Category Archives: Geology

Proterozoic Contact

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My search continued today for an exposed contact between the upthrusted proterozoic igneous rock of the Rock Mountains and the Fountain sandstone formation. I returned to an obscure roadcut site I had examined a few months ago. Three (male) cyclists outfitted in expensive cycling couture (Spandex) were standing there nibbling on dainty little energy snacks next to the spot I needed to be as I pulled up and exited my vehicle with a rock hammer in hand. One seemed taken aback momentarily as I walked towards them with the chisled masonry hammer. It didn’t dawn on me until after they left why they were acting strangely- I startled them. Sorry fellas!  \;-)

With rock hammer in hand I scrambled up a steep and unstable scree slope adjacent to what appeared to be disturbed layer next to a gneiss formation. Down below, along the roadcut, a contact was visible between the gneiss and what appeared to be schist.  This dark material has a preponderance of mica with little gross evidence of stratification. I wrongly concluded that I was not near the proterozoic contact.

But as I followed this discontinuity further up the mountain I found clear evidence of a stratified sedimentary formation adjacent to the igneous rock. On a ledge high above the road I found an actual contact between what appears to be modified sandstone and gneiss. I found a sample that has the gneiss fused onto the layered rock that fractures into thin sheets much like sandstone or shale. Regrettably, I left the camera in the Jeep.

What appears to have happened is that the sandstone layer has been thermally modified along the interface due to the intimate contact with the upthrusted igneous rock. I had half-expected to see a simple interface between sandstone and an igneous rock. Instead, what I seem to be seeing at this site is a modified sedimentary layer that shows evidence of some localized metamorphic modification.

A nearby thin layer of rock in the interface zone appears to be glassy or vitrified, as though it has been partially melted. I do not interpret this to be a result of weathering. A rapidly approaching lightning storm forced me to cut my exploration short and run for cover.

So, I have some hypotheses beginning to take shape. Now the question is, how do I falsify my interpretations? I certainly have much to learn about petrology.

Mineral deposits on other worlds

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As one begins to understand the manner in which mineralization and elemental concentration occurs as a result of terrestrial geology, it is only natural to wonder how this would occur on other worlds. On earth, the concentration of the elements in the form of mineral deposits is a partitioning phenomenon that benefits greatly from fractional crystallization, metamorphic modifications, and from a variety of transport mechanisms.

Fractional crystallization of magmas provides a condition whereby a mixture of simple and complex ions may associate to form mineral compositions that partition from the molten phase by virtue of high solidification temperature. In this way, solid, higher melting compositions precipitate from a melt sequentially, leading to the selective partition of certain combinations of elements into a new solid phase. The molten phase may be enriched in certain combinations of other elements by default- many of which may be relatively volatile.

The composition and cooling rate of the magma will determine the nature of the solid rock that is formed after cooling.  Over time, rock may be lifted toward the surface and subjected to modification by hydrothermal action or by erosion and redeposition by gravity. Cooled igneous rock may be subjected to crystalline modification by exposure to heat further down the timeline.

Hydrothermal water, superheated under high pressure, is a major force in the formation of mineral deposits. The sulfides (and hydrosulfides) of transition metals (i.e., Au) are thought to be transported from source rock through cracks, faults, and porous formations to be deposited in locations where transport can no longer be sustained. The accumulation of economic quantities of uranium are thought to be the result of hydrothermal or aqueous transport as well.

So here is the point of this essay–  If preconcentration of elements to viable deposits is critical for the success of value extraction on earth, what about mining on the moon or Mars? To what extent are we dependent on these mechanisms to make viable the mining and extraction of useful materials?  If lunar geology has not been quietly concentrating minerals in the manner to which we earthlings have been accustomed, how will we come to grips with using native materials on the moon for self-sustaining habitation?

It is one thing to find x ppm of oxygen or y ppm of titanium in the lunar regolith. It is quite another to enable extraction of critical elements from low-value (dilute) material. The chemical energy inputs for processing will be severely limited owing to the scarcity of reducing materials on the moon or Mars. Reducing materials are really just reservoirs of inexpensive and useful electrons. Reducing materials would include carbon or electropositive metals for the reductive winning of other metals. 

In the absence of an inexpensive supply of electrons, all phases of extraterrestrial mining and processing will be subject to large cost multipliers. Cheap electrons are required to energize machinery, move materials, or conduct refining. All of these familiar activities are energy intensive on earth and there is no reason to think it will be different on another world. On earth, cheap electrons come in the form of diesel and coal. On the moon and Mars, it seems likely that solar and nuclear will energize most work for those who try to set up camp there.

