Zaranda

This is a somewhat isolated centre forming a prominent hill having an elevation of 600 m above the surrounding plains. It is circular, 5 km in diameter and unusual for the province in consisting predominantly of syenitic rocks. Bennett et al. (1984) distinguished an inner zone, which is an approximately circular area 2.5 km in diameter of trachytic rocks, and an outer zone of syenite and granite which is cut by basic dykes. The inner zone trachytic rocks are fine-grained, variably porphyritic, sometimes brecciated and cut by occasional bodies of syenite porphyry. They are composed of perthite phenocrysts in a matrix of aligned feldspar laths, a little quartz and, in some rocks, ferrohedenbergite and amphibole. The syenite of the outer zone grades outwards into granite, is variably medium- or coarse-grained and consists of perthite, quartz, ferrohedenbergite with sodium-rich rims, and tiny laths of aegirine, a sodic-calcic amphibole, generally as rims on pyroxene, and accessories including aenigmatite and chevkinite. The granite is texturally variable and besides perthite and quartz includes interstitial amphibole and abundant aenigmatite. The basic dykes that cut the outer zone extend into the country rocks and appear to be associated with a basic body located on the southeast of the complex. A gravity survey of the complex is described by Ibe et al. (1985). Pb, Sr and Nd isotope data on two syenites and a trachy-rhyolite are given by Dickin et al. (1991).