Antimonide, platinum group mineral, palladium-bearing mineral
Hardness: 4 to 5
Colour: Creamy white
Naldrettite has been found in several different environments:
In magmatic nickel-copper-platinum group element sulphide deposits.
In hydrothermal veins in porphyry coppers of the copper-gold type.
In platinum group element deposits of Alaskan-type zoned intrusions.
Occasionally in metasomatic antimony-arsenic sulphide ore.
Occasionally in metamorphic nickel–oxide ore.
Occasionally in podiform chromitites.
Naldrettite can form in a variety of igneous rocks, even involving minimal concentrations of palladium and antimony (CM 59.6.1801-1820).
At the Luanga complex, Carajás mineral province, Pará, Brazil, a new (2021) find of naldrettite occurs in a chromitite sample collected in the layered intrusion. Paragenetic association with alteration assemblages (ferrian chromite, iron hydroxides, chlorite) suggests precipitation of naldrettite from metamorphic hydrothermal fluids. The average composition of the sample shows major substitution of platinum and arsenic. These elements were derived from the breakdown of primary sperrylite, and were incorporated in naldrettite deposited by percolating fluids, at temperature below 350°C. Crystallisation of naldrettite generally occurs in the post-magmatic stage due to the activity of hydrothermal fluids containing volatile species antimony, arsenic, bismuth, tellurium and palladium (CM 59.6.1801-1820).
At the type locality, the Mesamax Northwest deposit, Ungava Peninsula, Nunavik, Nord-du-Québec, Québec, Canada, naldrettite was found in 2005 associated with monoclinic pyrrhotite, pentlandite, chalcopyrite, galena, sphalerite, cobaltite, clinochlore, magnetite, sudburyite, electrum and altaite. Other rarer associates include ungavaite, sperrylite, michenerite, petzite and hessite. Naldrettite occurs as anhedral grains, which are commonly attached or moulded to sulphide minerals, and also associated with clinochlore. Grains of naldrettite vary in size from ~10 to 239 μm. Naldrettite appears bright creamy white in association with pentlandite, pyrrhotite, clinochlore and chalcopyrite (MM 69.89-97).
The naldrettite was found in a drill core through the contact zone between massive and disseminated sulphide mineralisation hosted by amphibolite and serpentinite replacing pyroxenite and peridotite (HOM).
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