Introduction.
This belt lies to the south of the Geita
greenstone belt, and probably represents the same rocks on the other limb
of an anticlinorium (Fig.23). Lateriitisation of greenstone rocks is
intense so that bedrock is not well exposed. The west end of the belt is
covered by Pleistocene sands of ancentral Lake Victoria. Further west,
Bukoban sedimentary rocks (intruded by dykes), Kavirondian metasedimentary
rocks and Archaean granites dominate the geology. Magnetic patterns
suggest that the belt connects with the Ushirombo branch of the Kahama
belt to the southwest (Fig .16).
Mining and prospecting along the main
portion of the belt were active from the 1930s to the 1950s. The principal
mine was at Mawe Meru in the northeast part of the belt. This mine was an
underground operation working a high grade gold - quartz vein containing
copper sulphides. Total production up to closure in 1952 was between
80,000 and 90,000 tonnes with an average grade of about 25 g/t gold. To
the south was the intriguing El Dorado (Eureka) underground mine, which
worked a thin rubble zone at the base of the laterite above the
greenstone. Further to the west, at about the middle of the east -west
part of the belt, there was considerable activity in former times around
the village of Rwamagaza.
UNDP and Tanzania Government geologists
in 1965 - 1968 prospected this area and made extensive ground geophysical
surveys. Several prospects were later drilled. Results from the work at
the Old Buck Reef prospect were most encouraging and a small gold mine was
brought into production by STAMICO. Buck Reef was until 1990 the only
underground gold mine still working. Production was erratic due to supply
problems. The mine ceased production in January 1991. There has been
artisanal mining activity in the Rwamagaza area since 1974, with as many
as 20,000 miners exploiting the rubble zone at the base of the laterite.
The region to the extreme west of the
Lake Victoria goldfield remained under - explored until late 1990s. Recent
discoveries made in this region include the Kakindu prospect (Matabe).
Tulawaka deposit, Sheba prospect and the recent artisanal activities in
the Mwiruzi area in Biharamulo District. Tulawaka and Kakindu (Matabe) are
related to Rwamagaza greenstone belt while Mwiruzi may be related to the
Geita greenstone belt. The area has been explored by Pangea Minerals since
1977 and TANZAM 2000 since 1998. In 2002, most of the prospects in the
area were acquired by Barrick Gold and a gold mine is under construction
at the Tulawaka prospect.
Geology.
The few outcrops of bedrock are of a
massive, basic volcanic rock, with some thin beds of tuff. Zones of highly
magnetic bedrock under laterite cover are probably ultramafic in
composition. The former Mawe Meru Mine lies near the north edge of the
belt. Granite was exposed in trenches at surface here, but none was
recorded underground where deposits mention only greenstone.
The occurrence of nugget gold in the
rubble at the base of the laterite is a distinctive feature of the
Rwamagaza greenstone belt. The gold is not of alluvial origin, but appears
to have been formed in place by processes of supergene enrichment. As has
been demonstrated by the widespread activity, this type of deposit is
eminently suitable for small - scale mining.
Tulawaka Mine.
The Tulawaka gold deposit was discovered
in 1998 and is located about 200 road - kilometers west of Bulyanhulu and
is speculated to be part of the western extension of the Rwamagaza
greenstone belt (Fig.23).
Geology.
The main Tulawaka gold deposit called
East Zone, is hosted within a sequence of dominantly sedimentary rocks of
detrial, volcanogenic and chemical origin. All of these greenschist or
lower amphibolite facies. The metasedimentary rocks consist of fine -
grained bedded units, and include silicate iron - formations.
The West zone provides additional
resources to the project inventory and is being explored with the
objective of supplying additional sapprolite - type ore to the Tulawaka
plant.
The area was explored by Pangea Minerals
/ Northern Mining and, in 1997, a soil sampling programme was completed.
Major geochemical anomalies were identified, each measuring 300m in
strike. Drilling (RAB and RC) identified two - high grade gold bearing
zones. The best results are from East and West Zones which have grades
ranging from 1.7 g/t gold (3m) to 145 g/t gold (5m) and 3.1 g/t gold to
33.9 g/t gold (2m) over strike zones of 600m and 750m, respectively.
Gold mineralisation is associated with
disseminated sulphides, quartz veins and stringers (West Zone) or with
quartz - tourmaline veins and minor sulphides (East Zone). The deposit
remains open laterally and at depth, with gold mineralisation in the East
Zone extending over a strike length of 1.1 km.
Resources at the East Zone stand at 1.71
Moz at a grade of 14.19 g/t gold and cut off grade of 2 g/t. gold
containing 780,000 oz of gold.Other properties around Tulawaka are still
under active exploration to define additional gold resources from other
targets in the propertly.
