HYPERSPECTRAL MAPPING OF A HYDROTHERMAL VUG AND ITS WEATHERING PRODUCTS AT THE HAUGHTON IMPACT STRUCTURE, CANADA
We infer the following alteration sequence. Marcasite formed first at elevated temperatures and under acidic and reducing conditions. At low temperatures and under acidic and more oxidizing conditions, thin brown coatings of gypsum and jarosite formed on the marcasite through very limited interaction with water. Then, a popcorn-textured mixture of fibroferrite and copiapite precipitated on relatively flat surfaces below the marcasite from acidic and more oxidized fluids. Further interaction with water dissolved some copiapite and fibroferrite, creating acidic fluids that reacted with the calcite host rock to form dark red coatings of gypsum and ferric oxide and sulfate.
This sequence of secondary phases shows transitions from high to low temperature, acidic to more neutral, and reducing to oxidizing aqueous conditions. In addition, some changes in mineralogy reflect interaction of fluids with the calcite host rock in addition to the marcasite. The sequence of mineral assemblages resulting from water-rock interactions over a scale of meters is similar to those observed at gossans and oxidized massive sulfide deposits on a much larger scale. In addition, the boundaries between assemblages mapped here have redox gradients ideal for microbial colonization as proposed by Izawa et al. (2011). Finally, this vug is the modern, surface expression of a post-impact hydrothermal system and has abundant low temperature weathering assemblages despite the initial hydrothermal origin.