ABUNDANCE AND DISTRIBUTION OF DIAMONDS IN ECLOGITE REVEALED BY VOLUMEVISUALIZATION OF CT X-RAY SCANS

A diamond-bearing eclogite has been studied using industrial high-ener gy computed tomography and volume visualization techniques. Using this non-destructive technique, in which distinction between phases is bas ed on density differences, seven diamonds (five completely enclosed in the rock) have been isolated and viewed in three dimensions. Six diam onds appear to be single crystals of well-formed to malformed octahedr a. One is a spinel twin (macle). Partial to complete rimming by second ary barite provides sufficient density contrast with surrounding silic ates to allow the diamonds to be easily recognized by their morphology . They appear to be confined to a 1 cm-wide layer. Diamonds range in s ize from 0.9 to 2.4 mm in maximum dimension and are estimated to const itute 0.19 wt % of the sample, equivalent to a ''grade'' of 9500 carat s per metric ton. Several models for diamond genesis can be ruled out for this sample (e.g., pseudomorphs of graphite by diamond, precipitat ion as glomeroporphyritic aggregates from a magma), based on the detai ls of diamond distribution.