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Archive for April, 2010

Calderas of Juab County

Volcanic Calderas of Millard and Juab Counties, Utah

Usually, when one thinks of rocks and geology it’s all a bit impersonal; after all, they were formed in the distant past, in many cases hundreds of millions of years ago. Most of the rocks in western Utah, where I’m from, were laid down as ocean deposits during the Paleozoic Era. Now all the layers of shale, limestone, and dolomite have been thrusted, twisted, and even overturned, so that in some areas the Paleozoic rocks lie on top of younger Mesozoic rocks. How could this have happened? But in addition to these sedimentary rocks, there are some anomalies; whole mountains that puzzled me because they didn’t fit in. My grandfather, who lived next door to us in our small hometown of Deseret, would take me for drives out on the west desert looking for trilobites or pine nuts or just collecting rocks. One area we visited was Topaz Mountain at the southern end of the Thomas Range in Juab County, where one can find topazes just by walking along an arroyo on a sunny day, following the flashes of light. The rocks there are weird, with strange cavities and a light gray texture much different than the surrounding mountains. I wondered where it came from, how the topazes got there, how old the rocks were, and above all, how geologists were able to answer these questions.

Desert Mt. Pass

View from Desert Mt. Pass

This was all very interesting to me as a child, but then geology got personal. My father was a farmer and cattle rancher, and one day in June of 1971, we were hauling a load of yearling heifers out to our ranch in southern Tooele County (about 50 miles due north of Deseret). As we were driving our old 1952 model half-ton truck over the pass on Desert Mt., the brakes and clutch both failed at the same time and we found ourselves rolling down the steep and winding road without any means of stopping (the road has since been improved, as you can see at right. Back then the road cut along the left side of the pass and was much more dangerous). Dad tried to slow the truck down by ramming it into the embankment on his side, but the impact jarred the cab, flung open the door on my side, and threw me from the cab (this truck had no seat belts). Fortunately, there is a gap in my memory at that point for several seconds. The next thing I can remember is lying on my back looking at the truck as it rolled away from me and disappeared out of sight over the edge of the embankment. Then I saw my right leg, which was twisted unnaturally, with my thigh badly torn up – a whole piece of my thigh seemed to be missing, as far as I could see through the tattered remains of my pants. The best I can figure is that the rear dual tires of the truck rolled over my leg, breaking it in two places and tearing up the skin and underlying tissue badly. Or my leg dragged over the rough, sharp rhyolite rocks of the mountain. Or both.

Desert Mt. Rhyolite

Rhyolite formations at Desert Mt. Pass

This was a hot day in June. We had water and snacks, but my father had sprained his ankle and could not walk. This was before cell phones or even CB radios, and we had no way of getting help. You have to visit the west desert of Utah to appreciate just how isolated it is. Dad lit the truck on fire, hoping the column of smoke would attract attention from the ranchers (including my grandfather) across Ereksen Valley, but no one saw it. Hours dragged by. I was slowly bleeding to death as blood seeped out of my wound, and I was going into shock. After about five desperate hours, my father saw a car sitting on the road leading up to the pass; they had stopped when they came around the corner and saw the smoldering remains of our cattle truck. Dad stood up and waved, and they drove on up. The car was driven by a an elderly couple from Odgen, Utah: rockhounds who were out on the west desert looking for Topaz Mt. All they had was a hand-drawn, inaccurate map and they were off course by 40 miles. Dad was able to ride in to the nearest phone (about 15 miles) and call the ambulance and Doc Lyman from Delta. After several days in Intensive Care, two months in the hospital with skin grafts, and another three months in body casts, I was finally able to walk again. I am lucky to have two legs.

So my life was profoundly affected by the geology of Utah’s west desert. Desert Mt. almost killed me; Topaz Mt. saved my life. So I have understandably been curious about the geology of these two mountains. I can honestly say that I am a part of that geology – somewhere on Desert Mt. there’s a small patch of dirt that used to be me. And that geology is a part of me, too – the doctors were never able to get all of the small rock fragments out of my leg that had been ground in. Yes, I know it’s a bit grotesque, but it’s literally true.

