Luhombero

About 3 km west of Luhombero Hill and cutting Karoo rocks is a 3 m-wide dyke which contains biotite phenocrysts and spherulites; it is probably a phonolite. 3 km north of this occurrence another probable phonolite has been located which is feldsparphyric but free of biotite. A 750x570 m breccia-filled vent 9 km northwest of Luhombero Hill is traversed by the Rufiji River, cuts Karoo sediments and is filled with sedimentary fragments. The matrix is a brown carbonate, probably calcite, plus an iron-bearing carbonate, and is cut by irregular veins of pale brown carbonate. West of Luhombero Hill a series of carbonate veins are associated with a fault; the largest is some 60 m in length and 1.5 m wide. Calcite is dominant and sometimes forms rectangular patches which are probably pseudomorphs; magnetite and vermiculite are occasionally present. A specimen of carbonate rock with pyrochlore crystals has been collected in the area west of Luhombero Hill, but the exact locality is not known. About 4 km west-southwest of Luhombero Hill lies a crater-like depression with steep sandstone walls. In the floor of the crater are outcrops of carbonate rock containing biotite and angular blocks of sandstone.