Js. Ogola et al., FLUID INCLUSION AND CATHODOLUMINESCENCE STUDIES ON FLUORITE FROM THE KERIO VALLEY, KENYA, Journal of African earth sciences, and the Middle East, 18(4), 1994, pp. 309-323
The Kerio valley lies between the Elgeyo escarpment and the Tugen hill
s which mark the western margin of the Kenya rift valley. The main flu
orite deposits are located in the southern part of the valley at Kimwa
rer, Choff and Kamnaon. Three types of inclusion fillings were identif
ied: Liquid+Vapour, Liquid+Daughter Minerals and Liquid. The L+V type
is dominant. Inclusions occur as clusters, trails along the crystal gr
owth zones and as isolated ones. Low salinities, apparently lower than
the 5% wt. NaCl equivalent, were established. Homogenization temperat
ures suggest that fluorite mineralization took place at different stag
es and at temperatures between 120 and 180 degrees C. Isolated reading
s above 180 degrees C may be referring to the original inclusions in l
imestone. These measurements and the absence of CO2 in the inclusions,
as well as the occurrence of vugs and crustifications within fluorite
, suggest that mineralization took place at relatively shallow depths.
Emission spectrum lines representing Eu2+ Dy3+, Tb3+ and Sm3+ in fluo
rite were identified. Sm3+ was detected only in the pinkish luminescen
ce of veined fluorite: whereas the pinkish zone in banded fluorite con
tains Tb3+. Eu2+ which gives the strongest emission lines in the blue
part of the visible spectrum, apparently is responsible for the strong
blue cathodoluminescence (CL) in fluorite. The dominance of Eu2+ peak
s further points to the fact that fluorite mineralization in the Kerio
valley took place in an environment that was enriched in Lanthanide R
are Earth Elements (LREE). The presence of rare earths and radioactive
elements in fluorite points towards their enrichment in the environme
nt of fluorite mineralization. A juvenile origin of mineral forming so
lutions is proposed. Two generations of fluorite were established: all
otriomorphic fluorite, forming the matrix, and the idiomorphic variety
, occurring either in barite or in druzes in early fluorite. Barite in
turn farms idiomorphic crystals in allotriomorphic fluorite. Relies o
f calcite occur in both K-feldspars and in early fluorite. Oxides and
hydroxides of Fe, Mn,Ti and Al commonly occur in open spaces in fluori
te. Of significance is the presence of gold in fluorite. Fluorite mine
ralization is of hydrothermal origin in the post-Miocene era and was f
ormed as a result of metasomatic replacement of marble and open space
fillings.