The Rôle of volatiles in the formation of Virginia titanium deposits

Abstract

The feldspathic rock with which the titanium deposits of Virginia are associated appears to be an anorthosite, although the plagioclase is somewhat more sodic than in normal anorthosites. That is, this rock shows evidence of having been introduced as a mush‐like mass of crystals and intersititial magma, and of undergoing very thorough crushing during introduction. This rook was later very thoroughly altered by hydrothermal solutions which migrated through the fractures in the feldspar rook and new minerals including the titanium minerals—rutile and ilmenite—were introduced. The elements introduced into the feldspathic rock ware TiO 2 FeO, MgO, P 2 O 5 , and F. The other elements that went into the formation of new minerals were derived from the feldspar originally present. There was a distinct order in the abstraction of the introduced elements from the carrying solutions, as shown by the zonal relatione of the secondary minerals. Ferrous iron was abstracted first in the formation of the ferromagnesian silicates and ilmenite. Magnesium and titanium, in the absence of iron, traveled farther from the source of the solutions and deposited rutile and magnesian silicates. At greater distances most of the introduced elements had been abstracted from the solutions but notwithstanding this the feldspar was extensively altered, but without any marked changes between the chemical composition of the original feldspar rook and the resulting altered rook. ©1934. American Geophysical Union. All Rights Reserved.