Petrology and Geochemistry of a Small Greisen Zone in Southwestern New Brunswick

Abstract

<p>A peripheral flourine-rich zone of a small post-techtoonic adamellite stock located in southwestern New Brunswick is examined. This apogranite zone contains aplite dykes, small pegmatite, quartz-flourite and greisen veins. Endogenetic alkali metasomatic modification of an originally porphyritic adamellite has resulted in the intracrystalline replacement of groundmass and plagioclase by large orthoclase perthite and quartz porphyroblasts. Low K/Rb and Ba/Rb ratios indicate this zone has favourable potential for mineralization resulting from residual fluids.</p> <p>Fracture controlled greisenization shows complete replacement of feldspars by quartz-sericite aggregates. Variations in sodium content of the greisen in indicative of pH conditions of post-magmatic fluids. Early stages show strong leaching of sodium by acidic fluids. Mineralization associated with these types of greisens is minimal. Later stage tin rise greisens have associated albitization overprinting the physic assemblage representing increasing pH conditions of the fluids.</p> <p>The greisen zone is interpreted to be either adjacent to or below any possible zone of potential tin mineralization. Another possibility is the post-magmatic fluid phase was too small for significant development of later state greisens.</p>