Mineralogical and Morphological Studies of Travertine: A Comparison Study Between Silver Peak, Waikite, and Ngatamariki||

Abstract

Travertine is a common geothermal surface feature that forms by the deposition of carbonate from discharging bicarbonate thermal water. Travertine samples from two sites: Silver Peak, Nevada, USA, and Waikite, New Zealand, were examined to contrast their mineralogy, morphology, and chemical composition. These sites were chosen as they provided examples of travertine formed in different countries and in different geothermal settings. Travertine formed at Silver Peak is related to a deep-reaching heat-sweep system, Travertine at Waikite contains silica and is related to a flat terrain geothermal system where the heat source appears to be extensive, hot rhyolitic crustal rock. X-ray Powder Diffraction (XRPD) determined differences in the travertine mineralogy of Silver Peak samples were calcite, whereas samples from Waikite consisted of calcite with some samples also conteining silica (opal-A). Based on the XRPD trace samples from Waikite were slightly more crystalline than those from Silver Peak. The crystal size (> 100 ìm) of Waikite’s samples is larger than Silver Peak’s samples (~ 100 ìm) while some samples have no obvious crystal shape. Different morphologies exist between the Silver Peak and Waikite calcite. Also calcite/silica samples from Waikite show that amorphous silica is deposited above the water level. The depositional and hydrological conditions of these geothermal fields differs which influences the mineralogy, morphology, and chemical composition of their associated travertine deposits. Therefore, fine-scale examination of travertine enables us to better understand the hydrological setting (i.e. no hot intrusion Vs hot intrusion) and how the setting effects the formation of travertine.