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T-4518 <br />overprinting and subsequent widening of MSPC alteration by MSPCAA alteration. <br />79 <br />Though the same may be true of veins and related alteration in the Precambrian rocks, this <br />relationship was not observed there. <br />MSPCAA alteration is the only economically significant alteration type because it <br />developed during base- and precious-metal mineralization. The abundance of muscovite, <br />sericite, phengite and adularia suggest that a significant amount of potassium was <br />introduced into the host rocks by the mineralizing system. A potassium anomaly mark:c <br />mineralized azeas of the Caribou district <br />smecdte-kaolinite alteration developed during dolomite mineralization. It consists <br />of smecdte and kaolinite identified by x-ray diffraction of glycolated clay separates <br />(Appendix F). Francis (1987) described montmorillonite (a type of smecdte) alteration in <br />the neazby Caribou deposit. In both the Cross and Caribou deposits, it occurs as blue- <br />green soft friable rock with abundant fresh biodte (Fig. 46e). Smectite-kaolinite alteration <br />has no economic significance; it occurs primarily in monzonite and only in zones not <br />previously altered to MSPC or MSPCAA. <br />.~ <br />