A Hong Kong developer and his mining company have been fined hundreds of thousands of dollars over environmental damage in Cape York.

Magistrate Anthony Gett fined Dianne Mining $250,000 for the damage caused by leaks at a dormant copper mine southwest of Cooktown.

He also ordered managing director Peter Zhang to pay $50,000 after a report found the leaks from a catch dam could seriously harm aquatic animals 800 metres downstream.

The Cairns Magistrate Court heard there was no evidence the contamination had caused a loss for downstream landholders or a public health risk.

Mr Gett said neither party had prior convictions and had been cooperative during proceedings.

But he said they deserved a punishment to deter them from allowing damage to occur again.

Their early guilty pleas were taken into consideration and no conviction was recorded.

The parties were charged after inspections between May and July 2014 found ongoing seepage and no efforts to monitor or stop the highly contaminated water leaking from the dam.

The environment of heritage and protection says an order to fix the problem has still not been completed.

Part of the fines will pay for two projects to improve water quality in the area and the company will also pay investigation and legal costs.

The Department of Environment is seeking a rehabilitation order, which will be heard late next month.

The mine has not been operational for thirty years and the court heard Mr Zhang may have inherited some of the problems when he bought the site.

Despite the troubles, he intends to keep the mine, Mr Gett said.