Wednesday, August 14, 2019

GOETHITE FROM THE PIKES PEAK BATHOLITH


The hardest thing to see is what is in front of your eyes.

In my long-ago undergraduate days in western Kansas students commonly worked deciphering the stratigraphy of the Cretaceous Dakota and/or Kiowa  formations.  If you did not want a project in the limestones or chalk beds, then the Dakota/Kiowa was about the only possibility within close driving distance.  In fact, my senior project was tying to map crossbeds in the Dakota and describing some sections.  I remember the rock colors of the Dakota were mostly red or orange (or so it seems).  We usually described the non-quartz and -calcite visible minerals as iron oxide or limonite and moved on from there. 
 
These large concretions (~10-12 feet) have eroded from the Dakota (maybe Kiowa) in Ottawa County, Kansas at Rock City.
As life progressed, I simply thought all red or orange “stuff” in these sandstones was limonite or some such iron oxide—who cared about trivialities?  
A piece of Dakota sandstone (~ 5 inches width) composed of microscopic quartz crystals/fragments cemented by calcite but with much iron oxide/hydroxide filling voids between the crystals, and coating the surface.  What do I call it--"limonite" or goethite or iron oxide/hydroxide?
Only later in life when my first teaching assignment included Sedimentary Geology did I “start to care,” at least a little!  BTW, teaching sedimentary geology was a joy since originally, I was assigned Structural Geology, a course that was not one of my strong points ( have you ever tried working with, and understanding, stereonets). 
A stereonet is a powerful method for displaying and manipulating the 3-dimensional geometry of lines and planes (www.sciencedirect.com)--or so they say, not so much for me!
Along with Sedimentary Geology I labored big time in Ground Water Resources in Western Kansas (I had never taken any sort of a ground water course), Invertebrate Paleontology, and Intro to Geology.  Yep, four different course preps for a kid who was trying to finish his Ph.D. dissertation and was soon to be a new father.  Spring semester was about the same with Historical Geology, Intro to Geology, Field Methods, and something else.  I finished the first good draft of my dissertation on a dark midnight in mid-February and my son was born the next day.  I have trouble, even today, remembering much of that first academic year, 1970-71, except the pay was $9000 for the academic year and no commitment for a second year.  However, things were going my way when a new tenure-track contract came in mid-May just as the three of us were heading to Dinosaur National Monument where I had a summer position.  Life was good and I did graduate that summer (although the Park Service would not let me miss a day to attend graduation in Salt Lake City).  After that hectic year I resumed remembering “things.”  

