BENZAAZOUA Benzaazoua, and three co-authors, reported in 2007, that A multidisciplinary approach has been used to study Au occurrences within pyrite and arsenopyrite in four refractory Au ores from Colombia, France (Le Chaˆtelet and Villeranges) and Portugal (Neves Norte). The Au was characterized by optical and scanning electron microscopy and analysed using electron and ion microprobes to determine Au distribution, with particular attention to spectral interferences in electron and ion microprobes, background measurements in electron probes, and quantitative analysis using external standardization in ion probes. The ionic emission rate is proven to be dependent on the Au status; combined Au has a greater ion emission than metallic Au. Invisible Au occurrences are closely linked to As distribution. Gold bonding in arsenopyrite, examined by transmission electron microscopy, is shown to be dispersed within the FeAsS crystal structure. Typical growth patterns and As-Au diffusion zoning in pyrite and arsenopyrite may account for the very irregular distribution of Au in these minerals.
The authors concluded that A multi-analytical approach is needed to establish fully the nature of Au in sulphide ores. It consists of direct observation when Au is well expressed (visible), element analysis using electron, ion or proton probes to measure small Au contents, characterizing the chemical state of Au by wet chemical dissolution, determining the Au chemical bonding by various spectrometry techniques (Mossbauer, XPS, XANES, EXAFS, EPR, etc.), or by a crystallographic investigation followed by the use of XRD or TEM coupled with electron diffraction. This paper shows the results from some of these techniques on Au in pyrite and arsenopyrite collected from ore-bodies and processing plants where Au presents complex occurrences.
The Au within these ores frequently co-exists with particles of metallic Au in the same host mineral. The Au distribution within the pyrite and arsenopyrite is mainly non-uniform. Back-scattered electron images and X-ray mapping can reveal zoning and a common feature is Au-As overlap of zonings and positive correlation of local contents. Gold quantification by EMPA must take into account a background hole around the Au-La line that can lead to an underestimation of the amount present. SIMS is useful for mapping and quantifying the occurrences of very small amounts of Au.
Managed & Built by I2M Consulting, LLC | © 2010-
