COLLECTING INVERTEBRATE FOSSILS ON PUBLIC (BLM) LAND

On March 30, 2009, the Paleontological Resources Preservation Act (PRPA) became law on lands managed by various agencies of the federal government.  The law had been through numerous drafts before approval by the US Congress and subsequent signing by President Obama.   Although in 1999 the Senate Interior Appropriations Subcommittee asked federal agencies to prepare a report on fossil resource management, most rockhounds, and many professional paleontologists, believed that any new regulations would be written to protect vertebrate fossils (in my opinion).  However, unbeknownst to most amateur fossil collectors, the United States Forest Service (USFS) published (May 23, 2013) draft regulations concerning the collection of invertebrate fossils and plant remains on land managed by the Agency.  The comment period was 60 days and the Agency received few legitimate (non-form letters) concerns.  Candidly, the proposal caught most rockhounds “off guard” and it was tough for rock and mineral clubs to organize informative responses. In my opinion, rockhounds lost many, many collecting privileges associated with invertebrate fossils as the proposed rules are now codified as 80 FR 21588. However, in defense of the USFS, the Agency was simply interpreting tenets of the PRPA, and that is the magic word, at least for me---interpretation.

In December 2016, proposed regulations for lands managed by the Department of Interior (Bureau of Land Management [BLM]; National Park Service [NPS]; Fish and Wildlife Service [FWS]; Bureau of Reclamation [BR]) were published in the Federal Register and became available for comments (received no later than February 6, 2017).  The proposed rule [of Interior] would address the management, collection, and curation of paleontological resources from federal lands using scientific principles and expertise, including collection in accordance with permits; curation in an approved repository; and maintenance of confidentiality of specific locality data.

Most of the proposed regulations (formally known as A Proposed Rule by the Land Management Bureau and the Fish and Wildlife Service on 12/07/2016), but specifically subparts A through H, applies to all four bureaus---BLM, FWS, BR, NPS. Parts A through H are also very similar, perhaps mostly identical, to current USFS regulations (80 FR 21588).  However, Part I of the proposed rules notes some differences  between Interior (BLM and BR) and the USFS regulations regarding actual field collecting of common fossil plants and invertebrates. I should also note that PRPA does not allow casual collecting in areas administered by NPS or FWS.

So, what are some of the proposed items in Interior’s new rules and regulations---hereafter known as the Rule?  I will only hit on a few sections as the proposed Rule, as published in the Federal Register, is tens of pages long.

The Rule does not impose additional requirements regarding fossil collecting activities on permitted lands associated with general mining or mineral laws.  It appears that if you have a permitted mining claim the fossil plants and invertebrates are fair game for any collecting (§ 49.15 …states that the proposed rule does not impose additional requirements on activities permitted under the general mining or mineral laws).  Does this mean that if you are mining sedimentary rocks for minerals (such as barite or uranium) that any and all invertebrates may be collected?  I don’t know; however, that seems to be a reasonable assumption to me.  But remember, my interpretation of various regulations and codifications found in the Federal Register may be subject to suspect.  I do know, however, that a mining claim will not be approved by an Agency simply to allow a person/company to collect fossils.  Any approved mining claim must include some sort of a commodity and fossils are not such.  

The mining claim section of the Rule is an interesting one.  Around this part of the country one permitted mining claim would create more surface disturbance, and could destroy more fossils, than all the Colorado rockhounds added together.  BLM and USFS manage multi-purpose lands; however, some activities are much higher on the pecking order than rockhounding.  

Fossils found in an archaeological context are archaeological resources, and are not considered paleontological resources.  It is always best to not disturb archaeological resources.

An authorized federal officer at BLM or USFS (the person in charge) may decide that specific rocks/minerals, such as coal, chalk beds, diatomites, etc. are not subject to PRPA rules as paleontological resources.  However, there are a myriad of other federal regulations that may protect them.

The Department of Interior has specific Agency regulations concerning the collection of petrified wood on their managed lands.  Petrified wood is managed as a paleontological resource when on or from lands administered by NPS, Reclamation, and FWS. On lands administered by BLM, petrified wood (defined by the Petrified Wood Act of 1962, Pub. L. 87-713, 76 Stat. 652, Sept. 28, 1962 as agatized, opalized, petrified, or silicified wood, or any material formed by the replacement of wood by silica or other matter, and identified as a mineral material under the Materials Act of 1947) is subject to commercial sale at 43 CFR part 3600 and free use regulations at 43 CFR part 3622. Therefore, on BLM lands, petrified wood may be managed as a paleontological resource, but the savings provisions in PRPA (16 U.S.C. 470aaa-10) prevent the imposition of additional restrictions on the sale or free use of petrified wood. When it is not subject to sale or free use, petrified wood on BLM-administered lands may be managed as a paleontological resource and/or under the authority of FLPMA.  My old and used mind fails to understand this latter statement!  Why would not all petrified wood collected on BLM-managed land be free use?

PRPA rules do not apply to “Indian lands.”  However, lands managed by Native Americans always have collecting rules so avoid trespassing.

A federal authorized officer may restrict access or close a collecting area at any time.  Therefore, fossil collecting on federal lands will now essentially involve a visit or call to an agency office.

