The Brazilian mineral resources

Earth-Science Reviews, 17 (1981) 177--206 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

177

The Brazilian Mineral Resources HARTMUT BEURLEN and JACQUES PIERRE CASSEDANNE Departamento de Engenharia de Minas, Universidade Federal de Pernambuco, Recife, PE (Brazil) Instituto de Geoci$ncias, Universidade Federal do Rio de Janeiro, Rio de Janeiro, R J (Brazil)

ABSTRACT Beurlen, H. and Cassedanne, J.P., 1981. The Brazilian mineral resources. Earth-Sci. Rev., 177--206. The activity of the first generation of Brazilian geologists began in the early sixties. Systematic exploration work since then has evidenced some important new mineral reserves in Brazil. The most important examples are the 18 × 109 tons of high-grade iron ore (Caraj~is District), formed by supergene enrichment On iron formations older than 1800 m.y., the 2.5 × 109 tons of bauxite and similar reserves of kaolinite as residual enrichment in Cenozoic sediments in the Amazonas Basin (Oriximina, Capim); the potash and magnesium-rich evaporites near Aracajfi (Sergipe); the large residual concentrations of phosphate, anatase, pyrochlore and rare earths related to Cretaceous alkaline complexes with carbonatites; and some garnierite and asbestos deposits related to ultramafic rocks in the states of Goi~s and PiauL

INTRODUCTION

The present review will briefly discuss the geology of those Brazilian mineral products that at present are, or may become, of international interest in the future. The selected topics are grouped as follows: (1) Well-known, outstanding exportation products like iron ore, manganese, niobium, tungsten, quartz, magnesite and fluorite. Gemstones will be discussed in a separate paper in this issue. (2) Recently discovered deposits with major reserves that may attain an important role in mineral production in the future, such as bauxite, kaolinite, phosphate, titanium and potash salts. (3) Products with high-potential reserves supported by geological evidence, such as nickel, asbestos, chromite, gold, tin, lead and zinc, and copper. (4) The mineral fuels: petroleum, coal, bituminous schists and uranium. (5) A last section will summarize the present knowledge of the main metallogenetic epochs. First, however, a short review will be given of the data on present produc0012-8252/81/0000---0000/$07.50 ©1981 Elsevier Scientific Publishing Company

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tion, export, import, and reserves of the main Brazilian mineral products (Table I). It can be easily seen from this table that only ten products account for over 85% of the whole mineral production value, namely petroleum, iron, limestone, manganese, coal, gas, clays, gold, tin and gems. Of these only iron, manganese and gemstones may be considered as really abundant. Petroleum and coal production and reserves are highly deficient. Also deficient are the proved reserves and production of gold and tin. The large limestone and clay reserves will never become internationally important because of the low prices of these products. Among the other products listed in Table I, only niobium, tungsten, magnesite, zinc and fluorspar present significant export values, mainly as raw ores. Even for the majority of the exported mineral products, the Brazilian deficiency in technology is shown by the high importation values of derivative products (alloys and chemicals). This is clear for iron, tin, magnesite, zinc and fluorite.

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181

In other words, Brazilian industry is highly dependent on foreign supplies in the mineral sector. Despite the discovery of very important mineral reserves during the last few decades, it will not be possible to change this situation in the short term and without the contribution of significant foreign investments. The most important mineral deposits when referred to in the text, are followed by the abbreviation (in parenthesis) of the state and number according to the location map (Fig. 1). The state abbreviations used are as follows: Roraima (RR), Amap~ (AP), Amazonas CAM), Acre (AC), Rondbnia (RO), Parfi (PA), Maranh~o (MA), Piau/(PI), Cearfi (CE), Rio Grande do Norte (RN), Parafba (PB), Pernambuco (PE), Alagoas (AL), Sergipe (SE), Mato Grosso (MT), Goi~s (GO), Bahia (BA), Minas Gerais (MG), Esp/rito Santo (ES), Rio de Janeiro (RJ), S~o Paulo (SP), Paran~ (PR), Santa Catarina (SC), and Rio Grande do Sul (RS). OUTSTANDING EXPORT PRODUCTS