That’s why I’ve wanted to complete these episodes on the beryllium deposits of western Utah before doing any others, because telling that story includes the story of the geology of the area and how those two unusual mountains came to be there in the first place. The episodes are coming along nicely, and I have completed the geology section completely and offer it now for your enjoyment. The first episode (on the sources, uses, and geology of beryllium) will be ready in a few days; the second episode on the mining, refining, and hazards of beryllium will be ready by next week.

Here is the script of this section, in case you’d like to read along with the video:

Geologic Origins of the Bertrandite Deposits in Western Utah

To understand the origins of the beryllium deposits in the Spor Mts. we have to go back to when western Utah was still under the ocean. For hundreds of millions of years, this ocean floor built up gradual layers of shale, limestone, and dolomite. The North American tectonic plate began to separate from the rest of Pangaea about 200 million years ago and was moving westward into the Farallon Plate, which was subducting under the western margin of North America. The sediments carried down with it were heated and rose toward the surface to cool as the granitic plutons of the Sierra Nevada Mts. For the first time, the western half of Utah and Nevada rose above the ocean.

Overhead View of Topaz Mt. Area

Aerial View of Topaz Mountain Area

Then, about 150 million years ago, the North American Plate sped up; instead of moving about 2.5 cm per year, it leaped ahead at the breakneck speed of about 8 cm per year. Instead of subducting, the remnants of the Farallon Plate were pushed under western North America, scraping and dragging the roots of the continent with it. This friction caused a wave of thrust faulting and mountain building to travel west to east across Nevada (the Nevadan Orogeny), then across western Utah (the Sevier Orogeny) about 125-75 million years ago. A huge mountain range rivaling today’s Rockies sat on the Utah-Nevada border, with sediments washing off of it into an inland sea to the east to form the upper layers of the Colorado Plateau as dinosaurs wandered through the mud flats and swamps. These swamps became the coal deposits of central and eastern Utah.

As the thrust faulting continued east, it encountered the thick Colorado Plateau and bent it into the huge anticline of the San Rafael Swell. When it reached Colorado and Wyoming about 55-60 million years ago, the thrust faulting created the Laramide Orogeny that resulted in the Rocky Mountains, including the Uinta Mountains of northeast Utah.

About 50 million years ago the North American Plate slowed down again and the remnants of the Farallon Plate collapsed from underneath, pealing away in a wave that now traveled from east to west. A wave of volcanism traveled with it, moving back across Utah and Nevada. Much of the mineralization found in Colorado, Utah, and Nevada occurred at this time, including the silver, copper, zinc, lead, and beryllium deposits of Utah. In western Utah, the volcanism produced several zones of Andesitic volcanoes with calderas and ash flows, including the Thomas-Drum Mt. caldera along with calderas at Keg Mt. and Desert Mt., about 45-39 million years ago and continued for at least 30 million years through several phases. In the first phase, quartz-rich magmas formed the calderas and ash flows that covered much of the area and produced the gold, copper, and manganese deposits of the Detroit District in the Drum Mts. The second phase of area volcanism occurred as the calderas in the Spor and Drum Mountains subsided and were filled with rhyolite from the Dugway Valley caldera about 38-32 million years ago.

Utah during Oligocene Epoch

Utah During Oligocene Epoch, 30-40 million years ago

The ancient thrust faults and collapsed calderas created fractures, which served as avenues to intrude veins of mineral-bearing magmas. Beginning about 25 million years ago, a third phase of volcanism pushed domes of highly alkaline rhyolite rich in fluorine and beryllium up through these fractures. The fluorine and beryllium minerals formed gases that were injected into the thrust faults and eventually encountered ground water, which flashed into steam, shattering the surrounding rhyolite and forcing the beryllium minerals to precipitate throughout the fractures and empty spaces in the host rhyolite rocks. Gradually, minerals were deposited as crystals of topaz, fluorspar, garnet, and bertrandite in the Thomas-Spor Ranges, and red beryl in the Wah Wah Mts. Additional trace elements such as uranium, lithium, aluminum, zirconium, iron, and thorium were also deposited.

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Topaz-Spor Mountain area

Topaz-Spor Mt. area

I am continuing this series of posts on the sources, mining, and refining of beryllium ore. I am in the middle of editing the interview my students did in Dec., 2007 of Phil Sabey at the Brush Resources’ Delta Concentration Mill and will have the final videos done by next week. Today I’ve been creating a series of Flash animations showing the geologic history of the Spor Mountain area where the bertrandite deposits are located. Today’s post will be on the refining process used at the Delta Mill to concentrate the bertrandite and beryl ore into beryllium hydroxide.

