TRENDS IN METAL CONCENTRATIONS AND ASSOCIATIONS AS A FUNCTION OF PARTICLE SIZE IN MINE WASTES

Elevated levels of metal contaminants are of concern in a number of environmental systems. Such contamination come from a range of sources, but one of particular interest is that of mine tailings due to the extremely high levels of metals found in such materials. Examination of mine wastes for trends in metal concentrations as a function of particle size serves as an endmember model when trying to understand metal distribution, transport, and fate in the environment.

Mine waste and sediment samples were first gathered and studied from different mining regions throughout California such as former Au mines in the areas of Bodie and Red Mountain. These samples were initially separated through dry sieving into eleven different size fractions, ranging from particle sizes larger than 2830 μm to smaller than 20 μm. After separation, the mass of each fraction size was recorded to determine the mass distribution, and splits of each fraction size were analyzed to determine the concentrations of 48 different elements by Inductively Coupled Plasma Mass Spectrometry (ICP-MS).

The resulting data was represented in graphs displaying trends in concentration as a function of particle size. Percentages by mass of each element in each fraction size are also determined by the initial sample masses and the ICP-MS data. By looking at the concentration data, macroscopic trends were determined and each element was placed into one of nine categories that illustrate the relative trends of each of the 48 elements. Elements such as arsenic and mercury were of particular interest because most of the mine samples come from areas of known high concentrations of arsenic or the regions were either old gold or mercury mines.

From these analyses we can identify relationships between metals and particle size by examining their trends and associations and infer how this may relate to the environment. In addition, through the categorization process, correlations between elements can be discovered due to similarities in distributional trends. The techniques here are being used to determine mobility and bioavailability of metals, leading to a greater understanding of the environmental impacts that mine waste metals will have on a macroscale.