New Zealand Epithermal Gold
New Zealand is home to the world class Martha gold mine in Waihi (10 Moz+ Au), located within the highly prospective Hauraki epithermal district. As well as the Martha Mine (owned by Newmont Gold) there are over fifty further historical epithermal gold prospects, and numerous other mineral occurrences. These include the Golden Cross Mine (750,000 oz Au) and Karangahake (1 Moz Au).
Given the prospectivity of the region, Kenex has developed an exploration GIS and mineral prospectivity model for epithermal gold mineralisation for the Hauraki district, as well as the significantly underexplored Taupo Volcanic Zone and the Northland region. The Northland region was the subject of a New Zealand Government Northland 2012 competitive tender.
The review of the exploration data contained within the exploration GIS has been completed using the most recently accepted model for epithermal gold mineralisation. Predictive maps were developed that map possible source, transport, trap and metal deposition for epithermal gold mineralisation. The spatial analysis identified the following geological parameters as important for predicting epithermal gold mineralisation in New Zealand:
- Host rock preference of known deposits.
- Proximity to major faults and relationship to fault orientation.
- Lithology (basalt, andesite, dacite or rhyolite; flows versus pyroclastic rocks).
- Age of host rocks.
- Correlation with density of quartz veins.
- Correlation with density of faults.
- Geochemistry of host rocks.
- Proximity to calderas and/or ring structures.
- Proximity to or correlation with density of lineaments (Hauraki).
- Correlation with specific ranges of Au:Ag ratios.
- Correlation with As in exploration geochemical surveys.
- Topographic expression from DTMs and remote sensing data.
Using weights of evidence techniques, prospectivity maps were produced over each study area, assessing the probability of finding gold deposits based on input predictive maps that represent all stages of the epithermal gold mineral system model.
Updated Epithermal Gold Prospectivity Model
Following the development of the successful "Epithermal Gold in New Zealand: GIS Data Package and Prospectivity Modelling" – a collaboration between Kenex, GNS and the Ministry of Economic Development in 2003-04, we are pleased to advise that an updated version of a New Zealand Epithermal Gold prospectivity model has been completed and is available for purchase from Kenex.
The updated GIS has been compiled of available open file geological, geochemical and geophysical data relevant to the New Zealand epithermal districts and complements the recently released geophysical data acquired by the New Zealand Government for the Northland Region.
A structural geological review on regional as well as local controls on mineralisation has been completed and the structural model checked against the geology, geophysics and geochemical results where these are available. The geochemical data has been reviewed statistically at a regional scale to derive local anomaly levels for the relevant ore and pathfinder elements in rock and stream sediment samples. In summary the compiled GIS has been used to:
- Develop a prospectivity model to indentify the most prospective areas in New Zealand for epithermal mineralisation.
- Derive anomalous threshold levels for geological, geochemical and geophysical data.
- Identify missing data that needs to be collected to upgrade the prospectivity of targets.
- QA the database against exploration models being used.
- Review exploration models in relation to current exploration.
- Prioritise a list of those geological variables that are the best predictors of mineralisation.
- Review current exploration techniques in relation to exploration models used in the modelling.
- Review current exploration prioritisation in relation to prospect priorities identified by the modelling.
- Develop recommendations for follow-up field work.
The prospectivity model generated, along with the exploration GIS is a valuable tool that can enable companies to identify potential opportunities in New Zealands epithermal districts or they already hold tenements, to accelerate exploration, identify opportunities outside current tenement packages for joint venture or acquisition and get ahead of competition.
Furthermore, through the integration of prospect scale exploration data the models can be updated to provide exploration focus through prioritisation of targets that fall within held tenement portfolios.