Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences

Yllymakh

stripes

Occurrence number: 
136-01-025
Country: 
Russia
Region: 
Aldan
Location: 
Longitude: 125, Latitude: 58.25
Carbonatite: 
No

This mixed volcanic and intrusive complex of central type has an area of about 40 km2. It is circular and has a zonal structure which is complicated by a complex pattern of faults. Extrusive formations play a prominent role and are represented by pseudoleucite phonolites and peralkaline trachyte and their tuffs, which occupy zones in the western and eastern parts of the complex. The volcanics often contain small xenoliths and nodules of rocks of ultrabasic composition. The intrusive rocks cut through the volcanics and the earliest group includes malignites, melanocratic syenites and monzonites. The shonkinites and malignites form arcuate bodies and small stocks in the marginal parts and near to the complex. The malignites contain xenoliths of wehrlite and pyroxenite in which the olivine is more magnesian (Fo74) than in the malignite (Fo48). A later intrusive phase is represented by nepheline and pseudoleucite syenites which form large fault-bounded blocks in the interior of the complex as well as lens-like bodies of nepheline-bearing pegmatites. Both small xenoliths and large blocks (1.5-2 m) of feldspathized volcanic rocks are found in them. Throughout the complex the syenites are intensively sericitized and near late granites they are albitized. Dykes of pseudoleucite tinguaite occur within the volcanics and alkaline gabbroids. Alkaline leucocratic syenites (pulaskites) are younger than the nepheline syenites and contain xenoliths of melanocratic syenite, malignite, monzonite and phonolite. A central stock consists of aegirine granite and granosyenite, which cuts across the alkaline leucocratic syenites. Dykes of granite porphyry and granosyenite aplite are spatially associated with the granitoids. Intense metasomatic alteration of many rock types is manifest, but particularly in the volcanics, including replacement of dark minerals by aegirine, zeolitization and sericitization of feldspathoids and microclinization and albitization. In different syenites and in malignites postmagmatic changes have led to extensive recrystallization and the transformation of orthoclase into microcline and its replacement by albite. Albite-rich metasomatic rocks that were formed in linear zones among the nepheline syenites contain agpaitic accessory minerals including lamprophyllite, eudialyte, rosenbushite, loparite, lomonosovite, rinkolite and labuntsovite. Chemical analyses of rocks will be found in Orlova (1990) and Bilibin (1947); Chepurov (1973) describes melt inclusions in pseudoleucite.

Economic: 
Gold values of 3.64 ppm. in aegirine granite and 1.48 ppm. in pseudoleucite syenite have been found (Shnai and Orlova, 1977).
Age: 
K-Ar determinations on malignite and shonkinite gave 165±5 Ma, on melanocratic syenite 163±5 Ma, on monzonite 152±5 Ma, on trachyte 50±4 Ma, on pseudoleucite phonolite 142±5 Ma, on nepheline and pseudoleucite syenite 158±5 Ma, on alkaline syenite (pulsaskite) 133±4 Ma, on granosyenite 131±4 Ma and on aegirine granite 133±4 Ma (Orlova et al., 1986a; Orlova, 1990).
References: 

BILIBIN, U.A. 1974. Petrology of the Yllymakh intrusive. Gosgeoltekhisdat. Moscow and Leningrad. 235 pp.
CHEPUROV, A.I. 1973. Thermometric study of inclusions of melt in pseudoleucite minerals of the central Aldan district. Transactions (Doklady) of the USSR Academy of Sciences, Earth Science Sections, 213: 165-8.
EL'YANOV A.A. and MORALEV, V.M. 1974. On the problem of the deep structure of the Yllymakh volcano-pluton (central Aldan area). Izvestiya Akademii Nauk SSSR, Seriya Geologiya,‚ 1: 134-7.
KRAVCHENKO, S.M., KAPUSTIN, Yu.L., KATAEVA, Z.T. and BYKOVA, A.V. 1982. Agpaitic mineralization of the Mesozoic metasomatic rocks of potassic alkaline complexes of the Central Aldan. Doklady Akademii Nauk SSSR, 263: 435-9.
ORLOVA, M.P. 1990. Mesozoic stage of magmatism. In G.V. Polyakov and V.V. Kepezinskas (eds) Potassic alkaline magmatism of the Baikal-Stanovoy rift system. 65-123. Nauka, Siberian Division of the USSR Academy of Sciences, Novosibirsk.
ORLOVA, M.P., ARDONTSEV, S.N. and SHCHADENKOV, E.M. 1986a.
Alkaline magmatism of the Aldan shield and its specific mineralogical features. In I.M. Frumkin (ed) Geology and geochemistry of the ore-bearing magmatic and metasomatic associations from the Maly BAM area. 4-12. Yakutia Branch of the Siberian Division of the USSR Academy of Sciences, Yakutsk.
SHNAI, G.K. and ORLOVA, M.P. 1977. New data on the geology and gold contents of the Yllymakh massif (central Aldan). Geologiya i Geofizika, 10: 57-65.

Map: 
Fig. 2_231. Yllymakh (after Orlova, 1990, Fig. 27).
Location: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith