Chalcopyrite, in a small but rich Ni-Cu-PGE deposit

--- Sudbury, Ontario, Canada

[172 kb]

Figure 1. Two small pieces of vein material, essentially massive chalcopyrite with (invisible to the naked eye) platinum-group minerals and other species. The piece on the left includes some of the host rock, cut at a sharp contact by a vein. The sample on the right, representing a vein of visually pure chalcopyrite, was sawn, to enable the preparation of two polished mounts. Samples courtesy of Irwin Kennedy and Wanda Zyla.

"Rock of the Month #190, posted for April 2017" ---

Chalcopyrite -

globally the most important ore mineral of copper, forms in numerous different geological environments, such as porphyry systems, skarns, sedimentary deposits, and mafic-ultramafic melts.

History of the Occurrence

Broken Hammer was formerly part of the Wisner property, in Wisner township. It lies in the east part of the North Rim, due north of Val Caron. Chalcopyrite veins account for local high grades. This little, short-lived mining enterprise is well-documented. There is a location map (for the whole Sudbury basin, Intierra / Northern Miner, 2008); geophysical context (Balch, 2005); metallurgical test summary (Anon, 2006); regional exploration (Keevil, 2014) and more.

Broken Hammer was a small deposit, with an inferred metric resource of 0.251 MT grading 1% Cu, 0.1% Ni, 1.62 ppm Pt, 1.56 ppm Pd and 0.61 ppm Au (Anon, 2006). Testwork by SGS-Lakefield on a 175-kg sample indicated that the gravity concentrate contained 3700 ppm (0.37 wt.%) precious metals: 67% of Pt, 39% of Au and 9% of Pd. In contrast, the flotation concentrate (22% Cu) recovered 91% of the Cu, plus some Ni (34%), Pt (22%), Pd (68%) and Au (45%). Combined recoveries totalled 78% (Pd) to 92% (Cu). A 30,500-tonne bulk sample was fully shipped by late June 2011 (Tarikh, 2011), anticipating start of mining in 2012. The small deposit was soon mined out.

Mineralogy of the Zone, and the Sample

The Broken Hammer and South Zone deposits in Wisner township lie in intensely brecciated zones of the footwall. There are massive sulphide veins, disseminated or replacement sulphides, and quartz-dominated veins. Chalcopyrite is accompanied by millerite and magnetite, pyrite, quartz and hydrous silicates such as actinolite. Discrete platinum-group mineral (PGM) grains are often found as inclusions in sulphides and hydrous silicates. The PGM include tellurides typical of footwall deposits, such as merenskyite, michenerite and hessite, and also minerals uncommon at Sudbury, such as selenides: clausthalite, sopcheite, naumannite and bohdanowiczite. Other minerals include violarite, wittichenite, melonite, tetradymite, kotulskite and moncheite (Pentek et al., 2008). In the wider context, the ore mineralogy of sulphide ores from the footwall setting of the North Range is dominated by chalcopyrite, but over 60 ore minerals are known. In a recent study (Kjarsgaard and Ames, 2010) six deposits were sampled, in 3 settings, including veins at the Levack footwall deposit, the McCreedy East mine (see also Rock of the Month 115, McCreedy West), the 153 zone, and Broken Hammer.

Coarse, 10-20-mm sperrylite specimens, found in 2011, were sought by collectors (Wilson, 2012; Wilson, 2014, p.249; Moore, 2015, p.257; Moore, 2016, pp.515-516). Broken Hammer sperrylite is also featured in other publications (Paar et al., 2016). The fine crystals are hosted in in chalcopyrite, epidote, or quartz plus epidote matrix (Wilson, 2012). An introduction to a special issue of Canadian Mineralogist (McDonald et al., 2011) has a note on the naming of sperrylite, first discovered by Francis Lewis Sperry at the Vermilion mine in Denison township, near Sudbury: the cover photograph features sperrylite from Broken Hammer. Sperrylite, as an indicator mineral, has also been recovered from glacial sediments, in till 250 m down-ice of the Broken Hammer zone (McClenaghan et al., 2008; McClenaghan and Cabri, 2011).

References on Broken Hammer Deposit and Minerals,Sudbury, Ontario
MINLIB, 16 March 2017 (n=15, 2005-2016)

Anon (2006) Wallbridge milling tests work. Northern Miner 92 no.40, 15, 24 November.

Balch,SJ (2005) The geophysical signatures of platinum group element deposits. In `Exploration for Platinum Group Element Deposits' (Mungall,JE editor), MAC Short Course 35, 512pp., 275-285.

Intierra Mapping / Northern Miner (2008) Sudbury area, Ontario, Canada: mining and exploration activity. Northern Miner 94 no.16, map supplement, 09 June.

Keevil,M (2014) Lonmin doubles down on Wallbridge JVs in Sudbury. Northern Miner 100 no.36, 11,14, 20 October.

Kjarsgaard,IM and Ames,DE (2010) Ore mineralogy of Cu Ni PGE deposits in the North Range footwall environment, Sudbury, Canada. Abs. 11th International Platinum Symposium, Sudbury, 4pp.

McClenaghan,B, McMartin,I and Plouffe,A (2008) Base and precious metals indicator mineral research at the Geological Survey of Canada. Explore 138, 12-15, March.

McClenaghan,MB and Cabri,LJ (2011) Review of gold and platinum group element (PGE) indicator minerals methods for surficial sediment sampling. Geochemistry: Exploration, Environment, Analysis 11, 251-263.

McDonald,A, Huminicki,MAE and Martin,RF (2011) The mineralogy and beneficiation of PGM Cu Ni ores: preface. Can.Mineral. 49, 1345-1348.

Moore,TP (2015) Denver show 2014. Mineral.Record 46 no.1, 147-164.

Moore,TP (2016) Moore's Compendium of Mineral Discoveries, 1960-2015. Mineralogical Record, Inc., Tucson, 2 volumes, 809+813pp.

Paar,WH, de Brodtkorb,MK, Putz,H and Martin,RF (2016) An Atlas of Ore Minerals: Focus on Epithermal Deposits of Argentina. MAC Spec.Publ. 11, v+402pp. plus DVDROM.

Pentek,A, Molnar,F, Watkinson,DH and Jones,PC (2008) Footwall type Cu Ni PGE mineralization in the Broken Hammer area, Wisner township, North Range, Sudbury structure. Econ.Geol. 103, 1005-1028.

Tarikh,S (2011) Wallbridge eyes producer status. Northern Miner 97 no.23, 13, 25 July.

Wilson,BS (2012) New sperrylites from Canada. Minerals - the Collector's Newspaper, issue no.4, 1,8-10.

Wilson,WE (editor) (2014) Mineral Collections in Texas. Mineral.Record 45 no.5, supplement, 304pp.

Graham Wilson, 16-17 March 2017 (microscopy to follow)

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