THEORY OF LIQUID IMMISCIBILITY OF KIMBERLITE MAGMA.

Igor Kryvoshlyk.

Toronto, Canada. Phone: (416) 248-8514. E-mail: ikryvoa481@rogers.com

My first presentation of the theory of liquid immiscibility of kimberlite magma I made in December 1973 when I worked for Diamond Laboratory of the Central Research Institute of Non-Ferrous & Noble Metals (CNIGRI, now – YaGEER&D CNIGRI, ALROSA Company Ltd), city of Mirny, Yakutia, Russia. Thanks to bureaucracy, it took three long years to publish it in 1976 (my paper was accepted for publication in April 1975).The basic statements of this theory are:

1. Kimberlite magma consists of two extremely contrast melts: ultrabasic picritic melt (which has produced autoliths) and carbonatitic melt (which has created the matrix of autolithic kimberlites). The phenomenon of liquid immiscibility is a leading factor, responsible for generation of such emulsion.

2. There are texturally two main types of kimberlite rocks: massive kimberlites – “M-kimberlite” (Fig. 1 & 1a) and autolithic kimberlites “A-kimberlite” (Fig. 2). A-kimberlites consist of autoliths (small pieces of massive kimberlites) and matrix. M-kimberlites represent autolithic material for all 100 % [1, 8].

Fig. 1. Massive M-kimberlite. Slab. [26]. Fig. 1a. Massive M-kimberlite. Thin Snap Lake. section. [27]. 25x. PPL.

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Fig. 2. An ideal autolithic A-kimberlite. Fig. 2a. Transitional kimberlite. Slab. Spherical autoliths comprise about 50% Large autoliths comprise almost 100%of the sample. Pipe Lyogkaya. of the rock. Pipe Lyogkaya. Yakutia Yakutia. Surface Slab [29]. Depth ~ 20 m. [29]

3. Autoliths = “lapilli”, or “inclusions of kimberlite in kimberlite”, etc. Autoliths are the solidificated drops of subalkaline ultrabasic picritic melt. The matrix of autolithic kimberlites was produced by immiscible carbonatitic melt.

4. Fully developed autoliths have spheroidal (Fig. 2) shape at the size of approximately between 5 and 50 mm. This is typical case for the upper parts of diatremes. With the depth the size of autoliths has grow, and their shape became less spheroidal. Finally the concentration of the autolithic material getting closer to 100%, and autolithic kimberlite little by little transits into massive kimberlite (Fig. 2a). Pipe “Lyogkaya” (Moonsky field, Yakutia) is the best example [29].

5. Main number of autoliths has central kernel, represented by those components of kimberlite magma which have had a surface. In most cases they were mantle minerals (mainly macrocrysts of olivine) and xenoliths of wall rocks. They provided their surface for accumulation of picritic drops to create autolithic zones around central kernel. Sometimes globules of carbonatite melt have played the role of such kernels as well (Fig. 3).

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Fig.3. Fragment of carbonatite as a kernel of Fig.4. Layered piece of kimberlite is a autolith. Victor pipe, Canada. Thin section kernel of this autolith. Concentric 30x. PPL texture of autolithic selvages is quite clear. There is a gradual transit of autolith into surrounding kimberlite. 1.5x. Maliutka pipe. Yakutia. Slab. .

6. Sometimes autoliths have distinctive concentric texture (Fig. 4, 5) due to the different mineralogical or/and petrographical composition of their zones.

Fig. 5. Autolith with concentric-zoned Fig. 6. A sub-tangential texture of thetexture. Dal’naya pipe. Yakutia. Thin autolith due to the specific orientation of section. 2x. PPL. the laths of carbonate in the groundmass of autolith. Zarnitsa pipe. Yakutia. Thin section. 10x. PPL.

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7. Elongated particles of the autolithic zones, as a rule, have clear sub-tangential orientation (Fig. 6) around the kernel.

8. Sometimes the small portions of the kimberlite “tuff” were found inside autoliths, and also within the autolithic zones (Fig. 7, 8).

