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Posts Tagged ‘galena’

For the last week, I’ve been busy preparing for my classes at Walden School, including inventorying the science lab room (which is also my classroom) and planning out my course schedules. I’ll be teaching two sections of Chemistry, one of Astronomy, one of Computer Technology (a basic computer literacy course required in Utah), a section of Media Design, and a section of Video Production. This is, for me, a perfect schedule. In the meantime I’ve also been preparing a series of maps and 3D images of the Tintic Mining District, focusing on the ore deposits and the various mines located there. I’ve also prepared the script for this section of the video, which I have pasted below:

Mines in the East Tintic Mts

MInes and Roads in the East Tintic Mtns.

Tintic Geology

To understand how the ore bodies in the Tintic District were deposited, we have to start about 800 million years ago in the Precambrian Period when the western portion of the North American craton rifted away from the rest of the continent along a line where the Wasatch Front now lies – this Wasatch Line has been an important hinge line in Utah’s geology ever since. For the next 600 million years, a sequence of ocean sediments including dolomite, limestone, shale, and sandstone were deposited off the coast in the geosyncline that would become western Utah. Beginning 150 million years ago, Nevada and then western Utah were uplifted as the Farallon tectonic plate was pushed under North America. Like a throw rug being wrinkled up as it’s pushed over a hardwood floor, western Utah was folded by thrust faults into a large mountain range during the Sevier orogeny about 70 million years ago. This thrusting continued across eastern Utah and into Colorado and Wyoming during the Laramide orogeny, building up the Uintah and Rocky Mountains.

East Tintic Mines

Mines in the eastern portion of the Tintic Mining District

Then, about 50 million years ago, the Farallon plate began to collapse from underneath the continent. As it peeled away, a wave of volcanism moved from east to west across Colorado and Utah. Intrusive laccoliths rose to the surface, bulging up the LaSal and Henry Mountains in eastern Utah and forming explosive calderas in several places in western Utah. About 35 million years ago, a series of calderas formed in the area that would become the Tintic Mountains. A large andesitic volcano rose up from eruptions of ash and tuft.

Tintic Standard ore samples

Ore samples from the Tintic Standard Mine, eastern district.

About 31.5 million years ago, the volcano collapsed as the intrusive magma began to cool. Mineral rich fluids were injected into the surrounding limestone, quartzite, and dolomite as replacement beds. The hot magma caused the carbonate rocks to decompose; for example, limestone turns into lime or calcium oxide and carbon dioxide gas when heated. This left large cavities that then filled up with the mineral-laden magmas. These deposits are called stopes, such as the famous Oklahoma stope of the Chief Consolidated mine. The carbon dioxide released from the decomposing limestone and dolomite in turn dissolved into the hot magma, making it a kind of lava champagne, and reacting with it to form various exotic minerals, some of which are found nowhere else.

More Tintic ore samples

More ore samples from the Tintic District

The primary ore-bearing minerals in the Tintic District are enargite, tetrahedrite, galena, sphalerite, pyrite, marcasite, and native gold, silver, and copper. But many more minerals are present, including unusual minerals that blend copper, silver, tellurium, arsenic, sulfur, carbonates, hydrodixes, etc. At the Centennial Eureka mine, over 85 different minerals have been identified, ranging from common pyrite, malachite, and azurite to minerals found only here. It is the type locality (where the mineral was first identified) for leisingite, frankhawthorneite, jensenite, juabite, utahite, and eurekadumpite. Other rare minerals include xocomecatlite, carmenite, adamite, duftite, and mcalpineite.

These mineral deposits occurred around the edges of the caldera and formed the five large ore zones of the main Tintic District. The Gemini Ore Zone runs to the west of Eureka south to the north edge of Mammoth Gulch. The Gemini, the Bullion Beck and Champion, the Eureka Hill, and the Centennial Eureka mines (known collectively as the Big Four) are located on this zone.

The Chief-Mammoth Ore Zone begins under the center of Eureka and extends due south across the mountain to the east end of Mammoth Gulch. The Chief Consolidated mine is located on the richest ore body, which is right under the center of Eureka city; up the hill is the Eagle and Blue Bell mine, named for the beautiful deposits of azurite found inside. Further south over the top of Eureka Peak lie the Grand Central, Mammoth, Apex, and Gold Chain mines that are also part of this deposit.

Ore zones in the Tintic District

Ore Zones and Major Mines of the Tintic Mining District

The Plutus Zone branches off of the Chief-Mammoth Zone high up in the Tintic Mountains. The Godiva Zone starts just east of Eureka and runs southeast in a curve where it joins the Iron Blossom Zone, which continues in a curve south and then southwest. Some mines in these zones include the Godiva, May Day, Humbug, Beck Tunnel, Sioux, and Iron Blossom mines.

In the eastern section of the Tintic District, several zones of minerals were deposited and were among the last to be discovered because they are overlain by 400 feet of igneous rock. These bodies include the Burgin ore body, the Tintic Standard, and the North Lily bodies. Other bodies are located at the Apex and Trixie mines.

In the southern section of the Tintic District, the large replacement bodies give way to smaller fissure veins that are only two feet wide on average but can be up to 4000 feet long. Here, the mineral-bearing magma was injected into cracks and fault lines already existing in the host rocks. The Dragon mine is the only true open pit mine in the area; it sits on top of a network of fissure veins at the south end of the Iron Blossom Zone. Other mines in the area include the Swansea and Sunbeam mines at Silver City, the Tesora and Treasure Hill mines at Ruby Gulch, and the Showers mine at Diamond Gulch.

