INDICATOR MINERALS FROM THE CL-25 KIMBERL ITE PIPE, SLAVE CRATON, NORTHWEST-TERRITORIES (CANADA)

Discovered in 1994, the CL-25 Kimberlite is the first pipe of a new ki mberlite field situated near Camsell Lake, within the Slave Craton, ab out 100 km south of the Lac de Gras kimberlite field. The location of the new field is controlled by a fault zone of NE strike, subparallel to the McDonald Fault Zone bordering the Slave Craton in the southeast . The CL-25 is made up of an intensely-altered kimberlite breccia rich in xenolithic material; chiefly, fragments of metamorphic and magmati c rocks of the crystalline shield. This contamination is expressed in relatively high contents of SiO2 and Al2O3 determined in the rock. The X-ray microanalysis was used to study compositions of representative amounts of garnet, picroilmenite, and Cr-spinels from intrusion. The g arnets are represented by Cr-pyrope of the lherzolite, harzburgite-dun ite, and wehrlite parageneses (Cr2O3 = 0.1-14.2 wt.%; CaO = 2.8-12.1 w t.%) and grossular-pyrope-almandine garnets from various types of eclo gites. The magnesian ilmenites have wide variations in their MgO (3.4- 12.5 wt.%), TiO2 (29.4-52.9 wt.%); Cr2O3 (0.3-6.3 wt.%) content. Three genetic groups of magnesianilmenites have been recognized on the basi s of this compositional variation and calculated hematite content. The Cr-spinels are characterized by wide ranges in their Cr2O3 (23.1-63.4 wt.%), Al2O3 (0.3-32.4 wt.%), TiO2 (0.01-4.2 wt.%), and MgO (5.2-18.2 wt.%) content. A notable feature of the spinel population is the pres ence of chromites with low MgO (5.2-9.5 wt.%) and high magnetite compo nent (19-37 mole %). The CL-25 Pipe clinopyroxenes are typical Cr-diop sides (Ca/(Ca+Mg) = 0.43-0.49), containing 1.1-3.2 wt.% Cr2O3; 1.3-2.7 wt.% Na2O with low amounts of Al-IV.The petrographic and petrochemica l characteristics of the breccia making up the pipe and the the compos ition of the indicator minerals suggest that it is a group 1 kimberlit e. During ascent to the crust, the kimberlite magma which formed the C L-25 Pipe sampled a large portion of the lithosphere beginning from de pths corresponding to the diamand-pyrope facies.