The reason my memory was recently jogged about iron oxide minerals is that Mr. Rockhounding the Rockies (rockhoundingkw.blogspot.com), one of the premier collectors of minerals from the Pikes Peak Batholith (age around 1.08 Ga) gifted me an absolutely gorgeous specimen of goethite, an iron oxide-hydroxide [FeO(OH)].  It reminded me, again, that not all iron oxides/hydroxides look like rust, appear as a coating of clay (as in limonite), attract a magnet (magnetite), are a critical ore of iron (hematite), nor do they all come from sedimentary rocks.
Goethite collected from rocks of the Pikes Peak Batholith near Lake George. Width FOV ~5.6 cm.  As with many dark, metallic luster, minerals photography is difficult with my equipment.  The specimen is much more attractive than depicted in the photo.
Photomicrograph of a 1.0 cm. width FOV section of above.  Individual prismatic crystals are east to observe.
In our basic chemistry/physical geology courses we learned that iron occurs in two different oxidation states: 1) ferrous iron has a plus 2 charge (written as Fe++ or Iron II ) and needs to share two electrons with oxygen to form a neutral ion; 2) ferric iron has a plus 3 charge (written as Fe+++ or Iron III) and needs to share three electrons with oxygen to form a neutral ion.  Ferric iron is more stable than ferrous iron, the latter then commonly is oxidized (adds more oxygen) and becomes ferric iron.
Ferrous oxide is rare as a mineral due to its lack of stability and about the only mineral is wustite, a rare oxide usually found in meteorites and man-made slag from smelters.  The cation iron has a ++ oxidation state (plus 2) and the anion oxygen has a - - (minus 2) oxidation charge so they balance out: one iron (++) combined with one oxygen (- -) = FeO.
The major ferric iron mineral is hematite, Fe2O3.  Here you can see two units of iron (charge of +++) X 2 = 6 combine with three oxygen units (charge of - -) X 3 = 6  or +++ X 2 irons = 6 and - - X 3 = 6 oxygens.  So, it balances.  
There also is a major iron oxide mineral termed magnetite, Fe3O4  that appears not to balance!  However, magnetite is actually composed of both ferric and ferrous iron and should be written as: FeO-Fe2O3, one part of each (one unit of ++iron (2) and two units of +++ iron (6) = 8.  One unit of - - oxygen (2) and three units of - - oxygen (6) = 8.  Wow, it balances.
Iron minerals become even more complicated when one considers the iron hydroxides where the OH ion with a charge - - (minus 2) combines with iron.  As far as I can tell, ferrous (Iron II) can combine with a hydroxide ion, but only as a solution in the lab: Fe++(OH)2. One iron ++ and two hydroxides - .  So, one iron ++(2) combines with two hydroxides - -(2) and it balances.
Ferric (+++ or Iron 3) iron may combine with hydroxide to form a really rare and complex mineral called bernalite [Fe(OH)3]: One Fe+++ (3) combines with three hydroxides each with a charge of minus 1– to equal 3, and it balances.
Another major group of iron and oxygen minerals are the Ferric (Iron III) oxide-hydroxides: ferric iron plus the hydroxide ion plus oxygen.  The major mineral in this group is goethite, FeO(OH).  In goethite there is one unit of ferric iron with an oxidation state of +++ that combines with one oxygen (oxidation state of - -) and one hydroxide (oxidation state of -).  So, three of iron equals the two of oxygen plus the one of hydroxide, 3 = 3.
In reality, there are at least three named polymorphs of goethite---exact same chemical formula but crystallizing in different crystal systems: akageneite, lepidocrocite and feroxyhyte.
But, what about limonite, that rusty clay or black streak or “ironstone” or whatever that is common in the orange or red Dakota Sandstone of my youth.  Is the mineral ferric or ferrous iron and is it an oxide, or a hydroxide or an oxide-hydroxide? It turns out that limonite is not even a mineral [often written as Fe+3O(OH)-nH2O] but a combination of several “real” minerals---goethite, lepidocrocite, akaganeite, maghemite, hematite, pitticite, and “jarosite group” minerals and the term is used “for unidentified massive hydroxides and oxides of iron, with no visible crystals, and a yellow-brown streak” (MinDat.org).  Commonly, limonite is composed of goethite.
I am still not certain that I can identify goethite from limonite in many orange to red sedimentary rocks since both have similar colors (red, reddish brown, yellow brown, brownish black), similar hardness (5.0-5.5 or 4.5-5.0 in limonite[Mohs]), dull to metallic to adamantine luster, and a yellowish brown to orange-yellow streak, and often massive.  However, the goethite from the rocks of the Pikes Peak Batholith is different in that it often forms spectacular crystals.
The Pike Peaks goethite is composed of slender, flattened crystals that are elongated along the C-Axis, vertically striated, and exhibit a  metallic luster.  They form “clumps” of radiating crystals and appear to be black or brownish black in color.  However, the streak is brown to brownish yellow to yellow orange.  The crystals are secondary in nature and are derived by weathering (an oxidizing environment) of many different iron-bearing minerals.  Mr. Rockhounding the Rockies has collected his goethite specimens from the same cavities that produce amazonite and smoky quartz (see his web site for many photos).
To learn more about goethite, and especially Goethe, check out my Blog posting on April 23, 2012: Goethite, Goethe, and Kaninchen.
And finally, words of advice from Johann Wolfgang von Goethe (1749-1832): Every day we should hear at least one little song, read one good poem, see one exquisite picture, and, if possible, speak a few sensible words.
The hardest thing to see is what is in front of your eyes. See top of article. Johann Wolfgang von Goethe