Bertrandite and Fluorspar

Fluorspar with Bertrandite

Refining Beryllium Ore

With only 0.65 % beryllium oxide (or 4.5 lbs. per ton of beryllium) in the final ore, a process had to be engineered to economically concentrate the beryllium for final processing. The properties that make beryllium useful also make it difficult to extract from its ores. Robert Maddox, Howard Gimperline, Jack Valliquet, Richard Shank, and other chemical engineers at Brush Wellman’s plant in Elmore, Ohio in the early 1960’s devised a unique solvent extraction process. With refinements, the process was seen to be economical and the go-ahead was given to build a concentration plant as close to the mine and to railroad transportation and a good water source as possible. In Dec., 1967 a groundbreaking ceremony was held at the mine and in April, 1968 a ceremony was also held at the mill site north of Delta, Utah. By the end of 1969, the plant was producing its first beryllium hydroxide concentrate.

Process for refining bertrandite

Process for Refining Bertrandite Ore

The solvent extraction process removes the beryllium by first crushing and wet grinding the ore in a ball mill, then leaching it with sulfuric acid and steam in rotating tanks at 95 ° C to dissolve the beryllium. Thickening agents are added which help to settle the sludge in a series of flotation tanks while leaving the beryllium sulfate in solution. The sludge is stirred by counter current decantation and pumped from tank to tank as the dissolved beryllium sulfate is washed over the side to continue the process. The remaining sludge is finally discarded to a tailings pile.

Sulfation Tanks

Sulfuric Acid and Steam are added to the bertrandite to dissolve the beryllium

The beryllium is then separated from the sulfate using an organic compound, then stripped from the organic by ammonium carbonate. Impurities of iron and aluminum are removed through steam hydrolysis, which leaves the beryllium in the form of beryllium hydroxide, which is vacuum drum filtered. Since beryllium dust is toxic, this entire process must be done in a sealed system, including the final packaging of the beryllium hydroxide into blue drums for shipment.

Panorama of the Brush Resources plant

Panorama of the Brush Resources Beryllium Plant

There are a lot of impurities in the bertrandite ore; some that gave problems early on were the high sodium content, the high uranium content, and the zirconium. The leftover filtrate still has appreciable quantities of uranium, so it is pumped to evaporation ponds, then shipped elsewhere for final uranium processing.

Beryl crystals

Beryl Crystals Ready for Refining

Once it was proven that this process could compete economically with the beryl extraction process already being used, the go-ahead was given to build the Utah processing plant. A site was selected near the Union Pacific railroad tracks and the Sevier River north of Delta and south of Lynndyl in west central Utah. The plant was completed in 1969 and began processing ore that had already been mined and stockpiled. Brush Wellman was awarded the prestigious J. C. Vaalor Award for Chemical Engineering in 1970 for the implementation of this process. In 1978, an addition was built on the plant to allow the processing of beryl ore, making the Delta plant the only facility in the United States that processes either form of beryllium ore. When beryllium was identified by the U. S. government as a strategic metal for its critical uses in the aerospace industry, beryl ore was purchased from mines in Brazil and stockpiled. Brush Resources has now purchased this strategic stockpile and is extracting the beryllium from it.

Pouring molten frit

Pouring Molten Beryl Frit

To recover beryllium from beryl crystals, the crystals must first be destroyed, since the beryllium is tightly bound in the beryl crystal lattice. The beryl is melted at 1700 ° C in a furnace, then quenched rapidly in water to break the crystal lattice and turn the beryllium particles into a frit, with the non-beryllium materials removed as slag. The frit is heat-treated at 1000 ° C in a rotary kiln, ground up in a ball mill, and leached with steam and sulfuric acid at 325 ° C in a rotating drum to dissolve the beryllium. This solution is added to the bertrandite solution in the flotation tanks to continue the process. In 1980, additional flotation tanks were added to accommodate the beryl solution.

Heat treater kiln

All of these processes require careful control and monitoring to improve yields and ensure safety. Using a Continuous Improvement Process, the Delta plant has added computer automation controls and improved laboratory analysis. New flocculent agents and organic solvents have improved the extraction yields, and the plant now processes ore at a 99% efficiency level. Around 400 tons of bertrandite and about 10 tons of beryl ore can be processed per day at the Delta plant.

