Kaila Pipe

With a diameter of 600-700 m Kaila is one of the largest breccia pipes of the central Aldan. It intrudes Precambrian crystalline rocks of the Aldan shield basement and dolomites of lower Cambrian age, and cuts two small dykes of olivine lamproite. The larger part of the pipe is formed by crystal tuff breccias and xenolith-tuff breccias comprising a heterogenous mixture of small fragments of intrusive, or autolithic, fine-grained lamproite, and individual large crystals of altered olivine and feldspar aggregates which are cemented by very fine-grained clayish material, which usually comprises up to 30-40% of the volume of the breccia. Large blocks of intrusive lamproite, which reach several metres and sometimes tens of metres in diameter, are sometimes found within the breccia. Lamproites from these large blocks have a coarser texture than lamproites from fragments and autoliths as well as lamproites of the early dykes intruded before emplacement of the pipes. The fragmental lamproites are fine-grained porphyritic rocks with phenocrysts of olivine (10- 12%), which are pseudomorphed by talc and saponite, chrome- diopside (7-15%) and phlogopite (5-12%). The fine-grained groundmass consists of microlites of diopside, tiny laths of phlogopite, rare altered olivine grains, aggregates of poikilitic K-feldspar and glass, which is partly or fully replaced by vermiculite and saponite. Pseudoleucite is present in the groundmass of eruptive breccia fragments. Blocks of quartz sandstone and Precambrian crystalline rocks also occur in the