Über Josephinit, Awaruit, Souesit, Ihre Eigenschaften, Entstehung Und Paragenesis

Paul Ramdohr

Summary: The occurrences of native nickel-iron regarded as magmatic secretions from peridotites (awaruite, josephinite, souesite, etc.) are certainly formations of extremely low temperatures. This conclusion is drawn from studies of structure and paragenesis carried out principally on a considerable number of josephinites. Nickel-iron (Ni,Fe) is found veining not only the broken-down remains of older silicates but also the products of serpentinization. In these it is occasionally recognizable as of younger formation. Especially striking are loose, mossy distributions often passing over into skeletons and pseudomorphous structures after a cubic mineral. The occurrence of zoned, botryoidal structures with magnetite and gangue and even with limonite furnishes important evidence, and the association of (Ni,Fe) with native copper (sometimes in repeated alternations) is decisive. [i.e. of the recent formation of the (Ni,Fe).]

The genetic interpretation is difficult. Purely supergene reduction, perhaps under bogs, must be excluded. A thermal origin in the temperature range of talc formation is the most probable. Anyhow sulphides occur in association, and they are derived from an older but certainly not an orthomagmatic period. These sulphides already show a replacement series with increasing Ni content. The presence of nine such sulphides has been established, and only a few of them can be identified satisfactorily with commoner minerals. Although some are similar to well-known ores, they show a partial substitution of iron by nickel. Finally two or three are clearly sulphides of copper and nickel, not hitherto known as minerals.

One can assume, then, that native nickel-iron (Ni,Fe) is relatively widely distributed in serpentine areas but that its grains escape notice because of their minute size. The (Ni,Fe) alloys are only readily recognized when they are associated with valuable placer minerals in sand or when they are of unusual size or frequency.

Mineralogical Magazine; December 1950 v. 29; no. 211; p. 374-394; DOI: 10.1180/minmag.1950.029.211.13
© 1950, The Mineralogical Society
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