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chemical analyses for classification in most cases. The points plotted on figure 1 represent <br />chemical analyses of relatively unaltered samples. . <br />As a group, these rocks are distinguished by low silica concentrations (<49 wt% SiOZ), primitive <br />chemistries (high Mg/Fe ratios), and relatively high concentrations of Ni (>40 ppm) and Cr. <br />2.6 Group C: Niafic Lamprophyres, Phonotephrites and Tephrites <br />These rocks aze typically manifested as narrow (Qm), anastomosing a<td bifurcating dikes. They <br />aze found throughout the district, but conform to major structural trends. The dikes are <br />commonly porphyritic with biotite, pyroxene, amphibole and olivine phenocrysts (figure 4). The <br />phenocrysts aze enclosed within an analcime-rich feldspathic groundmass with biotite, pyroxene, <br />magnetite and apatite. In almost all cases, the rocks are substantially altered to clay and <br />carbonate minerals. <br />The compositions of these rocks suggest that they aze volatile-rich equivalents of alkaline <br />basalts. They show limited compositional variability (also reflected in [heir mineralogy), and are <br />classified as lamprophyric tephrites, phonotephrites and trachybasalts. Lindgren and Ransome <br />(1906) subdivide this group into three rock types; vogesites, monchiquites and trachydolerites (p. <br />90-97). In detail, however, the three rock types proposed by Lindgren and Ransome represent <br />end members of a continuous spectrum of compositions. <br />Figure 4: Photomicrograph of mafic <br />lamporphyre (40 x magnification, <br />crossed polazs). The large grain is a <br />zoned amphibole phenocryst (note <br />cleavage and habit). The red-brown <br />grains in the lower left are Ti-rich, <br />phlogopitic biotite. The groundmass <br />is composed of plagioclase, <br />r1 <br />LJ <br />Cripplr Creek & v¢ror GD(d mining Co. Shephrrd MJlrr.lnc. <br />~1DIMIONDIP-ORNE110056]lReryrtUnarRwa~].Jrc 7 Mnreh 1000 <br />