Mineralogy and petrology in the New Zealand Geological Survey 1865–1965

Abstract

Abstract The development of mineralogy and petrology in the New Zealand Geological Survey falls into four phases: (1) 1865–92: a period of reconnaissance geology and petrology without the aid of the petrological microscope except for observations of Cox in 1880, (2) 1892–1905: commissioning of Sollas to study rocks from Coromandel Peninsula was the only activity, (3) 1905–38: petrology used almost entirely, and generally to a minor extent, as aid to 1-mile mapping, (4) 1938–65: petrology and mineralogy undertaken by a separate Petrology Section, with independent investigations as well as aiding mapping; building up of central rock and mineral collections, and steady growth of staff and equipment. Minerals first described from New Zealand are taranakite (1866), awaruite (1886), tuhualite (1932), hydrogrossular (1943), huttonite (1950), wairakite (1955), and wairauite (1964). Four meteorites are known—Wairarapa Valley (1863), Makarewa (1879), Mokoia (1908), and Morven (1925); only the Mokoia meteorite, a rare carbonaceous type, was seen to fall. Data on New Zealand mineralogy are summarised in six tables which show the development of quantitative techniques—chemical analysis (1866), microscopical examination (1880), refractive index (1935), mineragraphy (1940), X-ray examination (1945 examination overseas; 1955 in New Zealand), electron microscope (1955), and electron microprobe (1964, examinations overseas). Undoubtedly the development of precise methods in mineralogy over the last 10–15 years is one of the most dramatic features of the century and marks the change from a qualitative to a quantitative science. Three rocks first described from New Zealand have since been recognised throughout the world—dunite (1864), rodingite (1911), and ignimbrite (1932). Data on New Zealand volcanic, plutonic, sedimentary, metamorphic rocks, selected mineral deposits and specialised economic applications, and other matters are summarised in 18 tables. Features of volcanic petrology are: the recognition of “andesite” or “Marshall” line (1912), the postulation of Cainozoic volcanic provinces (1941, 1960), the recognition of ignimbrite sheets in the Central North Island (1932), and of the importance of plagioclase-hypersthene mineral assemblage in rhyolitic rocks of the North Island. Data on the sequence of volcanic eruptions are still meagre, but attention is drawn to the importance of detailed petrological and mineralogical comparison of the Alexandra and Egmont volcanism as an aid in predicting the future behaviour of Mt Egmont. New Zealand ultramafic rocks are of five types: the great Ultramafic Belt of the South Island, diapiric serpentinite, gabbro-peridotite complexes, metamorphic serpentinite, and dunite mylonite. Many ultramafic rocks display a low-temperature contact alteration, especially Ca-metaspmatism resulting in the formation of rodingite but recently (1965) a high-temperature contact has been recognised in the Red Hills Other types of plutonic rocks are less known, a result of inaccessibility in mountainous terrains and the difficulties of rock correlation.