PERTH (miningweekly.com) – Swiss-listed diversified miner Xstrata does not believe that its Australian Mount Isa mine had exceeded the regulatory limit for lead concentrate, but rather that data from an air-quality monitor might have been incorrect.

The diversified miner on Monday responded to the Queensland Environment and Resource Management Department's request for answers about a possible lead leak at the operation, after it came under fire for potentially exceeding regulatory levels.

Climate Change and Sustainability Minister Kate Jones said the department, as environmental regulator, was preparing prosecution action against the company.

Xstrata explained that  an independent analysis of air monitoring over the period from October to December had indicated a potential exceedance at one of its five high-volume air-sampling stations in Mount Isa.

The remaining four stations in the area had remained within regulatory limits, as did the department’s heavy-metals air monitor, the miner noted.

Xstrata said it had acted "immediately", and that it had informed the Department of Environment and Resource Management that it planned to investigate the matter, particularly in light of other monitors not returning similar results.

“At that time, we committed to inform them of the outcome of this investigation within 30 days,” the diversified miner stated.

As part of the investigation, Xstrata Mount Isa Mines has been verifying the results obtained from the first laboratory, as well as reviewing any meteorological or operational data that might be linked to these results. To assist in verifying the results, samples were sent to two further laboratories for testing and analysis through three different methods, a process which had taken several weeks.

“It has now been confirmed that the results of the analysis undertaken by these two additional laboratories show that lead concentrations at the relevant monitor did not exceed regulatory limits during the October to December 2009 quarter.”

Xstrata COO for copper in North Queensland, Steve de Kruijff, said that the investigation was continuing to complete testing and examining the reasons why the initial results could differ from the three subsequent tests.

De Kruijff said that based on the diversified miner’s current findings, particularly the initial results from further laboratory testing, the company did not believe that the regulatory limit for lead concentrate during the December quarter, had been exceeded.

Xstrata has now advised the department that it had taken steps to verify the original analysis of samples collected at one of its air monitors.

He further noted that the retesting of the original samples by two laboratories, including a leading Queensland government-owned laboratory, returned correlated results over the weekend, namely that the lead concentration levels did not exceed regulatory limits.

“This is the first time that the analysis of samples from one of our air quality monitors has reported levels of lead above the regulatory limit, hence our concern that the initial results may have been inaccurate,” De Kruijff said.

“We are fully cooperating with Department of Environment and Resource Management, and will make all results of our investigation open to their review.”

To subscribe to Mining Weekly's print magazine email subscriptions@creamermedia.co.za or buy now.