Townend Mineralogy Laboratory specialises in the provision of mineralogy, petrology, and petrography services to Western Australia’s commodities industries.
Base metals, particularly copper, lead, zinc, cobalt and nickel occur as primary sulphides in various types of geological environments. These are principally studied in polished thin sections supplemented by SEM/EDS where non-stoichiometric minerals such as sphalerite are found, or where there are complex polymetallic sulphides to be identified.
Nickel has been important as secondary minerals in lateritic environments where it occurs as substitution in silicates, oxides etc., which are not specifically nickel minerals. The samples require a combination of petrography, XRD and SEM to properly locate the site of the nickel, and cobalt, which is also another valuable base metal that can be present.
The petrographic/mineragraphic examination of gold bearing rocks and cores etc. is concerned with the gold’s grainsizes, composition (silver content) and associated gangue minerals. In addition, in some deposits it occurs as tellurides, which must be identified.
Because of the low-grade nature of gold deposits, usually in ppm, locating the gold in the rock/core sample can be an issue. In the absence of obvious associates such as sulphides, the sample should be examined as fragments similar to RC chips allowing a more comprehensive search. The SEM may be used as a search tool where grainsizes are particularly fine. An alternate method is to crush the rock/core samples and concentrate the gold using heavy liquids, which is an in-house facility. Where coarse gold is suspected in the presence of sulphides, Townend Mineralogy Laboratory’s super panner is used to concentrate the former.
In arsenic bearing sulphide gold ores, the possibility of solid solution gold in arsenopyrite and pyrite must be tested. The presence of arsenic in pyrite is a guide to the presence of this type of gold. Ultimately, the quantity of this form of gold is determined by electron probe microanalysis.
Townend Mineralogy Laboratory has experience in high-grade hematite ores, martite-goethite ores, Channel Iron Deposit ores (CIDs), Detrital Iron Deposits (DIDs), magnetite and oolitic ores.
Core, grab and RC chip samples can be studied by optical microscopy to identify the main iron bearing minerals and their grain sizes, as well as the gangue minerals and their associations. The identification of secondary hydrohematite and goethite is important for metallurgical processes. XRD analysis can complement these studies with identification of important gangue phases such as kaolinite, quartz and gibbsite. SEM/EDS analyses, including elemental maps, are important for locating aluminium and silicon, which is especially important for CIDs and DIDs.
Rare Earth Minerals
Traditionally, rare earth minerals were only studied as monazite in mineral sand deposits. In recent times rare earths significantly increased importance has led to the exploration for monazite and other rare earth minerals such as xenotime, bastnasite and synchysite, in hard rock environments. While some minerals can be identified by polarising microscope, their proper elucidation usually requires the use of the SEM EDS. Ideally their study is a combination of petrography and SEM.
Where grades are high, the XRD is also used to identify rare earth species. Some rare earth minerals contain elevated thorium and uranium, which requires SEM/EDS analyses.
Rare earth bearing deposits that have been examined include Mt Weld, Cummins Range, Ilmaussaq (Greenland) and carbonatites in Brazil and Africa.
Uranium and thorium occur in a variety of environments and minerals. Frequently they are very fine-grained and difficult to identify by petrographic methods. Methods of examination are similar to those of the rare earths, using SEM/EDS and optical microscopy.
Graphite has recently become of interest economically. It has certain requirements in terms of flake size and lack of inclusions, which can only be determined by optical and SEM microscopy.