GONIOBASIS SPHERE

A HAND-MADE SPHERE OF GONIOBASIS IN MICROCRYSTALLINE QUARTZ FROM THE GREEN RIVER FORMATION, SOUTHWESTERN WYOMING.  THE TWO "BRIGHT" SPOTS ARE REFLECTIONS FROM THE LIGHT SOURCE.  THE WIDTH OF THE SPHERE IS ~8.75 CM.

At the recent AFMS show in Minnesota, I noticed a number of specimens labeled “Turritella Agate” that were offered for sale.  I always sort of flinch when I see that term since the specimens are not agate (in the true sense of agate being banded or included), and second, the fossils contained are not the gastropod (snail) genus Turritella ( a marine form).  But, I have come to sort of accept the term since the name “turritella agate” is well entrenched in the rock and mineral literature, and certainly specimens are sold as such in hundreds of rock shops and shows.

The “turritella agates” at the AFMS show were collected from southwestern Wyoming in the Green River Basin at a locality termed the Delaney Rim.  The Green River Basin was the site of a large freshwater lake during the Eocene Period of the Tertiary (34 my—60 my) termed Lake Gosiute, a body of water that teamed with life—including millions of high-spired snails of the genus Goniobasis or Elimia. 

It appears that the term “turritella agate” is here to stay in the rock and mineral trade.  However, savvy rock hounds will know that the snail is not Turritella and that the mineral is really not a banded agate (but is a microcrystalline quartz).  Whatever the case, a nice polished specimen is a wonderful addition to any collection.  I acquired my sphere from a close friend in Salt Lake City, Jim Madsen (now deceased).

SOUTH PARK: MAMMILLARY CHALCEDONY

A BEAUTIFUL AND QUITE LARGE (PENNY FOR SCALE) PIECE OF MAMMILLARY CHALCEDONY.

On a sunny morning last week I woke up with a thought about mowing the lawn, not an activity I really cherish.  But then some words of Walt Whitman jumped into my mind: I believe a leaf of grass is no less than the journey-work of the stars.  So, I reasoned that no person would want to destroy the work of stars and therefore a field excursion/road trip was in order!  Where to?  How about South Park?  Grabbing a large black coffee and a friend, off we went  for a day of mineral hunting with an another friend acting as a “private guide”.  There are a couple of great “things” about South Park: 1) good morning coffee, second cup for me,  and after-hunting ice cream may be found at the Bayou Salado store in Hartsel; and 2) there are some really interesting microcrystalline quartz varieties available, including petrified wood and colored chalcedony.  In addition to the coffee/ice cream, Dave and Lark at the store might give you a hint about collecting, or sell you some of their minerals or handmade jewelry.

South Park is both a topographic and structural basin, and along with North Park and Middle Park, owe their existence to the major mountain building event in the area, the Laramide Orogeny (late Cretaceous to Eocene).  Generally termed Intermontane Basins, North, Middle and South Parks are large synclinal basins complimenting the large anticlinal mountain ranges surrounding them.  

The eastern boundary of South Park is the Front Range (and its numerous subdivisions) and that demarcation is generally a large thrust fault (Elkhorn Fault).  In some localities along the eastern edge of the basin the Precambrian rocks of the mountains have been thrust about seven miles over the basin rocks (McGookey, 2003).  The western boundary of the basin is the Mosquito Range with a variety of Paleozoic rocks dipping under the basin-fill rocks.  Near the south end of the Mosquito Range are two peaks that seem quite prominent and very visible—Buffalo Peaks.  The rocks composing these peaks are volcanic in nature, including the Buffalo Peaks Andesite and various ignimbrites (hot churning gases and debris flowing by density from an eruptive center), and were deposited in a paleovalley during the Eocene-Oligocene.  Today, because of erosion, these old valleys are now high mountains and are an example of topographic inversion.  The north boundary of South Park includes several intrusive stocks of Laramide age.  The south boundary is perhaps the most interesting because of the large volcanic centers, including the Thirtynine Mile and Guffy volcanics (part of the Central Colorado Volcanic Field: CCVF).  Eruptions from these centers blocked the south outlet of the Basin and created a large lake and finally forced an eastward flowing outlet that was superimposed across the Front Range (McGookey, 2003).

