GOLD MINERALOGY – APPROACH AND CHARACTERIZATION
Process Mineralogical Consulting Ltd.
Over the years many approaches have been developed to clearly understand the nature, mode of occurrence, and associations of both free-milling and refractory gold in a wide variety of geologic environments and plant products. Many approaches can be taken to characterize the ore which may occur as complex fine grained gold, ultra-fine grained gold, coarse nuggety gold and complex As-rich refractory gold. The approach taken will be dictated by:
The nature of the ore or plant product
The amount of sample material available
The gold grade and the grain size distribution
In many cases the study scope will be limited by sample availability but is nonetheless possible to generate a significant amount of information. In a typical case a thorough gold characterization study carried out at Process Mineralogical Consulting Ltd. would include the following elements:
(Schematic of Gold Concentration for Mineralogical Observation)
• Multiple head assays -Establish the grade, homogeneity, variability, and nugget effect of coarse gold.
• Size fraction assays – Is the gold preferentially concentrated in a particular size class(es)?
• Ore microscopy / petrography of coherent ore slices or fragments – Textural and mineralogical relationships, mode of occurrence and associations of visible gold (>0.5µm in size), microbeam analyses of metallic Au and other Au minerals.
• Preparation of heavy mineral concentrates from sized fractions (screening) of crushed or milled head. – Heavy liquid (Lithium Meta-tundstate), and a Superpan table are utilized to concentrate heavy particles for examination of fractions. These methods will concentrate specific refractory gold host minerals for Fire Assay analysis and systematic mineralogical examination.
• Systematic scans using an Automated SEM or optical microscope of the heavy mineral Superpan concentrate, middling, and tailing fractions as well as the Heavy Liquid float fraction will detect all Au particles >0.5µm in size. The exposed surface area of the grains will be measured and converted to weight, and details of the mineral association recorded to provide liberation statistics in conjunction with illustrations.
• Diagnostic Leach Tests – Statistically determines the association and distribution of gold within the various gravity products to determine the leachable and non-leachable gold occurrences not seen by visual mineralogical methods. This allows for a complete reconciliation of the accessible gold occurring in the sample. Some inference can be made on the refractory amount of gold present. This can provide a practical approach to gold assessment that will give an indication of the processing methods to be considered in future test work.
The appropriate selection of the approaches detailed above, are used individually or together to provide individual gold characterization based upon the available sample size or the specific information required. In the case of initial gold showings and early deposit drilling a reasonably comprehensive study should be undertaken to provide maximum mineralogical information that can assess the future drilling, and impact on the future processing circuit and recovery. An initial detailed characterization can be carried out on selected representative ore types chosen to provide reasonable coverage of the gold grade range present as well as geological and / or mineralogical differences that may be present. This would result in a relatively small number of samples (5-10) and their detailed study should provide a thorough understanding of the nature, mode of occurrence, association and deportment of gold in each. This information can then be used to design an integrated instrumental analysis approach that can be used to analyze large number of samples in an appropriate manner to further understand the deposit as a whole for resource modeling and metallurgical modeling. In addition representative concentrator feed material, flotation concentrates and tails and leach feed material can be analysed in a similar manner to characterise losses and leach limitations based upon Au speciation, grain size or textural occurrence.
At Process Mineralogical Consulting Ltd. we have the experience, equipment and knowledge to help you to determine the nature and deportment of the gold in your deposit. For more information and a quotation for this service or other mineralogical services please contact one of our representatives in our global offices.
Process Mineralogical Consulting Ltd.
North / South America
Europe / Africa / Asia