Thomas Hacket was a London born mining geologist who trained and worked in Germany before arriving in Nelson, in 1857, as manager to the Dun Mountain Copper Mining Company, thereby making him the first professional geologist in New Zealand. His younger brothers Charles (1831-1901) and James Henry (1839-1914) also pursued geological careers, the latter in Australasia. In Nelson, Hacket advised on mining and engineering projects in the north of the South Island and acquired a good knowledge of the diverse rocks that make up New Zealand. He provided this information to the German geologist Ferdinand von Hochstetter who visited parts of the country, including Nelson, in 1859 and is recognised as the “Father of New Zealand Geology”.

In Otago, in the south of the South Island, Hacket at times assisted James Hector, the Otago Provincial Geologist who had been appointed in 1862, fresh from the Canadian Palliser Expedition. Hacket recognised that many Otago rocks were similar to those in Nelson and nearly 100 years later it was realised that these rocks had been offset 480 km by horizontal movement on the Alpine Fault. After Hector became the first director of the NZ Geological Survey in 1865, Hacket helped on various surveys, the most notable being of the coalfields of the South Island’s west coast.

Unable to get permanent employment, Hacket went to Australia in 1868 and was appointed a mining surveyor, then geologist, at the newly discovered Gympie Goldfield in Queensland. Hacket arrived just as the field was changing from an alluvial to a reefing one. He recognised the structure of the reefs and produced a geological map of the goldfield in 1870, ironically a year after losing his job when the Queensland Survey was disbanded. He then had a chequered career as a goldfields administrator at various Queensland goldfields until 1877. Except for his Gympie map, Hacket authored no major publications while in Australia. However, his foremost scientific contribution was to keep Hector informed of geological developments in eastern Australia. In particular, he realised that rocks in Gympie were similar to those in Nelson, a correlation not accepted until 130 years later. Hacket’s letters to Hector are in Te Papa, the Museum of New Zealand but the letters he received in return are lost. Hacket returned to New Zealand in 1878, dying in Nelson six years later.