PARK COUNTY, COLORADO.

At Hartsel, CO 9 and Park County 53 head south from Hartsel toward the small community of Guffy (CO 9) and the Thirtynine Mile Volcanic Area, a small remnant of the much larger CCVF.  Ash and other eruptive rocks from the CCVF cover an area of approximately 8500 sq. mi. including most of the “Sawatch Range, southern Front Range, Wet Mountains, northern Sangre de Cristo Range, and the areas between. Outflow aprons extended onto the High Plains to the east, merged with the San Juan volcanic field to the southwest, and overlapped the Colorado Mineral Belt on the north and west” (McIntosh and Chapin, 2004).  The major volcanism came from at least 10 calderas or eruptive centers with dates over a 10 million year span in the late Eocene into the Oligocene (38-29 Ma); however, volcanic activity continued into the Miocene (Wallace and others, 1999).  Post depositional faulting, dissection and erosion have produced the current landscape.

It was in this area of weathered volcanics that I was hunting for petrified wood, jasper, agate and chalcedony---and was quite successful.  Several localities produced good specimens and some of the wood was opalized in various colors.  But the most fantastic specimen I observed was a quite large piece of mammillary chalcedony, a beautiful and fantastic specimen.  The ultimate source of this specimen was most likely a vug in the volcanic rocks but weathering had left the piece exposed in a short-grass field.  But alas, it was not mine to take home; however, I do have the photos for remembrance!  

Coming back home across Wilkerson Pass a sort of peace descended upon me as I was again thinking of Whitman: Keep your face always toward the sunshine - and shadows will fall behind you.

REFERENCES CITED

McGookey. D. P., 2003, Geologic Wonders of South Park, Colorado with Road Logs: unknown binding. 

McIntosh, W. C. and C. E. Chapin, 2004, Geochronology of the Central Colorado Volcanic Field: New Mexico Bureau of Geology & Mineral Resources, Bulletin 160. 

Wallace, C. A., J. A. Cappa and A.D. Lawson, 1999, Geologic Map of the Gribbles Park Quadrangle, Park and Fremont Counties, Colorado:  Colorado Geological Survey Open-File Report 99-3 (with map).

A MODERN MINING BOOM

LOOKING WEST TO CACHE CREEK PLACER AREA AND THE SAWATCH.

 The Bureau of Land Management (BLM) has a citizen’s advisory group termed the Resource Advisory Committee (RAC).  I serve on the Front Range RAC with headquarters (BLM District Headquarters) in Canon City, Colorado.  At our recent quarterly meeting, held in Salida, the RAC had an opportunity to visit the gold placers along and near the upper Arkansas River.  The BLM has authority over much/most of the public land along the river from Leadville to Canon City and beyond to Pueblo.    They manage (very well in my opinion) the river for a variety of activities (often in conjunction with Colorado Parks and Wildlife as the Arkansas Headwaters Recreation Area) including fishing, hiking, mountain biking, camping, rafting and other water activities, and recreational gold prospecting.  Campgrounds (Railroad Bridge, Hecla Junction, Ruby Mountain, Rincon, Vallie Bridge, and Five Points) are well maintained and busy in the summer months; prospective campers should examine the possibility of making reservations.  I prefer Ruby Mountain since fishing is readily available, hiking is very nice in the adjacent Browns Canyon Wilderness Study Area (proposed as a National Monument), and pounding the rhyolite for red garnets (the “rubies”) is often productive.  Hecla Junction sits at the end of Browns Canyon and is near the site of an old fluorspar mine where “massive” (non-crystalline) fluorite may be collected.  Railroad Bridge is popular with gold panners.

MT. ELBERT, KING OF THE SAWATCH RANGE

Fishing for trout in the river is considered as world class, and a variety of river outfitters provide white water rafting, kayaking, and fishing opportunities.  However, visitors may try their skills along any of the numerous parking areas or campgrounds.

Gold panning brings many visitors to the Arkansas River and prospectors should be aware of special regulations and the fact that some claimed land exists along the river corridor.  Travelers interested in prospecting might want to examine the BLM's LR2000 database (www.blm.gov/lr2000) or contact the public room at the BLM state office for additional information (303-239-3600).  Another way to enjoy panning on the River is to join one of the local "gold clubs" such as Gold Prospectors of Colorado (www.gpoc.com) and participate in club activities.

