C14-22 n-alkanes in Soil from the Freetown Layered Intrusion, Sierra Leone: Products of Pt Catalytic Breakdown of Natural Longer Chain n-alkanes?

Soil above a platinum-group element (PGE)-bearing horizon within the Freetown Layered Intrusion, Sierra Leone contains anomalous concentrations of n-alkanes (CnH2n+2) in the range C14 to C22 not readily attributable to an algal or lacustrine origin. Longer chain n-alkanes (C23 to C31) in the soil were derived from the breakdown of leaf litter beneath the closed canopy humid tropical forest. Spontaneous breakdown of the longer chain n-alkanes to form C14-22 n-alkanes without biogenic or abiogenic catalysts is unlikely as the n-alkanes are stable. In the Freetown soil, the catalytic properties of the PGE (Pt in particular) may lower the temperature at which oxidation of the longer chain n-alkanes can occur. Reaction between these n-alkanes and Pt species such as Pt2+(H2O)2(OH)2 and Pt4+(H2O)2(OH)4 can bend and twist the alkanes, and significantly lower the Heat of Formation. Acknowledging the possibility of microbial catalysis and the difficulty of identifying a direct organic geochemical source of the lighter n-alkanes, this paper explores the theoretical potential for abiogenic Pt species catalysis as a mechanism of breakdown of the longer n-alkanes to form C14-22 alkanes. This novel mechanism could substantiate the presence of the PGE in solution predicted by soil geochemistry and illustrate processes involving the PGE. Graphical Abstract

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Stratigraphy, petrology, and platinum-group element mineralization of the early Proterozoic Penikat layered intrusion, northern Finland

Economic Geology ◽

10.2113/gsecongeo.81.5.1126 ◽

1986 ◽

Vol 81 (5) ◽

pp. 1126-1136 ◽

Cited By ~ 37

Author(s):

T. T. Alapieti ◽

J. J. Lahtinen

Keyword(s):

Platinum Group Element ◽

Layered Intrusion ◽

Group Element ◽

Early Proterozoic ◽

Platinum Group

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Platinum-group element mineralization in the upper part of the Penikat layered intrusion, northern Finland

Geologiska Foereningan i Stockholm Foerhandlingar ◽

10.1080/11035899109453811 ◽

1991 ◽

Vol 113 (1) ◽

pp. 51-53

Author(s):

Timo A. Huhtelin

Keyword(s):

Platinum Group Element ◽

Layered Intrusion ◽

Group Element ◽

Platinum Group

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Trace precious metals in major sulfide minerals from the Federova Tundra platinum group element deposit in the Fedorova-Pana layered intrusion, central Kola Peninsula, Russia

The Canadian Mineralogist ◽

10.3749/canmin.2000126 ◽

2021 ◽

Vol 59 (6) ◽

pp. 1711-1730

Author(s):

Louis J. Cabri ◽

Viktor V. Subbotin

Keyword(s):

Mass Spectrometry ◽

Electron Probe ◽

Platinum Group Element ◽

Layered Intrusion ◽

Group Element ◽

Drill Core ◽

The West ◽

Inductively Coupled ◽

Inductively Coupled Mass Spectrometry ◽

Platinum Group

ABSTRACT Drill-core samples from the basal Cu-Ni-platinum-group element mineralization of the Early Proterozoic Fedorova Tundra intrusion in the Fedorova-Pana layered intrusion, central Kola Peninsula, Russia, were studied in two separate projects in Canada and Russia. In Canada, trace precious metal analyses by laser ablation inductively coupled mass spectrometry of 323 base metal sulfide particles [pentlandite (101), pyrrhotite (98), chalcopyrite (25), and pyrite (99)] show that Pd is highly concentrated in pentlandite. Most of the analyses (71%) were done using two master composite samples of comminuted drill core representative of the West Pit and East Pit mineralization, FWMC and FEMC, respectively. Fewer analyses were made of three other comminuted drill core samples from the West Pit referred to as “lithology” samples: OLFW (olivine-bearing rocks), ANFW (leucocratic rocks), and GNFW (gabbronorite). In Russia, 120 polished sections sliced from drill core from the West and East Pits and from four other Fedorova Tundra intrusion deposits (Kievey, Northern Kamennik, Eastern Chuarvy, and Southern Kievey) were studied mineralogically. Platinum group mineral characterization and trace Pd electron probe microanalyses of pentlandite were done using polished sections from all six locations (n = 95). The trace electron probe microanalysis data for Pd in pentlandite from the West (n = 35) and East (n = 19) Pit samples, though at much higher detection levels, are considered to be comparable to the laser ablation inductively coupled mass spectrometry data. The Eastern Chuarvy samples show particularly high Pd concentrations averaging 0.49 wt.% Pd (n = 11) and as high as 1.64 wt.% Pd. The combined data from these studies guides our estimate that pentlandite accounts for 30 to 50% of the Pd in these ores and that Rh solid solution in sulfides may account for >98% of the total Rh.

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