Tulawaka Gold Mine, a low cost operated
open pit mine, became operational in March 2005, with an annual production
of 125,000 oz. The mine is operated by Pangea Goldfields (70%), a
subsidiary of Barrick Gold Corporation Project operator) and Northern
Mining (Miniere du Nord) of Canada (30%).
Buckreef Mine. Up to 2001, exploration
work at Buck Reef conducted by Ashanti and East Africa Mines has put the
Buckreef resource at 614,000 oz gold at an average grade of 4.08 g/t gold.
Two intersections drilled by Ashanti in the high - grade ore zone included
2 m at 18 g/t gold and 7 m at 6.36 g/t gold, which confirmed rich
mineralisation down to depths greater than 400m below surface.
Spinifex Gold initiated a major
exploration programme in 2002 aimed at increasing the resource base at
Buckreef / Rwamagaza. Two strongly mineralised zones, Bingwa and Tembo,
have been identified along the highly prospective Rwamagaza shear zone
adjacent to Buckreef Mine (Fig.24). Estimated inferred resources by
Spinifex are 89,000 tonnes grading at 19.6 g/t gold at Bwanga, 136,000
tonnes grading 10.0 g/t at Tembo and 641,000 tonnes grading 6.7 g/t at the
Rwamagaza Reefs.
The current total resource at Buckreef
Mine stands at 1.15 Moz gold and there is potential for high grades with
best intersection of 1325 g/t and increasing resource. Feasibility study
is carried out by Gallery Gold Limited of Australia.
The Buck Reef mineralised zone lies on a
major north - north east trending shear structure close to close to the
northern margin of the Rwamagaza greenstone belt. Mineralisation is
usually hosted in intensely altered mafic and / or ultramafic rocks. The
structure can be traced in airborne magnetics transecting the entire
Rwamagaza belt and further northeast through the granite terrain towards
the Geita and Lone Cone gold deposits in the Geita greenstone belt.
Buziba Creek.
At the east end of the Rwamagaza
greenbelt, a strong correlation is evident between the areas of eluvial
gold deposits being worked by artisanal miners and linear features visible
on aerial photographs (Fig.30). For considerable portions of their lengths
in the Buziba area, these linear features are probably due to the presence
of ultramafic rocks, examples of which are to be seen in specimens brought
to surface from some of the pits. Chrominium mica, fuchsite, has been
identified in the ultramafic rocks. Those parts of the magnetic anomalies
not exploited by artisanal miners are attractive exploration targets for
gold deposits mineable by open pit methods.
Nyamutondo.
The Nyamutondo area of artisanal mining
activity lies west of Rwamagaza (Fig.23) near the old Sabura Mine which
was active in the late 1930s and produced ore grading about 10 g/t gold.
Results from three holes drilled beneath this prospect by the UNDP did not
yield encouraging results. However, it is not certain whether or not
intervals were sampled where no quartz was visible but which could contain
disseminated mineralisation. The extent of artisanal activity, and the
proximity to Buck Reef Mine, suggests that Nyamutondo has potential for
veins or secondary enrichment zones beneath the well - developed laterite.
Mawe Meru.
In 1996, Tanganyika Gold NL began
exploration in Mawe Meru. This was prompted by the potential for discovery
of new deposits in view of the are�s historical production from old high -
grade gold mines and widespread artisanal mining activity. The exploration
work that ensued led to the discovery of the substantial Busolwa deposit
(RC drilled mineralised zone length of 1.3 km), new high grade shoots at
Main Reef and deeper mineralisation at the Ililika deposit.
Three mineralisation categories are
recognized:
Busolwa shear type - Strongly
silicified and altered shear zone in pyroxenite with 1-5%
Disseminated pyrite.
Porphyry stockwork type - Silicified
and altered quartz - feldspar porphyries within
Quartz stockworks and veins containing
2-5% pyrite.
Granite type - Quartz veined, hematite
altered granite with minor sericite and 0.5 - 1%
Pyrite
The deposit has only been drilled on
sections 100m apart and infill drilling on 50m sections is required for an
initial resource estimate.
MABALE - BUHUNGUKIRA
GREENSTONE BELT
Introduction. Scattered occurrences of
greenston 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, 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 met volcanic 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
kilometers 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 to 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 veins.
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 mineralized area in deformed quartz -
dolerite, sulphide 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 a global resource of 479,000 oz of gold at an average grade
of 1.3 g/t gold. The adjacent Isagenghe hill has 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 mineralized zones is 80m wide and is
outlined by several contiguous hills. The property has potential for open
pit mining.