The geology of the upper Arkansas River valley is interesting to say the least.  On the west side of the valley lays the Sawatch Range with 15 peaks, including Mt. Elbert (at 14,433 feet Colorado’s highest), exceeding 14k feet. The Valley is at an approximate elevation of ~7600 so there is a topographic relief of nearly 6800 feet.  The Sawatch Range is a large Laramide (refers to a crustal shortening mountain building event in the late Cretaceous and early Tertiary, ~72-~50 my) anticlinal structure that at one time included the southern part of the Mosquito Range east across the Arkansas River.  During the late Tertiary, a crustal extensional event culminated in a series of block faulted mountains and basins in central Colorado. The major topographic and structural feature in Colorado is the Rio Grande Rift Zone that trends from near El Paso, TX, to near Kremling, CO.  The Rio Grande River in New Mexico and Colorado, and the upper Arkansas and Blue rivers in Colorado all flow in grabens created in the fault system.  A graben is a down-dropped valley created by parallel faults on either side of the valley.  The rift system in the upper Arkansas River valley effectively split the Sawatch Anticline into two segments: the Sawatch and the Mosquito Ranges, separated by the Arkansas River.  This, and later, faulting helped create the spectacular topographic relief between the river valley and the mountains—Elbert, and other mountains, simply seem to rise straight up out of the valley.  

One particular area of interest for recreational placer miners along the upper Arkansas is an area known as Cache Creek.  Located near Granite, CO, along a creek flowing into the Arkansas with the same name, the placer area has a long history of producing gold. Discovered in 1859,  the gravels were first worked with pans and hand sluices but  low summer water flow in the creek hindered operations.  By 1863 water ditches diverting water had been dug and by 1889 hydraulic mining was dislodging tremendous amounts of gravel with major water resources being piped over the divide from Clear Creek to the south.  Most production had shut down by 1911 when Canon City and Pueblo successfully sued the gold companies for degrading (high sediment load) the water in the Arkansas River.  The BLM believes this was the first successful environmental lawsuit in Colorado.

 As with many/most former and “old” mining areas, fine gold was left behind by the hydraulic miners in the spoils area. And, for nearly 100 years the area was visited, on a somewhat sporadic basis, for recreational panning.  In 2000, the BLM acquired in excess of 2100 acres from the Conservation Fund.  The original goal of the BLM, in acquiring the acreage, was to help protect critical elk and riparian areas along the creek; recreational access was secondary in nature.

Since the Cache Creek acreage was acquired through a “recent direct purchase”, the General Mining Laws (43 CFR 3809) do not apply---the land cannot be claimed by private individuals or groups.  So, the BLM assumed that placering usage at Cache Creek would remain low (180 operating days) and therefore allowed the use of mechanical sluicing or high banking in a 26 acre core area.  The agency envisioned small scale recreational panning and sort of a “family orientated” activity.

A MINER OPERATING A HAND SLUICE.

 Wrong.  The “recession” arrived, the economy tanked, the price of gold skyrocketed, and miners were somewhat successful.  In addition, Cache Creek was well advertised in “prospecting magazines/journals” and on television and soon the place was crowded and any semblance of habitat was being destroyed, especially in the 26 acre core area.  People arrived from all parts of the U.S., many staying for the entire season (Memorial Day to the end of November).  Cache Creek was “in trouble”:  trees were being undercut and presented a danger to miners, “coyote holes” were dug and in danger of collapsing, water was being illegally diverted from private lands upslope from the BLM plot, sedimentation was vastly increasing, and miners were often in conflict with each other.  Cache Creek often resembled the boom mining areas of 150 years ago!

LARGE PITS AND COYOTE HOLES REMAIN FROM HIGH BANKING.

