J. Nolan

Determination of rare-earth elements, yttrium, scandium and hafnium using cation-exchange separation and inductively coupled plasma-atomic emission spectrometry

Abstract The determination of low levels of rare-earth elements (REE), Y, Sc and Hf in geological samples has been achieved using minor modifications to established ion-exchange procedures with subsequent analysis by inductively coupled plasma-atomic emission spectrometry (ICP-AES). A lithium metaborate fusion followed by dissolution in dilute hydrochloric acid was used to ensure complete sample decomposition. Sample solutions were loaded onto columns containing AG 50 W-X 8 ® cation-exchange resin, and unwanted elements were removed using elution with 1.75 M HCI followed by 1.75 M HNO 3 . Almost all potentially interfering elements were eliminated using this procedure (only Ba and Zr remaining), and residual inter-element interferences were easily corrected. By adding a small amount of oxalic acid to the 6 M HNO 3 eluant the Hf present in the sample was eluted with the REE, Y and Sc. Analytical data obtained by ICP-AES were judged to be sufficiently accurate and precise (± 5%) for most geochemical applications. Measured detection limits for Y, Sc and Hf were respectively 0.2, 0.1 and 0.2 μg g −1 in samples.

Silicothermal fluid: A novel medium for mass transport in the lithosphere

New experimental data from synthetic fluid-inclusion studies in the system K 2 O-CO 2 -SiO 2 -H 2 O (KCSH) show that a potassic, silica-rich (≈ 90 wt% SiO 2 ) fluid can coexist immiscibly with a supercritical, alkaline, aqueo-carbonic fluid and quartz from temperatures as low as 300 °C to more than 750 °C at relatively low geologic pressures ( 2 -rich fluids, if they form in the lithosphere, are likely to be important in the mobilization and transport of silica and large ion lithophile elements (e.g., K, Cs, Ba) and metals of economic significance (e.g., Au, Ag, U).

Laser ablation-ICP-AES for the determination of metals in fluid inclusions: An application to the study of magmatic ore fluids

Abstract The laser ablation-ICP-AES (L-ICP-AES) technique is an effective method for the multielement analysis of individual fluid inclusions. Recent tests on synthetic fluid inclusions and improvements in data processing suggest that the method is valid for the analysis of a range of alkali-, alkali-earth, and transition metals in single, large inclusions (> 30 μm) of moderate to high salinity (>20 wt% NaCl equiv.). The system, involving a small, perspex ablation chamber, a 1 J ruby laser focussed through an optical microscope, and a conventional ICP-AES instrument is discussed and applied to natural fluid inclusions in quartz from two contrasting types of magmatic-hydrothermal mineralization. Samples were selected from the San Pedro Cu-Au porphyry system, New Mexico, USA, and the Sn-W-Cu-mineralized Dartmoor granite of southwest England. Variable salinity, high temperature fluid inclusions in hydrothermal quartz from both environments display similarly high concentrations and ratios of Na, K, Ca, and Fe. The ore metals Cu, Zn, and Mn (but not Sn, Mo, W) were detected in inclusions from both environments. The estimated combined concentrations of up to 3 wt% show that these three elements are major components of these fluids. A method has been devised to estimate the confidence intervals of the measured concentration ratios. The confidence intervals obtained show that the analytical uncertainty for an inclusion is much less than the natural geochemical variation between inclusions so that geologically useful information can be obtained. A trend of increasing salinity with decreasing Na and K and increasing Ca and Fe contents is observed in inclusions from San Pedro, consistent with the continuous evolution of a magmatic aqueous phase exsolved from a low pressure melt during crystallization. In contrast, the combined compositional and microthermometric data for samples from Lee Moor, Dartmoor, suggest that a magmatic aqueous phase evolved from Fe-K-rich to Na-Ca-rich compositions during cooling and was periodically diluted by meteoric fluids.