Пироаурит, хидроталкит и манасеит от находище Крумово – нови минерали за България

Pyroaurite, hydrotalcite and manasseite from Krumovo Deposit –

New minerals for Bulgaria

Пироаурит, хидроталкит и манасеит от находище Крумово – нови минерали за България

Zhivka Janakieva¹, Chavdar Nachev², Denka Yanakieva³

Живка Янакиева¹, Чавдар Начев², Денка Янакиева³

1, 2, 3 – НМ „Земята и хората” (НМЗХ);

Key words: pyroaurite, hydrotalcite, manasseite, anion clays, Krumovo Deposit

Hyrdotalcite-like minerals are known also as layered double hydroxides (LDH), or anion clays. These are important natural or synthetic minerals with increasing practical potential as absorbents, catalysts, molecular sieves, anion exchangers, antacids, bactericides, combustion suppressors fillings, polymer stabilizers, etc. Their structures consist of layers of (Mg_1-xAl_x) (OH)₂ plus interlayers of anions and molecular water. Hyrdotalcite-like minerals are relatively rare and associated with low metamorphic formations. These minerals are found in salt deposits, which indicate that their formations don’t require high temperature and pressure. Subject of discussion is their nomenclature (Drits et al. 1987) and classification - carbonates or hydroxides (Zaneva, Stanimirova. 2004)

During the study of the ore samples from Krumovo deposit treasured in the “Earth and Man” National Museum, the samples collected by the authors and G. Stanisheva and V. Ivanova-Panayotova (placed by the Geological Institute of the BAS), the existence of minerals from the hydrotalcite-like minerals (pyroaurite, hydrotalcite and manasseite) has been proven. In the study of these minerals we have used microscopic, physical and chemical research methods. The x-ray tests were conducted using an x-ray diffraction-meter TUR M 62 (NMEM), at Cu radiation and Ni filter. The analyses of the individual phases were done using an energy dispersive spectrometer JFOL JSM 35 CF (Eurotest PLC), and SEM – using Philips 515 (SU “St. Cl. Ohridski).

Krumovo magnetite deposit (SE Bulgaria) is located in the eastern part of the Sredna Gora tectonic zone. This zone is characterized with development of sedimentary, volcanogenic-sedimentary, volcanoclastic and effusive rocks (Coniacian, Santonian, Campanian), as well as intrusive magmatism (Начев, and Начев. 2003). The magnetite mineralization in Mg-skarns is developed in the northeast contact of the Manastirski Pluton. The Manastirski Pluton composes of gabro, gabro-diorites and diorites, as well as dyke rocks – (gabro-diorite porphyrites, diorite porphyrites) (Панайотов and Иванова-Панайотова. 1954.) The magnetite bodies in Mg-skarns have a spatial, temporary and genetic connection with densely situated dykes, in the peripheral parts of the pluton. The intrusive rocks and Mg-skarns in the deposit are tectonically affected by the formation of systems of cracks, harnisches, zones of brecciation and cataclasis. Along these zones in the intrusive rocks relatively large quantities of epigenetic clynocoizite, chlorite and rarely thomsonite have developed. In the Mg-skarns and magnetite – low temperature serpentine (lizardite) and hydrotalcite-like minerals. This mineral association corresponds to zeolite facies (Спиридонов et al. 2000).

Investigated hyrdotalcite-like minerals (pyroaurite, hyrdotalcite, manasseite) from Krumovo deposit forms veinlets, stains, and cement in thin brecciate zones in tectonic magnetite ores (magnetite-forsterite Mg-skarns). The veinlets are up to 25 cm long and up to 4 mm wide. Some of the veinlets intersect hosted rocks and contain grains of magnetite, situated parallel to the veinlets walls. Described minerals are white, yellow-green, soft and talc-like. The latter, all three minerals can not be distinguished with non armed eye. Their crystals have tabular habit and their width varies from parts of the micron to 300-500 microns and thickness is 5-10 microns. As a rule, they form monocrystals, but twins are also observed (Fig.1,2,3,4). Sometime in hollow areas in magnetite they formed crystals, which are up to 1 mm for pyroaurite. In separate areas in magnetite described minerals reach up to 5-7%. Hydrotalcite and manasseite are less developed than pyroaurite. Usually they powdery coated ludwigite, associated with magnetite.

