Introduction.

Deposits of iron ore occur in several settings. In Tanzania, the most important of these are in a belt extending north of the Ruhuhu River and separated from Lake Nyasa by the high ridge of the Livingstone Mountains. The deposit, which has attracted the most attention, is Liganga with its titaniferous magnetite bodies. These bodies have been studied extensively and are discussed in McConnell (1944), Stockely (1948), Carter (1960) and Harris (1961).

Liganga.

Liganga is the largest of many similar occurrences in the mountainous country 60km south of Njombe. The Liganga and other bodies are steeply dipping lenses within an anothositic gabbro, in the Ubendian Supergroup. Several smaller lenses occur o9n the same strike as Liganga. Probably all represent magmatic segregations or injections from a crystallizing gabbroic magma, which have subsequently been metamorphosed along with the enclosing rocks. Geologically, the Liganga deposit is classified as intermediate between the "Bushveld Fe-Ti-V model" (no.3) and the "anorthosite Ti model" (no.7b) of Cox and Singer (1986).The rock consists dominantly of a groundmass of intimately intergrown magnetite and ilmenite, subhedral crystals of magnetic spinel, and veinlets of chlorite. By volume, the rock is typically 55% magnetite, 22% ilmenite, 10% spinel, and 13% chlorite. Chemical composition is about 50% Fe, 13% TiO2, 0.4%MnO, and 0.4% V2O5, 0.25% Cr2O3, and 0.01%P2O5. The magnetite-ilmenite integrowths do not allow physical separation of the minerals.

The inferred resource at Liganga is in excess of 1.500Mt of iron ore. Drilling conducted in 1973 at Liganga showed proven reserves of 45 Mt grading 52% iron. Pilot tests have shown that the ore can be smelted by the Elkem or Krupp-Renn processes, to produce acceptable low- titanium iron. Njau (1988) studied the possibility of recovering vanadium from the ore. The National Development Corporation (NDC) has been given the mandate to develop the deposit and is looking into possibilities of mining the ore and recovering titanium and vanadium together with iron.

Outcrop of titaniferous magnetite at Liganga Iron Titanium-Vanadium Prospect (Photo by P. Semkiwa)

Liganga has the advantage of being conveniently near the Ruhuhu coalfield 50 km to the south, the TAZARA railway 120 km to the north, and Lake Nyasa 50 km to the west. The paved Makambako-Songea highway passes through Njombe, which is 150 km from Liganga via secondary roads. The deposit represents an opportunity for the development of a large or small-scale mining in conjunction with other industrial enterprises.

Uluguru Mountains.

Several titaniferous magnetite bodies occur within an anorthosite body in the Uluguru Mountains, South of Morogoro. The geological setting and composition are similar to Liganga, but the 8 Mt resources and the grade of 40% iron and 10% titanium does not warrant economic exploitation at this time. The only advantage is the proximity to railway line/road and to Dar es Salaam port.

Mbabala.

At this locality, 10 km from Lake Tanganyika and north of Karema, lenses of magnetite and hematite occur within hornblende gneiss. A sample assayed 56% iron and 14.4% TiO2. The hematite appears to be a metamorphic replacement of magnetite.

The high titanium content, lensiod form and occurrence within hornoblende gneisses suggest that this is a metamorphosed Liganga-type magmatic segregation. The locality is near Lake Tanganyika but remote from all other infrastructure.

Manyora "Gondite".

Bedded metasedimentary rocks, 50 km southeast of Karema on Lake Tanganyika, consist of finely banded quartz and magnetite, with manganese oxides and the manganese-rich garnet spessartite. The metal content varies inversely with the proportion of quartz bands. The magnetite-rich material assays about 33% Fe, 30% SiO2, 10% Mn and 0.5% TiO2. The rock has been compared with the "gondites" of India. Many tens of millions of tone of rock are known but the low grade and complex metallurgy render near-term exploitation unlikely. Interestingly, traces of gold have been panned from adjacent streams.

Itewe.

Thisoccurrence is 10 km southwest of the town of Chunya. Investigations by a Chinese Team continued from 1974 to 1978. Mineralisation consists of limonite and hematite. A resource of 50 million tones containing 32% iron was estimated.