Category Archives: Mining

Pitchblende in the Wood Vein, Central City District

Recently I came upon a copy of Geological Survey Circular 186, 1952, F.B. Moore and C.R. Butler, Pitchblende Deposits at the Wood and Calhoun Mines, Central City Mining District, Gilpin County, Colorado. Like many Geological Survey documents, it contains a pocket with neatly folded scale drawings of the mine workings. These drawings chart the location and elevation of the shafts and drifts and give a best estimate as to the extent of the formation.

Vein Structure in the Central City District. (From Geologic Survey Circular 186, 1952.)

What is interesting about the map above is not so much the minute detail of the locations, but rather the obvious trend of the veins (solid lines with dots).  They are all east-northeast trending.  The country rock is largely precambrian granite gneiss and quartz biotite schist according to the survey. It doesn’t take long to figure out that the mine locations correlate with the veins.

Geological Survey maps of 3 levels of the Wood Mine, Gilpin County, Colorado (Geological Survey Circular 186, 1952).

The second figure was generated by Moore and Butler in 1950 and shows the locations of pitchblende occurrences in three levels of the Wood Mine near Central City, Colorado. The red dots indicate the location of pitchblende along the three drifts at the 135, 197, and 275 foot levels of the mine.

Profile of the Wood Mine, Central City District, Illustration from Geological Survey Professional Paper 371, 1963.

 The Wood Mine was an early and prolific source of pitchblende, though presumably it began as a gold /silver operation. The workings reportedly reached a depth of 600 ft.  The Wood vein is in a fault fissure that shows extensive alteration from hydrothermal action. The width of the vein varies with the type of country rock in which it is found, but ranges from from 1 to 18 inches and has been followed for a lateral distance of nearly 1000 ft.

The productivity of uranium mines is commonly expressed in terms of equivalent weight of U3O8 rather than weight of ore, given the large variety of mineral forms uranium is found to occur in. The figure above is from Geological Survey Professional Paper 371, P.K. Sims and collaborators, Geology of Uranium and associated Ore Deposits, Central Part of the Front Range Mineral Belt, Colorado. Extensive stoping has been done in an attempt to vertically intercept the vein. This was a common practice in hard rock mining- let gravity bring the muck to you.

Pitchblende was discovered on the dump of the old Wood shaft in 1871. Circular 186 reports that by the end of 1872, 6,200 lbs of ore containing 3,720 lbs of U3O8 had been removed. By 1916, 102,600 lbs of ore bearing 30,040 lbs of U3O8 equivalent had been recovered.  The high grade pitchblende was hand sorted and that below ca 10 % was discarded or lost in gold and silver processing.

In Circular 371, Sims observes that “Pitchblende occurs as small, discontinuous lenses and streaks on the footwall of the Wood Vein, which are separated by nonuraniferous vein material.”

What is intriguing is that pitchblende was apparently an item of commerce in the early 1870’s. Radium, extracted from pitchblende, was not discovered until 1898 by the Curies.  A procedure for the preparation of sodium diuranate, Na2U2O7 6H2O, was reported as early as 1849 (Patera, J. pr Chem. 1849, [i] 46, 182. Early uses of uranium yellow were in paints and stains for glass and porcelain. This pigment has also been used for the production of fluorescent uranium glass.

Uranium roll fronts

As a kind of hobby Th’ Gaussling has been surveying the literature on uranium occurrences in North America. Uranium is found in many interesting locations and as a result of several distinct kinds of ore forming processes.

Prospector with Geiger Counter

From Ballard &Conklin, Uranium Prospectors Guide, 1955 Harper & Brothers

For the most part, uranium ore body formation is the result of aqueous transport and deposition.  Uranium is found as a lode in vein formations in precambrian  igneous/metamorphic structures as in the case of the Schwartzwalder mine near Denver. In fact, there are many lode occurrences that contain a variety of uranium minerals in the Colorado mineral belt.

What seemed counterintuitive to me was the extent to which uranium is found in sandstone. Evidently I had developed a bias for connecting heavy metal occurrences with igneous/metamorphic formations.

