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Howardsville

Howardsville, Colorado on the Animas River.

So far on my tour through Colorado’s mining history, I have reported on how the ore was mined. Today, I got the chance to see how the ore was transported and processed at a mill. After completing my tour of the Old Hundred Mine near Silverton, I drove back down Stony Creek to where it joins the Animas River at a place called Howardsville, where some mining operations were still evident.

Arrastra Gulch

Google Earth view of Arrastra Gulch and Silver Lake. The Mayflower Mill is located at the bottom of the gulch in the upper left corner.

I stopped along the way toward Silverton at the base of Arrastra Gulch. This is the location of the main mining area around Silverton and one of the richest deposits in all of the San Juan Mountains. Before a proper mill could be built to process the ores, a Spanish-style arrastra was built here, which is a circular area with a flat stone floor and a central post with arms coming out. Each arm had a heavy stone or iron weight that hung from it and which would drag over the ore and crush it. Mules, donkeys, or even humans would be used to push the arms around in a circle. Once mills were built, the ore was transported to them from Arrastra Gulch and the high glacial circque above it (around Silver Lake) by tramlines or flumes. At one point as many as four separate overlapping trams were operating.

Arrastra Gulch marker panel a

Arrastra Gulch marker Part 1

The largest mill in the area was the Mayflower Mill (also known as the Shenandoah-Dives Mill) about two miles northeast of town. It was built in 1929 to process gold, silver, zinc, lead, and copper ores. Another large mill nearby was the Silver Lake Mill on the Animas River.

arrastra trams

Map of aerial trams in Arrastra Gulch near Silverton, Colorado.

Built of pre-framed Oregon fir and completed in six months for $373,000, the Mayflower Mill began processing ore in Feb., 1930 and continued in operation for 49 of the next 61 years, finally closing down in 1991. It is in fact still capable of operation, and all the original equipment is intact. The historical society allows self-guided tours that start in the machine shop, then move to the tram station, ore storage bins, ball mills, flotation cells, recovery system, assay office, etc.

Arrastra

A restored arrastra in Groveland, California. Heavy rocks were dragged around in a circle to crush ore.

It was an extensive operation, the biggest in the San Juan Mountains, and employed the latest technologies available in 1929, including the new techniques of ball mill crushers, froth flotation of sulfide ores, and recovery of base metals as well as gold and silver. These techniques are still used today in such places as the concentration plant at Utah’s Rio Tinto/Kennecott Copper operation, although the scale there is enormous.

Shenandoah-Dives mine

A sketch showing what the Shenandoah-Dives mine looked like during the 1930s. The aerial tramline connected with the Mayflower Mill.

For its 61 years of operation, it processed over 9,700,500 tons of ore to produce 1,940,100 ounces of gold, 30,000,000 ounces of silver, and over 1,000,000 tons of base metals.

Tramway in Arrastra Gulch

The aerial tramline connecting the Shenandoah-Dives Mine above Arrastra Gulch with the Mayflower Mill. The gulch is the canyon in the foreground, and the high circque is the basin around Silver Lake.

I used my camcorder to create a complete walkthrough of the mill, going in order from start to finish. At each stop I would stop the tape and take photos as well, and took my time to document everything. There were interpretive signs at each stop explaining what each piece of equipment did. Here is a rundown:

Mayflower Mill

The Mayflower Mill near Silverton, Colorado. A self-guided tour is available during the summer.

Processing Ore

The ore coming from the mines was about 5% metals and 95% waste rock (tailings). The metals have to be separated out, and this is done in stages so that all the metals (gold, silver, copper, lead, and zinc – the big five) could be individually removed and purified. This is done in three main steps: crushing, separation or reduction, and purification. The final step was done by a smelter off-site, but the first two steps were done at the mill.

tram station

Tram station at the Mayflower Mill. Full buckets descended from the mine by gravity, which also pulled the empty buckets back up.

The ore arrived in large open buckets by tramline. Gravity brought the ore down and allowed the empty buckets to move back up the loop. The ore was brought into the mill at the tram station and dumped, then transported by conveyor belt to the cone crushers. It was screened for size, and if too big would be returned to the crushers.

cone crusher

Cone crusher at the Mayflower Mill. It would crush the ore between rotating cones until it was pebble sized.