Microfossils, such as foraminifera and radiolarians, are paleontological resources and are subject to collecting rules---except if you are drilling a permitted energy well.  The drilling bit may then grind up as many microfossils as the driller pleases.  Yes, that last sentence was cynical.

Most individual rockhound collecting of invertebrate and plant fossils (excluding petrified wood) falls under the definition of casual collecting; therefore, such individuals may collect on BLM lands that are not restricted or closed--lands such as BLM-administered national monuments would be closed. The Rule notes casual collectors may collect common invertebrate and common plant paleontological resources…casually. Common invertebrate and common plant paleontological resources are invertebrate or plant fossils that have been established by the bureaus, based on available scientific information and current professional standards, as having ordinary occurrence and wide-spread distribution. But, and there are many “buts” in the Rule, not all invertebrate or plant paleontological resources are common. When in doubt, collectors should err on the side of caution and collect only the resources that they know are common. In other words, pay a visit to an Agency to find out what fossils an officer has decided are “common.”

So, what is a casual collector as defined by the Rule?  Casual collecting means the collecting without a permit of a reasonable amount of common invertebrate or plant paleontological resources for non-commercial personal use, either by surface collection or the use of non-powered hand tools, resulting in only negligible disturbance to the Earth's surface or paleontological or other resources.  Although this seems a restrictive definition, it is much better than the USFS definition: causal collecting is generally happenstance without intentional planning or preparation…, the view of casual collecting as an activity that generally occurs by chance without planning or preparation.  The “good thing” about the Rule and the USFS regulations is that they clarify the allowance of collecting certain fossils from their managed lands.

But here are additional “buts” of the Rule.  The casual collector may only collect 25 pounds per day, not to exceed 100 pounds per year---and this weight includes matrix.  This part of the Rule was modified after the codified collecting rules long established for petrified wood; however, there is a big difference between specimens of petrified wood and invertebrate fossils.  Petrified wood is usually collected without matrix while many invertebrate fossils are collected with matrix. Rockhounds do not want to take a chance of breaking the specimen by chipping away the matrix in the field.  Collectors also may not pool a total weight with their buddy in order to collect larger specimens.  What does this mean for the collection of larger fossils weighing over 25 pounds?  I don’t know.  Perhaps it indicates a permit is required?  However, an issued permit requires a collector give up his/her specimen to a museum or repository!

Collectors also may not disturb over 1 square yard of the landscape, and your digging buddy must be at least ten feet away from your land disturbance.  I am uncertain if a collector may have several disturbances per day?  At any rate, like all good rockhounds, collectors must fill in their disturbance holes.

This restrictive regulation on land disturbance continues to be a problem for me.  If the BLM really wants to stop major land disturbance, then I suggest examining extensive disturbance by domestic livestock, off-trail ATV and OHV riders, and even off-trail mountain bikers and hikers (among others).  I support these multi-use land activities, in moderation, but simply want to point out that land disturbance by rockhounds is minimal compared to these other large-scale activities.   

Casually collected fossils may only be used in a personal collection and may not be sold, bartered, used for financial gain, or research!  I presume this section also means that club members may not use the collected common plants and animals in their club silent auctions.  What about gifting a common plant or invertebrate during a club gift exchange?  Does bartering mean that fossil interest groups may not trade collected fossil specimens?  I don’t have those answers.  But to me the interesting aspect of this tenet is that the casual collector may not use his/her collected fossils for research!  The federal agencies want the collector to get a permit if any of the fossils are used in a research project. I presume the point behind this requirement is to make certain that fossils in the research project are documented as to provenance and placed in an accredited repository.  However, I would like to suggest that any casually collected fossils could be turned voluntarily over to a repository before results of the research are reported.  A case in point---our rock club-sponsored Pebble Pups and Junior Scientists collect fossils and actually write up reports (sometimes published) and present results at meetings where abstracts are refereed.  How can an agency expect a group of Pebble Pubs to submit a permit application (see below)?

Another set of questions, then, involves the definition of research.  If a collector completes a study on a casually collected fossils and later presents information on such organisms at a rock/mineral club meeting---is this research?  What if the collector “publishes” results of their study in a club or federation newsletter, or on a Blog---is this research?  Questions to be answered.  I do not want some of these restrictive clauses in the Rule to stifle the interest of our children and young adults. 

As with the USFS regulations, the Rule requires that only hand tools may be used in collecting fossils.  These excavation tools may not be motorized and must be light and small enough to be hand-carried by one person.  Does this mean that my geological hammer may not be carried in my backpack, or must it be hand-carried?  Does it mean that I cannot bring along a two-wheel cart to pack a 25-pound specimen back to the vehicle (my knees will not allow carrying 25 pounds plus equipment)?  Luckily, Interior listened to criticism directed at USFS over their regulation about size of collecting tools-- but not large tools such as full-sized shovels or pick axes.  I don’t have any trouble carrying a full-size shovel in my hand!

