Sperrylite: A New Find of World-Class Crystals

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10 mm sperrylite crystal, Broken Hammer Prospect,
Val Caron, Sudbury, Ontario, Canada

Probably the most exciting mineral discovery in Canada in 2011 was a new find of exceptionally large, museum quality crystals of sperrylite (PtAs2) at the Broken Hammer deposit in Val Caron, Sudbury, Ontario, Canada, in 2011. In the early Spring of that year, Wallbridge Mining, which owns the property, drilled and blasted a roughly 20 x 30 meter prospect pit. A Wallbridge employee discovered the crystals close to the edge of this pit. Later, smaller crystals in a different matrix were discovered in the wall of the pit. The newly discovered crystals are brilliantly lustrous, very sharply crystallized, and very pure. The largest crystals reach 15 mm in size. The large crystals were found in an area is no more than a few square meters, in a surface occurrence of a massive, rotted chalcopyrite-millerite matrix.


1.3 cm sperrylite crystal in 5 cm chalcopyrite matrix. M. Bainbridge photo.
This is considered the finest specimen from the Broken Hammer find.


4.5 mm sperrylite crystal on quartz-epidote matrix

THE BROKEN HAMMER OCCURRENCE

Surveyor Tom Johnson, a Wallbridge employee, collected the large crystals in the Spring of 2011. He found a few that were in matrix, but most were loose in the soil; these he recovered by panning. According to Mr. Johnson, the big crystals were mostly found in a zone of "…softer gossanous/brecciated sulfides and adjacent to previously shattered massive chalcopyrite." Johnson reports there were "…mud-like decomposed epidotes and sulfides in this area, and in that as well as in the shattered sulfides there was lots of loose and shattered crystals, as well as sperrylite dust and shards. I think I got most of this by panning." Johnson said, "I had the good sense to leave the few found in matrix intact. I knew exactly how spectacular these were, and was very careful." After digging through the top foot of the rotted sulphides in the deposit, the crystals he recovered became smaller and smaller, so the best part of the deposit appears to be exhausted. In May of 2011, Brad Wilson, who prepped the crystals for sale, collected smaller crystals to about 4.5 mm from the pit wall, a few meters below the sulphide outcrop, where they occurred in a variably gossanized quartz-epidote matrix. The combination of metamorphism of the matrix and the challenge of extracting crystals from the tough epidote-quartz, made it difficult to collect good crystals from this area. In August, 2011, Johnson and Wilson returned to Broken Hammer for their final collecting trip. In all, over 400 specimens were collected at Broken Hammer, ranging in size from 1 mm to 15 mm, with the crystal quality varying between poor and excellent.


Tom Johnson from Wallbridge Mining with a display of the finest sperrylite crystals
from Broken Hammer at the PDAC convention in Toronto, Canada in March, 2012.
Photo from the March 2012 Manitoba Mineral Society newsletter.

HISTORY OF THE BROKEN HAMMER DEPOSIT

In November, 2005, Wallbridge initiated an exploration program on the North Range of the Sudbury Basin. They found evidence of a copper-nickel-gold-platinum-palladium deposit that that suggested the area might be mined economically. According to the Ontario Ministry of Mines, in April 2011 Wallbridge opened a test pit and removed 30,000 tons of material for bulk sampling, which was delivered to Xstrata's Strathcona Mill in Sudbury in July, 2011. The net proceeds from the Broken Hammer bulk sample after mining, processing and treatment charges were just over $3M. Wallbridge reported that a pre-feasibility resource estimate will be completed in the second quarter of 2012. The economics of the deposit will determine whether Wallbridge will open a mine at Broken Hammer. If the deposit is not mined, then it is unlikely that any further crystals will be found.


Collecting sperrylite in the Broken Hammer pit, 2011


The Broken Hammer pit, 2011. Most of the sperrylite
crystals were found on the right side of the opening.

THE CULTURAL ARTIFACTS ISSUE

Canadian law prohibits the export of "cultural artifacts" with a value of $2,000 or more that are included in the Canadian Cultural Property Export Control List. So, specimens worth more than $2,000 that are "described mineral species" (i.e., for which scientific data, illustrations or descriptions appear in a professional publication), and that were recovered from Canadian localities, cannot be exported without a permit. The Control List also restricts export of a collection of 10 or more mineral specimens with a fair market value in Canada of more than $5,000, that were recovered from a specific mine, quarry or locality. It is still unclear whether export permits for sperrylite crystals that exceed these values will be granted or not. This is why the very few sperrylite crystals over 10 mm have not been put on the market. Until this issue is decided, the largest crystals will remain in Canada. And, because Wallbridge is a publicly traded stock, and their activities are subject to public scrutiny, there is reportedly no flexibility on this issue.

The mineral rumor mill is saying that both the Royal Ontario Museum and the Canadian Museum of Nature are attempting to acquire one of the best crystals. The asking price for each of the top three pieces is a mere $45-50,000.


The Broken Hammer Prospect is located just north of Sudbury, Ontario

CHARACTERISTICS OF SPERRYLITE

Sperrylite is a very rare platinum arsenide mineral and the only significant platinum ore. It was first described by H.H.Wells in 1889, and was named after Francis Louis Sperry (1861-1906), a chemist from Sudbury, Ontario, who discovered the mineral at the Vermilion Mine, Denison Township, Sudbury District, Ontario, Canada. Sperrylite has a metallic luster, an opaque bright silvery "tin white" color, and a hardness of 6 to 7. It exhibits chonchoidal fracture, and with a specific gravity of 10.6, is quite heavy even for metallic minerals. It forms crystals as cubes, octahedrons or pyritohedrons, though it is most often found in combinations of these forms. The resulting crystal shapes are similar to its cousin pyrite; both are members of the pyrite group of minerals, sharing a similar structure and exhibiting similar crystal habits.


10 mm sperrylite crystal on quartz-epidote matrix

OTHER OCCURRENCES

Very few localities on earth have been reported to have produced sperrylite. The two classic localities for this mineral are Sudbury, Ontario, Canada and the Norilsk Mining District in northern Siberia. Other localities include the Bushveld and Witwatersrand in South Africa; the Great Dyke of Zimbabwe; Noril'sk-Talnakh in Siberia; the Stillwater complex in Montana, USA; near the northern shores of Lake Superior within the Duluth complex in Minnesota, USA; the Jinchuan intrusion in China; and the Panton sill and Kambalda nickel camp, both in Western Australia. Sperrylite is also reported from numerous localities across Canada, Greenland, Spain, Finland, Russia, India, Brazil and other countries. ). It is also reported as micron-scale grains in the rare Rumuruti-type carbonaceous chondrite meteorites.


10 mm sperrylite crystal on chalcopyrite-millerite matrix. B.Campbell photo.


3.0 and 2.0 mm sperrylite crystals on quartz-epidote matrix


3.0 and 2.0 mm sperrylite crystals on 1.6" quartz-epidote matrix


3.2 mm sperrylite crystal on quartz-epidote matrix


3.2 mm sperrylite crystal on quartz-epidote matrix

Specimen photos © www.TreasureMountainMining.com, except as noted

Photos of the Broken Hammer Deposit courtesy of Brad Wilson

Click here to see our current selection of sperrylite specimens.

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