Hydrofluoric Acid‐Free Digestion of Geological Samples for the Quantification of Rare Earth Elements by Inductively Coupled Plasma‐Optical Emission Spectrometry

Rare earth elements (REEs) are very important to technological development as well as to geochemical and environmental studies. In this work, hydrofluoric acid (HF) was replaced by condensed phosphoric acid (CPA) in the digestion of geological samples, and the quantification of REEs was performed by inductively coupled plasma‐optical emission spectrometry (ICP‐OES). Six international reference materials (RMs), named DC86318, CGL 111, CGL 124, CGL 126, OKA‐2 and COQ‐1 and three Brazilian ore samples, named Araxá, Catalão and Pitinga were analysed. Only zircon and xenotime, which are potential REE‐bearing minerals, were not completely dissolved. Nevertheless, no REE associated with zircon was detected. The investigated digestion method presented many advantages: It was relatively fast (3 h), avoided fluoride precipitation, it was less hazardous because handling diluted H₃PO₄ is safer than HF, NH₄F or NH₄HF₂ aqueous solutions, it preserved the quartz fittings of the measurement equipment and the final solution contained lower levels of total dissolved solids than those produced by the fusion method.     

Shallow virtual source redatuming by multi‐dimensional deconvolution

Recently, new on‐shore acquisition designs have been presented with multi‐component sensors deployed in the shallow sub‐surface (20 m–60 m). Virtual source redatuming has been proposed for these data to compensate for surface statics and to enhance survey repeatability. In this paper, we investigate the feasibility of replacing the correlation‐based formalism that undergirds virtual source redatuming with multi‐dimensional deconvolution, offering various advantages such as the elimination of free‐surface multiples and the potential to improve virtual source repeatability. To allow for data‐driven calibration of the sensors and to improve robustness in cases with poor sensor spacing in the shallow sub‐surface (resulting in a relatively high wavenumber content), we propose a new workflow for this configuration. We assume a dense source sampling and target signals that arrive at near‐vertical propagation angles. First, the data are preconditioned by applying synthetic‐aperture‐source filters in the common receiver domain. Virtual source redatuming is carried out for the multi‐component recordings individually, followed by an intermediate deconvolution step. After this specific pre‐processing, we show that the downgoing and upgoing constituents of the wavefields can be separated without knowledge of the medium parameters, the source wavelet, or sensor characteristics. As a final step, free‐surface multiples can be eliminated by multi‐dimensional deconvolution of the upgoing fields with the downgoing fields.