The great unwinding of the once-in-a-century mining boom is only halfway through and another 50,000 jobs are still likely to be shed, according to the National Australia Bank.

NAB's research found that mining investment is currently more than halfway through the investment cycle, while employment is slightly below the half-way mark largely due to the labour intensity of the big LNG projects in Queensland and Western Australia.

"Our models suggest that mining investment is likely to fall by around 70 per cent from its current level over the next three years — implying that we are currently just over halfway down the mining investment 'cliff'," NAB head of Australian Economics Riki Polygenis said.

"We expect approximately 50,000 more mining jobs to be shed, which is expected to bottom out in the next two-and-half years," Ms Polgenis noted.

On the NAB's figures 122,000 mining construction jobs were created between the start of the mining construction boom in 2005 and its peak in 2013, compared to only 34,000 operational and 13,000 exploration-related jobs.

That has unwound with 46,000 jobs lost between the 2013 and 2015 financial years, although the rate of decline has stabilised recently.

The NAB expected net falls in mining employment to continue, particularly in Queensland and Western Australia, as the reduction in construction jobs outpaces the increase in operational workers in the mines.

Western Australia is likely to be harder hit given its investment cycle is less well progressed than in Queensland, and LNG plants tend to be more labour intensive than open cut mines.

Falling commodity prices to make things worse

At its peak, mining investment accounted for around two-thirds of economic growth in Australia between 2011 and 2012, when it represented around 8 per cent of Gross Domestic Product (GDP) compared to 4.25 per cent currently.

The NAB forecasts this will fall to 1.25 per cent, which is towards the lower end of pre-boom historical levels.

"At the same time, the larger-than-expected declines in commodity prices from their 2014 levels and the likely prolonged nature of the low commodity price environment has restricted the number of new projects announced," Ms Polygenis said.

"This suggests that mining investment will fall by more than otherwise would be the case."

Data from the Australian Bureau of Statistics on mineral and petroleum exploration spending has consistently fallen well below expectations in the past few years, with total metres drilled falling by 8 per cent last year.

"This is consistent with the observation that many producers have cut back on their exploration programs, especially at greenfield sites."

Ms Polygenis said this meant there is likely to be very little upside to mining investment and employment going forward.