More ore samples from the Tintic Standard Mine

More ore samples from the Tintic Standard Mine

The final chapter in the area’s geomorphology began about 17 million years ago when normal faulting created the Basin and Range province, lifting up blocks to form the mountain ranges of Utah and Nevada, including the East Tintic Mountains. Other blocks sank to form the valleys, such as the Tintic Valley. Erosion has exposed the ore bodies in many places, including the outcropping that George Rust stumbled over in 1869. It was to become the Sunbeam Mine.

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Electric speeder engine for pulling lead ore cars

Electric speeder engine for pulling lead ore cars

    The third section of my journey home to Utah from Philadelphia revolved around the lead mines of Missouri. On Thursday morning, Aug. 3, I was at St. Francois State Park near Bonne Terre, Missouri in the Old Lead Belt, and I toured the Bonne Terre Lead Mine as well as the Missouri Mines State Historic Site in Leadington.

Shovel built by the St. Joseph Lead Company

Shovel built by the St. Joseph Lead Company

    When French explorers made their way up the Mississippi River they came to a place where shiny, heavy rocks were scattered over the surface. This was rich galena ore, or lead sulfide, which forms shiny, dark-gray cubic crystals. They named the area Bonne Terre, meaning “Good Earth” and did some surface mining beginning about 1720. Later settlers took up the mining operations in the late 1800s and sunk shafts into the richest ore bodies, which extended in a rough line from just west of St. Louis southeasterly about 100 miles along the Mississippi River toward the toe of Missouri. This area, known as the Old Lead Belt, and 1000 miles of tunnels and chambers and 300 miles of railroad tracks were cut out of the native limestone. Another band of rich lead ore, called the Viburnum Trend, is still being mined further west. This is the richest lead deposit in the world, and supplied demand for lead for over 60 years.

Mule trail into the Bonne Terre lead mine

Mule trail into the Bonne Terre lead mine

    As the miners dug into the rocks at Bonne Terre, their first chamber, nearest the surface, didn’t have very much good ore. So they sunk further shafts and started a new level, this one much richer. It extended for hundreds of yards under the town of Bonne Terre, and used a chamber and pillar method of mining. The limestone rock there was solid enough that huge chambers over 40 feet high were eventually dug, with supporting pillars. When they had reached the edges of the ore body all around, they delved even deeper, sinking new shafts and creating a new level under the first two, with pillars carefully lined up on top of each other to keep the weight supported. This went on for a total of five levels, each one extending further out on the sides as the ore body widened, forming a huge pyramid of levels. Other lead mines in the Old Lead Belt did the same thing, and most of them interconnected so that when the mines were active you could travel through hundreds of miles of underground chambers and tunnels. Being in this mine reminded me very much of the Mines of Moria in the Lord of the Rings. I kept looking out for orcs . . .

 

Pillars and chambers in the Bonne Terre mine

Pillars and chambers in the Bonne Terre mine

    Once mining ended at Bonne Terrre, the lower levels began to flood with water since it was no longer being pumped out. Eventually the bottom three levels all flooded and part of the second level. The tour takes you down through the first and into the second level along the old mule trail, and for an additional fee, you can take a pontoon boat out on this billion gallon underground lake. It sounds like the perfect setting for a horror movie, but the only living thing in all this water is a large-mouthed bass named Bonnie that has to live off of worms the tour guides bring in. She was transplanted here ten years ago and still survives in this deep lake. She isn’t too lonely, however. Between the tours, cave divers come here regularly, and some TV programs have been here as well, including a season of Nickelodeon that was kicked off here and an underground wakeboarding contest sponsored by Red Bull drinks. I’m not sure how they managed to get the boats in and out – they can only come in through the shafts that lead to the surface. They must have been taken apart and reassembled in the chambers.

Shaft leading to the surface in the Bonne Terre lead mine

Shaft leading to the surface in the Bonne Terre lead mine

    After a very interesting tour, I traveled south ten miles to Leadington and Park Hills and went through the Missouri Mines State Historic Site. Built in an old lead mine/concentration plant building of the St. Joseph Lead Company, this museum has equipment on display as well as a world-class collection of rocks and minerals from Missouri and around the world. Some of their samples rival those at the Smithsonian.

Missouri Mines State Historic Site. Art Hebrank is on the left.

Missouri Mines State Historic Site. Art Hebrank is on the left.

 

 

 

 

 

They have been collected and the site is administered by Art Hebrank, who has been a geologist for the Missouri Department of Natural Resources and really knows his stuff. I had a very enjoyable talk with him, and he discussed some of the plans they have for renovating the site and expanding the museum. Right now, the museum is housed in the old power house while the rest of the site is a rusting ruin (but very fascinating for those of us who get into such things). I took a lot of photos and panoramic video there.

Specimens of copper minerals at Missouri Mines State Historic Site

Specimens of copper minerals at Missouri Mines State Historic Site

 

A ball mill for crushing lead ore

A ball mill for crushing lead ore

 

 

 

 

 

 

 

 

 

    I highly recommend that if you are interested in the history of Missouri or of mining or, like me, you want to know where the elements come from, then you should take the Bonne Terre mine tour and visit the Missouri Mines State Historic Site. It was definitely worth my time. Between the mine tour and the museum, I now have a the footage and photos I need to create an excellent podcast episode or two on Missouri lead mining.

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