The 26-year-old vanished from her home in Lightning Ridge on Friday after going for a walk, sparking a large-scale search and rescue operation.
She apparently tripped and fell down the eight-metre (26-foot) deep shaft, police said, surviving despite daytime temperatures of more than 40 degrees Celsius (104 Fahrenheit).
"The woman is lucky to be alive after police rescued her from a mine shaft in the state's north-west," New South Wales police said.
"She was brought to the surface with the assistance of an officer using a pulley and harness, and provided water."
Lightning Ridge, some 770 kilometres (477 miles) northwest of Sydney, is a world-renowned black opal mining centre, attracting hundreds of fossickers looking to hit the jackpot.
Small-time miners have dug countless vertical shafts in the area, with some dating back decades.
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