Unfortunately, Interior chose not to rid the regulations of the permitting process for small groups of rockhounds.  I argued against this rule implemented by the USFS without success.  As I read the rules, and perhaps they are beyond my comprehension, it is my understanding that groups of rockhounds heading out to collect some invertebrate fossils must have a permit.  I can understand permitting a group of professionals going out to quarry a marine limestone looking for specific ammonites.  I cannot understand requiring a permit in order for a club’s fossil interest group, or a group of Pebble Pups, heading out on a beautiful fall afternoon to do some prospecting for fossils! If a group of Pebble Pups, some as young as six years old, go fossil hunting at a locality where both common and uncommon invertebrate fossils may be found, then a permit is required (as I try to understand the Rule).  For example, I can envision local localities, actually a number of old quarries, where there is a mixture of common and uncommon lower Paleozoic fossils represented.  These quarries have been prospected for years and rockhounds have almost always submitted their interesting specimens to museums and repositories.  However, the permitting process is a very onerous experience for “ordinary” rockhounds, so what happens?  Collection without a permit continues, with loss of interesting specimens heading to a museum due to a fear of prosecution, or collecting stops and children and adult rockhounds simply drop out.

Assume that a permitted fossil prospecting activity could be pulled off, please note that all prospectors must deposit their fossil finds in a designated repository.  Can you imagine taking kids on a fossil hunt and then taking away their finds?  In addition, the rules and regulations concerning report writing are onerous (for most rockhounds) and would require additional time. 

As a former classroom instructor, I could not imagine applying for a permit every time I took my students fossil hunting.  Certainly, a permit was required whenever a student researcher was out collecting fossils and describing stratigraphy---these collected fossils were deposited in a repository.  In fact, during my early days of writing environmental impact statements (fossils) for projects crossing federal lands I devised my own permits (with approval from the agencies) from items like logging permits.  I am not against permits; however, I simply want to allow for some slack with non-professional collectors.

In addition, mandating that all permitees must deposit their fossils in an approved repository creates other concerns since the requirements for establishing a repository are pretty stiff.  Most colleges and universities with a scientific staff have something, a museum or curated collection, that could qualify as a repository.  But what about the poor old group of rockhounds---would nearby repositories curate their specimens without monetary assistance (Permittee is responsible for the costs, monetary and otherwise, of the permitted activity, including fieldwork, data analysis, report preparation, curation of the collection and its associated records consistent with subpart C of this part)?  I don’t know.  Once fossils are collected under a permit they remain the property of the Agency in perpetuity.  Even if a federal authorized officer removes the collected fossils from the research collection the specimens still remain in repository collection ”somewhere.”

My comments pertain to only a small part of the Rule but are, in my opinion, most directly related to fossil collecting by rockhounds and other amateurs.  I want members of our rock and mineral clubs, including Pebble Pups and Junior Scientists, to have an opportunity to collect fossils without fear of “breaking the law.”  I want these members to have an opportunity to study and photograph and learn about specimens without fear their work is research and requires a permit.  I want members, especially younger members, to have an opportunity to present information at professional meetings about their fossils finds without fear their study requires a permit.  But, I would also expect the mentors of the collector to require fossil specimens be offered to a museum and/or repository along with appropriate provenance information.  I believe there must be some middle ground in this entire permitting and land disturbance issue.  If not, we may begin to lose generations of future STEM graduates that our nation badly needs.

With that said, please note that I have several friends and acquaintances working in the federal agencies.  In fact, I take pride in the fact that some Agency paleontologists were my students and we have remained friends for decades---they do excellent work.  In visiting with these paleontologists, I have found they are, in their opinion, constrained by federal law found in the PRPA.  Perhaps they are; however, I still believe in compromise and middle ground and “working things out.”  Is this possible with the rules in the PRPA?  I don’t know.  Could interpretation of PRPA regulations be less “strict.”  I don’t know.

What I do know is that these new laws (USFS) and the proposed Rule (Interior) are almost impossible to enforce---I am not advocating breaking the law but simply stating my strong opinion that collecting of invertebrate fossils on federal lands will go underground.  Unlike vertebrate fossils, where poachers are interested in selling their unlawfully collected specimens, rockhounds collecting invertebrate fossils are interested in building up a personal collection, trading specimens with club members, and perhaps most importantly helping young children and their schools build collections.  Also unlike the somewhat easily identified vertebrate fossils (yep, that is a dinosaur skull so leave it alone), invertebrate fossils are much more difficult to identify.   I am guessing that most rockhound amateurs will have great difficulty identifying uncommon fossils (need a permit) from common fossils (casual collecting).

So, what advice can I offer?  Take the time to read, or attempt to read, the Federal Register: https://www.federalregister.gov/documents/2016/12/07/2016-29244/paleontological-resources-preservation.    After this little chore, rockhounds should submit personal comments, or even pooled comments by several members of the club; however, it is best to not use form letters.  Also, remember as you comment:

• Provide first and last name, city, state, & country. All other fields of information are optional. Keep in mind that much of this information is publicly viewable.
• Comments may be typed in the box provided or they may be uploaded as attachments (Word docs or PDFs only).
• Comments may be brief or in-depth/well-researched. Comments with facts to support them are much more useful (e.g., examples of overlooked scenarios). Keep comments civil and straightforward. Comments using offensive terms, threats, or other inappropriate language will be disregarded.
• Comments on the proposed rule must be received by February 6, 2017. 

And finally, stop in Agency offices (especially BLM and USFS) and visit with the geologists—they are a nice group of people.  The paleontologists in both the USFS and the BLM are stationed few and far between.  But again, if you are in their area stop in and converse with them.   