Uranium occurrences in sandstone take on certain characteristics as a result of ore forming processes. Uranium is often found in concentrated bodies called “roll fronts” or “ore rolls”. A roll front is a body of concentrated mineral with a lenticular cross section and is found in confined strata sandwiched between impermeable clays, shales, or mudstones.

Roll Front Cross Section

Adler & Sharp, Guidebook to the Geology of Utah, No. 21, Utah Geological Society, 1967, p. 59.

The action of oxygenated meteoric water (i.e., rain and surface water) migrating through a porous sandstone stratum will selectively mobilize mineral species that are soluble. In the case of uranium, the relatively insoluble U4+ compounds are oxidized to more soluble U6+ species which are then mobilized and flow in the formation.

Eventually, as the water flow encounters reducing conditions, U6+ gets reduced to U4+ and deposition occurs. Sandstone with organic material may be a net reducing environment and provide the necessary carbonaceous reductants to do the deed.

As the U6+ enriched aqueous flows encounter reducing conditions, deposition of U4+ insolubles occurs in a manner determined by fluid mechanical forces. The result is an elongated and tapered ore body confined to a narrow stratum.

Uranium roll fronts are common in many uranium districts. The Uravan uranium belt in the Colorado Plateau is a good example. Uranium is found concentrated in tuffaceous formations as well. An example of this is the uranium occurrence found in the 39 Mile Volcanic Field in the central Colorado mountains.

What is interesting to ponder is the geological effect of plant metabolic byproducts like oxygen. Oxygen directly contributes to a natural process that lead to the concentration of a scarce element like uranium. Plant life facilitating nuclear power. Hmmm.

Placer Gold Mining in the Wilderness

I recently had the occasion to sit and talk to an independent gold miner. This fellow had spend many seasons in the Yukon doing placer mining and had a few useful things to say about it.

In my friends experience the Alaskan placer mining season is very short- just 100 days or 2400 hours per year.  In that time you have to get your operation in place and process enough gravel and sediment through the sluices or centrifuge to isolate enough gold to make the process profitable. Sluicing and centrifugation are just forms of classification and your system must be able to separate gold particles in a manner consistant with the particle size range prevalent in the claim.

It is not uncommon for gold to be heavily represented in the 400 mesh range, or ca 0.037 mm particle size. In the old days, miners recovered fine particulate gold using amalgamation. Some large operations like Ashanti Gold in Cripple Creek use cyanide heap leaching to isolate the fines.

Sluicing operations in Alaska require considerable cash input and preparation. Sluicing generates considerable suspended solid and turbidity in the streams and the EPA, BLM, and wildlife agencies will have to be satisfied that the environmental impact is understood and minimized. Permitting is therefore a major hurdle for potential sluicing operations beyond the small scale.

My friend said that continuous centrifugation was necessary to capture the 400 mesh gold fines in the district he worked. As the capital equipment requirements increase, the volume of sediment to be classified must be scaled up to bring a satisfactory return on investment. Manpower and ancillary equipment requirements increase correspondingly. Soon you have a camp to maintain, payroll, and a crew to feed. In remote locations, air cargo transport is necessary to bring in the machinery and supplies. There is no Home Depot down the road to supply duct tape. Just like on a trip to Mars, you have to anticipate all needs and haul it in ahead of time.

A modest mining effort soon becomes a large logistics and financing problem. It’s a wonder that anybody still does this kind of thing. But, yet, they do.

Welsh Slate Mine

Just a quick comment on a mining related place to visit. If you find yourself knocking about in Wales, particularly near Snowdonia, it is worth taking the time to visit the Llechwedd Slate Caverns. It is quite sobering to see the working conditions the miners endured, hacking at dark rock in the flickering candlelight.