Friday, August 2, 2019

ARSENIDES FROM YOOPERLAND SHINING IN A BUCK MOON

The summer solstice was passed about six weeks ago, and my friends are upset when I causally mention that we have “lost” (and are continually losing) daylight here in Colorado Springs---about 45 minutes by July 31, another 66 in August!.  To emphasize, even more, that fall is on the way I noticed that some schools have started and conversation in the coffee shop is about the Broncos practicing up at Dove Valley in southeast Denver (the Rockies are out of fashion and no one is looking for a Rocktober).  One item that is sort of “out of whack” is the snowpack in the mountains---many ranges are still rather white and A Basin was still skiing on July 1.  Fishers are complaining about the high waters in virtually every stream with mountain runoff.  Unfortunately, the last count for drowning in the high-water streams was up to 12.  But fall is on its way and I can smell it when the morning temps are in the 50s here in the city, and cooler up in the mountains.  The “baby” birds have fledged and are out of the nest and my prairie grass has bloomed and started to cure.  Fruit and veggies are pouring into Farmer’s Market, especially from the truck farming area of Rocky Ford along the Arkansas River southeast of the city.  Bears seem everywhere in this part of the city and the cubs are growing, as are the fawns.  I am not ready for cold weather, but I do enjoy seasonal changes and fall/autumn is a wonderful time. We are finishing July with a Black Moon tonight, simply a rather uncommon second New Moon of the month.  It is similar to a Blue Moon, the second full moon of a month.


Did you know that neither a Black Moon or a Blue Moon are possible in the month of February since the cycle between these particular moons is ~29.5 days? Every 19 years February does not have a Full Moon!  We, at least in this part of the world, term the July Moon the Buck Moon due to the growth of antlers on deer, and boy are there some large racks around here.  I am certain that Mr. Rockhounding the Rockies (a meteorologist) is well aware of moon phases. 
All of my daydreaming about weather changes (along with decorations for sale in big box stores) reminds me that the holiday season is approaching down the road and along with that comes one of the classic Christmas songs—Grandma Got Run Over By A Reindeer (Randy Brooks).  That in turn reminds me of the Upper Peninsula of Michigan (UP) and the Da Yoopers who recorded the Christmas classic Rusty Chevrolet:  

Dashing through the snow
In my Rusty Chevrolet
Down the road I go
Sliding all the way
I need new piston rings
I need some new snow tires
My car is held together
By a piece of chicken wire

OK, I understand that I have a weird sense of humor, but it does not take much to make be smile.  And besides, Da Yoopers remind me that I purchased, at the La Crosse Show, a nifty arsenate mineral collected from the UP.


If you are not from the upper Midwest, at the mention of Michigan most rockhounds automatically think of the big to huge copper nuggets although some of my friends who did poorly in grade school geography class mix up the states of Michigan, Wisconsin and Minnesota.  These confused rockhounds shout out Lake Superior agates, and it is true that Lakers can be collected in all three states.
Yooperland (the UP) is connected to the Troll Land (lower Michigan) by the Big Mac (the Mackinac Bridge).
Big Mac is a suspension bridge about 5 miles in length.  Public Domaine photo courtesy of Justin Billau.
The original source of the Lakers, and the copper nuggets, is from the basalts (several different layers) 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).  The Rift is nearly 1400 miles long extending from northeast Kansas to Lake Superior with an eastern arm curving around and heading toward Ohio and a shorter arm trending west along the Minnesota-Ontario border.  Hugh amounts of lava erupted along faults while adjacent rivers from the uplands dumped thousands of feet of sediments (later sedimentary sandstones and conglomerates) into the lowlands of the Rift.  For some reason the Rift “stopped splitting” (a failed rift in geological jargon) and the continent healed. To fix this image in your mind, just imagine the top crust of a pie and how triple cracks develop during baking (but magnify it by zillions!). Perhaps the compression stopping the rifting was the result of orogenic activity (mountain building) on what we now know as the east coast of North America.  
The MRS is centered in Lake Superior with two well-defined arms and one sort of trending west.  Map Public Domaine (I think). 
Most of the rocks in the rift are buried below the surface of the earth and are only known from geophysical studies and drill holes.  For example, the Midcontinent Geophysical Anomaly (MGA) in Kansas delineates the rift since the concentration of magnetite in the Rift rocks creates a magnetic “high” that is picked up by geophysical instrumentation. However, rocks of the Rift become exposed around Lake Superior and the amygdaloidal 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.


