Annual Armidale Technical Session

On 16 June, over 30 people braved a cold Armidale winter night to hear two excellent technical talks. The event was our annual Armidale technical session which has been suspended for the past two years due to COVID restrictions. This event benefit the external geology students at the University of New England, and is held to coincide with their mid-year residential school. Attendees enjoyed networking before Paul Ashley and Branch Chairman Hennie du Plooy addressed the group.

Senior Geologist Blake Larter of Red River Resources gave a presentation on “Current Exploration at Hillgrove”. Hillgrove is Red River’s producing gold and antimony mine located 17 km east of Armidale. This deposit has been mined discontinuously by various companies since 1877, its fortunes fluctuating with the various commodity prices over that period.

Current exploration is targeting gold mineralisation below and between current and historic underground workings. Encouraging results have been achieved from a major drilling program.

One of the achievements of the current operator has been to simplify the model of the deposit from hundreds of individual old workings, to recognising four major structures within which the mineralisation occurs.

The second presentation was given by our committee member and geologist Kim Wright, about historic and current operations at Rio Tinto and Almaden in Spain.

The Rio Tinto copper deposit is in the Iberian Pyrite Belt of south-western Spain, and has been mined intermittently since around 3000 BC. The name translated from Spanish means “red river”, which is a reference to the strong red colouration of the river caused initially only by the natural weathering of the orebody outcrop.

Mining in historic times is most notable by the Romans. They conducted open cut and underground mining, and smelting operations. It is notable that the introduction of new technologies by the Romans, such as smelting furnaces, enabled significant advances in production. Another innovation at that time was pumping of ground water from underground workings. This was achieved with the use of multiple water wheels which were powered by human slaves in the manner of a treadmill.

More modern operations were conducted by various companies including the Rio Tinto company which took its name from the site. Current open cut mining of the deposit intersects numerous Roman underground workings. There is still economic potential around the historic workings. Ancient mining artifacts are displayed at the museum in the area.

Kim also gave a brief description of the historic mercury mine at Almaden in Spain. This deposit has been mined for many years, at least from 500 BC, and possibly as far back as 1000 BC. A notable feature of the ore was that native mercury would flow as a liquid out of the rocks. As you could imagine there were many people who developed mercury poisoning over the centuries. The mine is currently a historic site and museum.

Kim summed up his presentations by noting what can be learned from historic deposits like these. In summary:

• Orebodies can be very large indeed.
• Fluctuations in commodity prices can bring a deposit back into economic play.
• Technological innovations can bring a deposit back into economic play.
• When doing environmental assessments, it is important to establish baseline data before any disturbance has been carried out.

Thanks go to committee member Kim Wright for organising the event, and Yancoal for sponsoring the majority of the cost of running this function.