Pebbled: Mining 101, how we get our metals - Must Read Alaska
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Pebbled: Mining 101, how we get our metals

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By MARK HAMILTON / PEBBLED SERIES

Mining is actually a simple process made voluminous by the very low density of the sought-after minerals.  A mine with one gram of gold in every ton of earth would be sufficiently rich to take a look at.  Getting at that gram is the process I will describe.  Mining engineers might well wince at my description, but it is a way to understand for people like me who are not mining engineers.

First, you remove the overburden, the top layer of what we might call soil. In this overburden there is the layer in which plants grow so it is collected in an area to be redistributed upon closing the mine site.  The preparation for closure begins with the very first activity.  

With the overburden removed, the exposed rock will be blasted. The one blast per day is very carefully situated depending on the expected mineralization and the planned contours of the pit.  

Now you have some big rocks to deal with. These rocks are loaded onto trucks that bring them to the crusher. The crusher does what you might expect, it crushes the big rocks to rocks about the size of a brick, which are transported to the mill.  It’s called the SAG mill, which stands for semi-autonomous grinding.  Autonomous grinding would use the rocks themselves to grind.  Semi-autonomous grinding means you will put some steel balls in there to better control the size of the particles.  The various sizes and quantities of the steel balls determine the size of the end particle.  For the Pebble mine operation, the end particles would be about like sand.

This next part is quite surprising. The particles are poured into a huge vat of water, think of a large above ground swimming pool. Here they are essentially washed with a petroleum-based fluid whose primary utility is to attach long-carbon chains onto the minerals.  These chains make the minerals hydro-phobic (they don’t like water).  So, the process literally blows bubbles into the tank.  The minerals with their long carbon chains cling to the bubbles and float.  The process is called “flotation,” so that’s easy to remember. The froth at the top of the tank is swept off (think of a bar tender pouring a glass of draft beer and swiping the excess froth off the top).  

The surprise to me was the similarity to washing clothes. At your home you will fill a tub of water, add some type of petrochemical detergent that will attach a long-polymer chain to the dirt you want removed. In this case the process is somewhat reversed, in that it will make the dirt hydrophilic (mix with, dissolve in, or be wetted by water).  Wash away the water and the dirt goes with it.  In neither processes do the bubbles do any cleansing, they are simply a bridge to the mineral or the dirt.

All of the material that did not float (the overwhelming amount of the crushed material) constitutes the “tailings”.  These materials are not acidic (for the most part inert to slightly alkaline) and are deposited in the tailings-facility.  The description of the tailings facility will be presented later.  It is an important element in the understanding of the process and the discrediting of some of the most virulent false notions about the mining process.

Once the process has gathered the minerals attached to the bubbles, they are dried and ground further to a consistency about like talc. Then they go to a second flotation cycle. Here, most processes add cyanide to help with the extraction of gold.  This procedure is used by the overwhelming number of mining processes and is safe and reliable.  In the case of the Pebble project, the decision was made to not add cyanide because of all the misinformation campaigns about it.  People know that cyanide is a poison and that was quickly jumped on to bolster the false claims of a dangerous and toxic process.  Rather than fight the misinformation, Pebble decided to not use this technique and accepted foregoing the recovery of more than 10 percent of the gold.

That was a bold move, and not one that I would have chosen, since the practice is very common and has been used by mines all over the world and in Alaska for several decades with no incidences.  It demonstrates the power of misinformation.  The undeniable evidence of decades of demonstrated safety and reliability was overcome by scare tactics.  I don’t believe the choice paid any dividends, and certainly not enough to give up 10 percent of the gold recovery.

The tailings left from this stage are handled differently than the tailings from the first floatation.  These are called “PAG tailings” which stands for “Potentially Acid Generating.” These need special caution; and are stored separately from the bulk tailings of the first flotation process.  These, approximately 12% of the tailings, will be stored in a sealed and lined containment area covered with about five feet of water to ensure they have no access to oxygen, which could cause them over some time to be acidic. These tailings will be monitored throughout the mine life in a facility very close to the mine pit and ultimately discharged into the pit upon closure of the mine, eliminating the need to monitor them forever.

After the second flotation, the minerals will be dried and concentrated for shipment to the available smelters.  Sadly, there are no smelters available on American soil, so they will be sent overseas.  Although an issue for national security, currently the air quality issues associated with smelter operations make it extremely difficult to imagine the permitting of additional smelters in the United States.

The “Pebbled” series at Must Read Alaska is authored by Mark Hamilton. After 31 years of service to this nation, Hamilton retired as a Major General with the U. S. Army in July of 1998. He served for 12 years as President of University of Alaska, and is now President Emeritus. He worked for the Pebble Partnership for three years before retiring. 

Pebbled 1: Virtue signaling won out over science in project of the century

Pebbled 2: Environmental industry has fear-mongering down to an art

Pebbled 3: The secret history of ANWR and the hand that shaped it

Pebbled 4: When government dictates an advance prohibition

Pebbled 5: EPA ‘just didn’t have time’ to actually go to Bristol Bay

Pebbled 6: The narrative of fear

Pebbled 7: The environmentalists who cried wolf

Pebbled 8: Build your media filter based on science, not narrative

Pebbled 9: The history of hysteria

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  • I am for opening ANWR but against Pebble Mine. Maintaining a 12.8 billion ton tailings pond containing sulfuric acid at the head waters of Bristol for 10,000 years in the sub-arctic is a bad idea. Are we to assume in year 6,023 there will still be the budget (or a planet) for it? No one has been able to sway me on that.

