EPIDOTE: GREEN MONSTER MINE, ALASKA

Today a song popped up on the radio that remined me of a famous mineral collecting duo.  The crooner was Buck Owens, the song was Together Again, and the collectors were Art Montgomery and  Edwin Over.  I have previously commented on some of their expeditions and here is another blurb.

The year was 1936 (had to be summer) and Ed and Art were heading to the Prince of Wales Island along the coast of southeast Alaska (Berry, 2002).  The objective of this trip was to collect epidote crystals near Green Monster Mountain (perhaps inspired by the 1935 Smithsonian expedition), a former lead-copper-silver mining area where epidote crystals had been collected since around 1915; Ed and Art were off on anther adventure.  I keep thinking that 1936 was 80 years ago when tents were probably made of heavy canvas, the camping equipment would have been primitive (compared to today’s standards---no REI rain slickers), and work was in a coastal rain forest where temps are cool, humidity high, and rain plentiful (~95 inches per year). Tom Loomis from Dakota Matrix noted that the Green Monster Mountain epidote is some of the best in the world, and there are numerous epidote localities. Epidote from this locality should be coveted not only because of their quality but because of the effort it probably took to obtain specimens. If the mosquitoes don't get you at this locality the grizzly bears and green monsters will - in the pouring rain. 

The rocks that produce the epidote are mineralized marbles of the Wales Group (dates around 541 Ma, just about the Cambrian-Precambrian boundary) that have been cooked (contact metamorphism, high temperature) by Cretaceous granodiorite intrusions.  These types of deposits are known as skarns and at Green Monster Mountain specifically as garnet-epidote-diopside skarn meaning these metamorphic minerals are present and are associated with migrating hydrothermal solutions.   On a larger scale, garnet-epidote-diopside skarns are part of a larger group known as Copper Skarns that form close to intrusions and at/near plate subduction/transition zones (Meinert and Dawson, date unknown). Prince of Wales Island is near the Queen Charlotte Fault that runs from the Cascades (U.S. mainland) to mainland Alaska.  It is a transform fault (like the San Andreas) where the Pacific Plate is sliding past the North American Plate and is tectonically active.

I don’t have the slightest idea where Over and Montgomery prospected as epidote mines/diggings seem to be scattered over a wide area.  For example, Herreid and others (1978) stated: “the principal productive mineral deposits in the area are skarns containing copper, zinc, molybdenum, and gold around the Copper Mountain pluton (Cretaceous). The largest known deposit, the Jumbo Mine, produced 10,194,264 lb of copper, 87,778 oz of silver, and 7,676 oz of gold during the first part of the century (Kennedy, 1963). Museum-quality epidote and quartz crystals have been won from the skarns around the pluton.”

Kennedy (1963) also noted the Jumbo Mine deposits are famous for their epidote crystals. “Locally epidote is an abundant mineral in the skarn zone at the Jumbo Mine. It occurs as medium-sized irregular grains replacing garnet, in groups of radiating crystals surrounded by later quartz and calcite, and as coarse crystals of exceptional beauty and complexity of crystal form lining the walls of vugs. The epidote specimens from the Jumbo area are rivaled only by those on the Tyrol [epidote discovered in 1865 in Austria and often considered the world’s best]."

The epidote locality noted by MinDat at Green Monster Mountain is the Rex Prospect (Idela Prospect): “this prospect consists of three short caved adits and some pits and trenches that probably date from before WW I. All or most are on a large block of (14?) patented claims that extends northwest to the Green Monster Mine (CR153). The deposit consists of mineralized zones along faults in garnet-epidote-diopside skarn.”  

Epidote and quartz from Green Monster Mine, Alaska.  Width of photo ~8.0 cm.

I purchased my epidote quartz specimen a couple of years ago at the CSMS summer show from Terra Minerals who had received a flat from Jack Crawford; I thought mine was the best of the bunch!  The specimen is a mass of slender green epidote crystals whose numerous and non-orientated positions are known as jackstraw crystals are “going in every which direction.”  There is also a larger  terminated quartz crystal that has included epidote crystals.  One of the more interesting aspects of the specimen is a single epidote crystal that is only partially inserted into the quartz crystal.  I presume, but am not certain, that the epidote crystals formed before the quartz and are what The Quartz Page (http://www.quartzpage.de/inc_text.html) refers to as protogenetic inclusions. One characteristic of these epidote-first inclusions is that included fibers run through the entire crystal at random orientations. 