Once it was pebble sized, it would be transported to the Fine Ore Bin, which would hold 1200 tons of ore, enough for one full day of operation. The ore was then transported out of the bottom of the bin and mixed with water to form a slurry, then passed through a rod mill (which used long iron rods rolling around) where the ore was further crushed to a fine powder and sorted by a spiral classifier, an auger-like device that pushed the ore upward. If the ore was fine enough, it was pushed all the way to the top – if not, it would fall back down and be returned to the rod mill for further crushing.

rod mill

Rod mill at Mayflower Mill. Iron rods were fed into the mill, then allowed to roll around inside to crush the ore to the size of sand grains.

The powder, now the consistency of sand, was passed through a ball mill, with 2-3 inch diameter iron balls rolling around to crush the ore even finer. These balls were added frequently during the day through pipes from a ball bin. Now the ore was now the consistency of talc and fine enough to start to separate.

Spiral classifier

Spiral classifier at the Mayflower Mill. Ore slurry from the rod mill would be pushed up the spiral. If it was fine enough, it would be pushed over the top. If not, it would return to the rod mill.

The first metal to be separated was gold, using a system of settling jigs that pumped the ore through, allowing the heavier gold particles to settle out through vibration and suction. The lighter remaining material was passed on to flotation cells, where reagents and flocculents were added that would float the desired metals to the top of the tank solution while depressing or sinking the other metals. Lead was removed first, then copper, and finally silver and zinc removed in large tanks. The soapy bubbles would simply be skimmed off the top of the cells.

Ball mill

Ball mill at the Mayflower Mill. Ore crushed to the size of sand grains would enter the rotating drum and be crushed to powder by 2-3 inch iron balls.

The flotation cell solutions were then passed through filters with pumps that pushed the water through, drying out the solution to a damp cake-like material that was then shipped to a smelter for final refining, where it would be heated to drive off the sulfides. Each day, samples were removed and filtered through a squeeze press, then sent away to an assayer to determine the percentage of metals in each day’s run.

gold jigs

Gold jigs at the Mayflower Mill. Using air pressure, the lighter ore powder was suctioned away from the heavier gold particles.

Meanwhile, the gold filtered out by the jigs was sent through a concentration process. It would be passed over a shaking Deister table where the gold would be caught by riffles and formed a streak to be collected. It was mixed or amalgamated with mercury to remove the gold from the remaining waste ore. The amalgam was then formed into rounded boats or cakes and heated in a retort at 1200 ° F for 12 hours to evaporate the mercury, which was bubbled through water to condense it for reuse. The remaining gold was now called “sponge” and was about 80% pure. It would be sent off to a foundery for final purification. Four to five sponges would be produced each week. Each sponge weighed about 22 pounds. During the last year of the  mill’s operation (1991), a new process was developed that eliminated the need for mercury (which was highly toxic).

Lead cleaner cells

Lead flotation tanks at the Mayflower Mill. Reagents were added that would float the various metals, such as copper or lead, to the top of the liquid on soap bubbles which were skimmed off into the trough in front. The remaining metals were depressed to the bottom. Impellers would keep the solution agitated while blowing air through it.

Once processed, the waste material is called tailings and was made up of water and sandy ground rock. It was pumped down to settling ponds, where the solid tailings would settle out. This was an innovation of the Mayflower Mill, as previously the tailings would simply be allowed to flow into the Animas River. The high sulfur and iron content in the tailings would travel down the river and created the reddish stains on the rocks that I noted on my train trip up the gorge several days ago. At the Mayflower Mill, the ponds were shifted so that the solid tailings would build up a series of mounds downhill from the mill. These have now been collected into a large tailings pile near the mill.

Deister table

Deister table at the Mayflower Mill. It would shake, causing the gold particles to separate out against the riffles.

I found this self-guided tour to be fascinating from a chemistry perspective. The mill used a system of physical separations to crush, concentrate, and amalgamate the ore. The final smelting used a system of chemical separations. It is a perfect example of a chemical engineering process, and was continually upgraded and improved during its 61 years in operation. The mill could be run, during the night shift, with only three people. During the day there were additional people to do repairs and take samples, to run the gold process, and to run the machine shop. Shift supervisors oversaw the operation from the dog house, one man ran the crusher facility, and one man ran the flotation cells. This was the biggest operation of its kind in southwest Colorado and processed more ore than any other mill in the area.

gold sponge

A model of what gold sponge looked like after being removed from the retort furnace. The holes in it are caused by mercury vapor bubbling out.

