Kaolin Clay Deposits Associated with Fossil Geothermal Systems in New Zealand

Abstract

The occurrence of kaolinite in association with sinter caps in geothermal systems has been recognised for many years. Kaolins are used extensively in New Zealand in ceramics and as an industrial filler or coating pigment. During the and 1970's fossil geothermal systems in New Zealand were investigated to determine whether commercial kaolin deposits might exist beneath sinter caps. Surface prospecting of late Tertiary acid volcanic rocks for evidence of siliceous sinter and kaolin clays was followed up by core drilling of promising areas and detailed laboratory evaluation. This paper reports the results of investigations in the Northland and Coromandel regions of New Zealand in which two kaolin polymorphs, halloysite and kaolinite were identified. Commercially viable deposits formed by a combination of hydrothermal alteration and deep sub-tropical weathering were confirmed.