1.Ministry o Eneqy, Mines and Petroleum ResourcesfCARBONATITES AND SYENITE GNE,ISSCOMPLEXES IN METAMORPH0SE:DPRECAMBRIAN TO EARLYCAMIBR1:A:NSTRATA. OMINECA BELTMANSON CREEK AREA (93N/9) been deformed and metamorphosedto lower amphibolitefacies. The hostrocks include psammitic semipelitic mica toSyenite, monzonite and calmnatite occur together on schists,micaceousquartzitesandsomemarbleswhichstrikeboth the Lonnie (Granite Creek) andVergil (Brent) claims. southeasterly (15Oo-17O0)and dip steeply to the southwestThe two showings arelocated 3 kilometres apart, approxi-(7Oo-8O0)on average.mately 8 kilometres east of the placer mining village of The various rock units within each intrusive zone areManson Creek, 230 kilometres northwest of Prince George.distributed in interfingering lenses (Hankinson, 1958;Exposures are in trenches, between loo0 and 1.100metres Rowe, 1958; Halleran, 1980). The Lonniecarbonatite is upelevation, on wooded slopes; elsewhere outcrop is sparse. to 50 metres thick and traceable for nearly 500 metres (Fig-TheLonniecarbonatitecanbereachedbyanoldroad,which ure 27);theVergil showing is approximately30 mftres thickis passable by four-wheel-drivevehicle to within 1 kilome-and canbe traced for a few hundred metres.The effects oftre of the showing (latitude 554045N, longitudealkali metasomatism(fenitization) can be detected for a few1242315W). The Vergil showing,approximately5.5 kil-tens of metres beyond the intrusions.ometres from the nearest road, is accessible by helicopter oron foot (latitude 554245N,longitude 1242515W).CARBONATITESAt both showings, theintrusive rocks occurin single,W o varieties of carbonatite are present within the Lon-northwest-trending, sill-like sheets within uppermost Pre- nie complex: one is aegirine sovite in which the principalCambrian metasedimentary rocks the Wolverine Complexof components are calcite, microcline, perthite and aegirine;(Lang ef al., 1946). Both intrusive rocks and hostrocks have the other is biotite sovite, comprising calcite, b.iotite and~~~~~~ _-~~~~~ LEGENDS y e n i t em o n z o n i t em o n z a d i o r i t e ,,Aegerine-amphiboleenitefMylonitizedbiotitesoviteBiotitesoviteAegerine sovitelnferiayered ovife nd emipelitic chisl s a s sWolverine omplex iotite sammit?, C b ps e m i D e l i t i c c h i s tm i n o a u a r t z i l es, rFigure 21. Geological map of the Lonnie (GraniteCreek) carbonatite complex (contours metric), after Rowe, 1958Bulletin 88 37

2. usually plagioclase. Only biotite sovite occurs at the Vergil tain accessory muscovite, biotite, calcite and apntite.showing. Both the biotite and aegirine sovites are variably Nepheline syenite is also locally present and contains: sig-foliated and containapatite (up to 20%). magnetite and py-nificant amounts of zircon (3-15%).rochlore as accessory minerals. The biotite sovite may alsocontain zircon; columbite, ilmenorutile and ilmenite have FENZTESalso been reported (Hankinson, 1958). At the Lonnie show-ing, aegirine sovite occurs along the southwestern margin Pods andlayers of fenite occur within both the Lonnieof the complex and biotite sovite along the northwesternand Vergil intrusive complexes. The fenite is medium todark green in colour and rusty weathering. It consists ofmargin (Figure 27). The biotite sovite is variably myloni-aegirine and sodic amphibole (Plate 14) with microcline.tized, with the most intense shearing near the contact withthe country rocks. Enrichmentin zircon, pyrochlore, colum-plagioclase and calcite in varying amounts. The amphibolebite, pyrite and pyrrhotite has been