NZ Geochemical and Mineralogical Society

J. Rogers, first chairperson of the NZ Geochemical Group, in the introduction to the first newsletter, November 1965, wrote:

"I see the Geochemical Group as part of the New Zealand scientific community, that is, the scientists of the universities, government, and private enterprise. The prime purpose of this newsletter is to foster communication between members of this community who have an interest in geochemical work in common. Success of the Newsletter depends on all members being contributors. Let us hear, therefore, about your research and your views of the development and aims of the group. There should be plenty of material, as studies in applied, compositional, isotope, mineral phase equilibria, organic and solution geochemistry are in progress and New Zealand is an excellent natural laboratory for such investigations."

From an address to the NZGG Conference 30 March 1998 by A. J. ELLIS

Much of the beginnings of NZ geochemistry relating to the field of this conference began with geothermal energy developments from about 1950. A team of geologists, geochemists and geophysicists was created in the DSIR to understand better the workings of geothermal fields. I was fortunate to start work with Stuart Wilson, a pioneer NZ geochemist. Both of us being physical chemists we found out pretty quickly that variations in the composition of volcanic gases could be explained by temperature-dependent chemical equilibria. Fortunately, in this case high temperature thermodynamic data for the relevant gases was available from industrial chemistry literature.

At Wairakei and other geothermal fields abundant chemical analyses were obtained on the water, steam and gases discharged from wells and natural activity. This included element isotope ratios from Athol Rafter and his DSIR isotope chemistry group. At the same time Alfred Steiner, and later Pat Browne, outlined the hydrothermal alteration mineral patterns within geothermal fields, from drillcore analyses.

The variations in chemistry and mineralogy indicated potential geothermometers, but they needed calibration and interpretation. At that time there was almost no thermodynamic information on water solutions at temperatures over 100'C. So, we began our DSIR programme on high temperature and pressure aqueous solution chemistry and on hydrothermal mineral phase stabilities.

We were fortunate to have from the late 1950s both the field laboratory at Wairakei under Tony Mahon giving a wide range of information from wells and natural activity, and also an expanding high pressure and temperature experimental group in Lower Hutt which began to gather information on gas solubilities, carbonate solubilities, acid and base dissociation constants, thermodynamic data on salt solutions; also on hydrothermal mineral stabilities. The stabilities of dissolved sulphur species at high temperatures was determined and also the solubilities of metal sulphides and of gold in chloride/sulphide solutions.

It was necessary to develop techniques such as high temperature spectrophotometry, conductivity, solution density measurements and gold and platinum containment systems. Team members included Werner Giggenbach, Terry Seward, Byron Weissberg, Alan Reed, Tony Mahon and many visiting overseas scientists. We also had the advantages of an analytical team whose results one could believe, Reiner Goguel, John Ritchie, Watson Kitt, to name a few.

In the early 1960s Julian Hemley in the US Geological Survey and later Hal Helgeson at Berkeley produced classic papers on alumino-silicate/water equilibria and the thermodynamic interpretation of water compositions relating to co-existing mineral phases. Pat Browne and I applied this to NZ geothermal systems and came up with useful interpretations of temperatures, mineralogy, fluid composition and flow processes.

Our laboratory-derived thermodynamic data in particular allowed an increasingly quantitative approach to be taken. Athol Rafter, Bill McCabe, John Hulston, and others were also making good progress with calibrating isotope geothermometers. So, along with groups in the USA, Italy and Iceland we were getting a better understanding of the inter-relationships between temperatures, geothermal fluid compositions and mineralogy, and of applying this to the more effective harnessing of geothermal fields for energy production.

Ratios of the typical hydrothermal elements, chlorine, boron, fluoride, lithium and caesium, and ammonia are used in identifying and tracing geothermal waters. In separate studies we had obtained the concentrations of these constituents in Taupo Volcanic Zone rocks. The question then arose of how available they would be during contact with high temperature (100-600°C) water. Tony Mahon and I set up a series of simple experiments reacting a range of these rocks with high temperature water, and analysing the resultant solutions. The typical hydrothermal elements were found to be easily extracted, often at moderate temperatures and before major rock alteration occurred. As an example there was also selective solution of lithium, rubidium and caesium.

This raised the question, which is still debated, over how much the composition of geothermal waters is due to magmatic fluids and how much to solution from local rocks. Deuterium and 18O isotope analyses indicated that geothermal fluids were recycled meteoric waters.

In the 1960s and 1970s there was increasing interest in NZ in ore-forming solutions arising from the discovery of very high concentrations of arsenic, antimony, tungsten, gold and mercury in silicate deposits from geothermal waters; also from a renaissance in gold mining interests in extinct NZ geothermal areas. We extended rock/water studies with measurements of heavy metal mobilities from rocks into high temperature chloride solutions. Heavy metal extractions were considerable, as was seen later in practice during the investigations by other groups of deep ocean hydrothermal systems.

I am encouraged to see that much of our earlier work is still relevant to the studies presented at this conference. I have always appreciated having worked at the beginnings of rock/water interaction studies. It is clear that great progress has been made both in instrumentation and interpretations, which now makes some of our earlier work look quite crude.

It is good to see at the conference good cooperation and cross fertilization between such a wide variety of fields and backgrounds. This week's discussions have wide implications for the environment, energy, mining, oceanography, fresh waters, and waste disposal.

Over the years NZ has had great cooperation and scientist exchanges with groups all around the world, many of which are represented here today.