Ann: Positive Assay Results Continue at Callisto Discovery, page-139

My understanding is that it's an image processed from data collected during an aeromagnetic survey. The hot colours (white, red, orange, yellow) show magnetic highs and the cooler colours (green, blue, magenta) magnetic lows. Many ultramafic rocks are magnetic and can show up as hot colours on such images and hopefully the particular ultramafic host rocks that we are interested in (pyroxenite ? peridotite?) are showing up as the elongated roughly N-S feature on the eastern side (the Mt Thirsty sill). The hot colours to the west are thought to reflect komatiite ultramafic, another type of magnetic ultramafic rock.