The UP copper is also found in rocks associated with the Midcontinent Rift System.  Scientists at Michigan State University have described the (www.geo.msu.edu/geogmich/copper.html ) formation of UP copper as follows: most of the native copper occurs at the top of the MRS basalt in a unit known as the Portage Lake Volcanics/Lavas.  However, this series actually contains over 200 individual lava flows (now basalts and some rhyolite), and 20 discreet conglomerate beds, that collectively have produced over 11 billion pounds of copper.  Over one billion pounds of copper have been extracted from copper sulfides (mostly chalcocite, CuS) in the overlying Nonesuck Shale.  The original source of the copper was from secondary deep-seated hydrothermal solutions percolating toward the surface with native copper crystallizing in the open vugs and pore spaces of older Rift rocks.  Most of these native copper deposits are found in the Keweenaw Peninsula “sticking out of the UP into Lake Superior” and home of Michigan Technological University with the fabulous A.E. Seaman Mineral Museum.
An exhibit case in the Seaman Mineral Museum.  Photo courtesy of the Museum.
South of the Keweenaw, but still in the UP (and adjacent Wisconsin), are the Precambrian Iron Ranges where the original sedimentary rocks have been subjected to metamorphism creating the ores.  The mining of various iron ores “has had a long and significant on the socio-economic development of the Northern Peninsula, beginning in September, 1844…” (Heinrich and others, 2004).
The iron mining districts of Michigan in Yooperland.  Photo courtesy of Michigan Mining History Association.
So, although the copper and Lakers are the most familiar specimens from Yooper Country, the MRS and Iron Ranges have produced an amazing number of collectable minerals.  Interested readers need to consult Mineralogy of Michigan (Heinrich and others, 2004), and if ever traveling near the UP visit the A.E. Seaman Mineral Museum. 


I am always interested in arsenic minerals and so was able to secure a couple of specimens containing copper and arsenic, but they are a bugger to identify. There are two principle copper arsenides found in the Keweenawan rocks (Heinrich and others, 2004)—domeykite [Cu3As] and algodonite [Cu6As] and they appear, at least to an ole clunker like me, to be very, very similar in appearance—silver shiny, steel gray, massive, tarnishing to bronze to iridescent to dull dark (black)!  Both are soft at ~3.5-4.0 (Mohs).  They occur with other “silver-shiny” minerals such as skutterudite, nickel skutterudite, and silver in addition to brass-shiny arsenian copper.  However, there are differences between the two minerals: 1) algodonite is in the Hexagonal mineral system and the chemical formula is “officially” written as Cu1-xAsx where x=~0.15.  In my understanding the mineral contains 83.58% copper and 16.42% arsenic. The density averages ~8.5; 2) domeykite, Cu3AS, belongs to the Isometric crystal system and contains 71.79% copper and 28.21% arsenic.  The density averages ~7.65.  So, the additional arsenic (density ~5.7) in domeykite compared to less copper (density ~8.94) would reduce its density.  However, since the minerals are usually massive crystals cannot be observed visually, and both minerals are often found with other metallic minerals, so separation is often impossible to determine density. And finally, stuck in the middle of this mess is a rock called mohawkite that is a mixture of domeykite, algodonite, arsenian copper, skutterudite, silver and perhaps nickel.  

