MAPPING OF LIGHT-TONED VEINS AND NODULES OF THE JOHN KLEIN BOREHOLE WALL IN GALE CRATER, MARS

Curiosity's drill collects powdered rock cuttings and delivers them to the CHIMRA device that sieves the sample and delivers portions to the SAM evolved gas and isotopic analysis instrument and CheMin XRD/XRF instrument. Curiosity’s first drill hole, named John Klein, was drilled on Sol 182 in the sediments of the Sheepbed member of the Yellowknife Bay formation. The drill spot included surficial light-toned veins determined by ChemCam to consist of sulfate minerals. After drilling, vertical MAHLI images showed that the 6 cm deep borehole was partially filled with drill tailings to a depth of ~ 3 cm. Both the vertical MAHLI images and a later ChemCam RMI image of the far wall of the drill hole showed well-defined, light toned veins. Along with RMI images (Sol 227), a vertical series of LIBS points on the drill hole wall confirmed the sulfate composition of the light-toned veins. This led to angled imaging of the borehole with MAHLI to determine the subsurface distribution of veins and the geological context for the LIBS analyses. The MAHLI images were chosen to cover the borehole walls from four cardinal directions. Images with the best contrast were selected and processed to enhance the visibility of the veins and assemble a complete set of images of the walls. The vein surface area was then mapped and the vein-to-total surface area percentage determined, indicating that the vein surface area in the upper half of the John Klein hole is ~5.2%. This is higher than the abundances of sulfate minerals (anhydrite and bassanite) determined by CheMin XRD analysis (Vaniman et al., submitted), but within estimated errors the abundances are similar. Errors in the XRD analysis include sieving to remove a coarse fraction which can bias the results. This result has implications for the abundance of veins in the hidden portion of the hole, as the sample collected by CHIMRA only comes from below a depth of 1.5 cm. Therefore, the abundance of veins in the upper 3 cm of the hole is roughly representative of the abundance of the homogenized vein sample in the lower 4.5 cm of the hole. The imaging and mapping of the drill hole walls provides useful complementary data to the bulk analysis of drill cutting by CheMin and SAM.