Perhaps I am just a crusty old guy remembering “the good old days” of collecting.  But perhaps I am just an old guy seriously worried about the impact of the Rule (and USFS regulations) on school children, Pebble Pups, rockhounds, and interested amateurs.   I want to find a common ground with the USFS and Interior in the permitting processes, the land disturbance issues and the collecting limits.  Will it happen?  Another question that I cannot answer.

BLACK HILLS: TUFA vs. TRAVERTINE

Like most readers of this Blog, I often (always) peruse rock and mineral shops when visiting towns and cities across the nation.  This fall while camping in western South Dakota I paid a call to about all shops in the Black Hills.  Two of them had interesting and similar specimens with labels stating: 1) moss rock; and 2) coral rock.  Both rocks were labeled as collected from Cascade Springs.

Now that name brought back a flood of memories from days gone past.  I first visited the spring, located south of the city of Hot Springs, back in the mid-1960s while a student at the University of South Dakota.  I had several friends from the nearby small town of Edgemont and could tag along on their trips home.  I was first introduced to Cascade Springs in the form of lounging in the warm sun and sharing a few bottles of a cold adult beverage.  Later in life I visited the Springs on a field trip and even at a later time camped in a small tent in the area and watched the stars twinkle in a very dark sky.

At any rate, I might accept moss rock as an identification that could result in a sale to an unwary tourist, but coral rock is just basically an untruth.  All it takes is a couple of clicks on a computer to receive information that fresh water corals really do not exist in South Dakota.  Although I knew the answer to the rock identification question, I wanted relive some memories and so off we went to Cascade Springs (six miles to Cascade Springs; eight miles to Cascade Falls).

Although my mind may be used and a bit rusty, it certainly indicated “things” have changed since my last visit about three decades ago.  What I first noticed was the increase in vegetation around the Springs and the resulting stream outlet, especially the rather prominent displays of poison ivy.  I remember, at least my mind thinks it remembers, walking along the stream below the Springs without getting tangled in a mess of vegetation.  Today that is an impossible task.  Oh well, maybe that thought is true, maybe not!

Cascade Creek below the Springs. Note the massive vegetation along the edge.

Black Hills National Forest (BHNF) manages Cascade Springs as a natural area and picnic ground and per the Agency (see References) there are several rare plants growing near the springs: These species include “tulip gentian (Eustoma grandiflorum), beaked spikerush (Eleocharis rostellata), southern maidenhair fern (Adiantum capillus-veneris), and stream orchid (Epipactis gigantea).”  The plants like the availability of open water during all four seasons as the discharge temperature is a constant 67ºF---not a hot spring, as most people would testify, but not a cold one either.  However, most articles I read would characterize 67º as “warm water” and above the ambient air temperature.  The BHNF pegs its discharge rate as ~22.5 cubic feet per second, the largest spring(s) in the Black Hills.  The Springs emerge from six different outlets, now covered with rock debris and gravel, and water is captured in a concrete pool before wandering downstream in the newly formed Cascade Creek. Ultimately Cascade Creek reaches the local base level, the Cheyenne River above Angostura Reservoir. The Springs release water from the Paleozoic Madison Limestone (aka Pahasapa Limestone of Mississippian age) and the Minnelusa Formation (limestone of Pennsylvanian-Permian age), both common aquifers (collectively known as the carbonate aquifer) in the region and a source of springs, both hot and cool/ambient, in South Dakota, Wyoming and Montana.  Or, the Springs could issue from the contact of the Minnekahta Limestone [Permian age] and the Spearfish Formation [an aquitard shale of Permian-Triassic age], or from the contact of the Minnelusa and Opeche formations (a possible aquitard between the Minnekahta and Minnelusa formations).  The Minnekahta is sometimes included in the term “carbonate aquifer” noted above. 

A stratigraphic section showing aquifer units around the southern Black Hills.  Section courtesy of Gries (2009).

Ford and others (1996) opinion is that rainwater passing through surface soil horizons picks up calcium carbonate that mixes with the aquifer water and travels through the karstic solution cavities to emerge at springs or streams.  The biogenic activities in the soil horizons have high levels of calcium bicarbonate.

Tufa collected from Cascade Falls during a personal outing decades ago!  Note longitudinal views of plant debris (tubes) weathered out of specimen.  Note porous nature of tufa as compared to travertine pictured below.  Width of specimen ~13 cm.

Collecting pool for Cascade Springs.

Casts (the tubes) of plant debris in tufa from Cascade Falls. See longitudinal view in photo above. Diameter of tubes ~1-2 mm. 

Cascade Falls September 2016.

Cascade Falls ca 1930s.  Original postcard owned by, and courtesy of, www.neplains.com.

Cartoon showing tufa formation at Cascade Falls.  The water drops off a hard ledge of sandstone and then scours out a basin in the Skull Creek Shale.  Personal observation plus information derived from Ray and Rahn (1997).

Downstream two miles from Cascade Springs is Cascade Falls, one of the more famous “swimming holes“ in South Dakota, and the site of  several tufa layers.  It was always my impression that tufa was a calcium carbonate (CaCO₃) deposited in cool water situations as opposed to travertine (also a calcium carbonate) that forms in a warm to hot water environment.  Tufa generally is found attached to plants or plant debris, is usually quite porous and forms a carbonate layer over the plant debris that later “rots away” leaving behind tufa casts of the plants (and sometimes insects, vertebrates and mollusks).

