Underground Design in the SA Opal Fields

Dr. Tony Meyers

Since their discovery in 1915, the opal fields around Coober Pedy, Lambina, Mintabbie and Andamooka have been the largest producer of precious opal in the world. It is estimated that, up to the late 80s, they produced in excess of $25 million of rough opal per year, which represented about 80% of Australian and 75% of the world’s opal production. However, in recent years the miners have been experiencing a considerable downturn in production due to a lack of significant new discoveries while at the same time having to endure economic problems attributed to depressed prices for rough opal and increases in diesel, explosives and general living costs. This pressure has forced some miners to go “pillar bashing” in which they extract the rock in their pillars, which represent their primary support. By doing so they have created unsafe spans, caused large amounts of rock to become unstable which has resulted in rockfalls that have killed many of them. As a result of these and similar developments, there has been a push from the local Miners Associations, Mines Rescue, the local Councils and the Mining and Quarrying Occupational Health and Safety Committee (M&QOHSC), for all underground development in the opal fields, including that done in dugouts, to be done only after some basic design principles have been considered; principles which until recently have often been unknown or ignored.

This talk will provide an overview of a study involving Dr Meyers in conjunction with M&QOHSC which has, for the first time, sought to determine the engineering characteristics of the rocks in the opalised zone and the behaviour of these rocks once excavated. The talk will provide a general look at the overall geology of the region and the lure of the opal, it will provide an overview of the innovative mining methods used in the fields and it will discuss the results from the study. It will also discuss the novel manner in which the results are being presented to the miners, many of whom come from non-English speaking backgrounds and diverse cultures. (15 attendees)

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