 The BLM needed to take steps to control the situation and begin doing so at the start of this decade: a camp host was installed to help with dispersed camping problems and try to answer questions of visitors, undercut tree were eliminated and other large trees were marked with orange rings to signify “no undercutting”, law enforcement and other BLM personnel made more frequent visits, and mechanical sluicing (high banking) was eliminated.  “Things” have improved but the BLM needs to formulate additional plans and locate resources to pay for the mitigation.  For example, usage remains high, increased sedimentation is an increasing problem, and the diversion of water on private land seems illegal (my opinion).  The RAC and the Royal Gorge Field Office will work together to formulate options.  

MINERS OFTEN TRY TO "CLAIM A SPOT".

mike     

WHAT IS THAT GREEN STUFF? "MEDMONTITE"

CHRYSOCOLLA (FORMALLY KNOWN AS MEDMONTITE) FROM THE OK MINE. WIDTH IS 3.75 CM.

I love green minerals (but also red, blue, purple, etc.)!  Perhaps the copper content in many green minerals catches my eye?  Perhaps my fondness is due to various color deficiencies in my sight---I can “see” bright green minerals but have serious problems noticing more subdued green objects—like the green stoplights mixed in with various city lights.  I try to avoid driving in a city during Christmas celebrations, or at least have a stoplight spotter in the passenger seat!  So, I am always combing the hills and deserts for bright-colored minerals.

In the early 1990’s I was working on an Environmental Impact Statement (EIS) for a new petroleum pipeline that would run from southwestern Wyoming diagonally across Utah to near St. George and then on to southern California.  This was a great project and I hoofed many a mile looking for occurrences of important fossils.  The line crossed the Mineral Mountains near the Utah town of Milford (southwestern Utah) so I was able to take a closer look at several of the old mining areas to the west of town. 

The Beaver Lake Mountains are situated to the northwest of Milford and contain several small copper prospects and mines.  Some are skarn-type copper deposits (altered Paleozoic limestone) while others (i.e. the OK Mine) are copper porphyry deposits hosted in quartz monzonite; many produced a few thousand tons of copper in the early-to-mid 1900’s (Wilson, 1995).  In rummaging through mine dumps along the road near the OK Mine I picked up a small piece of greenish-colored something or other, called it malachite, and threw it in my bag.  We ran into a local mining geologist who said that I had a piece of medmontite, a name with which I was completely unfamiliar (and essentially am today)!

In getting ready for my CSMS presentation in September (the 20^th; Rockin’ Thru Utah), I was trying to gather together my Utah specimens and came across this long forgotten piece of medmontite.  So, the first thing that I did was to search the internet, and my books on Utah---not much luck.

   Mineral Data (www.mindat.org) noted medmontite was named in 1950 (Chukhrev and Anosov) and described as “a copper bearing mineral of the montmorillonite group”---it seemed to be a copper infused clay (and a synonym of cupromontmorillonite).  The presence of copper would explain the green color.  But, MinDat further noted that medmontite was discredited as a distinct species and was “simply” a mixture of chrysocolla and montmorillonite.  

So, my question was: what do you call the specimen?  And, I still don’t know the answer but I guess chrysocolla.  MinDat is mum on the subject and virtually no internet resources describing the discredited mineral could be located.  The closest I came was to note a crystal store in Oxfordshire, UK, selling medmontite specimens (£4.99 plus shipping but including VAT) from the OK Mine that are  “dead ringers” for my small piece.  They describe medmontite as a mixture of chrysocolla and mica that “is a stone of harmony”!

Wilson (1995) listed the following minerals from the OK Mine: malachite, azurite, bornite, chalcopyrite, pyrite, cuprite, brochantite, molybdenite, and chrysocolla.  Therefore, I guess I will go with chrysocolla, a hydrated copper silicate-- (Cu,Al)₂H₂Si₂O₅(OH)₄·nH₂O (but it still looks like malachite to my untrained mineralogical eye)!

mike 

PHOTOMICROGRAPH OF ABOVE SPECIMEN (2.40 MM WIDTH).

REFERENCES CITED

Chukhrev, F.V. and F. Y. Anosov, 1950, Medmontite, a Copper bearing Mineral of the Montmorillonite Group: Vses. Mineralog. Obshch. Zapiski, ser. 2, 79(1), 23-27.

Wilson, J. R., 1995, A Collector’s Guide to Rock, Mineral & Fossil Localities of Utah: Utah Geological Survey Misc. Pub. 95-4, 148 p.