This description of tufa and travertine has resided in my mind for decades but now was prodding my senses with a question—what is the temperature that distinguishes the formation of tufa from the formation of travertine? So, off I go to try and find the answer.

Travertine "terraces" produced by hot water springs at Hot Springs State Park, Wyoming.  See Blog posting May 13, 2011.

Ford and Pedley (1996) and Capezzuoli and others (2013) noted that travertine and tufa were often used indiscriminately as alternative names for fresh water limestone.  One person’s tufa seemed to be another person’s travertine.  This seemed especially true as I delved into the literature and found both names used for the same stratigraphic outcrops.  Capezzuoli and others (2013) defined the term travertine: “continental carbonates mainly composed of calcium carbonate deposits produced from non-marine, supersaturated calcium bicarbonate-rich waters, typically hydrothermal in origin. Travertine deposits are characterized chiefly by high depositional rates, regular bedding and fine lamination, low porosity, low permeability and an inorganic crystalline fabric. Bacteria and cyanophytes [photosynthetic bacteria] typically are the only associated organic constituents, due to the presence of unsuitable factors (for example, high temperature, high rates of deposition, pH and sulphur) for plant and tree growth (macrophytes). Aragonite rather than calcite may also be present… Such deposits are typical of tectonically active areas where geothermal heat flux (endogenic or volcanic) is high [generally higher than ~86º].”

Banded travertine collected from the Mayer "onyx" quarry in northern Arizona. Note compact nature of travertine and compare with photo of tufa above. See Blog posting March 20, 2015.

Tufa refers to “continental carbonates, composed dominantly of calcite and typical of karstic areas. These are typically produced from ambient temperature [generally less than ~68º], calcium bicarbonate-rich waters which are characterized by relatively low depositional rates producing highly porous bodies with poor bedding and lenticular profiles, but containing abundant remains of microphytes and macrophytes, invertebrates and bacteria. Secondary carbonate deposits (cements and speleothems) may also be associated. Aragonite is usually absent (except from peculiar high Mg/Ca ratio spring waters.”

It appears, then, that travertine does form in warm to hot waters heated by geothermal mechanisms, has a high rate of deposition, has low porosity and permeability, and does not contain the plant debris common in tufa.  Tufa forms in areas where ground water has traveled through rocks rich in calcium bicarbonate via fractures and caves [karstic], has poor bedding features, and contains plant and bacterial (“algal”) debris.  In addition, travertine often forms as mounds and terraces while tufa is often found in stream cascades and dams.

The water from Cascade Springs has its original source percolating through soil horizons over a wide area in the southern Black Hills and then traveling through the karstic cavities of the carbonate aquifer and therefore has a dissolved CO₂ content much higher than the local atmosphere. The turbulence created by CO₂-rich water flowing over the Falls degasses the dissolved CO₂, the water chemistry equilibrium is messed up (CO₂ level drops), and precipitation of tufa (CaCO₃) takes place. I have not seen studies on Cascade Creek but in a “normal” situation after degassing and precipitation, the pH of the stream water decreases and the acidity increases.  I presumed since the water at Cascade Springs was saturated with CO₂ that the pH would strongly basic; however, Lund (2016) noted the pH was neutral at 7.0.  But again, I am far from a water chemist.

At Cascade Falls the actual waterfall started as Cascade Creek flowed over a ledge of an indurated Cretaceous sandstone, the Newcastle Sandstone.  With this turbulence of the CO₂-rich water, tufa began to form on the Newcastle and actually raised the height of the Falls.  Cascade Falls has been around for a long time since the terrace levels above the stream are composed of tufa.  I suppose this signals that Cascade Creek meandered over the valley in the geological past and CO₂-rich water degassed and forced calcium carbonate out of solution as solid CaCO_3.  Visitors can easily see the tufa at the Falls while an observant eye can locate tufa on the stream terraces. I presume this is the collecting area for the moss rock and coral rock displayed in the shops.

Tufa forming at Cascade Falls.

Why is travertine absent at Cascade Springs? Evidently, there does not seem to be a source in the immediate area that would supply heat to the aquifers in the Paleozoic limestones.  However, a few miles away the city of Hot Springs was named for their warm spring water (something like 8-9 warm/hot springs) and became an early soaking spa and advertised “disease-curing” resort.  The Mammoth Hotel and Bath House was built in the late 1880s and their spring water was ~90ºF (Lund, 2016).  For many years one of the top attractions in Hot Springs has been a large constructed swimming pool known as Evans Plunge that is fed by 87ºF springs that release about 11+ cubic feet per second.  So, why the presence of hot/warm springs at Hot Springs?  Rahn and Gries (1973), in their extensive study of large springs in the Black Hills, could not answer that question with certainty.  Their first “supposition” was heat supplied by the earth’s normal geothermal gradient; however, their studies concluded that “the unusually warm springs near the town of Hot Springs are too warm to be explained by the normal geothermal gradient.”  So, what about their other possibilities: 1) magma or some intrusive body may lie at a shallow depth under Hot Springs; however, there is little evidence for that possibility; 2) the ground water could be warmed by chemical weathering reactions of the water flowing through the rocks.  This mechanism seemed a good possibility; 3) the ground water may have been heated by radioactive decay in nearby rocks.  Locally the community of Provo had a flowing artesian well where water was about 139ºF and was evidently heated by decay of radioactive minerals.  However, the thermal waters at Hot Springs are not very radioactive; 4) Precambrian rocks under the town may have created a higher geothermal gradient.  This may be possible but not probable.  In studying their publication, I really don’t believe Rahn and Gries found a reasonable (at least one they believed in) mechanism to answer the heat question and I have been unable to locate in the literature other possible heat sources.  The best that I could come up with was to note that several deep wells in the Madison (across South Dakota, North Dakota and Wyoming) have elevated water temperatures!