On the base of the individual phases analyses are given chemical formulas, and the unit-cell parameters are calculated using Unit Cell software (Table 1).

The data laid out above allow us to conclude that among the Krumovo deposit Mg-skarns with magnetite, which have been epigenetically transformed into zeolite facies, hypogenic minerals have developed such as Al-pyroaurite, hydrotalcite, manasseite, as well as their Fe-containing variations.

Table 1

№	Mineral	Chemical formulas	Standard unit-cell parameters	unit-cell parameters Angstroms
14797 NMEM	Al-pyroaurite	(Mg5.95Fe3+0.05)6(Fe2+1.80Al0.20)2(CO3)(OH)16.4H2O	a=12.4376, c=23.4126	a=12.4260, c=23.4268
KR-04	Al-pyroaurite	Mg6(Fe3+1.73Al0.27)2.(CO3)(OH)16.4H2O	a=12.4376, c=23.4126	a=12.4530, c=23.5049
23108 NMEM	Al-pyroaurite	Mg6(Fe3+1.59Al0.41)2(CO3)(OH)16.4H2O	a=12.4376, c=23.4126	a=12.4188, c=23.2319
BP-01	Fe-hyrdotalcite	Mg6(Al1.64 Fe3+0.36)2(CO3)(OH)16.4H2O	a=3.0461, c=22.7722	a=3.0575, c=23.2505
KR-05	hyrdotalcite	Mg6.02(Al1.92 Fe3+0.06)2(CO3)(OH)16.4H2O	a=3.0461, c=22.7722	a=3.1587, c=23,5081
617 EMNM	manasseite	(Mg5.95 e2+0.03)5.98Al2.02[(OH)16/(CO3)].4H2O	a=6.12, c=15.324	a=6.1311, c=15.1906
KR-01	manasseite	Mg6(Al1.98Fe3+0.02)2[(OH)16/(CO3)].4H2O	a=6.12, c=15.324	a=6.1179, c=15.4820
KR-06	manasseite	Mg6(Al1.8Fe3+0.02)2[(OH)16/(CO3)].4H2O	a=6.12, c=15.324	a=6.1480, c=15.5830

Fig. 1. Al-pyroaurite – aggregates from tabular crystals.

Fig. 2. Al-pyroaurite – twined crystals on pinacoide.

Fig. 3. Fe-hydrotalcite crystals on ludwigite

Fig. 4. Manaseite aggregates from tabular crystals.

Предмет на изследване на настоящата работа са образци от желязорудното находище Крумово, Ямболско:1. Авторски образци на Вера Иванова-Панайотова,Пенчо Бонев, Любомир Василев и Гергина Станишева, предоставени от Геологически институт при БАН на Национален Музей „Земята и хората”; 2. Колекции съхранявани във фондовете на Национален музей “Земята и хората”;3. Собствени сборове на авторите от района на находище Крумово.

При описание на образци, предоставени от Геологически институт при БАН на Музей “Земята и хората” попаднахме на минерала пироаурит.

Научна инвентаризация на образци от фондовете на Музея установи присъствието на хидроталкит-подобни минерали и в колекцията подарена от Геолого-проучвателно предприятие Крумово през 1986 год. В последствие при търсеща теренна работа в отвалите на находище Крумово бяха намерени значителни количества хидроталкит-подобни минерали в магнетит.

References

Начев, И. К., Ч. И. Начев. 2003. Алпийска плейт–тектоника на България. С., “Артик-2001”, 200 с.

Панайотов, В., В. Иванова-Панайотова. 1954. Младата интрузия от Манастирските височини и свързаните с нея орудявания. Год. УГП., 4, 221-270.

Спиридонов, Э. М.. В.М. Ладыгин, О.Н. Симонов. 2000. Метавулканиты пренит-пумпеллиитовой и цеолитовой фаций трапповой формации Норильского района Сибирской платформы. Москва, МГУ, 221-270.

Drits V.D., JT.N. Sokolova, G.V.Sokolova, V.I.Cherkashin. 1987. New members of hydrotalcite-manasseite group. Clays and clays minerals. Vol. 35, № 6.

Zaneva, S., Ts. Stanimirova. 2004. Crystal chemistry, classification position and nomenclature of layered double hydroxides. BGS, An. sc. conf. “Geology 2004”.