Figure 8. Botryoidal secondary mineral precipitate.(a) BSE image of a botryoidal, layered secondary mineral crust deposited on the edge of the igneous rock in sample C2. (b)Zoom-in on botryoidal crust, indicated by the yellow arrows.(c) BSE image of the botryoidal mineral crust in another location in C2. (d-g) Elemental maps of silicon, calcium, copper, and aluminum present in the section presented in (c).(h) EDS spectrum of spot 19 (secondary mineral, pane c), showing copper and aluminum enrichment, possibly indicative of chrysocolla. (i) EDS spectrum of spot 20 (lava rock, pane c), showing unaltered augitic pyroxene.
In sample B5 from Cave B, we observed a more complex secondary mineral precipitate, with additional elemental enrichments and more discrete layering (Figure 9). This precipitate was not as botryoidal in appearance as that of sample C2, but was also enriched in copper and displayed distinct layering when mapped with EDS. It is clear that the copper occurs in the entirety of the deposit alongside all other elements (Figure 9f), however the amount of aluminum it is associated with varies in the different layers (Figure 9g). Additionally, there is a manganese-enriched layer that occurs in a silicon- and aluminum-poor region, as seen when comparing Figures 9e to 9d and 9g.
We were able to better distinguish the distribution of elements in the precipitate by mapping a small area with an excitation voltage of 10 keV for better spatial resolution of elements (Figure 9h). The EDS map sum spectrum in Figure 9m shows copper, aluminum, manganese, and phosphorus enrichments. The elemental maps confirm that manganese occurs in silicon-poor regions (Figure 9i) and that manganese and aluminum are competing (Figure 9j). Comparing Figure 9j to 9i and 9k, it is evident phosphorus enrichment occurs in silicon-poor regions, suggesting discrete phosphate minerals that contain copper. The outer layer of the complex crust is carbonate-bearing, as seen by the increased carbon level in the elemental map in Figure 9l, distinctly separate from the strong carbon signal produced by the epoxy above it.