The project is being developed by Australian company White Mining with an 80% share and Itochu Coal Resources Australia.
Stage one of the project, opened on Friday by minister for Mineral Resources Kerry Hickey, encompasses open cut operations, with longwall construction to get underway next year.
The mine, 14 kilometres north-west of Singleton in the Hunter Valley, has recoverable resources of 104 million tonnes of thermal coal, primarily for export markets.
The opencut will produce up to 2.4 million tonnes per year over six or seven years, to be followed by a long-term underground phase producing around 3Mtpa.
White has approval to increase the run-of-mine throughput up to 5.2Mtpa if warranted by the market.
The initial construction of the mine employed 140 people and current open cut operations employ 100 workers. Once the mine ramps up to full production it will sustain 125 workers.
During November last year Henry Walker Eltin secured the six-year $200 million-plus development contract for Ashton.
The contract involved mining 13.7 million tonnes of coal and removing 68 million bank cubic metres of overburden.