region of north west Australia. Table 2 Semi-quantitative X-ray diffraction mineralogical data for 26 Dispersed Wall Coating accretion samples, 7 Floor Glazes and 5 Silica Skins/Stalagmites collected in the Kimberley region of north west Australia.