Geology Reference
In-Depth Information
Crustal zircons from two of the Kundelungu kimberlites
in the eastern group (Gungwania and Talala pipes) have
been dated, using U-Pb and Hf-isotope analyses, with results
indicating that the basement is Palaeoproterozoic in age
(Batumike et al. 2007 ). The kimberlites have intruded unde-
formed mudrocks, sandstones and limestones of the
Neoproterozoic Biano Subgroup of the upper part of the
Katanga Supergroup (Kampunzu and Cailteux 1999 ).
Palaeontological material from crater sediments from
the Cango (Kango) kimberlite (approximately 9.7 ha in
size) includes frogs (family Pipidae, subfamily
Xenopinae) , a gastropod (genus Planorbis ) and plant mate-
rial in an ostracod-rich matrix (genera Zonocypris and
Ilycypris) , and were initially interpreted as Late Jurassic
to Late Eocene in age (Saxby 1982 ). However, some of the
fossils are similar to those found in Eocene crater
sediments in the Mahene kimberlite in Tanzania (Jacobs
and Heredeen 2004 ) and in late Cretaceous crater
sediments in the Banke (Haughton 1931 ) and Stompoor
(Smith 1986 ) kimberlites in South Africa. Based on strati-
graphic evidence, Demaiffe et al. ( 1991 ) suggested a Cre-
taceous age for the Kundelungu kimberlites. Recent U-Pb
dating of groundmass perovskite of two of the bodies
(Kambeli and Msipashi pipes), which occur in the southern
end of the eastern group (Fig. 17.2 ), has provided an age of
32
17.4 Kasai Oriental Mbuji Mayi Kimberlite
Field (Mbuji Mayi and Tshibwe Clusters)
17.4.1 Mbuji Mayi Kimberlite Cluster
The first diamonds in Kasai Oriental Province were discov-
ered at Lukelenge by Young in 1918 along the Mbujimayi
River (Figs. 17.1 , 17.4 and 17.5 ). It was only in 1946 that
Magn´e recognized from an electrical survey that the rich
eluvial deposits were underlain by kimberlite pipes, locally
called
(Bardet 1974 ). The discovery of Massif-1
triggered large-scale systematic prospecting of the high
terraces and hills of the Bakwanga (Mbuji Mayi) area and
resulted in the discovery of a cluster of ten pipes (M1-M10),
six of which are crater- to diatreme-facies pipes and four are
interpreted as in-fills of kimberlite in topographic (karst)
depressions. These bodies comprise the Northern Group of
Mbuji Mayi kimberlites and nine of these occur in the MIBA
Mining License known as the
Massifs
(Fig. 17.4 ).
Follow-up work to determine the source of diamonds in
the Mbujimayi River and associated Mudiba and Katsha
tributaries resulted in the discovery of six further pipes to
the southwest of Mbuji Mayi town, inclusive of the Tshibwe
pipe (Fig. 17.5 ).
The kimberlite pipes of the Mbuji Mayi Cluster occur to
the south of Mbuji Mayi town and are primarily aligned
along an E-W trend (Figs. 17.5 and 17.6a ). They are
emplaced through Archean basement, and siliciclastic
sediments and stromatolitic, dolomitic limestones of Neo-
proterozoic age of the Mbuji Mayi Supergroup (Delpomdor
et al. 2013 ; and Chap. 2b), which are overlain by arenaceous
sediments of Cretaceous age. Narrow feeder pipes have
intruded through the hard limestones and expanded dramati-
cally into the overlying and unconsolidated sediments and
resulted in
Polygon
2 Ma (Batumike et al. 2008 ).
17.3 Kasai Oriental Kabinda Kimberlite Field
Two clusters of kimberlites were discovered during explo-
ration by the joint venture betweentheDeBeersGroupand
Bugeco S.A. to the east of the village of Kabinda, some
100 km east of Mbuji Mayi in the eastern part of Kasai
Oriental Province (Fig. 17.1 ). The Kasendou cluster was
discovered in 2005 and consists of eight bodies whilst the
two known kimberlites of the Lukashi cluster were found in
2007 ( www.bugeco.com ,Fig. 17.3 ). The kimberlites
include crater-facies volcaniclastic, resedimented volcani-
clastic and coherent magmatic varieties and were emplaced
through Neoproterozoic dolomitic limestones of the Mbuji
Mayi Supergroup with dolerite sills, and overlying Meso-
zoic siliciclastic sediments (Walker 2011 ). Micro- and
macro-diamonds have been recovered from some of the
kimberlites ( www.afdiamonds.com ) . The largest pipe is
estimated to be approximately 10 ha in size and the com-
bined total surface area of the kimberlites reaches some
35 ha. In 2008, De Beers withdrew from the joint venture
because of the worldwide economic crisis and the small
size and low grade of the kimberlites (African Diamonds
plc. 2009 ;USGS 2008 ).
intrusions. The upper
parts of the kimberlites show crater facies litho-types,
including resedimented volcaniclastic kimberlites (RVK)
and pyroclastic kimberlites (PK) (Fig. 17.6b ). The RVK
shows green and red breccias and tuffs, with variable
dilution and which often show graded bedding. The PK
is characterized by juvenile-rich micaceous kimberlites that
have a massive appearance on the scale of metres to deca-
metres. Country rock clast types are dominated by dolomitic
limestone, and subordinate crossbedded sandstone and shale,
and basement granite, gabbro, amphibolite and dolerite.
Hypabyssal kimberlite is largely absent.
Of note is the presence of sedimentary intervals in Massif-
3, separating kimberlite eruptive phases, including a 20 m
thick aeolian sandstone horizon and a 50 cm thick bio-
turbated clay bed (Fieremans, pers. comm. 2006), suggesting
that some of eruptive phases are separated in time.
'
champagne glass-shaped
'
Search WWH ::




Custom Search