The Rubikon pegmatites of the Karibib area, Namibia

Abstract

Abstract by author:

The pegmatites at the Okongava Ost farm, including the Rubicon pegmatites, occur in a medium- to high-grade metamorphic environment and contain abundant Li- and Be-minerals and other rare element minerals. The Rubicon pegmatites are composed of two ellipsoidal bodies known as orebody I and orebody II. Both these two bodies seem to have the same mineralogy. The Rubicon pegmatites have intruded in between a quartz monzonite of Pan African age (700-500 Ma), and a pegmatitic granite of late Pan African age (600-460 Ma). It is internally zoned and believed to belong to a group of pegmatites which reached the ultimate degree of alkali fractionation. There are about 15 pegmatite deposits in the Karibib pegmatite belt. Of these, Rubicon is the largest and the only economic, Li-mineralized deposit. Many phosphate minerals occur at Rubicon. Most of them are alteration and replacement products of triphylite and lithiophilite. The minerals described in detail in this study are beryl, petalite, pollucite, amblygonite-montebrasite, garnet, and muscovite. The principal physical properties, optical properties and unit cell dimensions are given. In addition, several silicates, phosphates, oxides, hydroxides and other minerals belonging to the Karibib pegmatite belt are generally described

Three major pegmatite belts exist in Africa: the Kibaran Belt, which is about 1 100 Ma old, the Damara Belt and the Mozambique Belt, both about 550 Ma old. Tin mineralization is common in the Kibaran and Damara belts throughout their total length of about 3 220 km, but not in the Mozambique Belt. Since the rare elements, including niobium and tantalum, are associated with tin mineralization, they are mostly found in the former two belts. Apart from tin, the general geochemical pattern of all three belts is rather similar

In Namibia, the Karibib area is the most important pegmatite belt hosting economic pegmatites. Many of these pegmatites are found within the metamorphic rocks of the Upper Precambrian Damara Sequence. The economic pegmatites have been intruded in three tightly folded formations: the mica schists of the Kuiseb, the doiomitic marbles of the Karibib, and the quartzites of the Nosib. Lithium-bearing pegmatites are situated within large bodies of pegmatitic granite as bosses, dykes and irregular masses