I believe this is domeykite in a calcite matrix.  The top view is of a "sawed" surface with large dark blob below the surface of the calcite.  The silver shiny streak is where the saw cut through the metal.  The middle view is a reverse side where the surface has been covered with some sort of protectorate.  The lower photo shows either bronze tarnished domeykite (I think) or perhaps arsenian copper. Width FOV ~2.9 cm.

A broken edge of the specimen showing "fresh" silver shiny domeykite with very minor quartz (Q) and the calcite matrix (C).  Width FOV ~ 2.0 cm.


The second specimen, a bright shiny-silver metallic color that causes major reflections with the camera.  The middle photo is with a greatly reduced light source that allows the iridescent tarnish to show.  There are streaks of what may be arsenian copper. The lower photo indicates to me the specimen is composed of arsenian copper, a dark, almost black, arsenide and then a much lighter silver colored arsenide.  This would make it mohawkite.  Width FOV top photo ~ 2.0 cm., bottom photo ~1.3 cm.

Both of my specimens are labeled as coming from the Mohawk Mine.  This is not surprising since early collectors often labeled any Yooperland arsenide as coming from the best-known location, the Mohawk Mine.  Heinrich and others (2004) reported that in 1900 and 1901, 105 metric tons of “mohawkite” was taken from the Mohawk Mine.  It is hard to believe that a number of arsenic minerals were not included in this figure!


I am uncertain what all of this means.  In the days of wet chemistry analyses (no electronic gizmos) geologists and chemists identified several other arsenide minerals; however, their favorite was mohawkite.  In todays world most of these early identified minerals are no longer considered valid minerals, including mohawkite.  The only thing certain to me is that arsenic and copper form numerous shiny specimens that are probably algodonite, domeykite, or mohawkite so rockhounds should be prepared to see any of these labeled as such!


So, I have two specimens.  One has a silver metallic mineral (on a fresh break but tarnished to a dull black on an “older” surface) in a calcite matrix with a few small quartz crystals.  I call this domeykite.  The second is a smaller specimen without matrix consisting of a shiny sliver mass with some arsenian copper (I think), a few small quartz crystals, some black mineral and some iridescence. I would like to call it mohawkite but perhaps I am pushing my luck!  While pouring over the photos in MinDat it appears, to me, that rather identical looking specimens are one person’s domeykite, another's algodonite, and another’s mohawkite!


I have also noticed that the arsenic must be tightly tied to the copper since there are numerous cabochons of these copper arsenides “for sale” on certain web sites.  Any "loose" arsenic would not be good to breath in!

REFERENCES CITED

Heinrich, E.W. updated and revised by G.W. Robinson, 2004, Mineralogy of Michigan: A.E. Seaman Mineral Museum, Michigan Technological Museum, Houghton.

This small posting is dedicated to Yoopers Pete and Jane probably relaxing on the front porch of their UP lake cabin.




Check out the web site www.dayoopers.com

Image result for yooper cartoons

Saturday, July 27, 2019

PHILIPSBORNITE, OSARIZAWAITE, AURICHALCITE: GRAND CANYON, ARIZONA

It is always nice to run across minerals at a show that you recognize as coming from a mine or area that no longer is available for collecting.  At the 2019 Tucson Show I was rummaging around Shannon and Sons Minerals and was delighted to find a specimen of philipsbornite (an arsenate) that was collected from the Grandview Mine in northern Arizona.  I then remembered that somewhere in my home collection thee was a specimen of aurichalcite from the Grandview that I had picked up at the Colorado Springs show a few years ago.  That little tidbit may seem insignificant to many readers; however, The Grandview Mine (AKA Last Chance Mine, Canyon Copper Mine) is located on Horseshoe Mesa in Grand Canyon National Park.  Most us know that mineral collecting is prohibited in national parks.  So, how did these specimens arrive in my collection?

A USNP sign above the mine states: “In 1890 prospector Pete Berry staked the Last Chance copper claim 3,000 feet below you on Horseshoe Mesa.  The Last Chance Mine began a 17-year flurry of activity here at Grandview Point.


Grandview (Last Chance) Mine ca. 1900. Photo courtesy of Minegates.com.

