The application of micro-infrared spectroscopy and cathodoluminescence to the study of natural quartz

Grant, Kevin (2002) The application of micro-infrared spectroscopy and cathodoluminescence to the study of natural quartz. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

An infrared spectroscopic investigation into the speciation of hydrogen in vein quartz samples known to yield an anomalous isotopic signature shows that samples containing a significant fluid inclusion population yield a normal hydrogen isotope signature (-39‰). Conversely, samples generating an anomalous dD signature (-103‰) contain a significant quantity of structurally incorporated defect hydrogen species. Additional experiments detailing the liberation of different hydrogen reservoirs at increased temperatures show that discrete hydrous species are released at specific temperatures. Temperature increments correlate with those previously described to generate anomalous hydrogen isotope signatures during stepped heating isotopic experiments.

Mid-infrared spectroscopy has frequently been applied to the study and identification of clay minerals. We show that the frequencies of the fundamental molecular vibrations obtained using standard and field-based sample preparation techniques are the same. Bands generated using both infrared absorbance and reflectance spectroscope are also in good agreement. Micro-infrared spectroscopy was used to characterise the products of hydrothermally altered plagioclase phenocrysts from the Chelopech Au deposit, Bulgaria proved successful. Samples from inside and outside the main silicified zone are dominated by kaolinite and beidellite respectively. Mineral characterisation was confirmed using XRD analysis.

Cathodoluminescence images of quartz phenocrysts from a porphyry copper related intrusion elucidate a punctuated, multi-stage, crystallisation history. Concentrations of Al-OH, Li-dependent OH and H-OH groups show significant spatial variability within crystals. This is attributed to irregular incorporation of these species during crystal growth. Regions of high Al-OH content correlate with those displaying bright luminescence response. Quartz-included apatite and biotite crystals are found at different locations within the phenocrysts. Calculations enables log fugacity ratios log(f_H2O)/(f_HC1), log(f_H2O)/(f_HF), and log(f_HF)/(f_HC1) to be calculated for the precipitating medium. A comparison between log fugacity ratios of the studied intrusion, with those from other porphyry copper settings, shows many porphyry systems to have experienced similar crystallisation conditions.