Beryllium Mining

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The aerial view above shows the location of the Brush Wellman beryllium mine near Spor Mountain, Utah. It is reportedly the only major beryllium mining operation in the USA and one of the very few economic beryllium ore locations in the world. The host materal is called “tuff”- a compacted and cemented volcanic ash composition. Coincident with this Be deposit is low grade uranium and fluorspar. Occurances of Cu, Au, and other base metals can be found in the area.

The concentration of Be in the ore body is thought to be due to the mineralization action of meteoric and hydrothermal fluids. The region is marked by the presence of 3 Oligocene-era calderas, with the Spor mountain Be mineralization found along the ring structure of the Thomas caldera.

The action of hot, saturated aqueous flows transporting solublized components from distant host bodies is one of the chief mechanisms for the appearance of “ore bodies” near the surface of the earth. Very often, such deposits are found in regions of faults and fractures of various kinds of rock formations. Mineral laden water follows the fracture system and, as it moves toward the surface, begins to cool and deposits the burden of now insoluble compounds. Deposition can occur due to simple solubility properties, redox from exposure to atmospheric oxygen, or via ion exchange with available chemical species to form high Ksp compositions.

This is nothing new to geologists who have been aware of these mechanisms for generations. But for a non-geochemical chemist like myself, the matter of how elements like beryllium come to be concentrated is less than familiar. Indeed, the question of how any element comes to be concentrated in rock formations is a question of increasing interest to Th’ Gaussling. I hope to spend a lot of time in the future exploring this matter.

The Cresson Vug

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The history of the Territory and State of Colorado is inextricably tied to base metals and precious metals. Gold and silver strikes were a big draw for the migration of population to Colorado from the 1859 Pikes Peak Gold Rush onward.  A map of the ore geology of Colorado reveals a few key districts or zones of enhanced mineral abundance. The Colorado Mineral Belt (CMB) is a band of ore deposits that are positioned diagonally across the middle of the mountainous part of the state, SW to NE, roughly from Durango to Boulder.

Other districts containing economically viable ore bodies exist outside of the CMB, notably the Thirtynine Mile Volcanic Field west of Colorado Springs. While rich deposits of gold were found near Central City and many other locations in the CMB, the relatively rare  gold/tellurium ore found near Cripple Creek and Victor on the periphery of the Thirtynine Mile Volcanic Field have provided approximately half of all the gold mined in Colorado. Gold has an affinity for tellurium and may be found combined with it in the form of the mineral calaverite.

In particular, the Cresson mine near Cripple Creek has been an especially rich producer of gold. In November of 1914, a 4 m x 8 m x 13 m cavity or “vug” at the 1200 ‘ level was found to be lined with gold telluride and other minerals.  Depending on which source you believe, it is reported that from 20,000 to 60,000 ounces of gold were removed from this small space.

The Cripple Creek volcanic complex is a highly altered, highly brecciated formation that has been described in detail elsewhere. The link provides a more detailed description and a bibliography.

Links updated 7/2/19.

A Nevada Cinder Cone

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Whilst doing a survey of Lithium mining in North America, I blundered into a small cinder cone. It is found in the Clayton Valley of western Nevada south and west of Tonopah.

A link from the University of Nevada, Reno, gives some details on this cone as well as some interesting photographs.

Just to the south of this cinder cone is the Chemetall Foote Corporation Silver Peak brine facility. Lithium rich brines are pumped into evaporation ponds for concentration of the lithium salts. US 7390466 says that the Silver Peak brines contain 0.02 wt % Li.  The richest Li brine can be found in the Salar de Atacama brines in Chile. The Atacama brines contain from 0.15 to 0.193 wt % Li.

Redoubt Volcano Continues to Show Activity

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The Redoubt volcano is making its presence known. It has played havoc with some petroleum infrastructure (Drift River Oil Terminal) and has begun to dump ash. Lahar activity has flooded a runway and generally made a mess. The photos below do not show the volcano in a major eruption. Most of the AVO/USGS close up shots seem to be taken when the mountain is quiet.

