Thermal contraction and expansion of quartz and its role in porphyry deposit mineralisation: A review

Abstract

Porphyry deposits are strongly associated, both spatially and temporally, with acid to meso-silicic intrusions. However, the mechanisms responsible for low-grade, large-volume mineralisation are not yet fully understood. Considering the relative thermal expansivity of key rock-forming minerals, measurements of their volumetric and morphological changes are critical to understanding the factors that control the emplacement of disseminated mineralisation. This study reviews the character and influence of differential thermal expansion between quartz and feldspar in porphyry deposits, with particular emphasis on the volumetric changes occurring at the α–β quartz transition. In a typical meso-silicic rock, expansion can reach approximately 1.2%. In addition, microfracturing and thermally induced openings can significantly enhance the transport and dissemination of late-stage mineralising fluids, with degassing resulting from thermal expansion further contributing to fluid enrichment and differential mineral deposition.