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Preparing surface blasting of native silver veins in Cobalt / Ontario

Historic image ca. 1905, Source : unknown


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Silver - Silber - Argent - Plata

Cobalt : Ontario : Canada : The "Silver Sidewalk" - an exceptional vein of native silver

Coordinates : 47°33'N , 79°41'W : Cobalt, Coleman Township, Timiskaming District, Ontario, Canada

 

Native Silver is a common mineral in many ore deposits, but aggregates of remarkable sizes are nonetheless rare. There is the famous "Silbertisch" of the St. Georg mine in Schneeberg / Saxony : a table shaped 2 x 4 m large, 20 ton aggregate of almost pure silver found in 1427, which Duke Albrecht used as diner table and which yielded 80.000 Mark silver after encoinment. There are also the equally famous wire silver aggregates of the Kongsberg mines in Norway. But the largest single mass of solid silver ever encountered seems to be the so called "Silver Sidewalk" in Cobalt, Ontario

The calm rural Lake Timiskaming community was shattered by the discovery of a rich silver bonanza on August, 7, 1903. Two Railroad workers - J.H, McKinley and Ernest Darragh - found pliable, silvery flakes of metal on the shores of Loog Lake, which soon turned out to be native silver, assaying 4000 ounces to the ton. A new silver rush was on and Cobalt - named after the accompanying cobalt ores - fast became a synonym for fabulously rich silver ore, which needed to just be picked up from the ground.

And so it was indeed. The government geologists, send out for further evaluation, enthusiastically wrote about "pieces of native silver as big as stove lids or cannon balls lying on the ground". There is another story about a fox lurking around at a local forge. The Blacksmith was so annoyed by the fox, that he threw his heavy hammer after the innocent animal. Luckily, the hammer missed the fox, but instead hitted a nearby rock face and exposed a glittering vein of silver, which soon became the famous LaRose mine...By the end of 1905 there were 16 mines in operation and the value of the shipped silver ore exceeded $1.300.000. !

But the largest silver vein was yet to develop. Actually, it was already known. In 1904 a prospecting party of four men discovered a vein of massive native silver along an old portage trail between Kerr Lake and Lake Girout. This so called "Lawson Vein" turned out to be 100 m long. Mining this vein however didnt start before 1908 in earnest, as there was disagreement among the syndicate members about the ownership of the find. When this was finally solved, mining started soon and the vein, which reached up to 0,5 m width was found to continue to a depth of 60 m below surface. Soon it become well known as the Silver Sidewalk and was considered the richest silver vein of its time in Cobalt, which was finally mined out by the above mentioned LaRose Mining Company.

Assuming a length of the vein of 100 m, an overall depth of 50 m and an average vein thickness of only 0,25 m, this is an ore mass of 1250 cubic metres. Assuming a total silver content of 75 % and given an specific weight of 11, this makes an overall weight of more than 10.000 t pure silver ! No wonder, that all four prospectors retired as wealthy men... Not much was left of this unique silver vein by 1915 and only small bits and samples of it survived to the present day in candian museums and private collections. The site of the discovery itself is protected nowadays and part of the Cobalt mining heritage trail.

 

Other notable & famous native silver occurences :

- First of all : The famous Kongsberg deposit in Norway with its magnificient and even giant silver wires.

- The legendary "Silbertisch" (silver table) of Schneeberg, Saxony / Germany, which was found around 1477. It was such an enormous block of silver, that Duke Albrecht once used it as diner table, hence the name "Silbertisch".

- Superb crystals of silver up to 2 cm have been found repeatedly in the Keeweenaw peninsula, Michigan, USA, namely in the White Pine Mine, the Copper Falls mine and the Kearsarge Mine.

- Large accumulations of secondary native silver from a well developed cementation zone occured together with chlorargyrite at St. Joachimsthal / Jachymov in Bohemia, giving rise to the famous "Joachimsthaler" mint, which lent his name to the later Taler and Dollar.

- Excellent arborescent silver aggregates are known from Mexiko in the states of Sonora, Chihuahua, Guerrero and Zacatecas.

- Large nuggets of native silver up to several kg occur both in the Ural mountains as well as in the Sorskoye deposit, Siberia, both GUS.

 
 

The discoverers of the Silver Sidewalk (Lawson vein) in 1904

Source : Mining Heritage Trail leaflet, Cobalt, Ontario (?)

Typical polished slab (5 x 5 cm) of a Cobalt native silver vein

Source : John. H. Betts

The "Silver Sidewalk" Essentials :


Mineralogy :

Almost pure native silver, with small amounts of silver sulphides, bismuth and cobalt / nickel minerals

Crystal Size :

About 100 m long, 60 m deep and up to 0,5 m wide.

Geology & Origin :

Hydrothermal fissure filling of native silver

Current status :

Mined out completely and smelted before 1915. Some small samples preserved in regional museums and collections. The site is part of a mining heritage trail now.

Remarks :

Possibly the largest mass of solid native silver ever discovered.
Ressources and relevant weblinks :

There are certainly some contemporary short articles and photos in regional newspapers available about this spectacular find, but there seems to be just one somewhat more detailed scientific publication :

Jones, B. (1990) : The Silver Sidewalk at Cobalt; in
Rock & Gem Magazine, Vol 20, No. 9, pp 32 - 38

A regional survey of the geology and mineralisation of the whole area was presented by :

Miller, G.W. (1913) : The Cobalt - Nickel Arsenides and Silver Deposits of Temiskaming (Cobalt and Adjactent Areas); in : Report of the Bureau of Mines, Vol, XIX, Part II, Toronto (1913)

There are also some online ressources about the history of Cobalt and its mines in general - click here for more information -, but unfortunately nothing specific about the Silver Sidewalk


 

 

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