Telluride, melonite group, forms a series with melonite, palladium-bearing mineral
Specific gravity: 8.547 calculated
Hardness: 2 to 3
Merenskyite is a principal palladium bearing
platinum group mineral. There are six
platinum group elements, iridium,
platinum, rhodium and ruthenium. They often occur together, and are often
alloyed with each other.
Merenskyite occurs typically in disseminated interstitial segregations of copper-iron-nickel sulphides and enclosing silicates. Associated minerals include moncheite, melonite, kotulskite, michenerite, sperrylite, laurite, cooperite, chalcopyrite, pyrrhotite, pentlandite, pyrite, chromite and magnetite (HOM).
At Ken Shoot, Kambalda Nickel mines, Kambalda, Coolgardie Shire, Western Australia, the major platinum minerals are sperrylite and moncheite, and the major palladium minerals are sudburyite, merenskyite, stibiopalladinite, palladoarsenide, michenerite and testibiopalladite; palladium also occurs in solid solution in palladian melonite. The presence of sudburyite, moncheite, merenskyite, michenerite, testibiopalladite, and palladian melonite in stringers and reaction zones indicates that their formation may be related to postmagmatic processes, in particular metamorphic segregation of sulphides and the interaction of ore sulphides with younger hydrothermal fluids (EG 81.1218-1225).
At the Limoeiro mine, Campo Formoso, Bahia, Brazil, the effects of weathering in the nickel, copper and platinum group element deposit reveal a progressive alteration of the abundant primary merenskyite in the supergene reaction front of the deposit. Pyrrhotite, chalcopyrite, pentlandite and minor platinum group minerals are typical of the fresh ore assemblage in the primary deposit. Weathering has produced a gossan cap about 3 m thick over the base metal sulphide-rich parts of the primary ore. Weathering effects are apparent as deep as 50 m with the oxidation of pentlandite and pyrrhotite to produce violarite and pyrite respectively. chalcopyrite is more stable, beginning to alter at a depth of around 20 m. The platinum group minerals start to alter at a depth of about 25 m where merenskyite becomes palladium-rich because much of the tellurium has been released into the adjacent goethite. With progressively more weathering towards the surface the merenskyite appears partially dissolved and pseudomorphed by goethite (CM 54.755-778).
At Fortaleza de Minas, Minas Gerais, Brazil, the nickel, copper and platinum group element sulphide deposit is hosted by komatiitic rocks of the greenstone belt. The deposit comprises:
(i) a main orebody, which is metamorphosed, consisting mainly of sulphide ores of early magmatic origin, and
(ii) platinum group element-rich discordant veins which are hosted in late faults that cross-cut the main orebody.
The platinum group element-rich ore is characterised by thin, discontinuous and irregular veins and lenses of massive sulphides hosted by serpentinite and talc schist. It is composed mainly of pyrrhotite, pentlandite, chalcopyrite, magnetite, carbonates and amphiboles, with minor cobaltite–gersdorffite, sphalerite, ilmenite, quartz, and rarely maucherite, tellurides and platinum group minerals. Omeiite, irarsite, sperrylite and nickel-bearing merenskyite are the main platinum group minerals, followed by minor amounts of testibiopalladite and an unknown phase containing ruthenium, tellurium, and arsenic. The platinum group minerals occur either included in, or at the margins of, sulphides, sulphosalts, silicates and oxides, or filling fractures in pyrrhotite, pentlandite and chalcopyrite, suggesting that they started to precipitate with these minerals and continued to precipitate after the sulphides were formed (CM 45.751-773).
At the Elatsite Mine, Etropole Municipality, Sofia Province, Bulgaria, the porphyry-copper deposit contains platinum group minerals associated with base-metal sulphides, including merenskyite, moncheite and palladoarsenide, in a magnetite–bornite–chalcopyrite assemblage. Other minerals, including linnaeite, carrollite, siegenite and rammelsbergite, which are uncommon in typical porphyry-copper deposits, but occur here, indicate a mantle derivation for this platinum group element–cobalt–nickel episode of mineralisation (CM 43.1355-1372).
