But now, GNS Science has created a new geological map of the area, showing exactly where it is.
The mapping project was done in collaboration with the University of Otago and OceanaGold, and has provided deeper insight of major earth structures and a new interpretation of the major gold-producing feature in the Hyde-Macraes Shear Zone.
The recently released geological 1:50,000 scale map focuses on the trans-crustal Waihemo Fault Zone, the economically significant Hyde-Macraes Shear Zone and the western edge of the Canterbury Basin.
GNS Science senior geologist Dr Adam Martin said the previously unknown geology below the surface was mapped using a combination of techniques, including compass readings, airborne geophysics, LiDAR and seismic lines.
"More than 50 years of science has been captured into a single map of New Zealand’s richest gold producing region.
"It is an exemplar collaboration between GNS, university and industry to understand faults, rocks and gold formation in this important piece of New Zealand."
Dr Martin said one of the goals of the mapping project was to support more gold exploration in the area in order to contribute to the economic wellbeing of the region.
The Otago Gold rush peaked in the mid-1860s and attracted miners from around the world, leading to the discovery of multiple goldfields spread throughout Central Otago.
The Hyde-Macraes Shear Zone was a hotspot for mining during this time and was now New Zealand’s largest gold-producing region.
He said new interpretations in the geological map suggested this major gold-producing feature in the Hyde-Macraes Shear Zone "pinches out" before heading offshore, allowing for more focused exploration in the inland area.
"At least two types of gold formation occur in the area.
"Historic mining 100 years ago targeted steeply dipping quartz veins which hosted gold.
"Modern-day mining targets the Hyde-Macraes Shear Zone that dips only shallowly, 10° to 20° to the northeast.
"Gold was emplaced when hot, hydrothermal waters flowed along this structure depositing gold along the shear zone some 135 million years ago.
"It is this shallowly dipping structure that has produced the majority of gold, and understanding it better helps in the search for similar gold-producing features."
The Macraes gold mine has been operated by OceanaGold since 1990, and has produced more than 5million ounces of gold, contributing to the local economy through employment, procurement, community investment and donations.