Fig.7. Autolith with the small portion of Fig.8. Broken autolith is identical to thethe “tuff” inside (t) which is identical to the autolith from Fig.7. Its shell (a) is absent “tuff” which has surrounded the autolith. at the left-bottom side of autolith. WhitePipe Zarnitsa, Yakutia. Slab. 3x arrow shows a movement direction of the “tuff” portion after autolith was broken. Zarnitsa pipe, Yakutia. Slab. 3x.

9. Fine-grained carbonate and serpophit along with equally dispersed small grains of magnetite and perovskite, sometimes with same size phlogopite, monticellite, clinopyroxene, and melilite is the main composition of the groundmass of autolithic material. Small (1 mm and less) idiomorphic grains of olivine-2 create porphyritic texture of autoliths.

10.Coarse-grained carbonate, glassy serpophit, some phlogopite, potassium feldspar and dusty magnetite with typomorphic minerals of carbonatites - baddeleyite and pyrochlore [16] are the major components of the matrix.

11.Relatively light carbonate fraction of carbonatite melt tends to create the matrix at the top of diatremes. That is why some kimberlites look like carbonatites (pipe Aikhal, Alakit field, Yakutia). Heavier

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serpophit dominates within matrix at the deep horizons of the pipes. Sanidine was found in the matrix of autolithic kimberlite of Yakutskaya pipe, Daldyn field, Yakutia [7]. Apatite is the common mineral of the matrix as well. The distribution of phlogopite as well as a distribution of all other minerals of the matrix is quite irregular. High local concentration of phlogopite can create “lamproite-like” rocks (Fig. 8) within kimberlite pipes.

12.Autolithic kimberlites = kimberlite “tuffs” are igneous (not a pyroclastic) rocks [1, 8].

13.The coalescence of drops of picritic melt produced the autoliths and blocks of massive kimberlites. Small fragments of carbonatitic material within such blocks look like xenoliths of limestones (even if no limestones among the wall-rocks) or like veins of postmagmatic carbonates. [1, 6].

14.Kimberlite pipes were filled up by just one sole eruption of kimberlite magma. Consequent differentiation of the both melts produced all possible kimberlite rocks varieties.

15.The cavity of diatremes was created by magma itself. The phenomenon of water hammer had occurs periodically in the head of ascending magma. Solidificated autoliths along with xenoliths gathered into cumulates, which plugged recurrently the originally elongated dyke-like channel of eruption. Water hammers transformed it into more and more isometric at the higher horizons. When magma met the plug, water hammer struck in all possible directions making a lot of specific grooves or striae not just vertical, but also inclined and even horizontal (A. Du Toit, 1906) [12].

16.In some cases, weakened water hammers produced “blind” diatremes, which never had an exit to the earth’s surface.

17.Deep inner overcooling of magma followed the moment of liquid immiscibility. This idea has its confirmation in number of experimental publications [14, 15, 17, 18, 19, 20, 21, 22]. Therefore, it is easy to see, why thermal effect on xenoliths and wall rocks was so low.

The implication of idea of adiabatic cooling cannot help. This could be good for compressible substances like gases, but inapplicable for liquids. Secondly, adiabatic process could decrease the temperature of very first portions of kimberlite magma, which were rich for volatile components. However, the most important is the thermal regime of the latest/final portions of magma, poor for volatiles.

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18.Sharp overcooling crushed hot mantle xeno- and phenocrysts (in approximately equal proportion, independently of their own hardness). If any outer mechanical force would crush such a super-hard mineral as diamond is, so this force must to grind to powder all other much softer kimberlitic minerals, however, they are survived.

19.Serpophit/lizardite is a volcanic glass of kimberlite rocks [3, 4, 5].20.Kimberlites are rich for titanium, potassium, phosphorus, hydrogen,

boron, fluorine, etc. that are catalysts of liquid immiscibility in experimental systems.

21.The word “Kimberlite” has to be used as an economic (not petrographical) term for diamondiferous variety of the wide range of ultrabasic subalkaline hypabyssal rocks rich for olivine and also for carbonate, mica, clinopyroxene, melilite, monticellite, potassium feldspar, etc. Petrologically it has to be a rock - mixture of carbonatites and group of ultrabasic silicate rocks [2].

22.At least some of diamonds could be generated by kimberlite magma itself during eruption. A long, well known list of undoubtedly crustal minerals among inclusions in diamonds (staurolite, quartz, hornblende, feldspar, plagioclase, etc) cannot be explained on the traditional basis. In addition, this can explain the numerous discoveries of diamonds in crustal xenoliths and wall rocks [24].