noted nearthe contacts is strongly pleochroic, x -turquoise, y - colourless, z - PNS-of the sovites with syenites (Hankinson, 1958). sian blue, with colour strongest at the rims. It issimilar tothe amphibole at the Aley complex, which has been itlenti-fied as magnesio-arfvedsonite(Miider, 1986, 1987). TraceSILICATE PHASES constituents in fenites include pyrochlore, magnetite andFeldspathic intrusive rocks, monzodiorite, monzonite zircon.and syenite, outcrop as lenticular masses separating the car- The hosting psammitic and semipelitic schists arc rec-bonatite units (Figure 27). These intrusive rocks consist ofognizably fenitized for a fewtens of metres beyond the in-potassium feldspar (orthoclase or microcline) and plagio- trusive contacts. Microcline, plagioclase and quartz areclase in varying proportions; plagioclase greatly exceeds major constituents, with aegiriue and arfvedsonite dissemi-potassium feldspar in the monzodiorites,in the monzonites nated throughout, presumably replacing the original maficthe proportions approach equality and potash feldspar silicate minerals. Biotite is present in trace amounts only.greatly exceeds plagioclase in the syenites. All phases con- Calcite, apatite, magnetite and zircon may be present andPlate 14. Blue pleochroic amphibole (rnagnesio-arfvedsonite)and finer grained aegirine (light green) in ultrafenite, Lonnie area.Longdimension of photomicrograph is2.5 millimetres, (colourpkoto,page 135).38Geological Survey !ranch 3. ~~~ ~~~~ ~~~~ ~~ ~~ ~ ~coarse-grained arfvedsonite, magnetite andfeldspar segre-gations are developed locally.GEOCHEMISTRY Carbonatites in the Manson Creek area are all truesovites, no magnesio- or ferrocarbonatites were observed(Figure 28; Table7. Aegirine sovites are depleted in silica)and aluminum and enriched strontium, relative to biotiteinsovites. Fenites are notably enriched in iron and sodium,relative to other lithologies (Figure 29; Table 7. With in-)creasing degree of fenitization, that is from recognizablemetasedimentsto ultrafenite, the rocks exhibit a systematicincrease in iron and alkalis relative to calcium (Figure 30a)and fenitization appears to be a combination of typicaliron-magnesium andalkali fenitization trends. The fenites,even ultrafenites (aegirine and arfvedsonite rich) are en-riched in sodium relative to typical pyroxene-amphibolefenites (Figure 30b). J Syenitic rocks are quite vaned in composition (Figures Figure 28. CaO-MgO-Fez03t+MnO carbonatite pht, Lonnie29and31;Table7)but,onaverage,plotwithinthemiaskitic complex.TABLE 7CHEMICAL ANALYSES OF ALKALINE ROCKS, MANSON CREEK AREA "~ ~~~~~~~~~~ ~Syenites and contact syenites Fenite 76 8 9 10 141113 121515 -Si02 1.70 12.70 12.0013.70 7.814 0 56.70 53.77 36.441.051.09 32.8844.5035.9638.8273.1557.82Ti02 0.02 0.670.71 0.010.08 0.03 0.02 0.530.030.40 0.200.66 0.380.28 0 6 0.83.4 3.653.26 7.46 0.367.573.06 16.70 15.38 12.142.4811.61A12036.792.2214.30 14.93 11.74Fe203T 1.406.21 5.70 0.37 5.39 1.44 0.570.80 4.840.59 2.63 19.60 6.91 18.6311.66 4.52 0.590.37 0.24 0.16 0.28 0.230.11 0.260.15 0.25 0.370.24 0.30 0.340.24 0.115 0.31 2.20 1.85 0.60 1.210.170.12 1.730.181.36 1.15 2.482.111.13 1.112.112CaO 52.90 36.10 43.72 6.09 9.78 20.1936.60 48.29 16.30 8.85 23.1210.90 14.56 0.3424.21 1.34Na20 0.44 1.21 0.99 5.57 2.46 5.79 10.333.48 4.97 5.37 10.30 5.550.36 6.94 3.53 3.99 0.12 2.45 2.04 0.49 0.19 5.365.84 1.894.821.50 4.430.24 0.50 1.14 1.61 0.ZI4.417.48 17.897.9817.476.56 18.06 0.4611.48 0.770.61 1.051.29 1.650.34 0.760.71 1.130.05 0.0499.27 98.8298.7498.24 99.8985.9399.2799.5599.5998.13ppmNi