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Now, when I finally found the
Colorado Springs group I had forgotten my camera. So, I have substituted some beautiful Mexican
Gold Poppies blooming in the desert.
They are a spring delight.
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My next journey was to visit the displays of the
Miners Coop Rock Show. I had been
hunting several days for the vendors as the show venue moved from the 2015
location. Of course I never bothered to
examine one of the Show booklets to locate a position; however, even the
booklet had a wrong listed location! At
any rate I found them on the west side of I-10 near the Ina Exit. I was particularly interested in this group
since at least three vendors were members of the Colorado Springs Mineralogical
Society (CSMS). In addition, a business
from Arkansas and another from Gardner, Colorado, were present with their
booths. These latter two are regular
vendors at our June CSMS event. After
visiting with the CSMS members, I diligently hunted through other displays and
came up with up a couple of nice blue specimens of a calcium copper zinc sulfide
known as serpierite [Ca(Cu,Zn)4(SO4)2(OH)6-3H2)].
Serpierite is another one of those nice blue copper
minerals ranging from a light to a dark sky blue with some almost a blue-green
turquoise color. It occurs in fluffy tufts, crusts, or aggregates of very tiny,
lath-like vitreous crystals. These small
crystals are transparent and some almost lack color. They are somewhat confusing, at least to a
soft rocker like me, in that the crystals are elongated along axis a and not
the “usual” c axis. In fact, they are
flattened along the c axis to produce the lath-like shape. Serpierite fractures easily into splinters
and seems quite soft (~2 Mohs). I tried
an unglazed porcelain plate and the mineral essentially leaves a white streak.
Serpierite is a member of the small Devilline Group. I
have a small specimen of devilline [CaCu4(SO4)(OH)6-3H2O]
where the small tuft of platy crystals are essentially impossible for me to
distinguish from serpierite. As one can
observe devilline is missing the zinc of serpierite. Add some cadmium in place of some of the
calcium in serpierite and the mineral becomes aldridgeite (structure the same:
isostructural).
Serpierite is a secondary mineral and found in the
hydrothermal zone associated with copper and zinc deposits. For example, at the type locality of
serpierite in the Lavrion District of Greece, there are numerous primary copper
minerals and primary zinc minerals such as sphalerite.
I have three specimens of serpierite from different
localities and all are somewhat different: Lavrion District, Greece; Creole
Mine, Beaver County, Utah; Bay Horse District, Challis, Custer County, Idaho.
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Photomicrograph of
serpierite collected from its type locality at the Serpieri Mine, Lavrion
District, Greece. Width FOV ~3 mm.
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The Lavrion District of southeastern Greece is
probably the country’s most famous and oldest mining area. There are signs copper was mined in the
years 3000 B.C—2000 B.C. corresponding to the Early and Middle Bronze Age. Of interest is that copper, along with tin,
is the major component of bronze. In 483
B.C. large deposits of silver were discovered and these mines had a direct and
major effect on the creation of the Athenian Empire---Classical Athens. The mines were abandoned in the 6th
Century A.D and reopened in the 1880s producing lead, silver, cadmium,
manganese and helped finance the building of the modern country of Greece. The ore deposits became exhausted in the
1980s. (above information from www.ancient-greece.org).
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Photomicrograph of
rosettes of lath-like crystals of serpierite collected from the Creole Mine,
Beaver County, Utah. Width FOV ~1 cm.
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My second specimen of serpierite was taken from the
Creole Mine in Beaver, County, Utah, one of the more mineral-rich counties in western
Utah. Information about the mine is
tough to locate; however, it was mined for scheelite crystals prior to 1943. Hobbs
(1944) reported that several hundred tons of ore containing 0.75% WO3
were mined out by 1943. Prior to that
mining activity lead and silver ores (probably silver- rich galena) were taken
from “massive sulfide replacements in limestones along the contact of a quartz
monzonite or granite dike.” The
scheelite was located in the overlying oxidized zone in masses of “limonite.”
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Photomicrograph of
numerous platy lathes of serpierite? Collected from the Bay Horse Mine,
Challis, Custer County, Idaho. Width FOV ~7 mm.
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Back in the 1980s I had an opportunity to help write
an Environmental Impact Statement for a proposed fluorspar (fluorite) mine near
the old ghost town of Bay Horse in the mining region of the same name. Specifically, I was looking at the paleontological
resources, if any, in the area of the proposed mine. I do not remember all of the details except
that we camped south of Challis along the beautiful Salmon River, the local
population was not overly friendly to strangers, and the massive deposits of
the Tertiary (Eocene, ~50-55 Ma) Challis volcanics held a gazillion pieces of
petrified wood.
The rocks examined at the proposed mine were part of a thick
section of something like 35,000 feet of Paleozoic marine rocks that have an
extremely complex stratigraphic and structural history (Hobbs and others, 1991). About the only fossils I remember finding
(but again my memory sometimes fades) were numerous graptolites in the black
shales. It was sort of eerie driving
through a deserted “ghost town” in remarkably good shape. The area was privately
owned and we did not stop to explore.
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Part of the Bay Horse
Mining District now incorporated into the Land of Yankee Fork State Park. Photo courtesy of www.deq.idaho.gov.
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The Bay Horse mining area deposits were first noted in
1864 by a prospector traveling along the river but the first lode claim was not
located until 1873. In 1877, a major
lead-silver vein was discovered and by 1878 a gold/silver rush to the area had
begun. The metals were found in replacement ore bodies (probably associated with
Cretaceous and Tertiary intrusives). In
1880, a 30-ton smelter was constructed, and within two years charcoal kilns
were constructed to provide the smelter with a local fuel source. By this time,
the town of Bay Horse had a population of about 300 and a complex of
substantial, permanent buildings. Only
nine years later in 1889 the smelter closed.
Evidently smaller scale production continued until 1925 as the ore was
transported south to a smelter in Clayton.
The Bay Horse District was a quite productive area as total mineral
production is estimated at ~200 oz. of gold, 6.3 million oz. of silver, 6.6
million lbs. of lead, and 39 thousand lbs. of zinc. (above from www.deq.idaho.gov)
Since I visited the area the State of Idaho made a
great decision and purchased the Bay Horse area and renamed it the Land of
Yankee Fork State Park. I look forward
to returning. And, I never paid much attention to note if the fluorspar mine was ever completed.
My third specimen of serpierite has an older looking
label stating it was collected in the Bay Horse area at Challis, Idaho. However, the descriptions of serpierite at www.mindat.org do not recognize the mineral at
Bay Horse. But I did find a reference in
the Handbook of Mineralogy, www.handbookofmineralogy.com noting the occurrence of serpierite from the
Bay Horse Mine at Challis. Maybe? Maybe not?
REFERENCES
CITED
Hobbs, S.W., W.H. Hays, and D.H. Mcintyre, 1991,
Geologic map of the Bayhorse Area, Central Custer County, Idaho: USGS
Miscellaneous Investigations Series Map I-1882 pamphlet.
Hobbs, S.W., 1944, Tungsten deposits in Beaver County,
Utah: USGS Strategic Minerals Investigations Bulletin 945-D.
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| AND SPEAKING OF ARIZONA GOLD AND ORANGE! |