One of the early resorts in Hot Springs, the Hotel Minnekahta.  Photo is from the Library of Congress collection and was taken by John Grabill ca. 1890.  

One can find travertine, or tufa, in the city of Hot Springs since it serves as a cement for the prominent beds of conglomerate along the Fall River.  In reference to the conglomerate, Gries (2009) stated that “at some time in the past, probably in late Pleistocene time, clay and gravel partly choked the [Fall River] canyon.  Then calcium carbonate, precipitated from the warm spring water, cemented them into solid rock.”  Is this travertine or tufa?   I was unable to identify with visual examination; however, the 87º water at Evans Plunge would suggest travertine.  Whatever the case, Rahn and Gries (1973) map of spring temperatures in the Black Hills has a nice anomalous, hot/warm, birdseye perched right on Hot Springs.

It seems as everyone in Hot Springs calls this "The Waterfall."  I am uncertain of the name or the source of the warm water.  Perhaps it comes from a spring above? Travertine is forming on rocks behind the falls. The cemented conglomerate is what caught my eye.

In contrast to the southern hot/warm springs the remainder of springs in the Black Hills are in the 40ºs-50ºs F range (Rahn and Gries, 1973).  One particular spring of interest is found about three miles above the junction (near community of Savoy) of Little Spearfish Creek and Spearfish Creek.  Here a spring in the Madison Limestone (aka Pahasapa) releases about 13 cubic feet per second of CO₂-rich water into Little Spearfish Creek. Little Spearfish Creek rapidly flows east toward its merger with Spearfish Creek but soon encounters a hard dolomite bed of the Ordovician Whitewood Dolomite, and thus, there is massive turbulence in the Creek and the saturated CO₂-rich water is degassed and tufa forms.  This feature is known as Roughlock Falls and is considered one of the more scenic spots in the Black Hills.  Again, the water is considered karstic in nature and flows through the quite porous Madison (Pahasapa) Limestone of Mississippian age. The water is “cold” but I could not locate an exact temperature but a nearby lodge owner told me the Falls freeze up in the winter.  It is interesting, at least to me, that the springs in the northern Hills seem cold water springs.  The northern Hills have numerous relatively young, ~50 Ma, igneous intrusions that would seem to be a good source of heat.  But then again, I am not a hard rock person or an aqueous geochemist or a hydrologist!

The upper falls at Roughlock Falls in Little Spearfish Canyon.  Note the heavy vegetation at the Falls and the formation of tufa where degassing of saturated water takes place.

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Old Postcard ca. ?? of upper and lower Roughlock Falls.  Even in the "olden days" the Falls attracted a massive amount of vegetation.

Cartoon showing how tufa forms on Roughlock falls.  Personal observation plus information derived from Ray and Rahn (1997).

Falls is the massive amount of vegetation growing along the Falls.  However, the Falls are managed by the South Dakota Parks and Recreation and they have built nice wooden platform viewing areas.  The area attracts numerous visitors wandering over from their drive up Spearfish Canyon.

I have not seen studies on South Dakota tufa and travertine but in other localities paleo-environmental studies have provided important information on climatic conditions at the time of deposition, as well as absolute dates---using carbon dating if the organic materially has not been biogenetically altered and is younger than about 50k.  Isotopic studies can help with absolute dates and often can provide information about climate at the time of deposition.  Since tufa contains plant material, at times vertebrate and arthropods fossils, as well as microfossil such as ostracods, scientists can use these fossils to articulate additional information about past environments.  For example, see Ollivier and others (2012).   But again, I have not observed environmental studies on travertine and tufa deposits in South Dakota.

REFERENCES CITED

Capezzuoli, E., A. Gandin, and M. Pedley, 2013, Decoding tufa and travertine (fresh water carbonates) in the sedimentary record: The state of the art; Sedimentology, v. 61, no. 1.

Ford, T.D. and H.M. Pedley, 1996, A review of tufa and travertine deposits of the world: Earth Science Reviews, v. 41.

Gries, J.P., 1996, Roadside Geology of South Dakota: Mountain Press Publishing Company, Missoula.

Lund, J., 1997, Hot Springs, South Dakota: Oregon Institute of Technology Geo-Heat Center Quarterly Bulletin v.18, no. 4.

Ollivier, V., P. Roiron, S. Nahapetyan, S. Joannin, and C. Chataigner, 2012, Tufa and travertine of the Lesser Caucasus: a light on the Quaternary palaeoenvironment of the Circumcaspian regions: Geophysical Research Abstracts v. 14, EGU2012-2124.

Rahn, P. H., and J. P. Gries, 1973, Large springs in the Black Hills, South Dakota and Wyoming: South Dakota Geological Survey, Report of Investigations 107.

Ray, C.M. and P.H. Rahn, 1997, The origin of waterfalls in the Black Hills, South Dakota:  Proceedings of the South Dakota Academy of Science, v. 76.

