"Rock of the Month # 221, posted for November 2019" ---

Native iron is poor in nickel, unlike the normal nickel-iron alloys that are major constituents of iron and stony-iron meteorites. While the most famous occurrence of native iron is Disko Island, west Greenland, where basaltic lava was reduced upon being erupted through a coal-bearing sedimentary sequence, there are a number of native iron occurrences in Russia, where basaltic lavas and associated intrusive rocks are common. Thus native iron was reported north of the Angara River, during placer gold mining in 1836-1843. The Burovaya, Murozhna and Uderei fragments of the pseudometeorite Angara were collected in the same area in 1885 (Pedersen, 2013). The Putorana plateau has been a noted occurrence, and samples may resemble mesosiderite stony-iron meteorites. As mentioned in this earlier "Rock of the Month", the Siberian Trap basalt magmatism can be distinguished from meteorites, and (Treiman et al., 2002) from lunar and martian basalts. Returning to this month's samples, there are a number of native Fe occurrences in central Siberia. These include localities in the Khungtukun, Khininda and Maimecha intrusions (Ryabov and Lapkovsky, 2010). In detail, sample to sample, the ratio of iron to total metal varies, from Ni-free native Fe to awaruite (Ni₃Fe). Native iron is enriched in siderophile elements, such as Cu, Ni, Co, Pt, Pd, Rh and Ge. Native iron ores formed in feeder columns where tholeiitic melts reacted with platform sediments (hydrocarbons and organometallic compounds are important in ore formation, reminiscent of Disko Island). The region east of Noril'sk-Talnakh includes Carboniferous coal -bearing strata. The Khungtukun massif is large, with an area of 900 km². It varies from 320 m thick in the north to 90 m in the south. Autoliths (fragments of feeder walls) are present, and the mineralogy is complex and quite exotic (Ryabov and Lapkovsky, 2010).

References

Pedersen,H (2013) The pseudometeorite Angara. Meteoritics & Planetary Science 48, 1091-1095.

Ryabov,VV and Lapkovsky,AA (2010) Native iron (-platinum) ores from the Siberian Platform trap intrusions. Australian J.Earth Sci. 57, 707-736.

Treiman,AH, Lindstrom,DJ, Schwandt,CS, Franchi,IA and Morgan,ML (2002) A "mesosiderite" rock from northern Siberia, Russia: not a meteorite. Meteoritics & Planetary Science 37, B13-22.