Halogen Contents of Mineralized Versus Unmineralized Potassic Igneous Rocks

Abstract

Previous studies have established the important role of halogens (Cl, F) for the transport of metals in ore deposits related to igneous rocks (Holland 1972; Kilinc and Burnham 1972; Gunow et al. 1980; Boudreau et al. 1986; Carten 1987; Webster and Holloway 1988, 1990; Richards et al. 1991; Webster 1992; Stanton 1994). It seems likely that the development of postmagmatic hydrothermal ore deposits depends less on the abundance of the ore metals than on the availability of appropriate mechanisms to concentrate, transport, and deposit the metals (Roegge et al. 1974). The presence of sufficient halogens such as CI and/or F in the magmas appears to be the most important chemical parameter (Roegge et al. 1974). Chlorine largely controls the abundances of chlorophile ore and associated elements (e.g. Fe, Mn, Na, K, Cu) in saline aqueous fluids that exsolve from a magma (Webster 1992), and it also increases PGE solubilities in both sulphide and silicate melts (Peach et al. 1994). In the rock-forming minerals, Cl generally occupies the hydroxyl sites of micas, amphiboles, and apatites (Fuge et al. 1986). The strong affinity of the halogens for potassium, particularly in micas, can be explained in terms of their electronic configurations (Cocco et al. 1972).