Mud & debris flows from Redoubt (Photo AVO/USGS)

Mud & debris flows from Redoubt (Photo AVO/USGS)

North Flank of Redoubt 1-31-09 (Photo AVO/USGS)

North Flank of Redoubt 1-31-09 (Photo AVO/USGS)

Redoubt Eruption Plume from MTSAT (photo National Weather Service)

Redoubt Eruption Plume from MTSAT (photo National Weather Service)

Redoubt Fumaroles 1-31-09 (Photo AVO/USGS)
Redoubt Fumaroles 1-31-09 (Photo AVO/USGS)

For detailed information on the Redoubt Volcano and it’s ashfalls and other activity, click to the Alaska Volcano Observatory (AVO).

Carlsbad Caverns

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Carlsbad Cave Popcorn

Carlsbad Cave Popcorn

The problem with Carlsbad Caverns today is the same problem that plagued it from the very beginning- it is very isolated and is not even on the way to many other places of major interest (except El Paso, of course). For the first 20 years or so, the cavern was primarily a source of bat guano fertilizer for the California citrus orchards. Slowly, and with the persistance of a few key individuals, word of this wondrous underground cathedral spread.

Today, Carlsbad Caverns is visited by approximately 500,000 people per year. The cavern is in remarkably good shape considering the large number of people who walk the several miles of underground trails 364 days per year.  Curiously, one of the big pollution concerns is lint from the clothing of shuffling visitors which settles on the formations.

The above photo is a snapshot of a common evaporite formation referred to as cave popcorn. The box in the photo encloses an area about the size of the palm of your hand and if you look closely, you can see water droplets clinging to the small mineral protuberances.  The colors in the photo are a good representation of most of the cavern.

Entrance to Carlsbad Caverns

Entrance to Carlsbad Caverns

The decorated caverns are the result of several kinds of chemical processes. The internal spaces were dissolved out of the regional limestone formation. This formation is thought to be the remnant of an ancient reef. It is believed that aqueous hydrogen sulfide migrated up from the anaerobic permian formations below and was subsequently (air) oxidized to more corrosive species.

The park people point out that H2S was oxidized to sulfuric acid which is responsible for the chemical digestion of the limestone. Sounds reasonable to me, though the chemistry of sulfur oxidation is full of many kinds of intermediary species on the way from sulfide to sulfate. The presence of gypsum (calcium sulfate) inside the cavern supports the claim that sulfuric acid was the corrosive agent. What was not mentioned was whether or not sulfate is found in the surrounding formations. [Note: a commenter made a good point about the bio-oxidation of sulfide]

Stalactites festooned with cave popcorn, Kings Palace caves, Carlsbad Caverns

Stalactites festooned with cave popcorn, Kings Palace caves, Carlsbad Caverns

The decoration of the interior spaces left by digestion of the limestone happened by the action of seepage of rainwater and carbonic acid though the upper layers of sedimentary rock. The water dissolves many mineral components including calcium. The calcium carbonate rich liquors seeping in from the roof of the caverns wetted the surfaces below and deposited calcite and other mineral species by way of intermittant accretion.

If you examine the few smaller and broken mineralizations along the trail, you can clearly see that the accretion results in substantially crystalline material. So, while the formations are not large calcite or aragonite crystals, the small scale structure is crystalline.

There is much to see in the world if you just bother to look. Along I-25 in southern Colorado is a modest looking feature. It is called Huerfano Butte and sits along the highway near Walsenburg. This igneous intrusion is more resilient to weathering than the surrounding sedimentary formations.  Radiating from the nearby Spanish Peaks are an array of dikes indicating the presence of past magma intrusion.

Huerfano Butte- a weathered igneous intrusion.
Huerfano Butte- a weathered igneous intrusion.

An synthetic chemist is in a great position to absorb some geochemistry. Once one is keyed into a bit of geology, the mechanisms of mineral formation begin to become apparent, with a little study of course. For myself, this is a great motivation to kick around in the weeds and explore the world. Gotta watch out for rattle snakes, though.

Gold Refining with Borax

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According to the GEUS, the Geological Survey Office of Denmark and Greenland, it is possible to concentrate and isolate gold from the ore using borax and charcoal. This method has the immediate benefit of making mercury “redundant” in gold isolation.

Extraction of gold by amalgamation with mercury is a simple means of producing metallic gold in the field.  After contact with gold enriched ore, mercury is evaporated into the air by direct application of a torch flame to the puddle of metal leaving purified gold metal.