Terminated quartz crystal with epidote inclusions.  Width of photomicrograph ~8 mm.

Jackstraw arrangement of epidote crystals.  Width
of photomicrograph ~8 mm.

Jackstraw arrangement of epidote crystals.  Width
of photomicrograph ~8 mm.

Note the different sizes of epidote crystal. The lower mass are "needles."  Width ~8 mm.

 In addition, there are numerous smaller and doubly terminated quartz crystals scattered around.  It is one of the more aesthetically pleasing specimens in my collection.

Note the large single crystal of epidote partially included in the quartz crystal.

 Epidote, a calcium-aluminum-iron silicate, is not an uncommon mineral occurring in a wide variety of metamorphic and igneous rocks; however, most specimens for sale at shows generally are large terminated (wedge variations) and lustrous green single crystals or “medium size” elongated and interconnected (jackstraw) crystals.  Some specimens containing numerous crystals are quire large measuring in several centimeters and make impressive displays.  Most of my previous epidote crystals were collected (with better knees) from the Calumet Iron Mine near Buena Vista in Chaffee, County, Colorado (see Post May 1, 2013).

Epidote almost always occurs in some shade of green and most collectors immediately recognize specimens that are the common pistachio green color. However, colors can range to almost a black to yellow to brown and all sorts of shades in-between.  Crystals leave a white/clear streak and are slightly softer than quartz at ~6.5 (Mohs).  They usually have a vitreous luster and darker colors are opaque while the very light shades are translucent/transparent. Epidote (Al/Fe-rich) is in solid solution (a transition) with clinozoisite (Al-rich) and it is often tough to distinguish between the two minerals.  Epidote is “usually” darker in color due to a higher iron content while clinozoisite is a “lighter” shade due to less iron in the mineral and more aluminum.  In addition, several members of the Epidote Supergroup are variations of the basic epidote.  Some have legitimate mineral names such as hancockite (enriched with lead) while others are simply noted as epidote-(Sr) and enriched with strontium.  All are similar “looking” (commonly prismatic crystals) and belong to the Monoclinic Crystal System.

AFTERTHOUGHTS

I simply find it amazing that the early collectors (including paleontologists) were able to access sites across the world with minimal support help.  I presume Over and Montgomery traveled to Prince of Wales Island by ship.  Did they then pack in collecting and camping equipment with animals or on their back? Did they employ "sherpas"?   How did they wrap and pack out specimens? Did they worry about grizzly bears? Today the Island only has about 5000 human inhabitants and Craig is the largest population center at 1500. Is Green Monster Mountain close enough to supply centers?  All of these, and more, are some of life’s persistent questions.

I don’t have access to papers or notes relating to the Alaskan Expedition. In fact, I was uncertain if Montgomery went to Alaska or if he stayed in New York to sell specimens.  However, George White (Berry, 2002) stated, “Other outstanding discoveries were made by the pair…Prince of Wales Alaskan epidote in 1936” and Crosby (2015) noted that “1936 brought new energy into the canyon [Clay Canyon in Utah collecting for variscite] with the entry of Arthur Montgomery and Edwin Over who had just been collecting epidote at Green Monster Mountain on Prince of Wales Island, Alaska.” 

REFERENCES CITED

Berry, R., 2002, History of the Colorado Springs Mineralogical Society: privately printed.

Crosby, D., 2015, Clay Canyon and the Little Green Monster variscite mine: www.mindat.org. 

Herreid, Gordon, Bundtzen, T.K., and Turner, D.L.,1978, Geology and geochemistry of the Craig A-2 quadrangle, Prince of Wales Island, southeastern Alaska. Alaska Division of Geological and Geophysical Surveys Geologic Report 48 p.

Kennedy, G.C., 1953, Geology and mineral deposits of the Jumbo Basin, southeastern Alaska: U.S. Geological Survey Professional Paper 251.

Meinert, L., Dawson, K., retrieved January 2019: http://earthsci.org/mineral/mindep/skarn/skarn.html