MABALE - BUHUNGUKIRA GREENSTONE BELT.
Introduction:
Scattered occurrence of greenstones
east of the Geita and Rwamagaza greenstone belts are referred to here as
the Mabale - Buhungukira greenstone belt (Fig.25). The rocks appear to
connect with the Geita greenstone belt to the west and with the eastern
part of the Kahama greenstone belt to the south. Several gold prospects
have been identified in the belt. The individual occurrences are Busolwa,
Kivugandi, Nyanghoma,Kasubuya (Usambiro), Mabogo, Itambu, Mwamazengo,
Luhala Hill, Kivugandi, Nyanghoma, Kasubuya (Usambiro),Mabogo, Itambu,
Mwamazengo ,Luhala Hill,Sima Hill and Kitongo. Prominent NNW - striking
sequences of BIF underlie these areas. In recent years, exploration
companies have carried out various exploration activities that have led to
some occurrences being developed into mineable gold resources. Others have
been found to be prospective and are yet to be developed. Published
geological maps at a scale of 1: 125,000 are available.
Geology.
The area is underlain by Archaean
greenstone rocks of the Nyanzian Supergroup. These rocks are dominated by
thick sequences of folded, banded and predominantly oxide facies iron
formations intercalated with both epiclastic and volcanoclastic
sedimentary rocks. However, in some of the areas, laterite covers the
underlying geology and thence rocks are sparse and biased to those areas
of exposed BIF and associated epiclastic sedimentary rocks. Elsewhere
mafic metavolcanic rocks are in contact with granitic terrain.
Mineralisation.
Many small occurrences of gold are
known, but the recorded production is small. Most of the prospects consist
of little more than a few pits and trenches in which gold has been noted.
Gold mineralisation at Kitongo is structurally controlled and occurs in
sheared mafic tuffs while at Luhala the mineralisation is associated with
quartz veins hosted by strongly altered porphyry bodies.
Kitongo and Isagenghe.
The two prospects are located a few
kilometres east of Smith Sound, approximately 55 km south of Mwanza
(Fig.25). East African Mines / Spinifex Gold is exploring them. Primary
gold mineralisation at Kitongo is structurally controlled along a
northwest trending regional corridor. The mineralisation is hosted in a
mafic volcanic sequence underlying a series of intermediate of felsic
volcanic units and sediments composed of cherts, BIF and phyllites. Gold
intercepts occur in strongly sheared mafic volcanic tuff and are
associated with intense silica flooding and quartz veining.
The main Zone is notable for high -
grade mineralisation and is open along strike and at depth. A new
discovery has been made at Isagenghe Hill,located west of the main zone.
RC holes intercepted extensively mineralised area in deformed quartz -
dolerite, suplhide bearing quartzo - feldspathic rocks and massive
sulphides. Released resources by Spinifex Gold in 2001 for Kitongo Main
Zone were 10.5 Mt of ore at an average grade of 1.42 g/t gold; including
measured (28%), indicated (57%) and inferred (15%) categories. This is
equivalent to global resource of 479,000 oz of gold at an average grade of
1.3 g/t gold. The adjacent Isagenghe Hill as an inferred resource of
75,000 oz of gold at an average grade of 14.4 g/t gold.
The total estimated resource at
Kitongo stands at 550,000 oz and Gallery Gold from Australia is validating
the existing database in view of increasing the resource.
Luhala.
Tan Range Exploration / Newmont
Overseas Exploration is exploring the Luhala property. Rotary Air blast
(RAB) drilling has outlined several wide zones of mineralisation
associated with quartz veins. Strongly altered felsic porphyry bodies host
these. Some of the interesting intercepts include: 8m grading 4.50 g/t
gold and 25 m grading 2.31 g/t. gold. One of the mineralised zones is 80m
wide and is outlined by several contiguous hills. The property has
potential for open pit mining.