An occurrence of allophane from Mangaturuturu River, Tongariro National Park, North Island, New Zealand

Abstract

A white X-ray amorphous material from the Mangaturuturu River, Tongariro National Park, is identified as allophane. The allophane is being precipitated from the cold river water and forms a deposit lining the base and banks of the river. The Mangaturuturu River precipitate is unusual for allophane in that no discrete peaks exist in the X-ray diffraction (XRD) trace. The allophane precipitates from riverine waters which are fed by springs enriched with CO2, that enters the groundwater system from a geothermal source. If the cause for allophane precipitation is geo-thermally derived CO2, we speculate that precipitation of allophane would increase leading up to and during an active phase of volcanism. The relative abundance of allophane may therefore be a guide to geothermal gas movement within the mountain and, hence, an indicator of geothermal activity of the volcano. This locality is only the second occurrence of allophane reported as a precipitate from riverine waters in New Zealand. The other occurrence at Silica Springs is also in the Tongariro National Park. © 1997 Taylor & Francis Group, LLC.