For a while the Last Chance Mine thrived.  The ore was rich; it claimed a World Fair’s prize in Chicago in 1893 for being over 70% pure copper.  But the high cost of packing ore to the rim, then shipping it to be refined, doomed the operation.  Berry and his partners sold the mine in 1901 to Canyon Copper Company.  The new owners continued mining but ceased when copper prices plunged in 1907.


Miners working in Stope B, 4th level in 1906.  Photo courtesy of Grand Canyon National Park Museum Collection.

Mining on Horseshoe Mesa, though short-lived, had a lasting impact.  Grandview became Grand Canyon’s most popular tourist area for about 10 years when Grand Canyon tourism was in its infancy. [Along with his mining endeavors, Berry and wife Martha started a tourist business at Grandview Point in the early1890s that remained the South Rim’s most popular destination until 1901. (Anderson, 2000)] The Grandview Trail, built by Last Chance miners to reach their mines now serves thousands of hikers each year.”

Ascarza (2014) noted that “Ore was transported from the drifts to the top of Horseshoe Mesa using a mule-powered hoist, then taken by pack train on the four-mile long Grandview Trail. 

The mules carried 200 pounds of ore per trip, averaging a trip and a half a day. Afterwards, the concentrate was hauled by wagon to Apex Junction and shipped by rail to the El Paso smelter.”  

Ross (1972) in nominating the mine area for the National Register of Historic Places stated: “A few years later [after 1907], William Randolph Hearst acquired the property and in 1940, he sold it to the National Park Service.”  I was uncertain about the mine history from 1907 to 1940 until I located some NPS historical documents that noted: “ William Randolph Hearst’s acquisition of Pete Berry’s and the Canyon Copper Company’s patented lands in 1913,totaling207.7acres,posed a much greater threat, as the newspaper magnate clearly had the political clout to disregard informal pressure and the capital to develop anything he wished. Hearst did taunt the NPS with rumors of grand develop-mental schemes but generally cooperated with authorities, agreeing to exchange 48.9acres at Grandview Point for 25.8acres elsewhere in 1926, and occasionally discussed the gift or sale of his lands to the government. Cooperation vanished, however, when Hearst’s attorneys once again broached the subject of a sale and the NPS responded with a Declaration of Taking in September 1939. Park officials sustained criticism from the regional press, chambers of commerce, local residents, and the county board of supervisors for employing condemnation, the only time it has done so in park history, and for offering only $25,000for the prime real estate. Hearst’s appraisers estimated its value at$367,000, and his lawyers fought for the higher figure until October 1941, when federal judge David W. Ling ordered the payment of $85,000. The taking, however, was legally effected in July1940.” (National Park Service, 2019).


A bat gate worker ogles a nice specimen left in the Grandview Mine.  Sorry you can"t take it home! Photo courtesy of Minegates.com.

I presume then that collecting of minerals from the Grandview Mine became illegal after the incorporation into Grand Canyon National Park (although I noted a specimen shown on MinDat.org was collected in 1966, another in 1997).  However, many years ago I asked geologists in Arizona about Grandview specimens seeing daylight.  A few informed me that collectors and/or tourists had often visited the mine after 1940 and illegal collecting did not finally cease until “bat gates” were installed in 2009.  These gates protect the Townsend's Long-eared bat colony, and various cultural artifacts, while keeping out human trespassers. 


Bat gate installed during 2009.  Photo courtesy of National Park Service Resource Management.

As I understand the situation (sometimes that is a stretch) the copper minerals were concentrated in breccia zones situated alongside structural flexing features.  MinDat.org stated, and this is important later on in this story, the “ore body is a pipe-like body [entirely] hosted in the upper Redwall Limestone.”  The Grandview Mine is the most famous mineral locality of these breccia pipes  (Anthony and others, 1995) and is associated with the Breccia Pipe Uranium District described by Wenrich and others (2018) and presented at the Metallic Ore Deposits of the American Southwest Symposium sponsored by the Friends of Mineralogy, Colorado Chapter.  I attended the August symposium but do not remember if she specifically mentioned the Grandview Mine.