Below is a one of logical explanations. Using classic hydrodynamic formula (9, p.377):

Q = 8.34 * [{dP / (Dm * L)} ^ (4 / 7)] * [(C ^ (19 / 7)) / (B ^ (1 / 7))]

we can receive the volume velocity of eruption (Q, cub. m / sec). dP – pressure overfall on the opposite sides of channel of eruption; for kimberlite magma dP = 45 kbar = 4.5 * 10 ^ 9 Pa, Dm – magma’ density, at least 2.5 * 10 ^ 3 kg / cub. mL - vertical length of the channel, 150 km = 1.5 * 10 ^ 5 mC – hydraulic diameter; for dyke:

C = (2 * X * Y) / (X + Y)

where: X – width of dyke, Y – length of dyke (horizontal).B – kinematic index of viscosity. According to (11, p. 444):

B = A / Dm

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where: A – viscosity, Pa / sec; if A = 1 (just for water-rich carbonatitic liquid, which was a transporting agent for kimberlite magma), so B = 4 * 10 ^ (-4) sq. m / sec.

The average dimensions for Siberian kimberlite dykes (10) are: X = 2 – 3 m, Y = 500 – 800 m, so C = 4.98 m.

So, Q = 8,236 cub. m / sec.

Linear speed of magma V = Q / Sd, where Sd – the size of the cross-section; for Siberian dykes Sd = 1,625 sq. m, so:

V = 5.1 m / sec.

The loss of the quantity of movement [dK] during single water hammer is:

dK = Mk * dV

where Mk – mass of magmatic column, dV – loss of speed during the water hammer.

Mk = Dm * L * Sd= 6.09 * 10 ^ 11 kg.

If to accept dV = 2.55 m / sec (just 50 % of its original speed),

dK = 1.55 * 10 ^ 12 kgm / sec.

If the duration of the loss of speed (dT) was 5 min, so the power of single water hammer was:

F = dK / dT = 5.17 * 10 ^ 9 N

During water hammers in the front of the magmatic column, the pressure 40 kbar (necessary for diamond growth) could be reached in the sphere with the surface of:

Ss = F / P = [5.17 * 10 ^ 9] / [4 * 10 ^ 9] = 1.29 sq. m

and the diameter:D = (Ss / π) ^ 0.5 = 64 cm

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Each water hammer could create a cavity:

U = F / (g * Dr)

Where: U –volume of wall rocks, F – power of single water hammer, 5.17 * 10 ^ 9 Ng = 9.81 m / sq. secDr – wall rock’s density, 2.6 * 10 ^ 3 kg / cub. m [13]So, U = 2.027 * 10 ^ 5 cub. m

An average kimberlite pipe has a volume about 505 * 10 ^ 5 cub. m [13]. Therefore, to create this size diatreme, the number of water hammers ca. 250 will be necessary. If to accept that the duration of single water hammer was 1 hour (5 min to loose the speed and 55 min to regain it back), time about ten days will be enough to create average kimberlite pipe. Statistically [25], 1,200 out from 3,211 known for the year of 1994 eruptions lasted 10 – 100 days, and 400 eruptions lasted 1 – 10 days.

It also looks big enough time for diamonds growth.

23.There is the fact, that each diamond mine contains huge number of different morphological varieties of diamonds (Premier Mine – about 1,000 [23]). It is hard to imagine the existence in upper mantle a thousands different diamondiferous rocks, which provided their diamonds for each separated kimberlite pipe.

REFERENCES:

1. Kryvoshlyk I.N. The Peculiarities of Morphology and Some Questions of Genesis of Autoliths in Kimberlite Breccias. Geology and Geophysics, # 7. 1976. Novosibirsk, (in Russian).

2. Kryvoshlyk I.N. About The Term of “The Kimberlite”. 1978. Deposited Manuscript # 859-78. Moscow, (in Russian).

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3. Kryvoshlyk I.N. To the Question of Studying of Autoliths in Kimberlite Rocks. 1978. Deposited Manuscript # 2115-78. Moscow, (in Russian).