At the Giant Mascot Mine, Hope, New Westminster Mining Division, British Columbia, Canada, the nickel-copper-platinum group element deposit is a deposit where the host rocks are characterised by abundant orthopyroxene and magmatic hornblende. The Giant Mascot intrusion is composed of ultramafic olivine-orthopyroxene and hornblende-clinopyroxene that intruded an earlier dioritic pluton. The ores consist of pyrrhotite, pentlandite, argentopentlandite, chalcopyrite, minor pyrite, troilite, and platinum-palladium-nickel bismuthotellurides (EG 111.57-87)
At the McBratney prospect, Bear Lake, Flin Flon District, Manitoba, Canada, the high-grade platinum group element–gold occurrence is hosted in chlorite-actinolite and chlorite schist. The metamorphosed host rocks are komatiitic and tholeiitic in composition. The occurrence comprises veins of massive sulphide with variable amounts of quartz, carbonate, clinochlore, chamosite, biotite, muscovite and a variety of platinum group minerals. The sulphides are mainly chalcopyrite, pyrrhotite and pyrite, with minor violarite, pentlandite, bravoite, marcasite, sphalerite, galena, millerite and cobaltite–gersdorffite. Magnetite, coloradoite, and gold–silver alloys occur locally. The platinum group minerals include, in order of abundance, tellurium-rich sudburyite, borovskite, an unknown palladium telluride–antimonide, sudburyite, sperrylite, temagamite and merenskyite. They are commonly found as inclusions in chalcopyrite, pyrite and carbonate, and are partially replaced by cobaltite–gersdorffite. Minor amounts of platinum group elements also occur within chlorite, carbonate, and stilpnomelane, and a gold-silver alloy is observed locally included in iron sulfides in association with sphalerite. It is suggested that the mineralisation is hydrothermal, and later than the regional metamorphic event. The platinum group minerals precipitated coevally with the nickel–iron–copper sulphides, chlorite–chamosite, biotite, carbonate and quartz at temperatures ranging from 250° to 350°C (CM 42.667-681, EG 105.1469-1490).
Near Rathbun Lake, Kawartha Highlands, Ontario, Canada, platinum, palladium and gold are concentrated in a hydrothermal copper-nickel sulphide occurrence. The mineralisation is associated with a sheared zone of an intrusion where hydrothermal fluids have altered olivine-poor gabbro to chlorite, sericite, quartz, epidote and biotite. chalcopyrite and pyrite, the principal sulphide minerals, occur as massive and disseminated mineralisation. Bismuth-bearing merenskyite and to a lesser extent kotulskite, michenerite and temagamite are the palladium-bearing minerals, whereas platinum occurs primarily in sperrylite (EG 81.1272-1277).
At the Shebandowan Mine, Hagey Township, Thunder Bay District, Ontario, Canada, merenskyite occurs in chalcopyrite and pyrrhotite from copper-rich ore. Grains enclosed by pyrrhotite are nickel-rich, whereas those in chalcopyrite are copper-rich (CM 16.659-663).
At the Raglan Mine, Raglan, Nunavik, Nord-du-Québec, Québec, Canada, the most abundant platinum group mineral is sperrylite, comprising a third of all the grains. Sudburyite and merenskyite make up the majority of the remaining platinum group minerals, with minor constituents including moncheite, temagamite and probably hollingworthite. The majority of the platinum group minerals are associated with sulphides and are either completely enclosed within the sulphides, or at a sulphide–silicate boundary. Platinum-bearing minerals are the predominant platinum group minerals associated with pyrrhotite and pentlandite in monosulphide solid solution ores. In addition, the platinum group minerals in chalcopyrite-rich ores are commonly platinum-bearing, with palladium-bearing platinum group minerals concentrated in secondary veins (CM 42.485-497).
At the Wellgreen deposit, Kluane District, Whitehorse mining district, Yukon, Canada, many platinum group minerals are associated with base-metal sulphides in the nickel–copper–platinum group element deposit. Various solid solutions occur in this deposit:
(1) palladoan melonite–merenskyite–moncheite
The associated platinum group minerals and platinum group element-bearing phases include sperrylite, stibiopalladinite, mertieite, geversite, tetraferroplatinum, native platinum, isoferroplatinum, froodite (?), hollingworthite, laurite, native iridium, rhodium-bearing cobaltite–gersdorffite and palladium-bearing ullmannite (CM 40.651-669).
At Genina Gharbia, Eastern Desert, Red Sea, Egypt, the intrusion is a small mafic–ultramafic complex comprising harzburgite, lherzolite, pyroxenite, norite and gabbro. The intrusion is not metamorphosed, but highly affected by faulting and shearing. The rocks have a high content of magnesio-hornblende and abundant phlogopite and fluorapatite. The copper–nickel ore forms either disseminations in peridotite or massive patches in gabbro, and consists of pyrrhotite, pentlandite, chalcopyrite, pyrite, violarite, cubanite and minor cobaltite–gersdorffite, nickeline, sphalerite, molybdenite and valleriite. Platinum group minerals are restricted to bismuthotellurides of palladium, including michenerite and the melonite–merenskyite series; no platinum minerals were identified. The platinum group minerals are usually associated with hessite, altaite, tsumoite, sylvanite and native tellurium. Ninety percent of the platinum group minerals and other telluride grains are located at sulphide–silicate contacts and as inclusions in altered silicates (CM 42.351-370).
At the Kevitsa mine, Kevitsansarvi, Sodankylä, Lapland, Finland, the deposit is a low-grade dissemination of nickel–copper sulphides containing platinum group elements. It is hosted by olivine wehrlite and olivine websterite, metamorphosed at greenschist-facies conditions. The sulphides consist of intergranular, highly disseminated aggregates mainly made up of pentlandite, pyrite and chalcopyrite, as well as nickeline and gersdorffite in some samples. Most platinum group minerals occur as single, minute grains included in silicates or attached to the grain boundaries of sulphides. Only a few platinum group mineral grains are included in the sulphides. Platinum minerals, mainly moncheite and sperrylite, are the most abundant platinum group minerals, whereas palladium minerals, mainly merenskyite, palladian melonite, kotulskite and sobolevskite, are relatively scarce, and most contain significant amounts of platinum (CM 40.377-394).
