Trace Element Compositions Of Samples Research Articles

Patterns of trace element composition of caustobiolites and carbonic fluids according to the results of correlation analysis: A summary of results

Trace element analysis is a well-known research method. The article discusses the results of calculations of correlation coefficients of trace element composition of samples with model chemical content of the Upper, Middle and the Lower crust and biota. Unlike the commonly used methods for comparing the content of individual elements and groups of elements, this method, based on the use of the entire set of available trace element data, provides more robust results. The factual basis of the analysis is a database compiled of a large number of analyzes by different authors and including trace element composition data of organic matter of rocks, solid caustobiolites and hydrocarbon and carbonic deep fluids. The results of correlation coefficient calculations at a quantitative level confirm the previously made conclusions of the polygenic source of trace elements in naphthides, mud volcanic and carbonic fluids. The method makes it possible to estimate the depth of bottom the corresponding fluid systems and the dominant type of the original organic matter. A number of new relationships between the correlation coefficient values of the trace element compositions of the studied natural substances are revealed, in particular, the trend of changes in the correlation coefficients values of trace element content in specimens with the composition of the Earth’s crust and biota in the process of transformation of the initial organic matter into oil and further into oil degradation products. The results of the analysis testify in favor of the previously proposed model of massive oil genesis according to the scheme of a non-equilibrium flow reactor. Confirmation of this model allows us to propose on its basis a system of predictive indicators of possible high oil and gas content, which is required by practice in connection with the depletion of reserves of shallow traditional hydrocarbon deposits.

The geochemistry of banded iron formations in the sukumaland greenstone belt of Geita, northern Tanzania: evidence for mixing of hydrothermal and clastic sources of the chemical elements

Major and trace element compositions of samples of Banded Iron Formations (BIF) from the Neoarchaean Sukumaland Greenstone Belt of Geita in northern Tanzania reveal that the BIF precipitated from hydrothermal solutions. Fe-Ti-Al-Mn systematics suggest that the hydrothermal deposits have been contaminated, by up to 20% by weight, with detrital material having a composition similar to modern deep-sea pelagic clays. SiO2 and Fe2O3 contents are 48.2 to 88.5% and 8.9 to 49.1% respectively. Al2O3 contents lie between 0.33 and 2.1% and show no correlation with either Fe2O3 or SiO2. Al2O3 is, however, positively correlated with Ti, Ga, Hf, Rb,Th, Zr and Sr but not with CaO, the alkalies and the total Rare Earth Elements (REE). The other major element oxides are generally present in negligible amounts. The samples are characterised by mean Zr/Hf and 144Sm/143Nd ratios of 48± 5 (2 SE) and 0.10±0.01 (2 SE) respectively, similar to mean upper continental crustal values. Shale-normalised REE patterns are nearly flat, except for small positive Eu and very slight negative Ce anomalies and reveal that, compared to average upper crust, the abundances of the REE in the BIF are up to an order of magnitude lower. Chondrite-normalised patterns are characterised by light (L) REE enrichment, flat to slightly depleted heavy (H) REE, slightly positive Eu anomalies and very small negative Ce anomalies. The HREE-depleted patterns are similar to patterns derived from granite-dominated upper continental crust and indicate that the bulk of the REE in the Geita BIF can not have been derived from a mixture of Neoarchaean sea water and bottom hydrothermal solutions. The trace element data, and the REE in particular, indicate that, despite their relatively low proportions, granitic detritus probably derived from contemporaneous felsic flows and pyroclastics are the cause of the dominant trace element geochemical signature of the BIF. Tanzania Journal of Science Volume 27 (2001), pp. 21-36