OTHER PRECAMBRIAN GOLD PROSPCTS.
Igawa-Msusule Prospect.
A group of gold
prospects occur in crystalline rocks in a zone running close to the Mbeya-Dar
es Salaam road for 20 km west from Igawa. Igawa is 116km east of Mbeya
town (Fig.41). The prospects consist of a cluster of placer and bedrock
occurrences of gold in little more than trace amounts. Stockley (1948)
provides cursory descriptions and suggests the area could be the
geological continuation of the Lupa Gold Field, which lies close to the
northwest. There are no records of systematic prospecting in this area.
Kitowero Prospect.
This area in the
Masasi High sector of the Usagaran Palaeoproterozoic province was
described by STAMICO geologists in 1981 as the Ngurumahinga River alluvial
gold prospect. It is far from any mining or other development except
artisanal mining of gemstones and minor gold. The topography is rolling
and covered with tropical scrub. Rock exposures are limited to a few
inselbergs.
STAMICO had been
attracted to the area by reports of alluvial gold in the Ngurumahiga and
Mbemkuru rivers (Fig. 36), and by the history of modest gold production
(400 gm) from the area in 1933-34. In addition, Geological Survey
geologists in 1950 reported finding alluvial gold at the mouth of the
Mbemkuru River, some 30km to the east. The prospects lie at the east
margin of the Selous Basin, where Karoo and younger sedimentary rocks are
in fault contact with Proterozoic rocks consisting of granitic gneiss,
biotite schist, garntiferous amphibolite and quartzite. "Magnetic
ironstone" was noted on Kitowero Hill and a few pegmatites were also noted
(Fig. 36). The regional structural trend appears to be northerly.
STAMICO carried out a
stream sediment survey and found gold in heavy mineral concentrates from
several streama including the Mbemkuru, Ngurumahiga,Muhuwesi, and Lumesule
rivers. The proportion of heavy minerals to total sample was not recorded.
Assays of the heavy mineral fraction as high as 12 g/t gold were obtained.
STAMICO geologists concluded that the alluvial gold was derived from an
unspecified source. Since most of the gold bearing streams drain
Proterozoic rocs and basins of Karoo and younger ages, there are a number
of potential sources.
Gold in the Kitowero
alluvial prospect could interpret as derived from a lode source in an area
between Kitowero and Ligwerro Hills (where outcrops of pegtmatites and
amphibolite occur to the southwest) (Fig. 36), where the Proterozoic rocks
are greenstones, here metamorphosed to almandine amphibolite facies. The
amphibolite on Ligwero Hill, the magnetic ironstone on Kitowero Hill, and
the swarm of "pegmatites", possibly meta-cherts or quartz veins, could be
the actual source rocks. The above interpretation could be tested by
further field examination of the area for metamorphosed remnants of an
older, possibly Archaean, mineralized greenstone sequence.
Samba Nguru Hill
Prospect.
Gold in the Dodoman
basemen is described by Barth, Massola and Weiser (1996), as observed from
prospects discovered by artisanal miners. Gold mineralisation in the
Dodoman basement is clearly associated with granitized relics of a deeply
eroded greenstone belt, and occur in poorly silicified shear zones in the
granitoid migmatites, in places closely related to contact aureoles of
prominent granite intrusions.
Mafulungu Prospect
(Simba Nguru Hill).
Gold was
discovered and a gold mining village was established in 1992 at the south-
western edge of the Simba Nguru Hill by artisanal miners. The hills
consist of a 12km long, narrow raft of Dodoman metaquartzite (fuchsite
quartzite), which consists of migmatitic falser gneisses. The ore body
being mined is not in the metaquartzites of the Simba Nguru Hills but it
in the basement migmitites. Altered greenstones are abundant in waste
dumps in the mine area.
Te gold assay of three
bulk sample yielded an average of 75 g/t gold for the fine grade ore
pounded and ready for panning. Barren quartz stringers and waste rock
contained 2 g/t gold. One sample of black hybrid metagranite from the
Kisigo River near the mine yielded 58 g/t gold. Microprobe analysis
revealed silver content of 4 to 5%, while only traces of copper (2%) were
detected.
Nzuguni (Mdengi
Hill) Prospect.
Nzuguni is located
12km east of Dodoma Municipality. History of gold mining at Nzuguni began
with artisanal mining in 1932, after the discovery of eluvial and alluvial
placers; it lasted only for a short period. In 1992, artisana; miners
resumed mining activities and established a mining village at Nzuguni.
The prospect consists
of quartz veins associated with a major shear zone striking NE-SW. Assay
of 90 samples yielded an average grade of 2,.3g/t gold (Williams 1936).
Microprobe analysis yielded silver contents of 3-20%.
Iluma Hill
Prospect.
Iluma Hill in the
Muhesi River Game Reserve is a prominent summit. Iluma granite is
intrusive into the basement migmatite series, striking 110-120. The
sequence is cut by prominent dolerite dyke striking 160 which produce
prominent magnetic lineaments. The ore body is in a silicified shear zone
in the outermost part of the Iluma granite aureole, located between
metamorphic rafts and intruding granite. The grade of the crude ore was
assayed at 80 g/t gold (1 bulk sample); a sample containing traces of
visible gold yielded only 5 g/t gold. The microprobe analysis yielded
silver contents in the gold of 12% and 14%.
Lukarasi Prospect.
Lukarasi prospect is
to considerable significance. It has been worked by artisanal miner since
early the 1990s. A speculative resource of 253,000t with an average an 6.5
g/t gold has been
Crushing of ore using
a ball mill at Sambaru gold small scale working (Photo by P.Semkiwa)
Estimated by UMICO,
for the first 10m from the surface. Mineralisation below 10m has not yet
been investigated. A small-scale mine is operated by UMICO since 1998.
Other prospects.
Several gold
occurrences are known to have local placer and or reef gold mineralisation
within Palaeoproterozoic rocks. These include Ruvu, Mvomero, Mindu,
Matombo (placer) Melela (reef)in Morogoro Region; Kwampepo (placer and
reef) in Ruvuma Region; Nachingwea in Lindi Region; Mchauru-Masasi
(placer) in Mtwara Region; Muhintiri, Matongo, Sambaru and Londoni (reef
and placer) in Singida Region; and Kilindi, Sakale (reef and placer) in
Tanga Region.