The Redskin granite: Evidence for thermogravitational diffusion in a Precambrian granite batholith

The 1000-Ma-old composite Pikes Peak batholith consists largely of medium- to coarse-grained biotite granite but is intruded by several smaller granite plutons. Two of these, the Tarryall Mountains batholith and the Redskin Granite (Hawley, 1969; Hawley and Wobus, 1977), are here interpreted as cupolas atop the main mass of the Pikes Peak batholith.

Chemical analysis for 38 elements in rocks from the Redskin Granite, the Tarryall Mountains batholith, and the biotite granite of the Pikes Peak batholith support the contention that the compositions of the smaller plutons are unlikely to have evolved from that of the main mass of the batholith by crystal fractionation. It is believed that these compositions arose through liquid-state fractionation processes, possibly the convection-aided thermogravitational model of Shaw et al. (1976).

It is important to recognize that the chemical signature of this fractionation process can be discerned in holocrystalline rocks as well as in their glassy equivalents because the process may be instrumental in the formation of some kinds of lithophile ore deposits.