PEGMATITE FIELDS OF SÃO PEDRO DE FERROS, ANTÔNIO DIAS AND MARILAC, MINAS GERAIS STATE, BRAZIL: PETROGRAPHIC CHARACTERIZATION

Pegmatites are rocks of granitic or metasomatic origin with grains from 30 mm to gigantic crystals that are formed in fluid phase of the magmatic liquid, enriched with incompatible elements, thats why they can be considered as gemstones and industrial minerals deposits. Both geological studied mineralizations in the present article were formed by an anatexis process, with fractional crystallization, or partial fusion. The Jatobá Mine in the Pegmatitic Field of


Introduction
Pegmatites are rocks of igneous or metasomatic origin, with equi to unequigranular texture, generated in discontinuities of contacts borders, in dikes or pocket shapes, in a crystallization process with a fluid phase [11].They are composed of alkali feldspars and quartz, and are usually present as accessory minerals like mica, tourmaline, beryl, and fluorite [13].
Pegmatites are distal deposits of granitic rocks, i.e., they form mostly in the peripheral regions of the plutonic body, as well as skarns, veins, massive sulfides, and epithermal deposits [9].The main economic interest related to the rock in this study is the exploration of beryl as gems, and as beryllium (Be) ore [7], as well as feldspars, widely used in the glass and ceramic industries [4].
In Brazil, there is a vast occurrence of pegmatites distributed in the Eastern, Northeastern and Southern Provinces [4], represented in Figure 1.
The Oriental Pegmatite Province (OPP) of Brazil is distributed along the states of Minas Gerais (MG), Espírito Santo and Bahia (Figure 1).The study area is within the OPP, in the Pegmatite Districts of Governador Valadares (DGV) and Santa Maria de Itabira (DSMI), in MG.The present work will focus on the Ferros -Antônio Dias (DSMI) and Marilac (DGV) Pegmatite Fields, where aquamarine and niobium tantalates occur.
A distinction will be made of the mineralogical composition of the samples collected in the field, emphasizing the presence of gems.Thus, it will be possible to indicate the relationship between the genesis of the rocks and the minerals formed, and to compare the results of the Pegmatite Fields studied.

EASTERN BRAZIL PEGMATITIC PROVINCE (PPO)
The divisions and subdivisions of the    In the southern part (Annexes IV), the country rocks can be a fine to medium leucocratic gneiss composed mainly of quartz, feldspar and biotite, also a medium-grained mesocratic foliated granite [2].
The pegmatite bodies are often simple and zoned (core of milky quartz, intermediate zone of K-feldspar and quartz and an undifferentiated zone with quartz, muscovite, kaolin, albite, and feldspar) [2].These bodies have dimensions of 10 to 50 m long and 5 to 10 m thick with a predominantly tabular shape and sometimes lenticular.Some are concordant with the host rocks, but others are discordant [8].
The essential mineralogy consists of alkali feldspar, muscovite and quartz, and the accessory minerals are beryl, fluorite, titanite, pyrite and garnet [8].
According to Silva [2], in the Second

Materials and Methods
The

JATOBÁ MINE
The visit to the Jatobá Mine, coordinates  According to the QAP Diagram [12] (Annex VI), the pegmatite rock sample was identified as a Tonalite.

Conclusion
The pegmatites of the Marilac and Santa
pegmatite areas were proposed by Ginsburg's et al. (1979), cited by Marciano [7].According to these authors, a Pegmatite Province is the grouping of pegmatite fields or belts of a single metallogenic unit.The Pegmatite Districts are inserted within the province and are differentiated through geological and geographical features.Pegmatite Fields unite rocks of a single formation type with the same age, igneous source, and geological-structural environment.The last subdivision is the Pegmatite Groups, where the morphological, structural, and textural patterns are well defined, as well as the structural control.The Oriental Pegmatite Province (Figure 1) occurs in the São Francisco and Mantiqueira Provinces with the stratigraphy represented in Annex I.It is located along the Araçuaí Belt and the Atlantic Belt, from Zona da Mata (far south) to the Itambé region in Bahia (far north), extending 800 km in length and approximately 125 km in width [3].The pegmatites of the region are both from granitic residual intrusive magmas, and anatectic origin, from partial fusion [8].
CFAD is in the Santa Maria de Itabira Pegmatite District (DSMI), and it includes other fields, such as the Guanhães-Sabinópolis field, in addition to CFAD[7] (Figure2).The DSMI is limited by Serra do Espinhaço, to the west, and by Quadrilátero Ferrífero, to the south [7].The CFAD is composed of zoned and simple pegmatites which are hosted in a volcanosedimentary sequence of Paleoproterozoic age, embedded in gneisses and granitoids.These pegmatites are embedded in the Guanhães Complex, which consists of gneisses and quartz-feldspar rich granitoids, with the presence of beryl and columbo-tantalite [2] [3].The dimensions of the bodies can vary from 50 to 100 m in length, and from 5 to 10 m in average thickness, with tabular to lenticular shapes, and discordant with the host rocks [8].As described earlier, the Santa Maria de Itabira Pegmatite District (SMIPD), in addition to encompassing the Ferros-Antônio Dias field, also includes the Guanhães-Sabinópolis field [7].For understanding, it is observed that the mineralogy of the two fields is similar, being characterized by the presence of mica, quartz, microcline, ferrocolumbitetantalite, euxenite, samarskite, monazite, fluorite, beryl, topaz, and garnet [8].The economic importance of this area is primarily because it is a generator of emerald, alexandrite, and aquamarine [2].Further northeast is the Governador Valadares District (DGV) (Figure 2), which includes the Marilac, Galiléia-Conselheiro Pena and São José da Safira Fields, a division proposed by Newman [8].Biotite-schist is the most common source rock, but granitoids and quartzites also occur [8].The pegmatites have tubular and lenticular shapes, concordant with the host rocks [3].In the mineralogy of the Pegmatite Fields, it is observed the presence of beryls and tourmalines in Marilac; lithium minerals and phosphates in Galiléia-Conselheiro Pena; and colored tourmalines in São José da Safira stand out [8].In addition, micas, feldspars (K and Na), spodumene, beryl, ambligonite, tourmaline and columbotantalite have been exploited since World War II from the pegmatites of the DGV.They are known for the quality of their gems and collectors' items, as there is a large quantity of agglomerated crystals [3].