We found that the Welsh speak Welsh amongst themselves and switch to English seamlessly when you walk to the cash register to buy something. It is hard to describe the sound of the language, though I hasten to add that pronunciation gets easier when you have some Cadbury chocolate stuck to the roof of your mouth. The unique Ll characters are pronounced as a light gutteral “chl”. Imagine whispering this romantic sound as you nibble on your darlings ear under the moonlight. Hey baby …

Retrocurricular Translocation of Post-Modern Emphasis in Chemical Pedagogy

I couldn’t resist a sarcastic allusion to post-modernism, whatever the hell that is. What could possibly be under such a bullshit heading? Well, all of my tramping around chemical plants from Europe, Russia, North America, and Asia as well as local mines and mills keeps leading me to an interesting question. Exactly who is being served in the current course of chemistry education? Is it reasonable that everyone coming out of a ACS certified degree program in chemistry is on a scholar track by default? Since I have been in both worlds, this issue of chemistry as a lifetime adventure is never far from my mind.

What are we doing to serve areas outside of the glamor fields of biochemistry and pharmaceuticals? There are thriving industries out there that are not biochemically or pharmaceutically oriented. There is a large and global polymer industry as well as CVD, fuels, silanes, catalysts, diverse additives industries, food chemistry, flavors & fragrances, rubber, paints & pigments, and specialty chemicals. There are highly locallized programs that serve localized demand. But what if you live away from an area with polymer plants? How do you get polymer training? How do you even know if polymer chemistry is what you have been looking for?

Colleges and universities can’t offer everything. They attract faculty who are specialists in areas of topical interest at the time of hire. They try to set up shop and gather a research group in their specialty if funding comes through. Otherwise, they teach X contact hours in one of the 4 pillars of chemistry- Physical, inorganic, organic, and analytical chemistry- and offer the odd upper level class in an area of interest.

Chances are that you’ll find more opportunities to learn polymer chemistry as an undergraduate in Akron, OH, than in Idaho or New Mexico.  Local strengths may be reflected in local chemistry departments. But chances are that in most schools you’ll find faculty who joined after a post-doc or from another teaching appointment. This is how the academy gets inbred. The hiring of pure scholars is inevitable and traditional. But what happens is that the academy gets isolated from the external world and focused on enthusiasms that may serve civilization in distant ways if at all. The question of accountability is dismissed with a sniff and a wave of the hand of academic freedom. Engineering departments avoid this because they are in constant need of real problems to solve. Most importantly, though, engineers understand the concept of scarcity in economics. Chemists will dismiss it as a non-observable.

One often finds that disconnects are bridged by other disciplines because chemistry is so narrowly focused academically. It would be a good thing for industry if more degreed chemists found their way into production environments. I visited a pharmaceutical plant in Taiwan whose production operators were all chemical engineers. Management decided that they required this level of education. But, why didn’t they choose chemists?  Could it be that they assumed that engineers were more mechanically oriented and economically savvy?

Gold mines will hire an analyst to do assays, but metallurgists to develop extraction and processing. Are there many inorganic chemistry programs with a mining orientation? Can inorganikkers step into raw material extraction from a BA/BS program or is that left to mining engineers?

In my exploration I am beginning to see a few patterns that stand out. One is the virtual abdication of  US mining operations to foreign companies. If you look at uranium or gold, there are substantial US mining claims held by organizations from Australia, South Africa, and Canada.

So, what if? What if a few college chemistry departments offered a course wherein students learned to extract useful materials from the earth? What if students were presented with a pile of rock and debris and told to pull out some iron or zinc or copper or borax or whatever value may happen to be in the mineral?

What if?? Well, that means that chemistry department faculty would have to be competent to offer such an experience. It also means that there must be a shop and some kilo-scale equipment to handle comminution, leaching, flotation, and calcining/roasting. It’s messy and noisy and the sort of thing that the princes of the academy (Deans) hate.

What could be had from such an experience? First, some hours spent swinging a hammer in the crushing process might be a good thing for students. It would give them a chance to consider the issues associated with the extraction of value from minerals. Secondly, it would inevitably lead to more talent funneling into areas that have suffered from a lack of chemical innovation. Third, it might have the effect of igniting a bit more interest in this necessary industry by American investors. The effect of our de-industrialization of the past few generations has been the wind-down of the American metals extraction industry (coal excluded).