Retort furnace

Retort furnace and gold button mold at the Mayflower Mill. The gold particles would be amalgamated with mercury, then heated in this retort furnace to drive the mercury off.

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Cripple Creek downtown

Downtown Cripple Creek Colorado

This is the second half of my trip to Cripple Creek, Colorado, over the Labor Day weekend. As I described in my last post, we traveled to Cripple Creek on Friday, Sept. 4, 2010 and arrived late at night. The next day, I started out by taking a guided tour of the Mollie Kathleen gold mine, then visited the Cripple Creek Heritage Center right across the road, taking photos of all the displays. They even had a scale model of the Mollie Kathleen.

Anaconda mines

Anaconda mine sites with Cripple Creek and Victor Gold Mine

Now for the rest of our visit: After taking some panoramic video shots of the town from the mine dump behind the heritage center, I drove back down Hwy 67 to the town. I was to meet my wife, ‘Becca, and our two children at 12:30 at the Cripple Creek District Historic Center at the east end of Bennett Ave. (the main street of town). I was a bit early, so I wandered around and took some photos and video of downtown, then ate lunch with my family. I had wanted to visit the Historic Center (a man at the mine told me it was worth visiting both museums) but didn’t want my family having to wait for me, so we decided instead to take the narrow gauge railroad tour. We were almost late for the train, and in the hurry my son William fell down and skinned his knee in the parking lot, so we were trying to get him bandaged up (fortunately we brought a first aid kit in the diaper bag) while the train pulled away. The loud train whistle frightened William some more, and I’m afraid the whole experience wasn’t very great for him or my wife, who had to hold him most of the way. My other son, Jonathan, was having the time of his life, pointing out all the rocks to me (at three he’s already a budding geologist). I tried to videotape the whole thing and take a few photos as well.

Headframes in Victor

Headframes in Victor, Colorado

The train headed south along the mountain grade, over some old tressles and fills, past many old mine workings, to a point about half way to Victor at the abandoned town of Anaconda. It was quite interesting to see the old mine shacks lower on the hillside and the new terraces and trucks working the higher hillsides for the Cripple Creek and Victor gold mine. On the way back we paused on a siding to let the next train pass, and the engineer pointed out the remains of Crazy Bob Womack’s cabin in Poverty Gulch, who was the first to discover gold in the district in 1890. We had a good view of Cripple Creek and Myer Ave., which was the notorious part of town.

WInfield Scott Stratton and I

Winfield Scott Stratton and I

We had to leave for Denver by 3:00, so we had just enough time to drive out to Victor and snap a few photos. There are many headframes on the hillsides around town, including those of Stratton’s Independence Mine and the Portland, which he had a share of. As we left, I had to take one more photo of myself seated on this bench with Stratton himself (well, at least a bronze replica of him).

Winfield Scott Stratton was the first big millionaire of the district, discovering his gold telluride deposit on July 4th, 1891. He had searched unsuccessfully for silver and gold for the previous 17 years, working as a carpenter during the winters to finance his summer prospecting expeditions. He had even built a sign for H. A W. Tabor in Leadville for his opera house while he was prospecting there. He finally decided he needed more education and took courses in mineralogy at the new Colorado School of Mines. In 1891, he scoured much of the Cripple Creek area and found nothing. On the evening of July 3, 1891, he had a dream in which he imagined going back to a granite ledge he had already passed over. The next day, upon revisiting the site, he noticed signs of gold telluride ore, and discovered rich veins in some boulders that had fallen off the main face of the ledge. He staked a claim and named it the Independence, which he eventually sold for $11 million to a group of British businessmen, the highest amount paid to date for any mine, and a large fortune at the time. But Stratton wasn’t one to blow all of his money; he’d learned from the example of Tabor, who was now ruined because of the Silver Panic of 1893. Eventually Tabor came to Stratton looking to sell some mine stock to help pay his debts. Stratton paid him $50,000 for the stock, but never bothered to record the sale at the mine office. Stratton eventually bought a house in Colorado Springs that he himself had built years before and lived there the rest of his life. I had read a biography about him a couple of years ago called Midas of the Rockies by Frank Waters (1937) and now I’ve finally visited the sites he helped to make famous.

