Barian feldspar and muscovite from the Kipushi Zn-Pb-Cu deposit, Shaba, Zaire

ABSTRAgT Barian-bearing feldspar and muscovite are associated with barite in the sulfide mineralization of the Kipushi Zn-Pb{u deposit (Zaire), hosted by Lower Kundelungu dolornites and dolomitic shales, in part brecciated, ofl,ate koterozoic age. The celsian (Cn) content of (BaK)-feldspan, which include celsian, hyalophane and orthoclase, varies from 1 to 84 mole 7o, but exhibits rwo discontinuifies, at Cn5-36 and Cn4j-56. The coexisting albite is mostly barium-free. The highest BaO content measured in muscovite is 7.66 w.Vo, but values around 6 wt.%o BaO are more common, even though the associated feldspars vary from Ba-bearing orthoclase to celsian. The replacement of K by Ba in muscovite follows the substitution BaAl = (K,Na)Si and is accompanied by increasing vacancies in octahedral positions and by the replacement ofAl by Ti. The muscovite also is phengitic, showing the exchange (Mg,Fe)'*Si* = ''Al'"A1. Structural and textural fabrics indicate that Kalangan regional metamorphism postdated the mineralization. It is characterized by mineral assemblages of the greenschist facies. We contend that barian muscovite and (Ba,K)-feldspar are metamorphic in origin, and that their baxium content was inherited from barite associated with the Zn-Pb{u