If you doubt the effect on future technologies of our present state of partial de-industrialization, look into the supplies of critical elements like indium, neodymium, cobalt, rhodium, platinum, and lithium. Ask yourself why China has been dumping torrents of money into the mineral rich countries of Africa.

I can say from experience that some of the most useful individuals in a chemical company can be the people who are just as much at home in a shop as in a lab. People with mechanical aptitude and the ability to use shop tools are important players. Having a chemistry degree gives them the ability to work closely with engineers to keep unique process equipment up and running efficiently.

Whatever else we do, and despite protestations from the linear thinkers in the HR department, we need to encourage tinkerers and polymaths.

This kind of experience doesn’t have to be for everyone. God knows we don’t want to inconvenience Grandfather Merck’s or Auntie Lilly’s pill factories. Biochemistry students wouldn’t have to take time away from their lovely gels and analytical students could take a pass lest their slender digits become soiled. Some students are tender shoots who will never have intimate knowledge of how to bring a 1000 gallon reactor full of reactants to reflux, or how to deal with 20 kg of BuLi contaminated filter cake. But I hasten to point out that there are many students with such a future before them and their BA/BS degree in chemistry provides a weak background for industrial life.

A good bit of the world outside the classroom is concerned with making stuff.  I think we need to return to basics and examine the supply chain of elements and feedstocks that we have developed a dependence upon. American industry needs to reinvest in operations in this country and other countries, just like the Canadians, South Africans, and Australians have. And academia should rethink the mission of college chemistry in relation to the needs of the world, rather than clinging to the aesthetic of a familiar curriculum or to the groupthink promulgated by rockstar research groups. We need scholars. But we also need field chemists to solve problems in order to make things happen.

Linkenschmutz

Links found whilst thrashing about the internets on my computer machine.

RCS Rocket Motor Components supplies, well, rocket motor components for the serious “non-professional”. RCS offers propellants, casting resins (i.e., polybutadiene), bonding agents, tubes, and other pieces-parts for the rocket builder. Good stuff, Maynard.

It turns out that my fellow Iowegian and former US President Herbert Hoover published a translated and annotated version in 1912 of De Re Metallica by Georgius Agricola (1556). Hoover’s translation can be found on the web and a copy is on display at the National Mining Hall of Fame and Museum in Leadville, CO. This work by Agricola is nothing short of amazing. A series of images of the text in the original Latin can be found as well.

It is interesting to note that Agricola (1494-1555)  and Paracelsus (1493-1541) were contemporaries in central Europe. Agricola, a Saxon, spent much of his time in Joachimsthal and Chemnitz whereas Paracelsus,  Swiss, is famous for being a bit of a wanderer. While I have not encountered a reference indicating whether these two polymaths had any knowledge of one another, they very much exemplify the meaning of Renaissance.

This USB temperature logger is pretty cool. I can hear it calling for me.

Here is a collection of links to monographs on Radiochemistry from LANL.

In pursuit of better slag- Fluorspar

On Saturday morning the kid and I arrived in Jamestown, Colorado, in search of mill sites and mine tailings. It does have a post office, but unlike many mountain towns it has managed to remain free of yuppie development. No Aspenization … yet.

This mining district lies on the northeastern extreme of the Colorado Mineral Belt. Once a hotbed of gold and silver mining, the area also produced considerable U3O8 and separately, fluorspar. Au and Ag ore bodies were enriched in copper, zinc, lead (galena), fluorite (CaF2), gold, silver, arsenic and tellurides.

UraniumCore announced in December of 2006 its purchase of 60 % interest in 88 claims in Colorado, including 46 unpatented claims in the Jamestown area. As seems to be the case in most minerals exploration activity in Colorado that I am aware of, the action is being driven by Canadian, Australian, and South African companies. The prinicpals heading up UraniumCore are Canadian.

