According to Itypeusa, the series of ancient rocks, which make up a large part of the basement of the vast plateau and most of the higher areas (maritime system and Goian system) are divided into two groups: the oldest format of gneiss, granites, syenites and mica schists belongs to the Laurentian system, while the most recent where schists predominate, quartz, itabirite together with limestone, is assigned by geologists to the Huronian system. This group, which is well developed in the Serre do Espinhaço, de Canastra, de Matta da Corda and in the Goian system, contains very rich mineral deposits of gold, iron, manganese and lead. This mineral wealth was known relatively late in the day, when systematic explorations were undertaken in some regions of the interior (geological commission directed by CJ Hartt: 1867).
It is certain that not a small part of the country’s future is connected with the exploitation of iron ores. Brazil contends with the United States for the primacy of their availability; both in one and the other state, according to OR Kunn (in The Iron Age, 1922), are found 23% of the iron deposits that can be used industrially; according to an official estimate, the iron ore deposits represent a reserve of about 11 billion tons.
Not infrequently the material forms a continuous mass, indeed real mountains, such as the compact masses of oligistus (itabirite) in the Pico do Itabira do Campo and in that do Itabira do Matto Dentro, in Minas Geraes. The largest deposits are found in this state, and in the finite states of Govaz, S. Paolo, Espirito Santo, Bahia, and in the two southernmost states of Santa Catharina and Rio Giande do Sul. The deposits, which sometimes reach the power of 600 m. and commonly contain about 65% of metal, they are mostly hidden under the forest mantle; hence the discrepancies about their extent.
Iron oxides prevail and above all sesquioxide and peroxide, which in Itabira’s itabirite make up 92 and 97% respectively. The clay and iron conglomerate called “ganga” on the site is also rich: the reserve of 100 million tons is calculated for the Gandarella field in Minas.
An important mineral product is gold, which is found in almost all the states of Brazil, and particularly in the two chains of Mantiqueira and Espinhaço and in the area between the S. Francisco side and those of Paraná and Paraguay, that is, in the states of Minas Geraes, Goyaz and Matto Grosso. Gold deposits also exist in S. Paolo, Rio Grande do Sul, Maranhão. The main active gold mine is that of Morro Velho or São João d’El-Rey, exploited by the company of the same name in the state of Minas Geraes; in 1909-10 the production of this mine was valued at more than 200,000 pounds. And there is reason to believe that Rio Grande do Sul can also have a real future in store for what concerns gold production. The production of silver and platinum is very scarce; much more important is that of manganese whose mineral offers more than 52% of metal. The Morro da Mina mine in Minas Geraes is now assigned an annual production of 60,000 tons. of mineral; but in 1915 it reached one million. Thus it is estimated that two fields near Corumbá can supply more than 100 million tons.
Brazil had a very fortunate period for the production of diamonds: discovered in 1727, in the Caete-mirim (near Diamantina), they were for a long time a characteristic of the state of Minas. Diamond fields were exploited in the ceniral region where Diamantina was built, and in the northern one where Grão Mogol is; the precious crystals are found above all in the quatennial floods, in the beds or on the banks of the rivers called grupiaras and exceed for clarity and thickness (the Estrella do Sul, discovered in 1853, weighed 254 carats) the diamonds of South Africa. offers the Matto Grosso (where Diamantino stands); amber specimens, of a tender green, the Goyaz. Famous are the black diamonds (carbonados) of Bahia, used for tunnel drillers: one of them, discovered in Lenções in 1895, weighed 3150 carats.
Corundum offer the diamond-bearing sands of Salobro (Bahia); rubies of various hues and sapphires are found in the sands of Piuna and Rio Doce respectively (in the state of Espirito Santo). Garnets are found in Bahia, Espirito Santo and in other states, but above all in Minas, where, near Ouro Preto, jasimemes of topaz are rich.
As far as is known, hard coal is scarce. However, in the states of Rio Grande do Sul (where the São Jeronimo mine produced a quarter of a million tons in 1924) and Santa Catharina, they can offer bituminous coal and lignite; its industrial use, however, is hampered by the considerable amount of ash and slag. Brown coal from the Gandarella tertiary basin (southern section of Minas Geraes) gives more de! 48% coal; the field of Fazenda de Bomfim, with a power of two meters, gave, after the construction of the trunk that connected it to the railway network, more than 100 tons. per day. Extensive peat bogs are in the states of Bahia (banks of the Marahú), San Paolo and Minas.
Considerable quantities of liquid fuel can be offered by the oil clays of the states of Bahia and Alagôas and by the black clay of which a large basin extends between S. Paolo and Rio Grande do Sul: rock salt mines are in the interior of Minas, Goyaz and Bahia, and large quantities of sea salt produce the states of Rio de Janeiro, Ceará and Rio Grande do Norte.
Even the importance of some mineral products such as that of marbles could increase, in the not too distant future, with a more rapid circulation. And perhaps new explorations will allow to increase, soon, the production of mica in Goyaz, Bahia and Minas; lead production in Minas, Rio Grande do Sul and Bahia, and graphite production in Minas and Rio de Janeiro.
The mineral springs are also noteworthy. Since 1908, the Centro Industrial do Brasil noted the importance of the “Aguas virtuosas” of Caxambú and the 15 novembro spring (table water), which belong to the state of Minas Geraes; and he warned: “Almost all the states of the Union have springs… thermal, hypothermic, cold, alkaline, acidic, iodophenic, sulphurous, arsenical, ferrous”. Indeed, notable mineral springs are eg. in Ceará (Caldas: sulphurous and thermal), in Bahia (on the banks of the Itapicurú: thermal), in Rio de Janeiro (“Salutaris”, near Parahyba do Sul: ferrous and gazous; “prototermale”), in Paraná (Xapecó: thermal with more than 34 °).
