Guli (Gulinskii)

This complex occupies a large area between the Maimecha and Kotui Rivers at the boundary of the Siberian platform with the Hatanga trough. It has an oval form of 35x45 km and, including the two thirds obscured by Quaternary deposits, has an area of 1500-1600 km2 (Egorov, 1991). Geophysical evidence indicates near vertical contacts and hence probably a stock-like form (Egorov, 1989). The complex was discovered by Sheinman (1947) in 1943 and at different periods was studied by Butakova (1956), Egorov (1991), Prochorova, Evzikova and Michailova (Prochorova et al., 1966), Vasiliev and Zolotuchin (1975), Zhabin (1965) and Kostyuk (1974). The country rocks of the Guli complex are volcanics (Figs 110 and 111), which have been described above (No. 1), and which include an extensive area of meimechites. The Guli massif, like many of the other alkaline-ultrabasic intrusives of the province, is a complex multi-stage pluton, as indicated in the following table: The predominant rocks of the complex are dunites, which occupy about 60% of the total area, and a range of types of melanocratic alkaline rocks, which extend over about 30%. All the other rock types, including melilitolite, ijolite, alkaline syenite and carbonatite, occupy less than 10% of the area of the complex. The earliest rocks of the intrusion (first stage) are dunites which form a curved area having a width of 9-10 km, which can be traced for 40 km. They are essentially olivine rocks with small amounts, less than 5% by volume, of clinopyroxene, titanomagnetite and chromite; accessory minerals include perovskite, phlogopite, calcite, clinohumite and spinel. During the second substage the dunite intrusives were cut by numerous bodies of ore pyroxenite that are composed mainly of pyroxene and titanomagnetite, which form about 10% of the volume of the dunites; apatite and titanite are accessory. In the southwestern part of the dunite body the ore pyroxenite grades into texturally similar porphyritic trachytic peridotites and olivine pyroxenites, which have a lower content of titanomagnetite. Nepheline, biotite-phlogopite, perovskite, apatite and titanite are present as minor constituents. After the formation of the ultrabasic rocks a second stage of evolution of the pluton is marked by the intrusion of melilitic rocks. The melilite magma gave rise to a large (0.6x5 km) partial ring body in the southern structural centre of the massif and three smaller stocks 8 km to the southeast of the main ring. The composition of the rocks - melilitolite and kugdite - is characterised by the predominance of melilite over olivine, which in melilitolite is up to 90% of the volume. The accessory minerals are pyroxene, nepheline and titanomagnetite. During the third intrusive phase a series of alkaline mafic and ultramafic rocks, which are compositionally similar, were emplaced in the following succession: sub-stage 1 melteigite-malignite-shonkinite; sub-stage 2 melanephelinite-alkaline picrite, and sub-stage 3 jacupirangite-melteigite. The most widespread rocks of this phase are the jacupiragites and melteigites which are characterised by the presence of pyroxene, in jacupirangite up to 90%, and nepheline, which in melteigite is from 10 up to 35-45%. Also present is titanomagnetite, phlogopite, apatite, titanite, perovskite and secondary natrolite, cancrinite and calcite, with sometimes up to 10% of K-feldspar in jacupirangite, which thus grade into malignite. The malignite and shonkinite of sub-stage 1 also have specific compositions and contents of pyroxene, which in the malignite is modally 35-45% while in the shonkinite clinopyroxene + barkevikite comprise 60-70%. Nepheline forms 20-30% of the malignites and 0-7% in shonkinites; they also contain up to 25% of K-feldspar, up to 10-15% titanomagnetite, biotite, apatite, fluorite, albite, zeolites and calcite. The rocks of the first sub-stage form stocks within the dunites and are associated closely with the rocks of the second sub-stage. The rocks of the melanephelinite-alkaline picrite series (second sub-stage) are grouped into three large belts, which are up to 2 km across, and are also represented by dyke-like bodies of alkaline picrite (nepheline and biotite-pyroxene, as well as olivine). In the northeastern part of the complex there are olivine melanephelinites, in which there are shonkinite xenoliths, and to the east there are melanephelinites and olivine melanephelinite with nepheline picrites. In the southern part of the complex melanephelinites and olivine melanephelinites occur which sometimes have an ophitic texture. The jacupirangites and melteigites of the third sub-stage are cut by veins of ijolite and ijolite pegmatite which represent the fourth intrusive stage. The pegmatites are composed mainly of nepheline (55-65%) and clinopyroxene (25-40%) with accessory titanomagnetite, phlogopite, perovskite, titanite and apatite. In the centre of the complex are several bodies of fine- to medium-grained peralkaline syenite (the fifth stage) which are composed of up to 65% K-feldspar, aegirine and small amounts of nepheline. Rocks of the sixth and final stage comprise essentially carbonatites and phoscorites. The phoscorite rocks (first sub-stage) consist of 20-30% olivine, 30-60% apatite and 25-50% magnetite, and are present as xenoliths in calcite carbonatites (second and third sub-stages) and veins in melanephelinite and jacupirangite. The rocks of the carbonatite group form two massifs - the Northern and Southern (Fig. 114) and are represented by fine-grained calcite (third sub-stage) as well as dolomite carbonatite (fourth sub-stage). Apart from the dominant carbonates the carbonatites also contain apatite, magnetite, phlogopite, more rarely forsterite, aegirine-diopside, pyrrhotite, pyrochlore, dysanalyte, calzirtite and others.