Exploration geologists require mineralogical information that can aid them in recognizing key features in the field and when logging drill core. The ability to map mineralogical and chemical characteristics at the hand specimen or drill core scale allows features in question to be identified for future reference (Fig.1). Additionally, key relationships in the paragenesis of economic minerals can be identified. This is not only useful for the exploration geologist in guiding further work, but this information can also be used to direct initial metallurgical testwork at an earlier stage in the program such as resource level drilling.
An example of drill core and character sample mineralogy is given below where the spatial distribution of native gold and gold minerals in coarser grained pyrite veining highlights the association of Au with late pyrite (Fig.2). This also identified Au-telluride minerals as part of the Au-deportment distribution which warns the metallurgist to expect potentially poorer recoveries from slower dissolution kinetics associated with tellurides. The association of all identified gold grains and gold minerals with the coarser vein pyrite also suggests a possibility for coarser grinding and thus energy savings. This information can be determined at the drill core stage, well ahead of testwork and at the same time, providing information to the geologist on controls over gold mineralization. The aim at this stage is twofold; firstly to provide identification of characteristics in question to the geologist and secondly, to provide information to the metallurgist that can focus the future metallurgical test work.
Figure 1. Matching the detail and analytical capability of a scanning electron microscope with the need to examine samples on a macro-scale using half drill core or equivalent.
Figure 2. Coarser-grained pyrite (yellow veins) carries native gold grains and Au-telluride minerals in contrast to barren very fine-grained disseminated pyrite hosted in the quartz (grey) and feldspar (pink) metasedimentary rock. Au mineralization is a late stage event and the Au-telluride mineral fraction will give poorer Au recovery. The mineral map is for a 2.5 cm solid section character sample.