MINERALOGICAL AND TEXTURAL CONTROLS ON THERMAL CONDUCTIVITY – AN EXAMPLE FROM SOUTH TABLE MOUNTAIN, GOLDEN, CO

A material’s ability to conduct heat and the ability to measure such a property has led to the utilization of thermal conductivity and the testing thereof in a wide range of research areas and industries. Controlling factors include, but are not limited to, a rock’s mineral assemblage/rock type, fluid type, fluid saturation level, porosity and permeability, crystal structure and crystal orientation.

As part of a larger study into the installation of ground source heat pumps to deliver geothermal energy, we present integrated results from stratigraphy, automated mineralogy, and geotechnical and thermal conductivity testing carried out on a 300-foot wireline core section obtained from South Table Mountain, Golden, CO. The aim of this study is to link lithologic units, mineralogical and also textural changes (e.g. grain size distribution, laminations etc.) within key units of the Upper Cretaceous- to Late-Tertiary-age Denver Formation and the overlying Tertiary-age shoshonites with physical (thermal) variations. With nearly 90% wireline core recovery and approximately 70% Rock Quality Designation (RQD), this study presents a unique opportunity to evaluate a very detailed record of the Denver Formation (interbedded horizons of shale, siltstone and lenticular andesitic sandstone). Initial results suggest that, even though thermal conductivity values are generally low and display only a narrow range, mineralogical and textural changes are greater than previously recognized. Hence, findings of this study will greatly contribute to our understanding of the relationship between a rock’s intrinsic characteristics and its ability to conduct heat.