Automated Scanning Electron Microscopy (ASEM) systems are applied in the mining industry to quantify the mineralogy of the ore feed and products. With society pushing towards sustainable mining, this quantification should be comprehensive and include trace minerals since they are often either deleterious or potential by-products. Systems like QEMSCAN^® offer a mode for trace mineral analysis (TMS mode); However, it is unsuitable when all phases require analysis. Here, we investigate the potential of detecting micron-sized trace minerals in fieldscan mode using the QEMSCAN^® system with analytical settings in line with the mining industry. For quality comparison, analysis was performed at a mining company and a research institution. This novel approach was done in full collaboration with both parties. Results show that the resolution of trace minerals at or below the scan resolution is difficult and not always reliable due to mixed X-ray signals. However, by modification of the species identification protocol (SIP), quantification is achievable, although verification by SEM-EDS is recommended. As an add-on to routine quantitative analysis focused on major ore minerals, this method can produce quantitative data and information on mineral association for trace minerals of precious and critical metals which may be potential by-products in a mining operation

Sustainable mining, including the utilisation of an ore body to its full potential, is becoming increasingly important for human society as the demand for metals increases. In order to maximise the recovery of useful metals, detailed characterisation of the ore prior to processing is vital. Characterisation should include major and minor ore minerals, gangue minerals, and also trace metals. Trace metals despite their low abundance are often particularly important, either due to their high economic value and criticality for society, or their negative impact on the quality of the main commodity recovered and/or the environment. To properly characterise trace metals in an ore deposit the use of micro-analytical techniques is necessary. Nowadays, a plethora of techniques exist, each with their own strengths and weaknesses. In the mining industry, automated scanning electron microscopy systems are widely used. These systems allow for rapid mineralogical characterisation and quantification of a sample and are commonly used to quantify the mineralogy of the ore feed and subsequent products. Operators of these systems benefit from prior knowledge of the mineralogy of a sample/deposit to fine-tune their processing software to deliver data of highest quality. In this study, a method to improve trace metal characterisation in ore deposits with automated scanning electron microscopy systems is presented. It is implemented as a case study on the Liikavaara Cu-(W-Au) deposit in northern Sweden. The deposit is enriched in several trace metals including Au, Ag, Bi and Sn, and is planned for production in 2023. The mine will produce Cu as the main product and Au and Ag as by-products, and the processing of the ore will be performed in the nearby Aitik plant. For this study, a detailed geological and mineralogical investigation of the deposit was performed prior to analysis with the automated scanning electron microscopy system. A good understanding of the mineralogy is necessary to be able to select a representative sample for the subsequent automated analysis and to guarantee optimal data quality produced by the automated system, and to judge the performance of the automated system, to improve the method of analysis.

Manuscript 1 deals with the geological description and genetic aspects of the Liikavaara ore deposit. Results indicate that Liikavaara is an intrusion-related vein-style deposit. Mineralisation is hosted by quartz-tourmaline and calcite veins in a metadiabase that is partly metamorphosed to biotite schist. A 1.87 Ga granodiorite intrudes the footwall. Aplite dikes, genetically related to the intrusion, crosscut the metadiabase host rock. Mineralised veins are concentrated in and around these dikes.

Manuscript 2 deals with method development of automated mineralogical analysis. A sample from a mineralised quartz-tourmaline vein at Liikavaara was analysed in great detail with the QEMSCAN^® system. Apart from ore minerals in major and minor abundance the sample also contains ore minerals in trace quantities, e.g. Au and Ag minerals. The sample was analysed using two different analytical settings, at two different laboratories, one typical of a production-focused industrial approach and one quality-focused scientific approach. A first analysis using the industrial approach was unable to detect any Au and Ag minerals in the sample. By modification of the QEMSCAN^® mineral reference library, through iterative use of the data from both the industrial- and the scientific approach, detection and quantification of Au and Ag minerals was successful. This method can be implemented as an add-on for routine industrial analysis by automated scanning electron microscopy systems to gain information on trace metal occurrence and distribution. This information can then be used for targeted sample selection for further in-depth analysis of the trace metal content and occurrence in the deposit.

The Liikavaara Cu-(W-Au) deposit is situated proximal to the Aitik Cu-Au deposit in northern Sweden. It shows occurrence of scheelite and enrichment in trace metals including Au, Ag and Bi. In this study, petrological, mineralogical and geochemical investigations of the host rocks and ore, and geochronological analysis of a footwall intrusion were carried out. The ore is hosted by a metadiabase partly metamorphosed to biotite schist. The wall rocks are composed of metavolcaniclastic rocks of andesitic to basaltic composition. A granodiorite intrusion occurs in the footwall and related aplite dikes cut the deposit. Veins of quartz (±tourmaline) and calcite are numerous. Mineralisation is bound to these veins and their distribution is controlled by the aplite dikes. Chalcopyrite, pyrrhotite and pyrite are major in abundance. Sphalerite, galena, scheelite, molybdenite and magnetite are minor. Gold occurs native and as electrum and Ag is mostly bound in hessite and acanthite. The bismuth mineralogy is diverse but native Bi, pilsenite, bismuthinite, and tetradymite are common. A single grain of Sb (breithauptite) was observed. The major and minor minerals show intergrowth and replacement textures. The trace minerals are found as inclusions, along the borders and in cracks in the major sulphides, sphalerite, molybdenite and quartz. The footwall intrusion is dated at 1.87 Ga and suggested to be the source for ore genesis. The dikes may have acted as pathways for the magmatic hydrothermal fluids that carried the ore from the intrusion to the host rock.

The Liikavaara Cu-(W-Au) deposit is located in the Gallivare ore district in northern Sweden, a few kilometres east of the renowned Aitik Cu-(Au) deposit. Its enrichment in Critical Raw Materials and its scheduled production for the near future make the Liikavaara deposit ideal as the subject of a case study on improved ore characterisation using various micro-analytical techniques. Here we present a general overview of the mineralogy in Liikavaara to provide a base for future micro-analytical studies. The deposit lies within Palaeoproterozoic volcanosedimentary rocks of andesitic composition. A unit of biotite schist hosts the ore. Mineralisation in Liikavaara is mainly controlled by quartz-(calcite)-(tourmaline) veins. Aplitic dykes and calcite veinlets also cut the deposit. Ore minerals are chalcopyrite, pyrrhotite, pyrite, sphalerite, galena, and molybdenite. Non-sulfide sources include scheelite and minor magnetite. The deposit is affected by alteration such as sericitisation, calcification, tourmalinisation, epidotisation, and chloritisation. The genesis of the deposit is up to today not determined and studies are few. However, the deposit's spatial proximity to a mineralised granodiorite dated at ca. 1.87 Ga offer some similarities to the Aitik deposit and its 1.89 Ga quartz monzodiorite. A primary magmatic origin with later IOCG overprint could therefore be a possibility.