Abstract:
The elemental distribution of trace elements in banded Australian sedimentary opals from the Lightning Ridge region
was investigated using secondary ion mass spectrometry (SIMS). Data were acquired using both spot analysis and spatial analysis
by stepping incrementally across samples in line scan mode. Opal specimens were found to be fairly homogeneous within
bands. A relatively sharp change in elemental concentration was, however, observed at the interface between bands for selected
elements (Ti, V, Co. Cu. Zn, Y). Although some elements were observed to change significantly in concentration between bands,
the concentration of a number of elements (Na, Mg, AI, K. Ca, Mn, Fe) were observed not to vary significantly between bands.
The consistency in concentration of these elements between the bands suggested that the adjacent bands in the opals studied were
formed coincidentally. These observations were consistent with data acquired using laser ablation ICP-MS (BROWN et al. 2004)
and, hence, consistent with the solution depletion sedimentation model proposed as the mechanism for band formation in banded
opal.
