Towards Exploration Tools for High Purity Quartz: An Example from the South Norwegian Evje-Iveland Pegmatite Belt

Abstract

High Purity Quartz (HPQ; quartz containing less than 50 ppm trace elements) is of increasing economic significance due to its use in certain high-tech components (computer chip/semiconductor manufacture) and in green technologies (silicon wafer production). Current HPQ deposits (hydrothermal veins/leuco-granites/alaskites) are rare and volumetrically small. Unless significant new deposits are found, increasing demand will raise its prices, elevating the strategic nature of this limited commodity. The large volumes and simple mineralogy of pegmatites and the high chemical purity of their constituents make them an attractive target for HPQ. PhD studies are being carried out on quartz from the Evje-Iveland pegmatite field of the Bamble-Evje pegmatite cluster, southern Norway. The area was targeted due to its well constrained geological setting and previously identified potential for HPQ. The aim of the investigation is to develop exploration tools for HPQ by determining the genetic history of the pegmatites and mode of HPQ formation.

The study is focussing on 7 pegmatites and their country rocks. Each shows typical pegmatite zonation, with quartz/feldspar intergrowths at the margins, a massive quartz core and a variety of accessory (including REE-bearing) phases. The proximal Høvringsvatnet granite was previously suggested to have supplied late-stage, highly fractionated melts to form the pegmatites. However, from their trace element systematics (no relationship was observed between trace element content and degree of fractionation in each pegmatite body), and a difference in U/Pb age of approximately 70 Ma, the pegmatites cannot be related to the granites. From field evidence (corroborated by geochemical modelling) the pegmatites formed by ‘in situ’ anatexis of country rocks; some locally, some from distal sources.

Some pegmatites contain brecciated feldspar and replacement quartz. From LA-ICP-MS analyses, hydrothermal quartz, compared with magmatic quartz, typically contains lower quantities of trace elements. Hydrothermal material shows relatively elevated levels of Al and Li, low Ge and a complete absence of Ti, indicating relatively low temperature hydrothermal formation. Different quartz domains (from SEM-CL imaging) show distinct δ18O values; late stage low trace element zones show values consistent with meteorically derived fluids. In situ LA-ICP-MS studies will provide further information about the characteristics of the fluids which have replaced/refined magmatic quartz to form HPQ. This beneficiation process is a potential mechanism for the generation of economically significant HPQ deposits.