Special thanks go to Phil Sabey for the tour of the Brush Resources plant and for providing the brochures, Powerpoint presentations, and photos upon which this post is based.

Phil Sabey in Chem Lab

Phil Sabey in Analysis Lab

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The next videos that will be completed for the Elements Unearthed Project are two episodes on the sources, mining, refining, and uses of beryllium. I’ve written a few posts previously about this topic, and as I continue to organize and prepare materials to use in the videos (which will be edited over the next week), I have created several diagrams that describe the process used for surveying and developing open pit mines at the Brush Resources’ Spor Mt. mine site in western Utah. You might say, “Beryllium? Why should I care about some rare metal that I’ll never use in my lifetime?” But you’d be surprised. You are already using beryllium (for example, the electrical contacts inside the automatic windows of your car use a beryllium-copper alloy because it can handle frequent changes in heat and resists corrosion better than many other alloys). Beryllium is also an essential metal for medical, nuclear power, and aerospace applications. I’ll discuss more of beryllium’s uses and its refining and sources in a later post, but in this post let’s talk about how the bertrandite ore is mined.

Spor Mt. beryllium deposits

Location of Bertrandite in Western Utah

Mining Operations at Brush Resources

The bertrandite ore found in the Spor Mts. is very similar to clay (an aluminum silicate) and looks like common dirt except it has a slight pinkish color. It’s also associated with fluorspar or fluorite, which is often a deep blue to violet color. One is tempted to think the more colorful fluorite is the mineral we want, but it’s actually the crumbly pink coating found on the fluorite nodules. Elsewhere in the Spor Mts., the fluorite has been mined commercially.

The first attempt at mining the bertrandite ore was started by Anaconda on their claim. They tried hard rock mining, but the soft altered rhyolite of the ore body proved too dangerous to mine that way.  One day, while the miners were all having lunch, the mine caved in. Fortunately no one was hurt, but it was determined then that the only safe method was open pit mining.

Exploratory drilling

Exploratory core drilling

Potential mine sites are surveyed by drilling core samples every 100 feet to map out the general location of the ore bodies. The bertrandite deposits in the Spor Mts. are located in a mineralized zone of altered rhyolite tuff that overlies a bedrock of limestone. This soft and crumbly altered layer is overlaid by a tough, hard layer of unaltered rhyolite with about the same composition and hardness of granite. All of this is further overlaid by a layer of gravel, loose rock, and sand deposited by Lake Bonneville during the last ice age. Since the ore body is tilted, it occasionally reaches the surface (where it was originally discovered) and in other places dips so far below ground as to be unfeasible to mine. Several mine sites, such as the Blue Chalk and Roadside I sites have already been mined, but enough reserves have been mapped to last at least 50 more years at current production levels.

Planning an Open Pit Mine

Planning an Open Pit Mine

Once the location of the ore body has been generally mapped out, mining engineers plan out an open pit structure that will reach the ore with the least disturbance to the overlying layers while keeping the sides of the pit terraced to safely prevent rockslides and excessive erosion. Once the plan is approved, a contractor is hired to remove the overburden, usually in the winter and spring months. The loose alluvial gravel and soil is removed first and set aside for later reclamation. The hard rhyolite is blasted and removed, and the altered rhyolite layer is also removed to within about seven feet of the bertrandite ore.

Removing the Overburden

Removing the Overburden

A second phase of core drilling is carried out, with holes every 25 feet to more accurately map out the exact ore locations. For a typical ore body, between 40 and 60,000 cores are drilled and sampled every two feet. 3D structural maps are prepared to identify where various grades of ore are located. The ore is then removed carefully; a technician with a portable field berylometer walks before the bulldozer and stakes out the locations of the ore grades that are being removed; a self-loading scraper scoops up the ore and moves it to stockpiles where it is sorted by grade into the same pile. The ore is then transported by 18-wheeler to the processing plant near Delta, Utah, about 50 miles southeast. High-grade ore is mixed with low-grade ore so that all the bertrandite coming to the plant has about the same percentage of beryllium. The final ore has less than .65% beryllium, or about four pounds per ton.

Next Post: Refining Beryllium Ore

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