METHODOLOGY FOR THE CLASSIFICATION OF MARBLE AND HORNFELS WASTE AT THE ANTAMINA MINE

The primary objective of this work is to evaluate and improve upon the waste rock classification system for a carbonate waste rock with high neutralization capacity. The current parameters used for classification are solid phase arsenic and zinc content, with some consideration for sulfide and visible oxide content. The approach to developing a classification procedure for each waste rock type was to integrate data obtained from mineralogical characterization, ongoing field cell experiments, and sequential and diagnostic leaching experiments.

Marble and hornfels waste rock samples were characterized using conventional analytical techniques such as particle size analysis, surface area determination, ICP analysis, optical microscopy, and scanning electron microscopy. In addition to these techniques, a Mineral Liberation Analyzer was used to determine modal mineralogy, mineral chemistry, ratios of sulfides to carbonates to silicates, and sulfide liberation by volume and surface area.

As an extension to this, sequential and diagnostic leaches were developed in order to identify and quantify the labile and non-labile elements in the various mineral phases and to characterize metal mobilization under acidic, circum-neutral, and alkaline conditions. The results of the initial characterization work, from the MLA in particular, were used to explain the observed leaching behaviour. Data and observations from the on-going field cell study were also used to validate trends and results obtained from the leaching experiments. The sequential leaching procedure was used to partition trace metals into five categories: ion exchangeable metals, carbonate bound metals, iron and manganese oxide bound metals, sulfide bound metals, and residual (silicates). This procedure was used for the determination of the solid phase sources of metals and to provide some insight into potential weathering behaviour and metal mobilization. A subsequent diagnostic leach was conducted in order to observe waste rock leaching behaviour under alkaline conditions (pH ~ 11); in particular the mobilization of elements such as arsenic, antimony, copper, molybdenum, and zinc.