Chuck Bednar for redOrbit.com – @BednarChuck
NASA’s Curiosity rover has discovered two-tone mineral veins on a layered mountain which provides new clues of multiple fluid movement episodes on Mars, including some that occurred later than the wet conditions that formed after lake-bed deposits at its base.
Analysis of rock samples obtained by drilling at three different targets lower on the mountain has revealed what Discovery News has dubbed “a Martian mineral jackpot,” as each of them had a different mineral composition, with the most recent containing a silica mineral called cristobalite.
“Ice-cream sandwiches” reveal geologic history of Mars
The two-tone veins are located at a site known as Garden City in the Pahrump Hills region of Mount Sharp, and the US space agency explained that they look like a network of ridges which stands above the now-eroded bedrock in which they were formed.
The ridges, some of which are approximately 2.5 inches (6 centimeters) high and 1.25 inches (3 centimeters) wide, bear both bright and dark materials. NASA scientists believe that those layers indicate how Mount Sharp shows the geologic history of that region of Mars.
“Some of [the mineral veins] look like ice-cream sandwiches: dark on both edges and white in the middle,” said Curiosity science team member Linda Kah from the University of Tennessee, Knoxville’s Department of Earth and Planetary Science. “These materials tell us about secondary fluids that were transported through the region after the host rock formed.”
These types of veins typically form when fluids move through cracked rock, depositing minerals in the fractures and often altering the chemistry of the surrounding rock. Curiosity had found a bright veins composed of calcium sulfate at previous locations, NASA noted, and the new area’s dark material contains evidence of at least two secondary fluids, according to Kah.
Determining for the composition and timing of those fluids
The goal now, she explained, is to learn more about the chemistry of those fluids and to figure out the sequence of events that may have impacted the rocks in the area. Some of those events are understood: the mud that formed lake-bed mudstones located near the rover’s landing site had to have dried and hardened prior to the formation of the newly-found fractures.
Dark material lining the fracture walls are from a previous episode of fluid flow than the white veins of calcium sulfate, although each of those events also took place after the cracks formed, the agency added. The drilling sites, carefully selected following six months of examination of the Pahrump Hills region, also revealed clear differences in mineral ingredients.
“We investigated Pahrump Hills the way a field geologist would, looking over the whole outcrop first to choose the best samples to collect, and it paid off,” said David Blake of the NASA Ames Research Center in Moffett Field, California, principal investigator for Curiosity’s Chemistry and Mineralogy (CheMin) analytical laboratory instrument, explained.
The first site, “Confidence Hills,” had the highest levels of clay minerals and hematite, each of which usually form in wet conditions. The second, “Mojave,” had the highest level of jarosite, an oxidized mineral that contains iron and sulfur and which forms in acidic conditions. The third, “Telegraph Peak,” had little or no evidence of clay minerals, hematite or jarosite.
“The big thing about this sample is the huge amount of cristobalite, at about 10 percent or more of the crystalline material,” Blake said. In addition to cristobalite, a mineral form of silica, the site also appears to contain small amounts of another form of silica, quartz. It is possible that the processes removed other ingredients, leaving behind the silica. Alternatively, the dissolved silica may have been delivered by the fluids, or was deposited along with the original sediment.
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