Mining investment from Australian companies has declined with only 25% prepared to invest in major projects in 2012, compared to 52% last year, according to a report by Newport Consulting.

The Mining Business Outlook report draws on interviews that took place between April and June 2012, with 55 mining executives participating.

The report also found that only 20% of mining executives were optimistic about the market, down from 57% in 2011, and more than a third were not optimistic, compared to 13% last year.

Mining leaders cited escalating business costs, tough market conditions, volatile commodity prices, particularly for coal, and labour shortages as factors behind their business outlook.

The study noted that industrial relations are "compounding" the present skills crisis, with one in five mining projects said to be stalled as a result of union action.

Mining leaders were also critical of taxes such as the Minerals Rent Resources Tax introduced on July 1, 2012, and the Carbon Tax in the face of falling commodity prices.