It is thought that there are millions of miners who scratch out a subsistance living working a small patch of ground for gold. It’s called small scale mining. In the course of this activity, environmental contamination can accrue to the immediate area as well as the watershed at large. Sadly, the toxicological insult to the miners from exposure to mercury vapor can be severe.

This method is an inexpensive and simple alternative to the mercury process. Perhaps the chemistry community has something to contribute by way of education or improved methods of extraction.

8/25/10  Update.  I have revisited this post and am compelled to comment further.  While I am unable to offer a good chemical explanation for the effect of borax on gold ore, I can say that the use of borax as a flux  for smelting goes back to the 19th century during the American gold rush period.  The process described in the link appears to be a smelting process for enriched ore containing elemental gold, as opposed to sulfide, or sulphuretted ore. The function of a flux is to modify the flow and phase separation properties of host rock so as to partition away from the gold phase or layer.  In other words, a flux modifieds the slag to help the gold to separate cleanly from the rock.

It’s the Schist and a Lot More

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The Front Range of Colorado is roughly comprised of those mountains that can be seen from the eastern plains. There is no precise definition that I am aware of, so this will have to do. 

Superficially, these mountains run north/south and appear to be organized into ranges, which are really just a series of roughly parallel ridge structures punctuated with the occasional high points that are refered to as peaks. The origin and orientation of these ranges is defined by the orientation of faults and with the effect of eons of erosion to form river channels. Erosion has the effect of removing the weakest materials and leaving behind the most resistant rock structures.

The present epoch of the Rocky Mountains are the result of the Laramide Orogeny, the most recent period of mountain building thought to have begun 70-80 million years ago in the late Cretaceous period. The cause of this mountain building episode is attributed to a shallow angle of subduction of the Kula and Farallon plates below the western margin of the North American plate.

Geologists propose that the shallow subducting slab of ocean bottom applied a drag on the root of overlying continental lithosphere. These forces lead to the broad belt of disturbance to the overlying rock leading to the formation of the Rocky Mountains.

As mountian building proceeded, overlying sedimentary formations were bent and fractured along the margins of the upward moving rock. Today these sedimentary formations are visible in the form of ridges of protruding lamanellar sandstone, mudstone, and shales whose surface planes sit at a high angle  relative to the horizon. The uppermost sedimentary formations are exposed further east in the plains, and as one moves a few miles closer to the mountains, the deeper and correspondingly older sedimentary formations are exposed. These parallel ridges of exposed, upthrusted sedimentary formations are collectively referred to as “foothills”.

Along much of the northern Colorado front range, the westernmost sedimentary formation that abutts the metamorphic rock is called the Fountain formation. Adjacent to this upthrust of metamorphic rock is a layer of disturbed Fountain formation that has been drug upwards to a near vertical orientation. If you have been to Boulder, Colorado, and have seen the Flatirons, you have seen the Fountain formation. Red Rocks Amphitheater and the Garden of the Gods are also part of the Fountain formation.

Here is my question- Somewhere, there should be an interface (I think geologists call it an unconformity) between the metamorphic and sedimentary formations. Where can it be inspected? A road cut or riverbed?

So, it turns out that Th’ Gaussling’s brother owns a spread that is comprised of Fountan formation sandstone. He has a mountain. And down from this mountain and into his yard come elk, deer, mountain lions, bear, and rattle snakes. One of his house cats, in fact, was last seen in the jaws of a cannibalistic mountain lion trotting off to a quiet spot to munch this fresh, tender kitty morsel.

To satisfy my curiosity about this interface, Th’ Gaussling was out in the brush scrambling over snow covered rocks, cactus, and yucca looking at examples of the Fountain formation and, nearby, a formation comprised of schist and gneiss. Not surprisingly, I did not find it in a single outing. But I was close- it’s buried in deep rubble, no doubt. The hunt continues.

Redoubt’s Rumbling Redux

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The Redoubt volcano along the Cook inlet in Alaska is showing seismic activity according to the Alaska Volcanic Observatory (AVO). Seismic activity may be a precursor to eruption. Dedicated seismic recorders show frequent bursts of activity on the volcano.  The USGS has a website with advice and information aimed at helping people cope with an ashfall. 

In the past, the prevailing winds have carried the ashfall in an easterly direction over and past Anchorage. According to AVO, Redoubt is a stratovolcano located several hundred km west of Anchorage. It has reportedly erupted explosively six times since 1778, with the most recent being in 1989-90.

Note to Wal-Mart:  You may want to stock up the anchorage stores with extra brooms and shopvacs.