Siderophile element

Siderophile elements in the zonal structure of ore geochemical systems ... 

Detailed mineralogical studies have shown that pyrite of different generations is the main form containing siderophile elements, and their zonal distribution is connected both to the position of wall rock pyritization zones and to the concentration changes of these elements within the pyrites. 

The presentation on sections, plans and 3-D models provides examples of the distribution of siderophile element. 

A model of an ore geochemical system has been developed (Goldberg et al, 2003), which can be applied to ore entities of various categories ore bodies, deposits and ore regions. The nuclear section of the system contains a zone of accumulation of the principal ore and associated elements. The peripheral areas contain zones of depletion of ore-forming elements. Anomalies of siderophile elements (Ni, Co, Mn, Ti, V, Cr), which are the subject of this paper, are located on the periphery of the nuclear sections of these systems. 

In areas of accumulation of ore-forming elements the siderophile elements, as a rule, form zones of lower concentrations relative to the background concentration. Experience shows that these zones most probably contain ore bodies and deposits... 

This example shows possible mineral forms of occurrence of siderophile elements in ores and ore-surrounding zones. 

Barnes, S.J., Prichard, H.P., Cox, R.A., Fisher, P.C., Godel, B. 2008. The location of the chalcophile and siderophile elements in platinum-group elements ore deposits (a textural, microbeam and whole rock geochemical study) Implication for the formation of ore deposits. Chemical Geology, 248, 295-317. 

The analysis of rock samples was conducted in the chemical laboratory in Ust-Kamenogorsk, Kazakhstan. by inductively coupled plasma mass spectrometry, and the equipment used was an ELAN-6100 (US) mass spectrometer. In the present abstract the distribution of two elements zinc (as the basic ore-forming element) and titanium (of the siderophile element) is examined. The sensitivity of the analysis is 5 ppm for Zn and 0.05% for Ti. The analytical results for Zn and Ti are presented on contoured... 

Glikson A. and Allen C. (2004) Iridium anomalies and fractionated siderophile element patterns in impact ejecta, Brockman Iron Formation, Hamersley Basin, Western Australia evidence for a major asteroid impact in simatic crustal regions of the early pro-terozoic Earth. Earth Planet. Sci. Lett. 220, 247-264. 

Iron oxides present in coal are generally stable for the relatively short period of time that they are exposed to combustion temperatures. Therefore, siderophile elements (e.g., Ni, Co, Mo, Pt, Pd, Au) that are incorporated within iron oxides are also expected to remain stable, and escape any significant thermal transformation reactions (Bums 2003). Similarly, lithophile elements (e.g., Ba, B, Cr, Mn, Sr, V) that are initially found in association with silicates and aluminosilicates in coal are expected to be incorporated within the glassy fraction of coal ash upon thermal transformation of their parent minerals (Bums 2003). 

Two different kinds of metals are found in chondrites. Small nuggets composed of highly refractory siderophile elements (iridium, osmium, ruthenium, molybdenum, tungsten, rhenium) occur within CAIs. These refractory alloys are predicted to condense at temperatures above 1600 from a gas of solar composition. Except for tungsten, they are also the expected residues of CAI oxidation. 

Iron meteorites offer the unique opportunity to examine metallic cores from deep within differentiated bodies. Most of these samples were exposed and dislodged when asteroids collided and fragmented. Although irons constitute only about 6% of meteorite falls, they are well represented in museum collections. Most iron meteorites show wide variations in siderophile-element abundances, which can be explained by processes like fractional crystallization in cores that mimic those in achondrites. However, some show perplexing chemical trends that may be inconsistent with their formation as asteroid cores. 

Siderophile element diagrams used to classify iron meteorites. Modified from Scott and Wasson (1975). 

Elemental abundances in CR2 chondrites normalized to the Cl composition and plotted in order of decreasing volatility from left to right. Lithophile elements are shown with open circles, siderophile elements with black circles, and chalcophile elements with gray circles. CR2 data from Kallemeyn etal. (1994). 

In most respects, asteroid 4 Vesta is geochemically similar to the Moon. As judged from howardite-eucrite-diogenite (HED) meteorites (see Chapter 6), Vesta is an ancient, basalt-covered world (Keil, 2002). Its rocks are highly reduced, and its depletions in volatile and siderophile element abundances resemble those of lunar basalts. And like the Moon, Vesta is hypothesized to have had an early magma ocean. The exploration of Vesta is now in progress, and within a few years we may have enough data to discuss it in a similar way that we have considered the Moon. 

Chondrite-normalized abundances of siderophile elements in the Earth s mantle. The measured concentrations do not match those expected from low-pressure metal-silicate partition coefficients determined by experiments. Modified from Tolstikhin and Kramers (2008). 

Righter, K., Drake, M. J. and Yaxley, G. (1999) Prediction of siderophile element metal-silicate partition coefficients to 20 GPa and 2800 °C the effects of pressure, temperature, oxygen fugacity, and silicate and metallic melt compositions. Physics of the Earth and Planetary Interiors, 100, 115—134. 

Warren, P.H., Kallemeyn, G.W. and Kyte, F.T. (1999) Origin of planetary cores evidence from highly siderophile elements in Martian meteorites. Geochimica et Cosmochimica Acta, 63(13-14), 2105-22. 

Siderophiles elements that prefers to combine with iron rather than some other element. 

Rehkamper, M., and Halliday, A. N. (1997) Separation of Pt, Ir, Pd and other siderophile elements from geological samples with application to trace element geochemistry. Talanta 44, 663-672. 

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