The formation of quartz aggregates in ultra-acid volcanics from eruptive breccias of the Pechenga structure (Kola Peninsula)

doi:10.15406/ijh.2019.03.00160

International Journal of

eISSN: 2576-4454

Hydrology

Mini Review Volume 3 Issue 1

The formation of quartz aggregates in ultra-acid volcanics from eruptive breccias of the Pechenga structure (Kola Peninsula)

Petr Skuf in

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Geological Institute of the Kola Science Center of the RAS, Russia

Correspondence: Petr Skuf?in, Geological Institute of the Kola Science Center of the RAS, Apatity, Russia

Received: October 17, 2018 | Published: January 30, 2019

Citation: Skuf’in P. The formation of quartz aggregates in ultra-acid volcanics from eruptive breccias of the Pechenga structure (Kola Peninsula). Int J Hydro. 2019;3(1):39-41. DOI: 10.15406/ijh.2019.03.00160

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Introduction

In the ore field of the Zhdanovsky Cu-Ni deposit of Pechenga structure, on the eastern flank of the Productive suite, bodies of eruptive breccias of a bimodal kagusite-picrobasalt composition are observed, which are observed in the form of split straight-line accordant dikes confined to the contact of the rocks of Productive suite and overlying rocks of the Matert suite. The author was in some difficulty when trying to identify these exotic rocks and considered the most correct to give them the name "Kagusites", which is S.I. Tomkeev provides for non-feldspar ultra-acid magnetite rhyolites of the African volcano Kagusi.¹

Dikes of this group can be traced for hundreds of meters along the strike and fall of the host rocks and reach a thickness of 25-30 meters. The dikes cut ferro-dolerite sill-like bodies that are common in the section of the Productive suite, and in turn are cut by the intrusions of the ore-bearing gabbro-wehrlite association (Figure 1). Macroscopically, these are dense massive fragmentary lava with a breccia texture, in which randomly distributed fragmentary material is immersed in a matrix represented by vitroclastic microlava-brereccia having a composition of subalkaline picrobasalt enriched in Ti, Mg and Fe (Table 1) and constituting 20-50% of the rock volume (Figure 1). The size of the debris varies from psammite particles to lumps having more than 400 mm in diameter; form is angular, rounded, lamellar. More than 90% of the debris is represented by iron-rich ultra-siliceous lavas (kagusites) – dense glassy rocks of black or light gray color, with a conchoidal fracture characteristic of siliceous rocks. Large fragments of cagusite, “floating” in the vitroclastic matrix of eruptive breccia, sometimes have a drop-shaped and spindle-shaped, often twisted shape - a sign of synvolcanic plastic deformations of lava fragments; often, a crust of quenching with a thickness of 0.5-1 cm, composed of glass material and turbid with finely dispersed magnetite, is fixed in fragments. The structure of kagusite is micro-porphyritic or crypto-porphyritic; the number of porphyritic crystals is from 3 to 8% of the rock volume, the composition is quartz, sometimes dipyramidal quartz, which forms pseudomorphs in the crystals of high-temperature cristobalite; rarely albite and anorthite; the main enclosing material is an isotropic aggregate of the smallest quartz grains, sometimes of honeycomb shape. Among porphyritic phenocrysts, volume-decomposing feldspar and quartz crystalloclasts typical of modern eruptive breccias are often observed. Among the kagusites, two coexisting varieties of black and light gray can be distinguished (Figure 2).

Figure 1(1) Schematic geological map of a section of the Ore field to the west of the Zhdanovsky deposit. Legend: 1, Cu-Ni ore; 2,3, metaperidotites; 4, pyroxenites; 5, gabbros; 6, ferrodolerites; 7, rocks of the eruptive breccia of kagusite-basalt composition; 8, metasediments; 9, faults; 10, occurrence of rocks.

(2) Eruptive breccia of kagusite-basalt composition (sample photo). Fragments of a kagusite are immersed in basalt vitroclastite.

(3) Rounded kagusite isolations in the eruptive lava-breccia of basalt composition (outcrop photo).

(4) Coarse fragmentary sintered tuff (outcrop photo). Porphyritic black fragments - eucrites, rounded and ribbon-like fragments with a fluid texture - kagusites.

Components	1	2	3	4	5	6
SiO₂	49.59	41.63	83.62	94.73	42.49	86.1
TiO₂	1.65	1.56	0.27	0	1.78	0.51
Al₂O₃	12.75	11.83	2.73	0.34	12.3	3.22
Fe₂O₃	7.98	4.03	1.01	0.53	5.45	1.18
FeO	4.06	6.71	1.29	1.78	12.82	3.75
MnO	0.17	0.19	0.04	0.01	0.2	0.06
MgO	10.23	7.2	1.36	0.18	5.96	1.77
CaO	4.07	10.85	3.41	0.8	11.77	0.98
Na₂O	4.2	3.54	1.5	0.1	0.38	0.09
K₂O	0.24	1.35	0.14	0.03	0.16	0.01
H₂O^-	0.12	0.1	0	0.06	0.33	0.25
H₂O⁺	3.2	3.69	1.66	0.35	5.05	2.05
P₂O₅	0.13	0.12	0.19	0	0.12	0
CO₂	0.12	6.38	2.13	0.59	0.65	0.26
Stot	1.26	1.19	0.02	0.4	0.55	0
∑	99.77	100.37	99.37	99.9	100.01	100.23
Rb	10	n.det.	5	n.det.	4	0
Sr	118	n.det.	71	n.det.	90	n.det.
Ba	140	н.оп.	40	n.det.	80	n.det.
Ni	n.det.	200	n.det.	100	200	100
Co	n.det.	50	n.det.	0	90	0
Cr	n.det.	460	n.det.	190	500	400
Cu	n.det.	160	n.det.	40	n.det.	25
Zr	115	n.det.	25	n.det.	n.det.	n.det.