USNFS: www.fs.fed.us/wildflowers/regions/Rocky_Mountain/CascadeSprings/index.shtml

For a great story about the “old” resort town of Cascade: “Of all the “ghost towns” in South Dakota, the grandest one may have been Cascade, sometimes referred to as Cascade Springs because of the nearby hot springs. Back in 1892, its heyday, the town had about 400 people and 50 businesses, including a hotel, a sanatorium and a bowling alley.”  See http://www.capjournal.com/news/dakota-life-the-life-and-death-of-cascade/article_212d861a-2ebe-11e6-876d-e7d8d36ea850.html

SCAPOLITE: A SORT OF FORGOTTEN MINERAL

Why should things be easy to understand?

Thomas Pynchon

Scapolite is one of those minerals that sort of rings a bell somewhere in the recesses of your mind; however, you cannot quite pinpoint the location! About the only thing that finally surfaced in my mind came from basic mineralogy and pointed out that scapolite is usually an alteration product of feldspar (which one?), and is a metamorphic mineral (which facies?)!  I sort of left it at that point until a few years ago when I saw some beautiful faceted gemstones labeled “scapolite.”  Perhaps my mineralogy factoids were a figment of my imagination for those faceted gems looked nothing like some less-than-spectacular specimens I remembered from class.  

Perhaps I could forgive my mind since I was a third-year college student trying to reconcile memorizing mineral crystal systems with understanding the bombing of the 16^th Street Baptist Church in Birmingham and the assassination of President Kennedy in Dallas.  In fact, the assassination of Kennedy is one of those moments in history that persons of my age have imprinted on their minds--- I was heading to Mineralogy class!  Why did the crystal systems matter when young girls and presidents were being murdered?  I guess the short answer is that I did not want to return to my home town and work in my father’s gasoline station.  And then, there were rumors about “goings-on” in southeast Asia with the military draft picking up and men of my age learning a new trade.  So, back to learning about Monoclinic and Hexagonal minerals (and I never really understood the Systems and became a paleontologist).  And, scapolite became lost!

Age is an issue of mind over matter.  If you don’t mind, it doesn’t matter.

Mark Twain 

Scapolite reappeared in my mind back in 2012 when I was working on a post describing idocrase/vesuvianite.  The latter mineral was named by the famous German mineralogist Abraham Gottlob Werner and an informal variety of scapolite is called werernite.  Long story---read the November 18, 2012 Blog posting.  At any rate, I then took scapolite from the back recesses and shoved it toward the front of my mind and four years later am finally getting around to describing some specimens that I picked up along the way!

Scapolite is a silicate but is not really an individual mineral!  It is a solid solution series between end members marialite (sodium chloride rich) and meionite (calcium carbonate rich): Na₄Al₃Si₉O₂₄Cl to Ca₄A_l6Si₆O₂₄CO₃.  The sodium and calcium are interchangeable with each other as are the chlorine and the carbonate radical, therefore leaving an infinite number of chemical compositions. In addition, the calcium may include some strontium while the sodium may include potassium. And SO₄ may substitute for some CO₃ (Evans and others, 1969).  It appears that “pure” end members never occur in nature so intermediate compositions are the norm; however, these intermediate members vary considerably in chemical composition and remain unnamed.  Members of the solid solution series are essentially indistinguishable (visual) from each other and therefore scapolite is simply used for all. 

Scapolite comes in a variety of spectral colors ranging from colorless to white and yellow, purple, blue, red, green, pink, brown, gray, orange and various mixed compositions.  However, all varieties have a white streak. The transparency ranges from completely opaque to translucent to completely transparent while the luster ranges from vitreous to dull and pearly.  As scapolite weathers to “mica” the luster becomes dull and the diaphaneity becomes opaque. The hardness of ~5.5-6.0 (Mohs) makes gemmy varieties more suitable for pendants rather than rings.  Scapolite crystals are Tetragonal and generally come in two distinct forms: short and fat, or long and prismatic.  Gemmy varieties are usually prismatic and commonly striated.  A couple of my specimens show masses of non-gemmy and opaque crystals.  Many times, crystals fluoresce under both short and long wave UV.

Scapolite is one of the few minerals that have a “square” cross-section that helps in identification.  Compare photos below of a weathered crystal from Monmouth Township, Ontario, Canada, with a crystal diagram from the Goldschmidt atlas and found on www.mindat.org and courtesy of www.smorf.nl.

Cross-sectional view of scapolite crystal, non-terminated, collected from Grenville Terrane near Bancroft, Ontario.  Note square shape of crystal and compare with sketch below.  Width of crystal ~1.6 cm; length ~2.3 cm. 

Crystal diagram of scapolite from the Goldschmidt atlas and found on www.mindat.org and courtesy of www.smorf.nl. Note square shape.

