THE GEOCHEMISTRY OF PHLOGOPITE AND CHLORITE FROM THE KIPUSHI
Zn-Pb- Cu DEPOSIT, SHABA, ZAIRE
MUMBA CHABU
Laboratoire de Métallogénie, Université de Lubumbashi, B.P. 1825, Lubumbashi, Zaïre
Abstract
Phlogopite and chlorite have been found in the Kipushi Zn-Pb- Cu deposit, which is
hosted by Lower Kundelungu dolomite and dolomitic shale of Late Proterozoic age, and by
karstic chimneys and solution-collapse breccias. Electron-microprobe analyses of these minerals indicate that
the highest fluorine contents, ranging from 4.41 to 6.39 wt.%, are found in ore-related phlogopite, which also
is the most magnesian (XMg may exceed 0.99) [XMg: Mg/(Mg + Fe)] and the closest to
the phlogopite end-member [Xphl (Mg/total octahedral cations) up to 9.95]. These F contents are compatible
with the Fe-F avoidance rule and with a disordered distribution of atoms on the octahedral and OH-F
sites. In general, Xphl, F and Si vary sympathetically, whereas Xphl and VIAl are negatively correlated. Chlorite exhibits
a very low F content (0 - 0.73 wt.%) and a considerable spread in composition, with XMg values ranging from
0.32 to 0.84. The more Fe-rich chlorite is associated with Fe- rich sphalerite (up to 7.86 mol % FeS)
as the dominant sulfide. Chlorite in association with chalcopyrite ores has XMg values around 0.76. The most magnesian
chlorite (XMg 0.83) occurs in barren shale of the "Série récurrente", above the mineralization. Calculations
of log[f(H2O)/f(HF)] based on calibrated F<0150>OH exchange relations between fluid and biotite indicate
higher relative activity of fluorine in mineralized areas than in barren rocks. Phlogopite and chlorite are
considered to be of metamorphic origin; their composition is interpreted in terms of 1) increasing f(F) and f(S2)
as the orebody is approached, and 2) changes in bulk composition. The emplacement of the orebody probably
predated the peak of the Lufilian (Katangan) Pan-African orogeny (650-500 Ma).
Keywords: Kipushi Zn-Pb-Cu deposit, Katangan, Lower Kundelungu Group, phlogopite, chlorite,
XMg, F-OH exchange, Lufilian orogeny, Zaire.