Victor Colorado

Downtown Victor Colorado

There is still much I would like to do and see here. I would like to hike some of the paths in Victor, take the tour of the open pit mine, and view the whole valley from the Eagles overlook. But that will have to wait for another trip. At least I have gathered enough footage and photos to make a great video of the Cripple Creek mining district.

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Mollie Kathleen sign

Sign for the Mollie Kathleen gold mine

Over Labor Day weekend I traveled with my family to Denver to visit my brother-in-law’s family. On the way, we stopped off at Cripple Creek, Colorado, to tour the gold mining district. I’ve been near there twice before but never took the chance to stop and visit, so this time I determined to get there no matter what. Since we left after my classes were over on Friday at 2:45 p.m., with occasional stops for food and stretching, we didn’t get into our motel until 2:30 a.m.

Mollie Kathleen mine

Mollie Kathleen gold mine

On Saturday I got up early and drove a couple of miles out of town on Highway 67 to the Mollie Kathleen gold mine. I arrived about 8:50 and the first tour was at 9:30, so I took the time to take photos around the mine site of the old equipment and original headframes. One person there told me a bear had walked through the site just ten minutes before I arrived.

Old headframe at Mollie Kathleen mine

Old Headframe at Mollie Kathleen Gold Mine

At 9:30 we donned hard hats and were loaded tightly into the double-decker man skip to travel 1000 feet down to the bottom level of the mine. Jim Smith was our tour guide, and of all the tours I’ve taken of mines around the country, this was one of the best. Not only did he explain how the equipment was used, he actually demonstrated it (it is still in working order). We saw how hydraulic drills, stope drills, muckers, bucket dumps, and other types of equipment were used by the miners. The tour lasted about an hour. I videotaped the whole thing, but wasn’t able to take many photos because we moved through the tour fast enough that I couldn’t use both cameras at once.

Mucker model

Scale model of a mucker, Cripple Creek Heritage Center

Mollie Kathleen mine tour

Jim Smith explains stoping drill, Mollie Kathleen mine tour

Jim described how miners would discover a gold vein or deposit, and shafts and crosscuts would be dug into the bottom of the deposit so that it could be stoped upward (following the deposit as it twists through the rock), standing on planks using a stoping drill that could jam and flip you off the plank at any time. Some deposits were found filling cavities called vugs, where the gold would replace the granite rock and form rich veins. The normal grade of ore assayed at about $2 of gold per ore car; some of these vug deposits, such as the one in the Cresson Mine, assayed out at over $4000 per car. Miners were paid $3 per day at that time (the same as miners in the Tintic District in Utah) and it was common for miners to “high grade,” or smuggle rich ore samples out in the false bottoms of their lunch pails.

Crosscut tunnel and ore car

Crosscut and Ore Car, Mollie Kathleen mine

Mary Catherine (Mollie Kathleen) Gortner discovered the mine in 1891 shortly after Bob Womack and Winfield Scott Stratton had discovered their gold lodes. She was visiting her son, who was prospecting in the camp, and walked up Poverty Gulch to where he was working. As she sat down to rest, her foot kicked a rock that looked like promising gold float, and she followed the rock to its source (which had already been missed by numerous miners) and memorized its location – she was too afraid of someone jumping her claim to even mark it. When the rocks she hid in her dress assayed out as rich gold ore, she returned and staked a claim as one of the few women mine owners in the district. Since then, the Mollie Kathleen has been in more-or-less continuous operation as a producing gold mine; the Lanning family that owns it now still goes in during the winter to mine out veins. They can make a small profit, with gold at over $1200 per ounce now (the main problem for the gold mines in the district isn’t the lack of gold, but the lack of a local mill to process it). But the main source of income now is from the mine tours.

Cripple Creek Colorado

Cripple Creek, Colorado from Heritage Center

After the tour I visited the Cripple Creek Heritage Center across the street and took some panoramic videos of the town, as the view was great. There were headframes on most every hill and holes everywhere where prospectors had tried and failed to find gold. At the top of the major hills was a huge continuous tailings pile from the Cripple Creek and Victor Gold Mine, a large open pit/surface mining operation that is still operating. They are concentrating the ore through leaching the tailings piles, and it is interesting to see this modern mining operation superimposed on the older, historic mines.

Next post, I’ll describe the towns of Cripple Creek and Victor and some of the mines in the area.

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