    • Well stated!! The publicity BS this issue has generated is awful!! Good Alaskans like you and me being trampled ( fear mongers) becuause of our common sense opposition to a project sponsored by NON ALASKA AND NONUSA COMPANY!! To say nothing of Mark Hamilton failed UA leader.

    • You need to take a look at local geology before making that conclusion. Mount Chiginagak is a volcano on the AK Peninsula that periodically empties its crater lake downhill into the Bristol Bay watershed thru Mother Goose Lake and King Salmon River. Water is highly acidic with dissolved metals. The dumps do a number on the lake and damage salmon returns downstream for a few years afterwards, but for some reason they return. Even better, they NEVER damage overall catch in the Ugashik commfish district. Crater lake dumped at least 3 times, 2005, mid-1970s, early 1950s.

      Bottom line, acidic water with dissolved metals isn’t particularly healthy for fish. But we have an actual example of nature doing it on a regular basis and commfish does just fine in the watershed for over half a century Pebble will move heaven and earth to make sure it doesn’t happen. Cheers –

      • Check out the Aniakchak Caldera and Surprise Lake, this is a volcanically active caldera with a lake that has sockeye salmon spawning and living in the volcanic lake.
        .
        Jo-Jo Lake, Devil’s Cove Lake, and Dakavak Lake are other examples of lakes heavily influenced by volcanic activity that have land locked salmon, kokanee.

  • A mining lecture from the man who diminished the UA School of Mines by consolidating it with the School of Engineering, and then gave away the old UASM building for a multi-million dollar renovation to be used exclusively as a Native cultural center, used ONLY for Natives. This old hypocrite is now counting his state and military retirement money, while laughing at the mining industry. Yet, he’s too much of a coward to address this issue. This series is a complete joke.

    • Hamilton says in his opening, “mining is a simple process…….”
      Well, he certainly simplified it by slashing the Mining Engineering budget at UA when he was president. Something is wrong with this fellow. He might be harboring some kind of guilt or shame. Whatever it is, he sounds like a demented old man with some festering scores he has to settle. These kind of guys, who sit around and count their retirement every morning at the breakfast table, usually drift off into oblivion. Hamilton brings no value to any debate. His hypocracy and double speak are widely known around this state. A politician in search of an office that no one else wants.

  • Misinformation is used as a tool by politicians and the radical left, truth is the enemy. When it comes to Pebble, most believe the lies and do no research on the facts. Pebble is attacked by outsider environmentalists and sportsmen. Their goal is to lock up Bristol Bay for ever and the funny thing is that Bristol Bay Native Corp. supports these groups. I’m thinking money has changed hands.

  • The mismanagement and associated sums wasted by Pebble developers have told prospective investors throughout the world that Alaska is a place to misspend a lot of money. The Alaska brand has been damaged. Pebble is an excellent case study in how to make every possible public process and resource development planning mistake, to then double-down on those mistakes. It has been money going to its rightful owners I suppose. But the disservice to Alaska done by the Pebble developers, and by the small handful of public officials who never take a minute to look at a picture will not be duplicated for a long time, I hope. For all that I really think it is a mineral prospect that could actually have been developed responsibly. Mining on the moon now looks more likely however. Stupid is as stupid does. Is there some way we can blame this on Biden (as it looks like the kind of success and competence he best exhibits). Somehow I think I would feel better if those two Pebble officials who were duped by the environmental skirt got some, but I don’t believe they did.

  • Very good read and l for one am very appreciative of the General for taking his time to inform us. Ty

    • A simpleton’s explanation of how the mining process works. A third grader’s report. A dive into the shallow end of the pool. A besmearchment to the mining profession. Why is Hamilton doing this? He hated miners when he was the UA President. Now this! Are we looking at dementia, or is this some cruel joke by a rich guy who is hell-bent to get even?

      • You, however, are erudite, and that’s why you rely on series of ambiguous accusations, followed by several fallacious, ad hominem attacks.

        • Wayne:
          If what you say is true, then why wouldn’t Mr. Hamilton comment here and explain his actions? I doubt Mr. Geivette is making ambiguous accusations. They seem consistent, factually based, and provable by examination of Mr. Hamilton’s record. Mr. Hamilton has been given a platform here at MRAK, a series of platforms in fact, to opine on the Pebble Project. He was a highly paid advocate of Pebble before it’s development was rejected. But searching Mr. Hamilton’s record of the mining industry prior to Pebble, yields some interesting material. He did in fact single-handedly consolidate the mining engineering curricula at UA into the broader engineering curricula in exchange for a Native Center on campus which caters to Natives only. The old Brooks Building at UAF, which was the center piece of the Mining College, is now the new Native Culture Center……….a refurbishment that cost many $millions. This was a slap in the face not only to the faculty and staff at the Mining College, but also to the hundreds of miners and mining operations which rely on the expertise of the School of Mines. The UA School of Mines was started in 1921. Mr. Hamilton seems to want to avoid this topic as it will require some prior justification that runs inapposite to his current advocacy………..which is to support Pebble, and other mining offshoots. Until Mr. Hamilton decides to explain his prior actions while UA President, I think Mr. Geivette will continue to appear in this series, and challenge him accordingly.

  • Why does Hamilton want this platform? No one cares about Pebble anymore. Further, Hamilton seems to have a lot of enemies. I don’t think anyone reads his opinions anymore.

    • Take a look at what is found along with copper and gold – rare earths, which we need for our renewable energy future. Pebble’s gonna get dug sooner rather than later. Cheers –

  • Yawn.
    The pebble guy is on rocky ground.

    • Yeah, for a guy who knows squat about mining. But he sure knows how to run a university system into the ground with unnecessary costs, and his own luxurious living style paid for by the state of Alaska while he was president.

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