Katete

Katete is situated in the most southwesterly part of the Zambezi-Luangwa rift, the main part of which lies in Zambia to the north and northwest. The complex cuts Karoo sandstones which overlie Precambrian granite and gneiss. It comprises solely carbonatites, of which several varieties were mapped by Lee (1974), and a number of small vents of carbonatite agglomerate to the west and south of the central complex. There are numerous small kimberlitic bodies in the general vicinity. The margin of the main intrusion is marked by a zone of brecciated quartzite up to 15 m wide, fractures in which are filled with aegirine-augite, amphibole, chlorite and iron oxides. The most extensive carbonatite is a silicified variety which appears to overlie dolomitic carbonatite, the contacts being gradational. It consists principally of quartz and iron oxide pseudomorphs after carbonate, which indicate that this rock is probably the result of silicification of dolomite carbonatite. Accessories include barite, monazite, magnetite and fluorite. The dolomite carbonatite sometimes displays a steeply dipping banding, which also wraps around xenoliths, which include quartzite, granite and gneiss. Lee (1974) describes the rock as containing phenocrysts of dolomite, siderite and calcite up to a centimetre in diameter in a carbonate matrix and circular patches of monazite, barite and quartz. Magnetite, pyrochlore and fluorite are rare. The xenoliths, which are 1-10 cm across, mostly have phlogopite reaction rims and those of granite and gneiss contain aegirine-augite and secondary perthite. Manganiferous and iron-rich carbonatite outcrops in the northern part of the complex and the latter also in a small area further south. The manganiferous carbonatite is black and consists of plates of calcite in fine-grained manganese oxide. Barite is a common accessory and pyrochlore and monazite also occur. This rock grades into the iron-rich carbonatite which is described as a sovite rich in iron oxides. Manganese oxides are also present as is a little barite, pyrochlore and monazite. The iron-rich carbonatite further south is fresher and consists of siderite and ankerite with secondary calcite and manganese oxides. Twelve agglomerate vents ranging from 8 to 60 m in diameter are scattered around the complex. The agglomerates consist of a range of xenoliths in a carbonate matrix of dolomite with dolomite, ankerite and siderite phenocrysts and minor barite and magnetite. Granite and gneiss xenoliths may be completely fresh or partially or totally replaced by phlogopite with sometimes a little aegirine-augite. Other xenoliths are of unaltered Karoo sandstone and ankeritic or sideritic carbonatite. Carbonatite dykes and sills cut the Karoo sandstones over an area of 75 km2 around the complex. They vary from 10 cm to 1.5 m wide and up to 200 m long. They are similar in composition to the dolomitic carbonatite of the central complex and xenoliths are common. Partial chemical analyses, with some trace elements, of the principal carbonatite types are given by Lee (1974) and indicate that they are all magnesio- or ferrocarbonatites.