AGATES AT THE AFMS

THE GYM AT HOPKINS HIGH SCHOOL WITH EXHIBITS AND DEALERS

Agates, agates and agates; more agates than I have seen in my entire life---all spread out on tables and cases at the annual American Federation of Mineralogical Societies annual show and meeting.  This gala event was hosted by the Minnesota Mineral Club and held in Minnetonka, Minnesota (Twin Cities metro area).  The club sponsored a number of formal seminars on agates (paid admission) plus several free presentations concerning the honored gemstone.  Because of previous scheduling conflicts, I was only able to attend the Saturday events but was overwhelmed by the expertise of the presenters, as well as by the sheer numbers of agates displayed in formal exhibits, and “for sale” by the dealers.

DOES THIS SEEM AN OXYMORON?  I THOUGHT ALL GEODES WERE "OLD"!

It was easy to observe that the major emphasis of the show (exhibits and dealers) was on the famous Lake Superior Agates (the Lakers).  That fact is understandable since Minnesota is the major home of most of the discoveries in shoreline gravels of Lake Superior, although later glacial action has moved specimens into adjacent Wisconsin, Michigan and even South Dakota (and perhaps others).  The original source of the agates is the basalt located in the Midcontinent Rift System (MRS).  This geological rift (think about the great East African Rift Zone) begin to form in the Precambrian (Proterozoic Era) perhaps 1.1 Ga splitting the stable part of the North American “continent” or plate (referred to by geologists as the craton).  For some reason the rift “stopped splitting” (a failed rift in geological jargon) and the continent healed.  Most of the rocks in the rift, generally igneous and sedimentary, are buried below the surface of the earth and are only know from geophysical studies and drill holes.  However, the rocks become exposed around Lake Superior and the agates erode from the basalts.  Since the rift rocks include substantial amounts of iron, the agates have some sort of a red or orange color---oxidized iron.  Most likely the agates formed post-deposition of the basalt and are the result of percolating silica-rich groundwater filling the many vugs or vesicles in the basalt.

A MIGHTY LARGE AGATE.

The second most popular agates at the show were the Fairburn Agates from neighboring South Dakota.  I have written about these gems in previous articles but can only restate the obvious---they are spectacular in all aspects.  Generally Fairburns are found on the plains in states surrounding the Black Hills, with most discoveries in South Dakota.  The original source was from the Paleozoic Minnelusa Formation in the Black Hills—generally termed Teepee Canyon Agates at their source.

OFTEN FAIRBURN AGATES ARE NOT "CHEAP".

A BUNCH OF FAIRBURN AGATES.

The meeting and the show were a great success and the Minnesota Mineral Club is to be congratulated for their hard work and dynamic membership.
mike          

WHOA, NICE CEPHALOPODS!

Coiled cephalopod, Hoploscaphites sp., in concretion.  This same concretion contains Baculites, gastropods, and bivalves.

 South Dakota has an amazing variety of geological features present on the landscape and an interesting array of formations cropping out along the roads.  I have a particular love for the state since in 1965 I left my home in central Kansas and traveled north for additional education.  It was a long trip, 325 miles, for a small town kid sort of striking out on his own (my undergraduate education was less than 100 miles away from home, and in the same state).  In fact, it was downright scary!  

The first thing that I noticed upon my arrival in eastern South Dakota was the fact that most of the rock exposures were covered by what we lovingly called “glacial crap”.  The second was that in some of the stream valleys, where a few exposures existed, there were old friends from western Kansas—the Niobrara Formation, Carlile Formation, Dakota Formation, etc.  These rocks made me feel more “at home”!

But the real excitement came from our field trips to “West River” and the badlands and the Black Hills.  I had visited these areas the previous summer on a road trip with a couple of college buddies but at age 20 our minds were mostly on other “things”.  We poked around at the rocks, collected a few, did some hiking but always kept our eyes out for the other “things”.  I knew that I wanted to return to South Dakota with a knowledgeable guide.  And so I did.