I thought scapolite was perhaps a mineral indicative of a specific metamorphic facies.  However, I have learned the “mineral” occurs in a variety of metamorphic conditions ranging from regionally metamorphosed schists and gneisses to higher temperature and pressure amphibolites and granulites (usually as an alteration of feldspar minerals and producing non-gemmy crystals).  In addition, scapolite, at times gemmy, is found in marble produced by contact metamorphism. At other times scapolite in these calc-silicate rocks contain inclusions of clinopyroxene, quartz, titanite and calcite (Ocean Drilling Program).   It is also found, at times, in pegmatites associated with contact metamorphism, and basalt ejected from volcanos.  I certainly am far from a mineralogist/petrologist but have spent numerous hours reading “lots of articles” concerning scapolite, and trying better to understand the chemistry and genesis.  I have somewhat failed in my understanding and concluded that it is a very complex mineral found in several different environments and is quite difficult to identify as to a specific mineral.

Just because we don't understand doesn't mean that the explanation doesn't exist.       Madeleine L’Engle

My collection includes two specimens composed of a non-gemmy mass of opaque crystals collected from around Bancroft, Ontario, Canada.  Also from near Bancroft is a single, squat weathered crystal. 

Above two photos are masses of opaque, non-gemmy scapolite crystals.  Note nice terminations on crystals with T pointer and nice square shape with SQ pointer..  Width FOV top ~4.0 cm, bottom ~4.3 cm.  Both specimens have tiny crystals of an amphibole (katnophorite/hornblende??) and ferroan phlogophite on reverse.

  

Map of proto-North America showing addition of crust (yellow) to continent in late Precambrian by plate collision tectonics (Grenville Orogen).  High temperature and pressure accompanies these collision events and creates large expanses of metamorphic rocks and allows for the formation of minerals like scapolite. Map from Karlstrom and others (1999).

The Bancroft area of Ontario, part of the Grenville Province, is thought to have been the margin of North America during the Proterozoic part of the Precambrian.  The rocks are composed of two tectonic elements: 1) high-grade gneisses that were part of the 1.7-1.4 Ga continental margin; and 2) a package of volcanic, plutonic, and sedimentary rocks that are thought to be a collage of arc components accreted at ca. 1.17 Ga (island arc material stuck onto the early continent by plate collision) (Keck Geology Consortium, 2011).

From the Dara-i-Pech pegmatite field, Chapa Dara District, Konar Province, Afghanistan, I have several small gemmy crystals lavender in color.  The crystals are prismatic in nature and have at least one terminated end.  The location of the crystal mine is in the northeastern part of the country where lower Paleozoic rocks are intruded by Cretaceous-Tertiary granite and granodiorite intrusions (creating contact metamorphism--cooking the limestone).   Due to political instability in Afghanistan, specifics about gemstone localities are difficult to ascertain.  

Nice gemmy scapolite crystals.  length of longest crystal is ~1.1 cm.

I also have a partial violet crystal from the Marble Occurrence, Morogoro Region, Uluguru Mountains, Tanzania.  As best that I can determine, the area is the site of plate collisions in the latest Precambrian.  Metamorphism and thrust faulting left small patches of marble on older rocks (Fritz and others 2009).  If you have the inclination to read about some really complex geology, check out the Fritz article!

Partial crystal of gemmy scapolite with undetermined inclusions.  maximum width of crystal ~1.1 cm.

And finally, I have a beautiful, free form cab of crystal-clear, gemmy scapolite collected from Espirito Santo, Brazil (along with a second specimen, a nice gemmy, prismatic crystal).  Espirito Santo is a coastal Brazilian state north of Rio de Janeiro and east of the famous mineral-producing state of Minas Gerais.  It was difficult to acquire much information about the area except that really gem quality aquamarines are mined from the Mimoso do Sul Mine.  The gem bearing rocks are latest Precambrian in age (100 Ga to 54 Ga) and seem related to the Aracuai Orogeny and include a wide variety of metamorphic rocks and igneous intrusions.  The Aracuai Orogeny added crustal rock to the local Brazilian Craton. I presume, but remain uncertain, that the gem scapolite came from some of the marble units.

Prismatic, gemmy, clear with yellow tint, scapolite crystal. Length ~3.0 cm.

Gemmy, clear with yellow tint, free-form cab of scapolite. The X is beneath the cab to show the transparent nature of the crystal (thickness 6 mm.).  Length ~2.3 cm.

So, when it comes to scapolite:  I don't think I'm old enough or experienced enough to give anyone any guidance. All I would like say is that as long as you're having fun, I think you're doing the right thing.                Sania Mirza

REFERENCES CITED

Evans, B.W., D.M. Shaw, and D.R. Haughton, 1969, Scapolite stoichiometry: Contributions to Mineralogy and Petrology, v. 24, issue 4.

Fritz, H., V. Tenczer, C. Hauzenberger, E. Wallbrecher and S. Muhongo, 2009, Hot granulite nappes—Tectonic styles and thermal evolution of the Proterozoic belts in East Africa: Tectonophysics, v. 477.

Karlstrom, K.E., S.S. Harlan, M.L. Williams, J. McLelland, J.W. Geissman, Karl-Inge Åhäll, 1999, Refining Rodinia: Geologic Evidence for the Australia–Western U.S. connection in the Proterozoic:  GSA Today, v. 9, No. 10.

Keck Geology Consortium, 2011, Anatomy of a mid-crustal suture: Geology of the Central Metasedimentary Belt boundary thrust zone, Grenville Province, Ontario:  http://www.keckgeology.org/2011-ontario-canada.

Ocean Drilling Program, Unknown date, Macroscopic description of calc-silicate rocks:  http://www.odp.tamu.edu/publications/161_SR/chap_18/c18_3.htm