While my brother-in-law is Canadian and while I would actually like to retire in BC, I can’t help but say that I would like to see more US companies involved in mineral exploration. There has to be a back story here.

Initially we tried to visit the 11 acre Burlington fluorspar mine site. This site was the focus of some environmental trouble for the locals in Jimtown. Unfortunately, the site was thoroughly fenced off, so interesting photos were not to be had. According to one website, Honeywell has completed remediation of the site.

Driving back towards Jimtown from the Burlington mine the kid spotted some old timbers jutting out of the hillside, so we stopped. Following what could only be a tiny stream of tailings runoff (having orange iron sediment) we found the remains of a mill site along a small creek.

Jamestown Fluorspar 9-26-09 near Burlington Mine

Jamestown Fluorspar 9-26-09 near Burlington Mine

On the tailings pile we found some purple fluorspar and some rocks which under magnification, resemble gold ore I have seen elsewhere. There was the familiar sulfide odor in the area indicating the presence of surfaces of unoxidized sulfide minerals.

Fluorspar is used in iron and steel manufacture in quantities of up to 10 kg/ton of steel. Limestone and dolomite are added to molten iron in the steelmaking process (fluxing) to bring impurities out into a slag phase. We synthetic chemists have an analogous situation with “rag layers” or emulsions. Near as I can tell, slag resembles lava in the sense that it is a molten silicate.

Metallurgists apparently have to provide conditions for extraction and phase separation of unwanted components in a melt. A slag phase may be rich in silicates among other things. According to references I have seen, fluorspar is added to the mix as a fluxing agent to “increase the fluidity” of the slag, which I interpret as causing a decrease the slag viscosity. Whether this is purely a rheological effect or also a sequestering effect is inclear at present to me.

Metals Odyssey

My efforts in finding a particular actinide mine today failed miserably. Apparently, gentrification and McMansion horse operations have restricted the only access road for rabble like myself. Looks like I’ll have to get actual permission to visit the site. I’ll be more forthcoming with the identity of the mine when I can get a first hand account and pictures.

I did find some interesting pegmatite veins elsewhere. Pegmatite intrusions (or zones) may be enriched in interesting metals like rare earths. My samples could just be feldspar, but the xtal habit seems different.

This is the problem with being an “independent scholar” in this field. If I want an ICPMS or GDMS to get a sub-ppm level elemental assay, I have to fork over ca $400 a pop to get some numbers. An XRD is only good down to ~1 % phase purity. I could find a real geologist to pester, but that wears out fast. Gotta find a way to get some analysis done economically.

I spent some time panning for placer gold in a creek downstream of Ward. It was a complete bust. I drove away with a backache and wet feet. There are no lode mines visible in that area, so perhaps the absence of gold was determined by others long ago.

Aspen Starting to Turn COlor September 2009

Aspen Starting to Turn Color September 2009

Day Trip to the Central City Mining District

The Central City mining district had its origin with the Pikes Peak gold rush. Placer gold deposits found in Denver area streams were quickly played out. Miners followed streams like Clear Creek up the canyon to their source, staking claims on the placer deposits in the streams along the way.  Eventually, the placer deposits played out causing miners to search for the lode deposits along the hillsides. Underground hardrock mining was the inevitable outcome of placer depletion.

The Pikes Peak gold rush began in 1859 and is named after the high  mountain peak that is visible from 100 miles into the eastern plains. While the immediate area of Pikes Peak produced little or no gold, it was a useful point of reference for arriving miners and settlers.

In many ways, the various gold rushes in American history are simply examples of economic bubbles 19th century style. The discovery of a resource that can generate substantial streams of cash will attract large numbers of wealth seekers. Not surprisingly, chance favored the early arrivals in the bubble. Many a weary participant gave up, hoping only to break even. Others realize that there is more stability in providing supplies and services to the miners.

