2012

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Variations in mineral composition of lamprophyllite malinitovom in stock.

Akimenko M.I. (akimenko.alkaline@gmail.com), Sorokhtina N.V., Asavin A.M., Kononkova N.N.

(Vernadsky Institute, Moscow)

Malignite rod has been studied. There is represented as elongated, rounded body, which drilled by hole to a depth oh 94 m. Rock is consist of nepheline, feldspar, arfvedsonite, aenigmatite, lamprophyllite, astrophyllite, shcherbakovite, sodalite, aegirine-augite, ilmenite, goethite, rhodochrosite.

The mineral composition was analyzed by Electron Micro Probe Analyzer Cameca SX-100. There are two generations of lamprophyllite (Fig. 1, 2): euhedral pale yellow crystals and large xenomorphic crystals that are deep yellow. Each generation is characterized by zone structure of the grains: strontium-rich core and a boundary of barium (Fig. 3), at the same time lamprophyllite II generation is more barium (Ba/Sr > 1) (table 2), while for lamprophyllite I Ba/Sr < 1. Rock chemical analysis showed the changing content of strontium to the well, in the range of 25, 65 - 80,6 m it increases significantly, while the content of barium remains constant (Fig.4).


Fig. 1. Lamprophyllite I generation develops enigmatite, lamprophyllite II generation "corrodes" lamprophyllite I.	Fig. 2. Lamprophyllite II generation "corrodes" lamprophyllite I and generation arfvedsonite II.

Table 1. Chemical composition (wt%) lamprophyllite I generation

Na₂O	10.05	10	10.29	9.83	10.43	10.08	10.84	10.46	10.36
K2O	1.44	1.56	1.4	2.12	1.72	1.76	1.42	1.58	1.68
CaO	0.8	0.81	1.05	0.82	1.06	1.02	0.99	0.77	1.02
SrO	8.71	8.75	12.57	8.71	9.6	9.32	11.98	10.62	10.88
BaO	9	10.58	6.71	11.42	7.67	9.63	7.07	10.13	8.64
MgO	1.36	1.31	1.36	0.96	1.09	1.36	1.26	1.32	1.17
MnO	0.54	0.63	0.61	0.71	0.8	0.79	0.66	0.61	0.74
SiO₂	29.29	29.04	30.12	29.46	29.9	29.84	30.61	30.06	30.5
Al2O₃	0.22	0.2	0.16	0.18	0.15	0.18	0.18	0.18	0.18
TiO₂	26.78	26.75	29.23	27.99	28.75	27.63	28.49	27.59	29.14
FeO	4.01	4.1	4.45	4.37	4.7	5.05	4.72	4.23	4.67
ZrO₂	0.27	0.3	0.19	0.41	0.15	0.18	0.04	0.32	0.06
Nb₂O₅	0.65	0.44	0.14	0.78	0.14	0.06	0.12	0.79	0.12
Ta2O₅		0.07	0.03	0.04	0.16	0.07	0.11	0.21	0.06
ThO₂		0.05	0.24		0.09		0.05	0.08
UO₂	0.25	0.32	0.17	0.32	0.25	0.19	0.27	0.18	0.13
F	2.45	2.59	2.31	2.91	2.22	3.22	2.59	1.36	2.41
Total	95.83	97.5	101.03	101.03	98.88	100.38	101.42	100.49	101.76
Ba/Sr (Apfu.)	0.69	0.81	0.36	0.88	0.53	0.69	0.39	0.64	0.53

Table 2. Chemical composition (wt%) lamprophyllite II generation

Na₂O	K2O	CaO	SrO	BaO	MgO	MnO	SiO₂	Al2O₃	TiO₂	FeO	ZrO₂	Nb₂O₅	Ta2O₅	ThO₂	UO₂	F	Сумма	Ba/Sr (ф.е.)
9.24	3.07	0.73	4.21	16.03	0.58	0.51	29.09	0.24	27.29	4.26	0.09	1.05		0.01	0.5	2.03	98.93	2.57
9.05	3.06	0.73	4.62	16.08	0.55	0.39	29.62	0.48	26.94	5.26	0.04	0.85		0.02	0.56	1.68	99.93	2.35
7.43	3.36	0.9	5.73	12.19	0.53	0.92	30.5	0.21	29.29	5.64	0.12	0.4			0.66	2.31	100.19	1.43
7.57	3.02	0.78	5.62	13.96	0.65	0.78	29.94	0.45	28.52	5.38	0.06	0.13	0.05		0.57	2	99.48	1.67
8.56	2.4	0.75	6.61	10.57	0.95	0.92	32.29	0.38	25.82	9.27	0.05	0.13			0.41	1.87	101	1.08
9.74	2.57	0.91	6.7	14.62	0.64	0.79	29.46	0.22	27.47	4.82	0.14	0.36	0.1	0.05	0.35	2.28	101.22	1.47

Fig. 3. Content of SrO and BaO in lamprophyllite from depths of 7, 17, 51, m (brown colored rim of the grains, blue – central zone).

Fig. 4 Change in the contents of Ba and Sr (ppm) on the borehole (m).

Minor changes to the contents of Ba and Sr in malignite throughout the depth, leaves the controversial question of the processes leading to the evolution of the composition lamprophyllite. On this issue in the literature, there are several point of views the evolution of the compositions lamprophyllite associated with the accumulation of barium in the melt during the evolution of the magma [1] or to changes in postmagmatic breed, which took place during the enrichment and accumulation of barium in lamprophyllite [2].

References:

1. Zaitsev V.A, Thesis for the degree of Candidate of Geological and Mineralogical Sciences, , Peculiarities of chemical composition and formation conditions of minerals and titanite lamprophyllite in the Lovozero massif, Kola Peninsula, Moscow, 2005.

2. Azarova, J.V. Genesis and several minerals typomorphism lamprofilit-baritolamprofillit of complex lujaurite-malinitov Khibiny massif, New data on minerals,., 2004.