At Varallo Sesia, Sesia Valley, Vercelli Province, Piedmont, Italy, melonite, merenskyite and moncheite occur as minute grains dispersed within pyrrhotite, pentlandite and chalcopyrite. Electron microprobe analyses indicate that melonite and merenskyite cover the whole range of nickel-palladium substitution, confirming the existence of a complete solid solution between these phases (EG 81.1213-1217).
At the Fedorovo-Pansky massif, Murmansk Oblast, Russia, the layered mafic intrusion has an olivine-poor gabbro zone that hosts copper-nickel-platinum group element mineralisation with disseminated sulphides, mainly pyrrhotite, chalcopyrite and pentlandite. The mineralisation is palladium-rich and the most common platinum group minerals are merenskyite, moncheite, kotulskite, sobolevskite and michenerite; less common are sperrylite and vysotskite-braggite. The copper-nickel-platinum group element sulphides are primarily magmatic in origin (EG 97.1657-1677).
At the Aksug copper-molybdenum deposit, Todzhinsky District, Tuva, Russia, the ore-bearing porphyry complex developed in intrusions of gabbro-diorite-plagioclase granite. Palladium mineralisation occurs in massive chalcopyrite veinlets in zones of intensely propylitised rocks. A study of palladium-rich ores on a scanning electron microscope showed 2–5 micron sized merenskyite inclusions in chalcopyrite. The merenskyite is associated with electrum, monazite, cobaltite, tennantite and strontium-bearing baryte (CM 48.656-658 ).
At the Uitkomst Complex, Waterval, Nkangala District, Mpumalanga, South Africa, platinum group elements dominated by palladium are present in the nickel-copper-cobalt bearing massive sulphide ore. The mineral assemblages here are indicative of formation temperatures probably less than 490°C. The distribution of the individual phases recorded for the deeper part of the ore body indicates an increase in michenerite grains towards the base of the zone, an antipathetic relationship between merenskyite and michenerite, and a concentration of testibiopalladite grains at the top and the base of the zone. The platinum group mineral grains are preferentially associated with pyrrhotite and generally located along grain boundaries (South African Journal of Geology 104.287-300).
The type locality, the Merensky Reef, Bojanala Platinum District Municipality, North West, South Africa, is an ultramafic intrusive. Melanorite, leuconorite and anorthosite contain a platinum group mineral assemblage that is predominantly moncheite and merenskyite. The platinum group minerals are rarely enclosed by chromite. All the platinum group minerals are predominantly associated with base-metal sulphides and are likely to result from late, low-temperature processes superimposed on the magmatic ones (CM 42.423-437).
The main platinum group minerals in descending order of abundance are braggite, cooperite, moncheite, laurite, kotulskite, merenskyite (4 vol %), a platinum-iron alloy, palladian electrum and sperrylite. The remainder (less than 1 vol %) include atokite, paolovite, rustenburgite and mertieite. The earliest platinum-palladium minerals to crystallise from the sulphide liquid are platinum-rich, with the replacement of cooperite by braggite, and moncheite and merenskyite by kotulskite, as evidence of a later palladium metasomatism (EG 77.1367-1384).
At the Aguablanca Mine, Monesterio, Badajoz, Extremadura, Spain, the nickel–copper–platinum group element ore deposit has a magmatic origin, and has been reworked by later skarn-related hydrothermal activity. Base-metal sulphides are associated with gabbro and dolerite, with fragments of pyroxenite and peridotite. These rocks show a pervasive retrograde alteration with an early overprint of actinolite, chlorite, epidote, albite, serpentine, followed by later growth of talc , chlorite and carbonates. The base-metal sulphides consist of pyrrhotite, pentlandite and chalcopyrite, overprinted by fluid-deposited pyrite (CM 42.325-350).
At Arthrath, Aberdeenshire, Scotland, UK, the prospect occurs within a group of mafic–ultramafic rocks emplaced broadly synchronously with the later stages of amphibolite facies metamorphism of metasedimentary units. Platinum group elements associated with zones of copper–nickel–iron sulphide mineralisation have been identified. The palladium is hosted primarily in merenskyite enclosed in base-metal sulphide (CM 45.335-353).
At Talnotry, Newton Stewart, Dumfries and Galloway, Scotland, UK, arsenic-rich magmatic sulphide mineralisation is hosted by a diorite intrusion. A relatively abundant and diverse platinum group mineral assemblage is present and is dominated by sperrylite, irarsite and electrum, with subordinate merenskyite, michenerite and froodite (MM 68.395-411).
At the Stillwater Complex, Montana, USA, the presence of a platinum-iron alloy, isoferroplatinum, platinian rhodium, rhodian platinum, palladian gold, cooperite, laurite, braggite, vysotskite, moncheite, kotulskite, merenskyite, sperrylite and stibiopalladinite has been confirmed (EG 71.1352-1373)
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