Elemental Analyses

Elemental Analyses

Elemental analyses using ICP-OES, ICP-MS and XRF have numerous potential applications in sedimentary geology.  The simplest use is as a stratigraphic tool, particularly where subtle changes in accessory minerals or clay type in otherwise monotonous sequences may result in significant variation in chemistry.  Such variation may be too small to be discerned using routine petrographic or mineralogical methods. Elemental data allow a 'chemostratigraphy' to be established for a  defined reference section, which can then be used in correlating adjacent sections.

Other applications of elemental analysis include:

  • The distinction of differing sediment source terrains

  • Evaluation/quantification of oxidation/reduction conditions during deposition based on the relative abundance of redox-sensitive elements such as Mn, Fe, Co, Ni, Cu and Zn

  • Determination of otherwise undetected diagenetic alteration in carbonate sequences (based on Sr-abundance); this is particularly important where techniques such as Sr-isotope analysis are being considered, and where diagenetic alteration would invalidate results.

Example ICP elemental dataset

Partial elemental dataset from separated belemnite samples.  The Sr, Fe and Mn abundance values highlighted in red are significantly different from those of other samples, suggesting diagenetic modification.  The associated Sr/Sr isotope values and age determinations are similarly anomalous, and were disregarded in this instance.  Samples from Upper Jurassic source rock facies of East Africa.

Elemental analysis techniques offered by Oolithica include:

  • X-Ray Fluorescence (XRF)
  • Inductively Coupled Plasma – Optical Emission Spectrometry (ICP-OES)

  • Inductively Coupled Plasma – Mass Spectrometry (ICP-MS)

XRF analysis provides abundance data on a wide range of major and trace elements. It is a relatively cheap analysis, but precision is significantly less than that attainable by ICP.

ICP-OES analysis is an inexpensive technique that provides precise data on the abundance of major elements (Si, Al, Fe, Mg, Mn, Ca, Na, K, P), trace elements (e.g. Ba, Co, Cu, Li, Ni, Sc, Sr, Ti, V, Y, Zn, Zr) and rare-earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, Lu)

ICP-MS analysis is more costly than ICP-OES but provides ultra-high (parts per billion) resolution elemental abundance data, and is particularly suitable for quantifying heavy elements such as Pb, Th and U.  With close sample-spacing this technique can be used to calibrate spectral gamma wireline logs, or to produce a relatively low-cost spectral gamma pseudo-log where wireline data are not available.

Detection limits of ICP-OES vs ICP-MS (in ppm unless otherwise stated) are as follows:

Element    ICP-OES      ICP-MS

Al2O3        0.01%          0.01%

CaO            0.01%          0.01%

Cr2O3        0.01%          0.01%

Fe2O3        0.01%          0.01%

K2O            0.01%          0.01%

MgO           0.01%          0.01%

MnO           0.001%        0.001%

Na2O         0.01%          0.01%

P2O5          0.01%          0.01%

SiO2           0.01%          0.01%

TiO              0.001%        0.001%

LOI              0.01%          0.01%

Ag               0.5              0.5

As               5 (0.5++)      5 (0.5++)

Au               ppb++)         (2 ppb++)

Ba               (2ppb++)       3

Be               1                 1

Bi                0.4              0.1

Br                (0.5++)         (0.5++)

Cd               (0.5+)           (0.5+)

Co               1                 1

Cr               20               20 (5++)

Cs               0.5              0.1

Cu               10               10 (1+)

Ga               1                 1

Ge               1                 0.5

Hf               0.2              0.1

In                0.2              0.1

Ir                 (5 ppb++)      (5 ppb++)

Mo              2                 2

Nb               1                 0.2

Ni                20 (1+)         20 (1+)

Pb               5                 5

Rb               2                 1

S                 (100+)          (100+)

Sb               0.5 (0.2++)    0.2

Sc               1 (0.1++)      1 (0.1++)

Se               (3++)            (3++)

Sn               1                 1

Sr                2                 2

Ta               0.1              0.01

Th               0.1              0.05

Tl                0.1              0.05

U                0.1              0.1

V                 5                 5

W                1                 0.5

Y                 1                 0.5

Zn               30 (1+)         30 (1+)

Zr                2                 1

La               0.1              0.05

Ce               0.1              0.05

Pr                0.05             0.01

Nd               0.1              0.05

Sm              0.1              0.01

Eu               0.05             0.005

Gd               0.1              0.01

Tb               0.1              0.01

Dy               0.1              0.01

Ho               0.1              0.01

Er                0.1              0.01

Tm              0.05             0.005

Yb               0.1              0.01

Lu               0.01             0.002

Ga               1                 1

Ge               1                 0.5

Hf               0.2              0.1

In                0.2              0.1

Ir                 (5 ppb++)      (5 ppb++)

Mo              2                 2