A Trip Underground

††††††††††† July 16 Ė The mining history of Juneau has fascinated us and we wanted to enjoy as much of it as possible.† While at the mining museum we had heard of a tour that was done on the grounds of the old Alaska Gastineau processing plant.† The trip was pricy and you didnít get to go into an actual mine, rather you walked into a conveyor tunnel that was a few hundred feet long.† While we were on the Adventure Bound we overheard two passengers talking about the tour.† We asked them about it and they highly recommended it, saying it was more than just a walk down an old tunnel.† So we took a tip a local had given us and called the tour company first thing in the morning and asked them if they had any discounted last minute spaces on any tours (they often will sell extra seats cheap at the last minute because the cost per tour is the same whether the tour is full or empty).† The trick worked and we scored a deal on the 10:15am tour, which had only six other people on it.†

††††††††††† Gold processing plants were traditionally built on the side of hills to take advantage of gravity to move the ore (downhill) along the process.† Under the leadership of Bart Thane the Alaska Gastineau Mining company thrived.† He was able to raise a large sum of money and build a state of the art processing plant that was the most advanced plant of its day.† Recovering gold from the ore is an involved process and several different strategies have been employed over the years.† Basically, the ore is removed from the mine in large chunks about 2 feet in size.† The ore is then crushed and ground until it is sand.† The gold flakes and dust are heavier than the sand and they can be separated from the sand.† Lead is often also found in gold ore and it also settles out with the gold and the next step is to separate the lead from the gold which can either be done chemically or in a controlled melting process.† Some mills would subject the sand that was left over from the first step to a separate chemical process to get the gold that was missed.† The success of Bart Thaneís operation was in how he set up the mill and which combination of processes he used.

††††††††††† The mine entrance was two miles away from the processing plant and the ore was brought in on mining trams.† Our tour started out at the rail yard where equipment was stored and maintained.† There were two trains of 12 cars each used in the operation.† While one train was loading in the mine, the other was unloading at the plant.† Salvage operations after the mine closed took away all of the track and the original cars and engines.† All of the equipment we saw was left over from recent work exploring the mine and mountain to see if it would be worthwhile to reopen the mine.† The most recent attempt closed down in 2000.† The only remnant of the original operation was the collapsed ruins of the railroad superintendentís house.† From the rail yard we went to the ruins of the coarse crushing plant.† The ore cars entered the building on the top level and using a machine called a tipple four cars at a time were turned upside down to pour out the ore.† The ore was held in a bin and fed into a jaw crusher which was like a giant nut cracker and it broke the ore down to pieces a little bigger than a basketball.† From the jaw crusher the ore slid down into the _____ crushers where it was broken down to softball sized pieces.† The ___crushers looked like a giant ice cream cone with a corkscrew auger in the middle.† The ore would get caught between the corkscrew and the side wall and would get crushed.† As the core got closer to the bottom it got broken into smaller pieces until it was small enough to fall out the hole in the bottom.† One of the innovations of the plant was how they stored the ore at this point.† Instead of building a large concrete bunker, they blasted a giant chamber in the mountain over three hundred feet high, directly under the coarse crushing plant.† The crushed ore fell out of the plant and into this chamber were it was held until it was needed at the processing plant.† The chamber could hold enough ore to keep the processing plant running for over a day in case there was an interruption in the flow of ore from the mine.†

††††††††††† At the bottom of the holding chamber was the conveyor tunnel which transported the ore at a steady rate to the processing plant.† The tunnel was originally equipped with two conveyor belts so that if one broke down they had a back up to keep the ore flowing.† The conveyor tunnel was the featured stop on the tour.† We were greeted by Ziggy, a miner who had worked the mine during one of the modern attempts to reopen it.† Ziggy, who was quite a character, gave us a safety brief and had us put on hard hats for our trip into the tunnel.† Once we were inside, Ziggy explained some mining terminology and gave us an overview of how a modern mine worked.† We walked to the end of the tunnel and saw the large hatches under the storage chamber where the ore once flowed from.† During one of the modern attempts to reopen the mine a side shaft was excavated off of the conveyor tunnel as part of a mining training class held in anticipation of a need for skilled miners when the mine reopened.† We walked down to the end of this shaft where Ziggy explained blasting theory.† We then put in earplugs and Ziggy fired up a modern air powered rock drill for about 30 seconds.† It was loud and messy (the drill shoots high pressure water into the hole to control dust), but in the short time it ran it drilled 4 inches into the rock (and the hole was about 2 inches in diameter).† We then walked back down the tunnel and stopped at a piece of equipment.† All of the rock and ore that are created in a blast are called muck and the person or machine that puts it in an ore car is called a mucker.† Ziggy demonstrated the mucker, which was also powered by compressed air (and loud).† Almost all mine equipment is air powered to reduce the risk of gasoline fume explosions.† Diesel fuel is used in mines because at average mine temperatures it will not develop fumes that could explode and is considered safe.† We exited the tunnel and headed down the mountain to the base of the processing building which was originally over 10 stories tall.

††††††††††† The conveyors from the tunnel entered the plant on the top floor.† The ore was then feed into roller crushers which were like a giant set of clothes wringers that broke the ore down to golf ball size.† After the roller crushers the ore went to the ____tumblers.† These where long cylinders that turned round and round like a cement mixer.† The tumblers had pieces of imported Danish flint (the hardest rock they could find) inside.† As the tumblers turned the flint would fall onto the ore and break it up until after a few hours the ore was crushed into sand.† Some mills used cannon balls instead of flint, but if they used a gravity method to separate the gold from the sand they had to use a chemical process to separate the iron dust generated in the tumblers from the gold dust.† The use of tumblers and flint in gold processing was one of Bart Thaneís innovations (he borrowed the technique from copper processing).† The sand was then mixed with water and passed over a series of inclined ridged grates which trapped the gold (and lead) that was in the ore and allowed the sand to get washed away.† The sand water mix was then pumped onto the tidal flats.† When they say mining built Juneau theyíre not kidding as most of downtown is actually built on top of mine tailings on land that was once tidal flats.† The mix of gold and lead dust and flakes was collected and then melted to make bars of lead/gold mixture.† These bars were sent to Seattle where a lead processor subjected them to a precise melting process (lead melts at a different temperature than gold and this difference can be used to separate them).† The lead processor kept the lead as payment for his services and the mine got the pure gold bars.

††††††††††† Our final stop on the tour was a gold panning sluice where we were all taught to pan for gold.† Everyone found a little gold which we got to take home in a vial (we think they seeded the pans).† At the gift shop (we have yet to see an attraction without one, even the Shrine of St. Therese had one), we enjoyed the squirrels who have learned to take peanuts off of your shoe or from your hand.† Stacie bought a pin for her backpack.

††††††††††† The rest of our day was uneventful.† We went to camp for a late lunch and then it was off to the laundromat.† We werenít out of clothes yet, but it was a cold rainy day, and we didnít want to do anything outside.† On our way through the campground we saw a beaver on a pond.† After dinner we broke down everything except the tent as we had a 7am ferry with a 5am check in time (arenít we on vacation??)