ANCHORAGE - State mining coordinator Tom Crafford says he remains confident that ongoing exploration drilling at the proposed Pebble mine in Southwest Alaska will have no significant impact on fisheries resources.
Crafford also said the current state process for keeping the public informed on its permitting procedures is transparent, in the face of increased public interest in the proposed Pebble prospect, located at the headwaters of the Bristol Bay watershed.
Crafford's letter of July 3 to fisheries researcher and consultant Carol Ann Woody commented on water quantity, water quality, and monitoring and reporting issues. It was in response to concerns raised by Woody in her letter of April 2.
Crafford said Woody's concerns about reactivity of Pebble ore, acid mine drainage, metals leaching and potential contamination from various metals in relation to the number, depth and location of drill holes were valid issues that would be addressed if and when Pebble proceeds to development permitting.
"They are really not issues of concern for the on-going drilling exploration program at Pebble," he said.
The potential for the ore to generate acid is tied not only to the amount and type of sulfide minerals present, but to the exposure of those sulfide minerals to both water and oxygen and certain bacteria, Crafford said.
It is the oxidation of the sulfide minerals, predominantly pyrite, that leads to formation of sulfuric acid, and removal of any one of those essential components - water, oxygen or sulfides - prohibits acid generation, he said.
"This is the premise behind submarine disposal of sulfidic tailings," he said. "The layer of water atop the tailings prevents the access of oxygen to the sulfide minerals, thereby preventing oxidation and the generation of acid."
Crafford also said there is ample evidence that oxidation and acidification are not issues in relation to the deep drilling at Pebble East, and that nearly all of the drill holes are being plugged with either cement or bentonite slurry after completion. Bentonite, a naturally occurring clay mineral that swells in the presence of water, is the major component in benseal, a product used to seal the drill holes after completion, he said.
Crafford acknowledged that acidic rock drainage and metal leaching is a serious negative potential consequence of mining in general.
"It is a major issue of concern at Pebble and any development proposals must address in extreme detail how acidic rock drainage/metal leaching will be mitigated/prevented," he said.
However, because of the depth of the Pebble East orebody and the methodology and scale of the on-going exploration drilling program, this is not an issue of current concern, he said.
In her April 2 letter, Woody detailed numerous concerns about the exploration process and their potential effects on the salmon spawning stream network - the Talariks, Koktulis, Kaskanak and Chulitna - which ultimately flow into Bristol Bay's two largest salmon producing systems, the Nushagak and the Kvichak.
A fisheries biologist, Woody served on the Pebble technical advisory team for the U.S. Geological Survey before resigning to work independently.
Woody asked a number of specific questions regarding the amount of water used in the exploration drilling process, monitoring of groundwater and changes in local water chemistry.
She said elevated concentrations of copper, zinc and arsenic, which occur in the Pebble prospect, could all be toxic to fish at levels just above that which is naturally occurring.
She also repeated earlier concerns that baseline data collections on natural water flows and geochemistry were conducted by mine backers at the same time as the exploratory drilling program. That limits the ability to assess changes to water flow and chemistry, she said.
Crafford reiterated that the burden of defending all baseline environmental studies collected in support of future permit applications and National Environmental Policy Act analyses for potential development of projects rests with the applicant.
Meanwhile, drill crews are working around the clock to gather samples to identify rich vanes of copper, gold and molybdenum beneath the surface.
The 2008 drilling exploration program, with a budget of $140 million, continues at Pebble East, said Sean MaGee, a spokesman for the partnership. MaGee said an average of 180 to 200 people are working on site daily.
"We are approaching the point where this time next year we will be presenting a preliminary proposed mine plan," he said.