3.1.3. Mineralogy

The QEMSCAN® analysis by CSM agreed with the mineralogy described by light optical microscopy and SEM of the selected sample (see Section 2). Major and minor sulfides and silicates were confirmed. Electrum, hessite, and Bi-minerals were all detected (Figures 6 and 7d). Additionally, traces of molybdenite, cassiterite, uraninite and Ag-minerals (other than hessite) were detected. Many of these phases mark single pixels in the mineral map. The fine-grained clusters of calcite observed during petrographic analysis were resolved to be complex intergrowths of calcite, ankerite and Fe-Ox/CO3 (mostly goethite) (Figure 7d,e). Bi-minerals were categorized into Bi-tellurides and native bismuth/bismuthinite. No differentiation was made between Bi-tellurides (e.g., pilsenite and tetradymite). Similarly, native bismuth and bismuthinite were grouped together due to difficulties in separating Bi and S at the scan resolution in QEMSCAN® analysis. A total of seven pixels were identified as electrum (Figure 6). Follow-up work with the SEM-EDS confirmed these pixels correlated with six different grains of native Au and electrum in the sample. The grains were typically associated with quartz and often found within areas rich in Bi-minerals. The Au grains ranged in size from 6 × 12 μm to 2 × 3 μm (Figure 6). This means, despite their sub 10 μm grain sizes, a 10 μm resolution scan was sufficient to detect them. Further SEM-EDS studies revealed several more native gold and electrum grains (mostly <5 μm) in the immediate surrounding of the grains detected by the QEMSCAN® scan. Additionally, sub 5 μm droplet-shaped grains of native bismuth with partitioning of gold were frequently observed [19]. None of the pixels corresponding to these grains were identified as Au-minerals by the QEMSCAN® analysis of CSM.

Mineralogy was less detailed for the Boliden AB data set. Only 13 phases were distinguished by Boliden AB compared to 23 phases at CSM (which included all 13 phases from Boliden AB) (Figure 7). Minor sulfides were compiled under "other sulfides". Similarly, silicates were grouped together with the exception of quartz, tourmaline and chlorite. For trace metals, only "Bi-minerals" and "Au, Ag minerals" were distinguished but no pixels were identified for the latter. This means that the routine industry scan did not detect any gold grains from the analysis.

**Figure 6.** Areas of the QEMSCAN®mineral map by CSM (left) containing pixels identified as electrum (red) and corresponding backscattered electron images of the same areas by FEG-SEM (right). Gold grains detected by CSM and Boliden AB (after reprocessing) are false-colored in the BSE images. The Au grains detected by the CSM scan are also magnified. The magnified images are secondary electron images recorded by FEG-SEM.

**Figure 7.** (**a–e**) Optical microscopy images and corresponding areas in the QEMSCAN® mineral maps of CSM and Boliden AB. In (b), the smaller squares show a magnified image of the underlying area to highlight differences in the micro fracture density between the optical images and the mineral maps. The CSM map includes all the minerals presented in the legend. The original Boliden AB map does not subdivide groups and uses "Silicates" instead of "Biotite". The final version by Boliden AB uses the same mineral list as CSM but lacks "Ankerite", "Jacobsite" and subdivision of "Au, Ag minerals". It includes application of the "boundary phase processor" on chalcopyrite and a single-element entry to the SIP (database) with a 25% intensity threshold for Au.