Iron

Three of the world's most important iron formations are found in Brazil: the Iron Quadrangle near Belo Horizonte (MG-55, 58); the Serra dos Caraj~s (PA-7); and the Urucum District at the Brazil--Bolivia frontier (MT-66). The latter will be discussed later because of its enormous manganese reserves. The Iron Quadrangle extends over 7000 km 2 east and south of Belo Horizonte and is well known for its large production of high-grade iron ore and important manganese and gold deposits. A very long list of publications on this area is well summarized by Dorr (1973). The high-grade ore, with over 60% iron, is of two types: the massive "hard hematite" and the even larger "soft hematite" bodies. The former is derived from itabirites (folded and metamorphosed, quartz-hematite iron formation) by hydrothermal enrichment in low-pressure zones during or after metamorphism, with individual ore bodies up to 500 million tons in size of hard hematite as concordant lenses in axial zones of folds, or related to fault zones. The bodies of the second type seem to be formed by supergene leaching, up to several hundreds of meters in depth, either of massive hematite or of normal itabirire. The exploitation of the soft ore started only a few years ago. The reserves of high-grade ore certainly range around 10 billion (109) tons in the whole area. The itabiritic protore is known as the Cau6 Formation and averages 250 m in thickness and contains 20 to 40% iron. Upwards the itabirites grade into dolomites of the Gandarela Formation. Both are included in the Itabira Group, covering the mainly coarse clastic Caraqa Group and are overlain by the fine clastic Piracicaba and coarse clastic Itacolomi groups, all belonging to the Middle Precambrian Minas Supergroup. No volcanogenic rocks have been reported either in the Itabira or in the Cara~a groups. Only the phyllitic units of the Piracicaba Group m a y be volcanogenic. Fiebiger

182 (1975) studied the distribution of organogenic paraphines and suggested an origin of the itabirites by precipitation of terrigenous iron solutions by local biogenic oxidation of sea water. The Minas Series overlies the Archean Rio das Velhas Series with the basal volcano-sedimentary Nova Lima Group (including manganese protores and gold deposits) and the clastic Maquin6 Group. In the Iron Quadrangle, according to Schorscher and Guimar~es (1976), both the Minas and the Rio das Velhas Series were metamorphosed in the greenschist facies and the amphibolite facies was reached only in nearby granitic intrusions. The whole area is interpreted as an allochthonous tectonic block that overthrust the migmatitic basement, coming from the southern end of the Serra do Espinha~o, 100 km to the east. Thus the Minas Series should be correlated to the Espinhaqo Supergroup. The Caraj~s Iron District (PA-7) was first reported by Tolbert et al. (1968, 1971). The high-grade ores, averaging over 65% iron, were formed by supergene enrichment related to Eotertiary peneplanes at 650--800 m, preserved over younger surfaces. The parent rocks are intensively folded and metamorphosed banded iron formations (100--300 m) intercalated in extrusive amygdaloidal mafic volcanic units, together forming the Gr~o Par~ Group. The coarse to fine clastic sediments of the Gorotire Formation unconformably overlie the Gr~o Par~ Group. A granitic intrusion in the Gr~o Par~ Group was dated at 1800 m.y. Ruy et al. (1973) identified the parent rocks of the iron ore as itabirites, similar to those of the Iron Quadrangle. Suszczynski (1973) distinguished them as typical volcanogenic by the high magnetite-martite, Ti and P contents, from the classicial itabirites of Minas Gerais. The supergene enrichment extends over 400 m in depth, averaging about 100 m. The proved high-grade reserves are 1.8 × 109 tons. Additional high-grade reserves are estimated at 16 × 109 tons.

