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.