2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 13
Presentation Time: 8:00 AM-12:00 PM


GOLDNER, Brian D.1, THORLEIFSON, L. Harvey2 and WELSH, James L.1, (1)Geology, Gustavus Adolphus College, 800 West College Avenue, St. Peter, MN 56082, (2)Minnesota Geological Survey, University of Minnesota, 2642 University Avenue West, St. Paul, MN 55114, bgoldner@gustavus.edu

Garnets are used as indicator minerals for diamond exploration because garnet-bearing mantle xenoliths are commonly associated with diamondiferous kimberlites, with the underlying assumption that these xenoliths must originate in the diamond stability field. Erosion of these diamondiferous garnet-bearing rocks by glaciers or other processes will leave a dispersal train containing the more abundant garnet. Garnets from mantle xenoliths have been categorized into 12 different groups (labeled G1-G12) based on parent rock type and CaO, Cr2O3, and TiO2 contents. These groups aid exploration in that some garnets, principally those with harzburgitic and eclogitic affinities, are more conducive to diamondiferous pipes than other mantle rock types such as lherzolite. If garnets from these groups can be distinguished by using color rather than chemical analysis the process becomes more economic. A microprobe mount containing 318 garnets from groups G1, G2, G7, G9, G10, and G11 whose chemistries have already been determined were then viewed microscopically and digitized for color using a red-green-blue (RGB) scheme. While there appears to be an indication that some groups can be separated by color, for example G1 and G2 groups tend to be more orange, while groups G7, G9 and G10 tend to be more pink-purple, the data suggest difficulty in separating G9 (lherzolitic) from G10 (harzburgitic) garnets.