| | Magmatic and Postmagmatic Processes in Tin-mineralized Granites: Topaz-bearing Leucogranite in the Eurajoki Rapakivi ... |
 | | DEPARTMENT OF GEOLOGY, P.O. The 1·57 Ga Eurajoki stock in southwestern Finland is composed of biotite-hornblende-fayalite granite, biotite granites and late-stage topaz-bearing granite, as well as related topaz-bearing rhyolite (ongonite) dykes. |
 | | Cassiterite occurs in the Eurajoki stock in three different associations: (1) in the topaz-bearing granite as a ubiquitous accessory mineral; (2) in pegmatite dykes and pockets; (3) in greisen and quartz veins. |
 | | The occurrence of magmatic topaz in Eurajoki in two or more generations (euhedral topaz inclusions within quartz phenocrysts in rhyolite and quartz megacrysts in granite; topaz phenocrysts in rhyolite; subhedral topaz grains in the matrix of granite and rhyolite) is probably related to crystallization at different pressures. |
| www.oxfordjournals.org /our_journals/petroj/online/Volume_38/Issue_12/html/ega083_gml.html (6482 words) |