Wenrich and others (1992, 2018) noted “the northern Arizona metallic district can be thought of as a paleo-karst terrain, pock-marked with sink holes, where in this case most “holes” represent a collapse feature that has bottomed out over 3000 ft (850 m) below the surface in the underlying Mississippian Redwall Limestone. These breccia pipes are vertical pipes that formed when the Paleozoic layers of sandstone, shale and limestone collapsed downward into underlying caverns.”  The base-metal ores (copper and silver) may be related to, or similar to Mississippi Valley Type deposits where emplacement of ores suggest low temperatures (as opposed to hydrothermal emplacement).


The breccia pipe at Grandview is restricted to the Redwall Limestone (the dark blue layer near the bottom).  The uranium (the red blob in the brown layer near the middle), and hence the REEs and HREEs, accumulates in rocks younger than the Redwall and higher in the stratigraphic section,  Weinrich and others (2018) describe this schematic drawing as representing a typical, "complete" breccia pipe.

Besides the gold and silver the breccia pipes attracted the attention of the U.S. Atomic Energy Commission as they searched for uranium.  “In 1951, the U. S. Atomic Energy Commission contracted with Dr. Russell Gibson, Harvard University to make a radiometric reconnaissance survey of "red bed" copper deposits in the south-western United States for their uranium content, and possible production capabilities. He examined 36 properties in 4 states -Arizona, New Mexico, Texas, and Oklahoma. Properties examined in Arizona were the Anita Mine, Grandview Mine, White Mesa district, and the Warm Springs district. The old Grandview copper mine in Grand Canyon National Park exhibited the greatest uranium concentration of all the 36 properties examined.” (Arizona Geological Survey, 2019).

Perhaps even more interesting in todays geopolitical world is that Rare Earth Elements (REEs), and especially Heavy Rare Earth Elements (HREEs), are significantly enriched in the uraninite (UO2) found in many breccia pipes.  “Mixing of oxidizing groundwaters from overlying sandstones with reducing brines that had entered the pipes due to dewatering of the Mississippian limestone created the uranium deposits.” (Weinrich and others, 2018).  I wondered if REEs are also present at the Grandview Mine.

According to MinDat.org the Grandview Mine has produced 32 valid minerals and is the type locality of grandviewite, a copper aluminum sulfate (Cu3Al9(SO4)2(OH)29).  Anthony and others (1995) noted that erosion has removed large amounts of overlying rock and has resulted in the oxidation of the primary minerals.  A suite of secondary copper, zinc, iron, uranium, and arsenic minerals such as cyanotrichite, brochantite, chalcoalumite, langite, metazeunerite, scorodite, olivinite, and adamite was then preserved.  MinDat did not list uraninite as occurring in the pipe—with good reason, I guess! Weinrich and others (1992) believed that breccia pipes restricted to the Redwall Limestone have little or no uranium and REE potential since those pipes that do contain elevated gamma radiation (as at Grandview), the anomalies are entirely restricted to downdropped sandstone blocks from the Surprise Canyon Formation or the lower part of the Supai Group.

MinDat.org did note the presence of the radioactive copper uranium arsenates zeunerite and metazeunerite at Grandview. 
  
One of the specimens in my collection from the Grandview Mine is aurichalcite, a secondary zinc copper carbonate [(Zn,Cu)5(CO3)2(OH)6].  The crystals are pale green-blue, prismatic and lath-like that often radiate from a single point and cover the matrix (??gypsum).  They are “typical looking” aurichalcite crystals.

Aurichalcite crystals. Width FOV ~1.4 cm.

Photomicrograph aurichalcite showing individual crystals.  Width FOV ~7 mm.
 The really interesting specimen I acquired from Grandview is the rare lead aluminum arsenate, philipsbornite [PbAl2(AsO4)AsO3OH)(OH)6].  Philipsbornite is usually associated with lead deposits as a secondary mineral such as at the Red Lead Mine in Tasmania, Australia (home of the famous crocosite). Although several articles refer to the Grandview Mine as the single locality in the U.S. for philipsbornite, recent notes have indicated a second locality in Montana (see MinDat.org).