In the summer of 1966 I started a thesis project West River and to break up the driving from Chamberlain (my work station) I often stopped at the little community of Wasta.  Today Wasta is located at Exit 98 on high speed (75 mph legal but often faster) I-90.  In the “old days” Wasta was just a little store on U.S. 16 where one could purchase a cold soda, and explore the Pierre Shale.

I had previously examined a few outcrops of the Pierre in extreme western Kansas (Wallace County), mostly near McAllaster Buttes, and found the formation to be rather unfossiliferous (a few nondescript baculites) and kind of “ugly”.  The Pierre represents deposition in the deepest waters of the Western Interior Seaway during the latest Cretaceous, and many tens/hundreds of miles from the nearest shoreline.  I sort of put the formation in the back recesses of my mind---until I explored South Dakota!

The Missouri River Trench, as South Dakota geologists call the feature, exposes the Pierre from near the South Dakota—Nebraska border (Fort Randle in the south central part of the state) all the way north into North Dakota.  In fact, there are even exposures along the Missouri River near Yankton in the south eastern section.  Geologists from South Dakota Tech have been studying the unit for years and have described a number of new vertebrate critters.  In addition, invertebrate fossils are numerous.

From the Missouri River Trench west to the Black Hills (and beyond) the Pierre crops out at numerous localities but especially along the major streams. I found that special exposures were located along the Cheyenne River near Wasta.  Suddenly the Pierre lost its ugliness (my earlier opinion) and became exciting!

Exposures of the Pierre along the Cheyenne River yield concretions and these concretions are often fossiliferous.  Most fossils are mollusks including the pelecypods Inoceramus sp. and Pteria sp., the cephalopod ammonites Baculites sp. and Hoploscaphites nodus, the gastropods Margaritella flexistriata, Amauropsis sp., Drepanochilus sp., Anisomyon sexculcatus, the scaphopod Dentalium gracile, as well as the coral Micrabacia americana (Sharman, 2008).  But most collectors are not interested in the snails but in the beautiful straight-shelled cephalopods (Baculites sp) and the coiled cephalopod Hoploscaphites.  These ammonites often have mother-of-pearl present and the suture patterns on the shells are quite distinct.  They are really spectacular fossils and collectors will notice South Dakota specimens in museums around the world.

Baculites sp. in concretion.

 Today, as I understand the situation, the private land is very difficult to access and collect.  Therefore, if you plan on collecting I would suggest contacting the various rock and mineral clubs or rock stores located in or near the Black Hills.  I have found them to be a wealth of information.

It is not always fun experiencing the aging process but---the alternative is not very appealing either!  What I do have are my memories and I often think of those days where collectors could wander around South Dakota, visit with the ranch owners in a friendly fashion, and bash open concretions looking for those ammonites.

REFERENCES CITED

Sharman, G. R., 2008, Petrology, Geochemistry and Paleontology

of Fossiliferous Concretions from the Cretaceous Pierre Shale, South Dakota [abs.]: Geological Society of America Abstracts with Programs, v. 40, no. 5, p. 85.

mike

COLORADO FIRE II

The good news is that I am back home and my house and neighborhood were undamaged.  The bad news is that 346 homes in the city of Colorado Springs were vaporized and reduced to ashes.  In addition, countless others have been damaged.  The good news is that there were no serious injuries (I believe) among the hundreds of emergency workers.  The bad news is that at least two bodies have been located in a burned residence.  The fire is the most destructive in the history of Colorado and thus far nearly 18,000 acres have burned; it is 55% contained.  In addition, the USFS noted that the growth potential for the fire is "extreme".  Somewhere near 32,000 people evacuated the fire area in Colorado Springs and perhaps 3000 of our friends in Teller County (Woodland Park) left their homes.  Today most of us are back home with the major exception of Mountain Shadows, the area experiencing the greatest home loss.

The fire captured my attention like no other natural event.  It was a sad situation to see homes burning, but on the other hand watching the forces of nature at work was a shot of adrenaline.  Many of us here in the mountain west live at or near the urban-wildland junction and so I suppose we should expect natural disasters.  As far as I known this is the first major burn along the range in recorded history.  The Ponderosa Pine forest was "full" and seemed waiting for the right moment to ignite.  The USFS and other agencies are attempting to ascertain the cause of the fire.

It is good to be home.  But, do rocks burn?

mike