Last month 38 temporary workers were laid off at the Penrhyn quarry

Two managers at the firm owned by Alfred McAlpine plc were suspended over accounting irregularities allegations.

The quarry at Cwt y Bugail in Blaenau Ffestiniog is to close, with the loss of 59 jobs.

Other jobs will go at Penrhyn and Gloddfa Ganol, bringing the total losses to 175.

Union leaders have entered a 30-day consultation period with managers to discuss plans to reorganise Alfred McAlpine's slate division.

Serious problems emerged last month when the company announced it had discovered what it described as "accounting irregularities" which could amount to �24m.

Snowdon building

Alfred McAlpine plc did employ around 400 people at four quarries in north Wales, Penrhyn in Bethesda, Gloddfa Ganol and Cwt y Bugail in Blaenau Ffestiniog and Pen yr Orsedd in Dyffryn Nantlle.

Transport and General Workers' Union officer Paddy McNaught said Alfred McAlpine had decided to concentrate on the roofing side of the business.

Last September it was announced granite from the Cwt Y Bugail quarry would be used to build Hafod Eryri, the new building at the top of Snowdon.

A spokeswoman said the Snowdonia National Park Authority was "obviously concerned" about the future of the workforce at the quarry, but the supply of granite was a "contractual matter" between Alfred McAlpine and the contractor Carillion.

"But," he added, "the authority will be keeping a close eye on the situation."