## 4 Results
### Gold Alloys in the Ildeus Intrusion
SEM-EDS analyses of the surface of large Cu-Ag-Au grains display the following compositional variations: Cu from 26.4 to 45.0 wt.%, Ag from 4.0 to 13.8 wt.% and Au from 51.1 to 62.5 wt.% averaging Cu = 32.9 wt.%, Ag = 7.9 wt.% and Au = 59.0 wt.%. Nine analyses include 0.3-0.8 wt.% Ni. The SEM-EDS analyses of polished cross-sections through large Cu-Ag-Au particles exhibit roughly the same results, as follows: Cu from 27.3 to 36.6 wt.%, Ag from 3.7 to 13.0 wt.% and Au from 58.0 to 63.2 wt.% averaging Cu = 32.4 wt.%, Ag = 6.9 wt.% and Au = 60.8 wt.%. All analyzed compositions of Cu-Ag-Au grains are plotted in the ternary Cu-Ag-Au diagram in Figure 7.  
Although cross-sections (cuts) through individual Cu-Ag-Au grains appear to be texturally homogeneous in reflected light and during standard SEM studies, EDS analyses of different points on polished surfaces reveal distinct compositional variations. In order to resolve these compositional heterogeneities, we carried out detailed high-resolution SEM-EDS studies of this area. First of all, we strived to obtain the highest contrast image, which clearly revealed the co-existence of dark and bright zones in these grains (Figure 6f). The difference in BSE colors typically indicate a difference in chemical composition, which was confirmed by the construction of individual elemental maps, which are presented in Figure 6g (copper), Figure 6h (silver) and Figure 6i (gold). These BSE elemental maps emphasized presence of dark and bright areas with difference in color representing fine-scale compositional variations in individual metal concentrations and different compositional zones (different colors in BSE images in Figure 6f-i) displaying some typical plastic defor  
Figure 7: Composition of Cu-Ag-Au compounds recovered from olivine websterite IL-5 plotted on ternary phase diagram modified after [64] with additions from [65]. Solid lines depict liquidus temperatures at different end-member compositions. Please see text for additional explanation. mation features. The composition of individual zones with different (dark versus bright) colors is estimated using both an EDS analysis of the selected surface points and elemental maps obtained through surface areal scanning. The results are summarized in the inset in Figure 7, where <<dark>> data points correspond to measurements within dark zones and <<bright>> data points reflect results from ribbon-like areas between the dark-colored zones in BSE images in Figure 6f,h,i. Copper concentrations within the dark areas vary from 30.4 to 33.9 wt.%, silver--from 3.8 to 7.2 wt.% and gold--from 62.3 to 62.7 wt.% averaging Cu = 32.4 wt.%, Ag = 5.1 wt.% and Au = 62.5 wt.% (total of 10 SEM-EDS analyses). Copper content in bright areas ranges from 25.8 to 29.4 wt.%, silver--from 8.6 to 14.0 wt.% and gold--from 60.2 to 62.3 wt.% averaging 27.5 wt.% Cu, 11.4 wt.% Ag and 61.1 wt.% Au (total of 9 SEM-EDS analyses). Based on these results, dark areas are enriched in copper (+4.9 wt.% Cu on average) and depleted in silver (\(-\)6.3 wt.% Ag on average) at a nearly constant Au content in reference to the bright-colored zones. The integrated bulk chemical composition of this grain is estimated by spectral scanning of a 150 \(\upmu\)m by 150 \(\upmu\)m area (rectangle on Figure 6f): Cu = 30.4 wt.%, Ag = 7.4 wt.% and Au = 62.2 wt.%, green polygon symbol in the inset in Figure 7.