Figure 2 .
Figure 2. Pegmatite Districts of Santa Maria de Itabira and Governador Valadares with the limits proposedby Newman[8] in dotted line.The colored boundaries proposed by Pinto et al.[8], will not be used in the present work[8] first stage of the work consisted of bibliographic research to obtain information about the origin and economic importance of the pegmatites.After data collection, the study has been chosen, being the Pegmatite Field of Ferros-Antônio Dias and the Pegmatite Field of Marilac.The maps used for orientation were the Geological Map of Santa Maria do Suaçuí and Marilac, for the Governador Valadares field [2], and the maps of Conceição do Mato Dentro, Ipatinga, Itabira and Coronel Fabriciano for the Santa Maria do Itabira field [2].Based on the CPRM pegmatite bodies registry [2] (maps represented in Annexes II, III, IV and V), the areas Jatobá Mine (DSMI) and Duas Cores Mine (DGV) were defined as targets for the work.After visiting the fields and collecting samples from each area, these samples were analyzed and described macroscopically for classification on the QAP Diagram (Streckeisen [12]).A thin section was also made for the Ferros-Antônio Dias Field (Jatobá Mine) and described microscopically.
706000L and 7856700N, located in the Guanhães Complex, took place on October 2017.Strong weathering was observed in the kaolin and in the host rock, the granite gneiss (orthogneiss).The mine comprises two bodies/veins, one mineralized and the other barren.The mine explores aquamarine, the blue variety of beryl; however, the minerals quartz (smoky and hyaline); K-feldspar; muscovite and biotite, and, more rarely, amethyst, fluorite and albite are also found.The Jatobá Mine is 30 meters long and 7 meters deep, has produced many gems of high economic value and is still active.After visiting the Jatobá Mine, two sample of pegmatite were collected of which one was described macroscopically (Figure 3).The sample is phaneritic, leucocratic, supersaturated in silica, with a massive structure, composed of K-feldspar, biotite, and quartz.K-feldspar (65%) has hypidiomorphic prismatic habit to xenomorphic crystals, with fine-to medium-grained (<1 mm to 3 mm).The biotite (20%) has lamellar habit, fine to medium grain size (<1 mm to 3 mm).Quartz (15%) presents granular texture with fine to medium grain size (<1 mm to 2 mm).According to the QAP Diagram (Annex VI), the pegmatite rock sample is classified as a quartz alkali feldspar syenite.

Figure 3 .
Figure 3. Pegmatite sample, classified as Quartz alkali feldspar in the QAP Diagram, with Kfeldspar grain size between < 1mm and 3 mm, biotite grains size between <1 mm to 3 mm, and quartz grain size between <1 mm and 2 mm, collected at the Jatobá Mine.

Figure 4 .
Figure 4. Pegmatite rock sample, classified as a Tonalite in the QAP Diagram [12], with plagioclase grain size between <1 mm and 1.5 cm, quartz grains size between <1 mm to 1.3 cm, and black tourmaline grain size between <1 mm and 1.5 cm, collected at Duas Cores Mine.The study of the thin section (Figures5 and 6) indicates the presence of microcline (40%), orthoclase (18%), plagioclase (15%), quartz (10%), biotite (7%), amphibole (5%), opaque minerals (3%) and accessory minerals (2%).The microcline found presents granular texture, with fine to medium grain size (1 mm to 3.75 mm) and irregular contact.On the other hand, the orthoclase is granular, with fine to medium grain size (0.3 mm to 3 mm), and irregular contact.The plagioclase shows granular texture, with fine granulation (0.4 mm to 0.9 mm), and irregular contact.In the sequence, the quartz shows granular texture and fine to medium grain size (0.2 mm to 3 mm), with inclusion of sericite, amphibole, and biotite, and irregular contact.Biotite showed hypidiomorphic lamellar habit of fine to medium grain
Maria de Itabira area (CFAD) are simple, predominantly zoned bodies, with a quartz core, rich in gem and industrial minerals.It was concluded in this work that aquamarine (Be3 Al2 [Si O6]18) from the Ferros-Antônio Dias Field forms in bodies closer to the core and its blue color is related to the intrusion of Fe in the mineral's structure [2].In addition, the pegmatites producing tourmaline (Na,Ca)(Mg,Al)6 [B3 Al3 Si6 (O,OH)3 0]) as in the Marilac Field, are positioned more externally in the intrusive igneous

Figure 7 .Figure 9 .
Figure 7. Block diagram representing the basic internal structure of zoned pegmatitic bodies and the relationship between zones [8].