Abandoned Mill Near Central City, CO (Copyright 2009, all rights reserved)

Abandoned Mill Workings Along Russell Gulch Road (Copyright 2009, all rights reserved)

While mineshafts, adits, and tailings piles still mark the landscape in most mining districts, what has been lost for the most part are the mills. The photo above shows the remains of a mill operation between Central City and Russell Gulch. Mills were a crucial link in the generation of wealth from mining activity.

Mill Along Russell Gulch Road

Mill Along Russell Gulch Road

Mills were constructed near the richer lodes and were configured in various ways. Some processing buildings were built along the hillside and early mills had chutes with which to convey material  within the facility. Later mills had conveyors to transport materials.

Remnant of Surface Workings, Central City, CO (Copyright 2009, all rights reserved)

Remnant of Surface Workings, Central City, CO (Copyright 2009, all rights reserved)

Cominution was a key operation of the mill. Large rocks had to be reduced in size to expose greater surface area for value extraction. Stamp mills were very common and consisted of a powered camshaft that lifted and dropped a train of heavy cylindrical hammers on the ore. The output of the stamp mill was treated in various ways depending on the nature of the gold bearing ore.

Gold ore near the surface might be of a more highly oxidized nature from exposure to oxygen entrained in meteoric water. In that case, sulfur would have already leached from the formation leaving a higher level of metallic gold. Such ore was more amenable to extraction by amalgamation. Stamp mills could be constructed with mercury covered copper plates on the output side of the stamps. The mercury would amalgamate the gold particles from the mill feed, selectively trapping them on the plate. The amalgam would then be scraped off the plates and the mercury removed by the application of heat to evaporate the mercury. 

Gold ore from deeper deposits resisted direct amalgamation, however, and roasting was used to free the sulfur (and tellurium) from the value. Highly sulfurized ores would be roasted to liberate the gold from the sulfur in the matrix. The resulting calcined ore might be milled or just subject to mechanical agitation to dislodge the gold particles in a sluice or by amalgamation (source- discussions with mining museum people. I would like to find better documentation, however).

The extent to which amalgamation was used in gold recovery is largely forgotten or left unmentioned. The USGS has excellent documentation on this topic.  Chlorination by the application of Cl2 and cyanide extraction were introduced by the end of the 19th century as well, but that will be the topic of another post.

The folded rock in the photo below is shown only because it is visually interesting. Note how the various layers show signs of differential erosion. Nothing astonishing, just a reminder that seemingly ordinary things can be very interesting if one stops to have a look.

I’m going to get hit by a car one of these days from stopping at roadcuts. I can only hope it is over fast.

Folded Rock Formation , Roadcut on CO 119 near Blackhawk

Folded Rock Formation, Roadcut on CO 119 near Blackhawk

Manganese on my mind

I spent much of the weekend reading up on, of all things, manganese chemistry. It turns out that there is a tourist mine in Salida, Colorado, that offers a glimpse of a manganese mine. It is rather dramatically called the Lost Mine and the tour includes a 4WD ride to the site. This tour is on the master list of future visits – my teenage kid groaned when I let this news slip out. Pretty funny.

What piqued my interest is a rock I picked up at a rockshop in Leadville recently. It is a low grade sample of dispersed rhodochrosite with a bit of pyrite grown into it. Rhodochrosite is a light pink to rose colored semi-precious crystalline mineral and also happens to be the state mineral of Colorado. It is fairly scarce and increasingly sought after for collection and for jewelry.

The light pinkish color of rhodochrosite stems from the oxidation state of Mn- Rhodochrosite is MnCO3. Depending on the ligand, the Mn (II) will have a high spin d5 electron configuration. The high spin d5 configuration requires a forbidden electron transition consisting of a jump between d orbitals and a spin flip on absorption of hv. Since this is a low probablility occurance, the molar extinction is low and accordingly, the color of the xtal is faint.

A fellow at the CC&V mine lamented that the ore body they process for heap extraction is loaded with manganese. He said that once they move the rock from the pit, the Mn levels cause it to become a pollutant (or some other term) as defined by the EPA. Manganese seems to be relatively abundant in parts of the Rockies.