Metallogeny of the geodynamic systems of the pulsating expanding earth
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101 Table 7. Principles of petrology classification of kimberlite, picrite and lamproite (Milashev, 1994 ) Рressure MPa Diamond-bearing subfacies of kimberlites Facies 4000. type I olivine type II phlogopite- olivine type III K-richterite –olivine type IY K-richterite- leucite Kimberlite’s Picrite’s subfacies of kimberlite (non diamond-bearing ) 2000 type I olivine type II phlogopite- olivine type III K-richterite - olivine type IY K-richterite -leucite Kimberlite’s Picrite , picrite porphirite Lamproite 0 olivine phlogopite- olivine K-richterite -olivine K-richterite -leucite Picrite’s K 2 O 0 1 3,3 7 %% The diagram ε Nd – ε Sr shows the genetic relation between kimberlites, enriched of potassium volcanic rocks and mantle nodules, K-richterite phlogopite lamproites, garnet phlogopite and garnet peridotite xenolithes from the province Kimberley in Western Australia ( Figure 4) (Hawkeswoath at al.,1985). 102 Figure 4. The diagrame Nb - Sr shows the variations potassium in kimberlites, volcanic rocks and mantle xenoliths. PKP (phlogopite K- richterite), GPP (garnet-phlogopite) and GP ( garnet ) are whole-rock peridotite xenolithe from the Kimberley area. The Group II kimberlite are mostly from Finsch mine, South Africa, and the Group I kimberlite are of South African Cretaceous kimberlites ( Hawkesworth, Fraser and Rogers, 1985 ). Reprinted with permission of Geological Society of South Africa. It is necessary to note that the Australian geologists, who opened the first diamond-bearing olivine lamproite pipe Argyle in 1979 in West Australia, had suggested, that there was a genetic relation between lamproites and diamond- bearing kimberlites (Jagues et al.1982; Atkinson et al. 1984). 6. ZONING OF DISTRIBUTION DIAMONDIFEROUS KIMBERLITES The analysis of geotectonic conditions shows, that kimberlite magmatism was appeared only within the platforms. The epochs of kimberlite volcanism are connected to the certain stages of tectono-magmatic activity of cratons. The beginning of kimberlite volcanism is dated to the finishing stages of long and steady uplift of platforms. All evidences testify to the spatial distribution of different facies of rocks within the limits of kimberlite provinces to their concentric zonal structure. As a rule, in the center of provinces there are kimberlite or lamproite fields of diamond subfacies, where all bodies are 103 diamond-bearing, however, only 8–10% from them have industrially profitable. In the transitive zone there are kimberlites of diamond-pyrope subfacies, where only 20% of bodies are weakly diamond-bearing and rarely profit to work. On the periphery of the provinces there are fields of pyrope subfacies without diamonds, which are frequently accompanied by picrite and carbonatite. It also meets incomplete zonal kimberlite provinces (Figure 5,6,7), (Krutoyarskiy, Milashev, 1964; Milashev, 1965; 1994). 104 Figure 5. Facies of kimberlites and morphology of the diamond’s crystals relatedtokimberlites on the Siberian platform. Reprinted with the permission of the Publishing House “Nedra”. The fields of kimberlites subfacies: I – diamond’s, II – predominantly diamond’s and partly pyrope’s, III – predominantly pyrope’s and partly diamond’s, IV – pyrope’s. V – ratio of diamond crystals (%%): octahedral (black), dodecahedral (white) and transitive forms (shadow). Names of the kimberlite fields: 1 – Kotiy-Maimecha, 2 – Kuonamka, 3 - Kuoika-Beenchime , 4 - Merchimden, 5 Lower-Ukukit, 6 – Omonos- Kutugun, 7 – Luchakan, 8 – Ogonor-Chomurdach, 9 – Upper-Muna, 10 – Daldyn, 11 – Marcha-Alakit, 12 – Little-Botuoby, 13 – Upper-Aldan, 14 – Chadobets, 15 – Oka. The morphology of diamond crystals in the kimberlites bodies and fields testifies about various thermodynamic (facies) conditions of the formation of diamond deposits, their safety, rating and value. Flat face crystals of diamond,as a rule, prevail in kimberlite fields of diamond subfacies. They are represented by octahedrons, dodecahedrons and transitional forms, less often by cubic and tetrahedron habit. In kimberlite fields of diamond-pyrope subfacies, the curve face crystals of diamond prevail over the flat face, which proves the significant dissolution of diamond crystals at the slower rise kimberlite magma to the surface of the Earth (Table 8, Figure 5) (Krutoyarskiy, Milashev, 1964). Table 8. Subfacies of kimberlites and morphology of the diamonds on Siberian platform (Krutoyarskiy, Milashev, 1964) Sufacies of kim- berlites Name of kimberlite fieids Type of kimber- lites Middl e weight of cry- stals (mg) Amount of diamond crystals (%%) flat facet tran- sitive forms O-D curve facet jo- ints who- le cry- stals H O Od Dd Diamonds 1.Malo- Botuoby 2.Daldyno- Alakit 3.Ulakhan- Muna type I, seldom type II 10 5 6 0.7 - - 72 23 24 19 15 11 - - - 8 62 65 20 28 20 20 38 37 Diamonds more than pyropes 4.Luchakan 5.Omonos- Ukukit type I and type II 7 11 3 2 23 38 16 5 - - 58 55 20 16 67 52 Yüklə 0,51 Mb. Dostları ilə paylaş:
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