LE3 .A278 2008

2008

Stanley, Cliff

Acadia University

Bachelor of Science

Honours

Geology

Earth & Environmental Sciences

A mineralogical and lithogeochemical study undertaken in the volcanic host rocks around the low-sulphidation, epithermal, Au-bearing Amaranth quartz vein in the Union Hill area, Waihi, New Zealand, has revealed the existence of three different vein-hosting lithologies in this area: plagioclase-porphyritic andesite, plagioclase-quartz-porphyritic andesite and a newly identified plagioclase-pyroxene-porphyritic andesite. These rocks have undergone three distinct phases of alteration: propylitic alteration, characterised by the presence of calcite, chlorite and albite; K metasomatism, characterised by the replacement of plagioclase by adularia and muscovite; and H metasomatism, characterised by the destruction of feldspar to form hydrous phyllosilicate minerals. Differences observed between primary (fresh) and secondary (alteration) mineral assemblages in the host rocks have been used to determine lithogeochemical parameters that may provide effective exploration criteria. Each of these parameters is based on molar ratios of elements within the observed mineral formulae. These alteration parameters are examined geochemically and spatially using Pearce element ratio analysis and a set of two vertical cross-sections through the Amaranth vein. Of the four parameters tested, a calcite alteration parameter (CO2/Ca) and a pyrite alteration parameter (S/Fe), were found to exhibit limited usefulness as vectors towards epithermal quartz veins. However, a K metasomatism parameter (K/Al) and a H metasomatism (hydrolysis) parameter [(2Ca-2CO2+Na)/(Al-K)] both exhibit consistent trends across two vertical cross-sections through the Amaranth vein, and thus appear to provide useful vectors to mineralisation.

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https://scholar.acadiau.ca/islandora/object/theses:534