Multi-element Associations Research Articles

Regional to detailed geochemical mapping of the Kariisk ore district, eastern Trans-Baikal region, Russia

The Kariisk ore district is situated in a dome-ring complex formed during late Mesozoic tectono-magmatic activity. The district comprises magmatic to post-magmatic vein-type mineralizations, which developed during four stages characterized by different mineral parageneses: (1) quartz-pyrite-tourmaline; (2) quartz-actinolite-magnetite; (3) quartz-arsenopyrite; and (4) quartz-carbonate-poly metallic. Geochemical surveys at regional to detailed scales involved ca. 12 000 rock samples which were analyzed for 40 elements including Au and associated elements Bi, W, Ag, B, As, Mo, Cu, Pb, Sn, and Zn. The results are presented as geochemical maps illustrating the distribution of anomalous gold and multi-element associations. The geochemically anomalous area shows a finger-like pattern radiating from the core of the ring complex and has a concentric zoning of element associations outwards from the margin of the core: W-Mo, Bi-Ag-B, Au-As-Cu-Pb, and B-Ag-Zn. These features are interpreted to reflect that the mineralising process induced by heat from the granitoid magma in the core of the complex occurred in a number of separate pulses.

Multi-element relationships and spatial structures of regional geochemical data from stream sediments, southwestern Quebec, Canada

A regional geochemical survey, covering an area of 10000 km 2 in the Grenville Province of southwestern Quebec, was carried out by the Quebec Department of Energy and Resources. The fine (<177 μm) and heavy fraction of stream sediments were analyzed for more than 25 chemical elements by ICPES and by INAA. This study aims to identify the main geological processes affecting the geochemical data of both media, by considering the multi-element relationships and spatial structures of the geochemical data. Fine fraction and heavy mineral concentrates were subjected to: (1) principal component analysis (PCA) to determine the inter-element relationships controlling the background variations; and (2) variogram analysis to establish the spatial continuity of geological phenomena associated with the factors of the PCA. The stability of PCA results was tested by using a bootstrap replication technique. Detailed geochemical and mineralogical studies were conducted on different densimetric and granulometric fractions in order to characterize the geochemical behavior of each fraction, and to relate the inter-element associations to a specific mineralogy. Our study shows that the fine and heavy fractions indicate different geochemical information. The background levels and the multi-element associations differ between both media. A principal component model shows that the fine fraction is strongly influenced by surficial processes, explaining approximately 55% of the data variability. Two factors accounting for only 23% of the data variability in the fine fraction are related to lithologies. The heavy fraction reflects lithological characteristics. Three factors, accounting for 51% of the variation in the data, represent mineralogical features of the principal lithologic units. Two other factors reflect geochemical components that could be related to mineralization or lithologies of interest for prospecting. The variograms reveal the different spatial variation components of the geochemical signals. They show high nugget effect (more than 40%), indicating the erratic occurrence of phases hosting geochemical signals in the sampled media. They allow the spatial scales of geochemical components to be recognized, and the geological phenomena associated with regional trends to be differentiated from those acting at local scales. Knowledge of spatial variation components provides useful information for estimating suitable sampling intervals with regards to geochemical surveys, and aids in proposing solutions for reducing the nugget effect.

Multi-element contamination of soils and plants in old mining areas, U.K.

Soils and plants were sampled from some old Pb-Zn mining and smelting areas in England. The results show that Pb, Zn, Cd, Ag, As, Sb and Hg concentrations in soils and plants from these areas are highly elevated compared with “normal background” levels and the control sites in this study. The enrichment and associations of metals are affected by three factors. (1) The nature of the underlying mineralised rock. (2) The mining activities which have produced widespread contamination. (3) The smelter pollution resulting in very high concentrations of metals in the immediate vicinity and downwind of smelters. The natural multi-element associations and multi-element contamination in these historical Pb-Zn mining and smelting areas are dominated by the presence of sulphide minerals. The typical trace element associations found are: in mining areas Pb-Zn-Cd-Ag-As-Sb-Hg; and in smelter sites Pb-Zn-Cd-Sb-As. These soil and plant results indicate that, in addition to Pb, Zn and Cd, the other toxic elements As, Sb, Ag and Hg are present as significant contaminants.

DEVONIAN CONODONT APPARATUSES AND THEIR VICARIOUS SKELETAL ELEMENTS

Recognition of four types of skeletal apparatuses of Devonian compound and platform conodonts, which conform in their basic plan to those already established in the Ordovician, Silurian, and Carboniferous, emphasizes the persistence of but a few structural types in the Paleozoic. The vicarious nature primarily of compound but also of platform elements in different multielement associations demonstrates mosaic evolution in Devonian apparatuses and has far-reaching taxonomic implications. Homologies of skeletal elements, for which a system of symbols is introduced, are evident in different apparatus types and show that the relationships of elements have been obscured by the older form taxonomy. Multielement analysis revises the taxonomic scope of the common Devonian genera, Icriodus, Polygnathus, and Ozarkodina. As a consequence of apparatus reconstruction, four new genera are proposed: Parapolygnathus, Cryptotaxis, Delotaxis, and Pedavis.