4. Kryvoshlyk I.N. To the Question of Possibility of Liquid Immiscibility in Kimberlite Pipes. 1979. Deposited Manuscript # 2440-79. Moscow, (in Russian).

5. Kryvoshlyk I.N. Autoliths and Some Conclusions of the Hypothesis of Liquid Immiscibility. 1980. Transactions of the Academy of Science of the USSR. V. 252, # 1. Moscow, (in Russian).

6. Kryvoshlyk I.N. The Globules of Immiscible Carbonatites in Kimberlite Rocks. 1981. Transactions of the Academy of Sciences of the USSR. V. 260, # 4. Moscow, (in Russian).

7. Kryvoshlyk I.N. Optically Positive Anorthoclase of Carbonatitic Matrix of Autolithic Kimberlite of Yakutskaya Pipe. Dep. # 1107-Ukraine.90: 7 pp. 1990, (in Russian).

8. Kryvoshlyk I.N. Brief Review of the Theory of Liquid Immiscibility of Kimberlite Magma. 1998. 7th International Kimberlite Conference. Cape Town. Extended Abstracts, pp. 473-474. Also:

9. Povh I.L. Hydrodynamics. 1964, (in Russian). 10.Kovalsky V.V. Kimberlite Rocks of Yakutia. Academy of Sciences of

the USSR. Moscow. 1963, (in Russian).11.Loytsyansky L.G. Fluid and Gas Mechanics. Nauka (Science)

Publication. Moscow. 1970, (in Russian).12.Clement C.R., Harris J.W., Robinson D.N., and Hawthorne J.B. The

De Beers Kimberlite Pipe – A Historic South African Diamond Mine. Mineral Deposits of Southern Africa. 1986, pp. 2193-2214.

13.Milashev V.A. Pipes of Explosion. Nedra. 1984, (in Russian).14.Todd P. Silverstein. The Real Reason Why Oil and Water Don’t Mix.

Journal of Chemical Education. Vol. 75, No. 1, January 1998.15.Grande T. On the Thermodynamics of Glass Forming AgI- and

Ag2S’- Based Melts. Proceedings from The International Harald A. Oye Symposium, Trondheim, Norway, Feb. 2-3, 1995, 349-356.

16.Frantsesson E.V. The Petrology of Kimberlites. Moscow. 1967.17.Karapetiants M.H. Chemical Thermodynamics. Goshimizdat.

Moskow-Leningrad, 1953.18.Semenchenko V.K. The Surface Phenomenons in Metals and Alloys.

Gos. Izdat Technical-Theoretical Literature. Moscow, 1957.19.Semenchenko V.K. Selected Chapters of Theoretical Physics.

“Education”, Moscow, 1966.

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20.Kitaigorodsky I.N., Khodakovskaya R.Ya. Pre-crystalline Period in Glass and its Significance. “Glass-like Condition”, part 1, “Catalyzed Crystallization of Glass”, Academy of Science of the USSR, Moscow-Leningrad, 1963.

21.Storonkin A.V. Thermodynamics of Heterogeneous Systems. Part 1. Leningrad University Publication. Leningrad. 1967.

22.Anikin I.N. Main Peculiarities of Crystallization of Mica (Phlogopite) from Melt. “The Growth of Crystals”, # 12, 1977.

23.Trofimov V.S. Geology of Deposits of Natural Diamonds. Moscow, “Nedra”, 1980.

24.Botkunov A.A. Some Regularities of Distribution of Diamonds in “Mir” Pipe. “Transactions of All-Union Mineralogical Society”, part 4, 1964.

25.Simkin T., Siebert L. Volcanoes of the World. Geoscience Press, Tuscon, Arizona, 1994.

26.www.meteorlab.com/Frame01/mantle.htm 27.www.rasny.org/mineral/Kimberlite/index.htm 28.Hetman, C.M., et al, Lithos, 76, 2004, 51-74.29.Kryvoshlyk, I. 1983. PhD Thesis. Moscow University.

IMPORTANT NOTE.

This theory was ignored for many years. At the present time it became a classic point of view. The impressive list of publications and even PhD dissertations by those “scientists” who used to use somebody else’s ideas confirms a justice of my theory. Should I be thankful to these plagiarists? Should I attach their list?

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