Philipsbornite from Grandview is usually an earthy mass of tiny, yellow to yellow-orange, indistinguishable crystals.  If not in an earthy mass, it can be somewhat hard at ~4.5 (Mohs) and have a vitreous luster.  It just looks sort of dull except that it is studded with blue crystals that have been identified as osarizawaite and green aggregates that may be brochantite.  Now, osarizawaite (an iron aluminum copper sulfate; [Pb(Al2Cu)(SO4)2(OH)6]) is usually listed as having green or teal blue or green-yellow color.  However, a Michael Kline photo on the MinDat.org Grandview Mine gallery describes his specimen as “Yellowish clusters of minute Philipsbornite with blue Osarizawaite and green Brochantite.” Description of a similar specimen shown on findingrocks.com states, “ the Osarizawaite is the finest I've seen for the species, featuring crystals of unusual size, form, clarity, and color-- deep blue! The green crystals have not been analyzed but appear visually similar to the omnipresent Brochantite on Grandview specimens."  So, I am sticking with the tiny blue to blue-green crystals as the uncommon osarizawaite.  Whatever, the specimen has some unusual copper minerals and I feel “lucky” for being able nab them at a show.


Earthy, vuggy, yellow, yellow-tan philipsbornite with scattered blue crystals of osarizawaite.  Width FOV ~8 mm.

Bright blue crystals of osarizawaite.  Width FOV ~8mm.

Microcrystals of yellow philipsbornite.  Width FOV ~4mm.

More "solid" philipsbornite.  Width FOV ~4mm.

Mixture of "solid" philipsbornite, ?brochanite, earth philipsbornite, and osarizawaite.  Width FOV~4mm.
 

Blue osarizawaite, clusters of green ?brochanite microcrystals (center), and yellow to yellow-green philipsbornite both "earthy and vuggy as seen best in top photomicrograph.  Width FOV 5.25 mm (top) and 7 mm (bottom).
There are specimens from the Grandview Mine out there in the mineral world, but they do not often appear on the market.  With the bat gates now locked, and collecting prohibited, any specimen is probably from some collector breaking up their collection.  However, I noted that in 2010 more than 1,200 mineral specimens from the Grandview Mine were added to the Grand Canyon National Park’s Museum Collection (Grand Canyon National Park, 2012).  You may download Quest For The Pillar of Gold (22.5 MB PDF file) a Grand Canyon Association monograph about mining and miners of Grand Canyon.



REFERENCES CITED


Anderson, M.F., 2000, Administrative History of Grand Canyon National Park:  Grand Canyon Association, Monograph 11.

Anthony, J.W., S.A. Williams, R.A. Bideaux, and R.W. Grant, 1995, Mineralogy of Arizona (third Edition): University of Arizona Press, Tucson. 

Arizona Geological Survey, 2019: docs.azgs.az.gov/OnlineAccessMineFiles/G-L/Grandview...

Ascarza, W., 2014, Mine Tales: Mules aided Grand Canyon’s Grandview site: Arizona Daily Star, July 21, 2014.

Grand Canyon National Park, 2012, Canyon Sketches: V. 25.

Holland, F.R. Jr, 1972, National Register of Historic Places Inventory-Nomination:  Last Chance Mine. 

Weinrich, K. J., G.H. Billingsley, and B.S. van Gosen, 1992, The potential of breccia pipes in Mohawk Canyon area, Hualapai Indian Reservation, Arizona: U.S. Geological Survey Bulletin 1683-D.

Weinrich, K.J., P. Lach, and M. Cuney, 2018, Rare-Earth elements in uraninite-Breccia Pipe Uranium District Northern Arizona in Delventhal, E. (ed), Minerals from the metallic ore deposits of the American Southwest symposium: Friends of Mineralogy-Colorado Chapter.

AND FINALLY, WHAT EVERY ROCKHOUND THINKS ABOUT!!!!
Thanks to Bill Keane.