Table 1 The chemical composition of bimodal kagusite-containing associations of eruptive breccias of areas of Zhdanovsky deposit and Lake Sari-Yarvi (wt.%, ppm)

Note 1-4, rocks of the region of Zhdanovsky deposit; 1,2, subalkaline Mg-basalts from the matrix of eruptive breccia; 3,4, kagusites from fragments of eruptive breccia, respectively, low alkaline; (3) and alkali free (4); 5,6, rocks of the Lake Sari-Yarvi; 5, low alkaline ferrobasalt from fragments of eruptive basaltic lavobreccia; 6, alkali free kagusite from fragments of eruptive basaltic lavobreccia.

Light-gray leucocratic kagusites have almost monomineral quartz composition and are often observed in black, melanocratic varieties in the form of tuber-like and lenticular isolations with sharp, distinct contacts; at the same time, the characteristic cryptoporphy structure is preserved both in the isolations and in the enclosing black kagusits (Figure 2). Leucocratic kagusites, along with picrobasalt, sometimes form peculiar bimodal variolite micro-lavabreccia, in which the kidney-shaped and cluster-shaped aggregates of glassy kagusite, turbid by a finely dispersed magnetite rash, are immersed in variolite picrobasalt material (Figure 1). In thin sections, a peculiar two-phase system of coexisting variolitic isolations of leucocratic (kagusite) and melanocratic (picrobasalt) compositions is observed. Such interrelationships of contrasting phases can be explained only from the position of liquate liquid immiscibility in high-iron melts during the formation of liquate pairs like classical examples such as eucrite-liparite or ferrobasalt-liparite.²

Figure 2 Rocks of eruptive breccia of the kagusit-basaltic composition from the section of the Productive suite (thin sections photo).

(1) & (2), A form of likvate kidney-shaped kagusitic isolations (light gray) in basaltic vitro-clastite; x 15; 1 - without analyzer; 2 - with the analyzer;

(3) The form of likvate kagusitic isolations, a fragment of the previous section; x 60, without analyzer;

(4) Strip-like isolation of alkali-free kagusite (gray) in a low-alkaline kagusite (dark gray); x 35, with the analyzer.

From Table 1, it can be seen that the kagusites of the described bimodal eruptive breccias are represented by two types of rocks - low-alkaline kagusites (black varieties) and alkali-free kagusites (leucocratic varieties of light gray). The SiO₂ content in the low alkaline kagusite is 83.62%, and the total Fe is 2.5%; Na₂O + K₂O = 1.64%, with a predominance of Na₂O. The content of SiО₂ in alkali free kagusite is 94.73%, and total Fe is 2.31%; Na₂O + K₂O = 0.13%, with a predominance of Na₂O. In all cases, the matrix of eruptive breccia is sub-alkaline iron-rich picrobasalts. A peculiar body of ferrobasaltic lavobreccia with fragments of alkali-free kagusites was established in the area of Lake Sari-Yarvi, north of the Kola Superdeep Well.³ Having a size of up to 450 m in diameter and a complex rod-shaped form, this body pierces a powerful sill of gabbro-dolerites at the contact of rocks of the Productive suite and the suite of Matert. In addition to the acute-angled fragments of basaltic ferrodolerites, this body is crowded with rounded kagusite fragments measuring 0.2-0.5 m in diameter (Figure 1).

The content of SiO₂ in the kagusite from the area of Lake Sari-Yarvi is 86.1%, and total Fe is 4.9%; Na₂O + K₂O=0.1%. A distinctive feature of the kagusitic bimodal association areas of Lake Sari-Yarvi and Zhdanovsky deposit is enrichment of some siderophilic and chalcophilic elements, in particular, Cr, Cu and Ni. Kagusites have a cryptofelsitic structure, enriched with finely divided magnetite and permeated with a network of quartz veins. Lavobreccia matrix is represented by subalkaline picrobasalt. The chemical composition of kagusite, as well as low-alkaline ferrobasalt is given in Table 1.

Acknowledgements

None.

Conflict of interest

The author declares that there is no conflict of interest.

References

Tomkeev SI. Petrological English-Russian explanatory dictionary. Volume 1. Mosk Mir. 1986;285.
Marakushev AA, Bezmen NI. Variolites and their petrogenetic significance. Vestn Mosk Univ Ser Geol. 1987;5:62‒77.
Skuf’in PK. Kagusit-basaltic splitting in igneous rocks of the Pechenga structure and the influence of this process on the formation of sulfide-noble metal mineralization. Bull Mosk Ob-va isp Nature section Geol. 2010;85(3):52‒68.