Manganese Two mining districts are responsible for the bulk of the Brazilian manganese ore production: the Serra do Navio (AP-2) and Lafaiete (MG-59). The Serra do Navio District is formed by a granitic--gneissic basement covered by amphibolites and interbedded gneisses, quartzites and biotite schists of the Jornal Group, and quartzites, biotite schists with carbonate and gondite lenses of the Serra do Navio Group (Scarpelli, 1966). Herz and Banerjee (1973) suppose an age older than 2500 m.y. for the metasediments, based on interpretation of geochronologic data of the Guyana Shield and the evidence of three tectonic phases in the Serra do Navio Group, the last one dated at 1700 m.y.- They also support a magmatic origin for the amphibolites of the Jornal Group. Lima et al. (1974) join the Jornal and the Serra do Navio to the Vila Nova Group and suppose an age between 2200 and 1800 m.y., based on new geochronologic data. The oxidic manganese ore, averaging 48% Mn, formed by supergene enrichment of two protore types: a carbonate one with about 30% MnO2 and a silicate one with 5--25% MnO2.

183 According to Scarpelli (1966), the protore lenses attain up to 30 m in thickness and several hundred meters in length, and are enclosed in graphitic biotite schists of the Serra do Navio Group. The carbonate protore would have been formed in strong reducing lagoonal environments. The ore bodies strike northwest paralleling the fold axis along more than 10 km. The supergene ore reaches several tens of meters in depth. This district has already produced about 20 million tons of ore. The estimated remaining reserves amount to 25 million tons averaging about 40% MnO2. The present production is about 2 million tons per year. The Lafaiete District presents a sequence of orthoamphibolites (Herz and Banerjee, 1973) and metasediments, including carbonate and silicate Mn-prototes, correlated with with Nova Lima Group in the Iron Quadrangle. This sequence can be traced for more than 200 km from S~o Jo~o del Rei in the southwest to Lafaiete up to the Iron Quadrangle and Saude in the northeast, forming complex synclinorial structures in the migmatitic--gneissic Archean basement. The Lafaiete District, including S~o Jo~o del Rei and Saude areas, have already produced over 11 million tons of high-grade manganese oxide ore, coming from over twenty individual deposits (Dorr et al., 1958). The high-grade reserves of the most important deposits, like Morro da Mina (Merid), have already been exhausted and the carbonatic protores are being mined. The protore lenses reach up to 50 m in thickness, averaging about 15 m, and extend over several hundred meters, along the general northeast strike. Intensive isoclinal folding enlarged the original thickness and together with faults and fractures aided the supergene enrichment. Most frequent wall rocks are amphibolites and graphitic micaschists and phyllites. The carbonatic protore averages 20--30% Mn and is composed of rhodocrosite, rhodonite, spessartite, tephroite, Mn-amphiboles and minor alabandine. No primary oxides were detected. Also in the Rio das Velhas Series some minor iron formations are found. Minor manganese deposits occur in the Minas Series formed by supergene enrichment of manganiferous itabirites or of manganiferous dolomites. The Urucum District (Mutum District in Bolivia) (MT-66) is a flat lying and unmetamorphosed iron-manganese region that originally extended over at least 1000 km 2 (Dorr, 1973). The iron--manganese formation, up to 300 m thick (Santa Cruz or Cercadinho Formation), covers the mainly coarse and immature clastics of the Urucum and Puga Formations. The whole sequence is known as Jacadigo Series and, according to Almeida (1974), was formed in marginal basins of the Upper Precambrian Paraguay-Araguaia geosyncline, covering the Craton do Guapord basement. Earlier interpretations supposed a Cambro-Ordovician age. The banded iron formation is composed of more or less recrystaUized colloidal silica, hematite and cryptomelane. Haralyi and Barbour {1974) distinguish four superposed bandings, according to the thickness. A minor one is not cyclic and averages 0.2 mm. A cyclic banding averaging 3 mm is supposed to be annual. Supposed pluriannual cycles range in the centimeters and meters, and may be

184 related with long-term climatic changes. The richest manganese macroband, 6 m thick, is found at the base of the formation and on the Brazilian side. Six other manganese macrobands were observed above, but with generally decreasing Mn contents and thickness while iron increases. The manganese seems also to decrease to the western, Bolivian side. The reserves of the whole district were estimated by Alvarado (in Dorr, 1973) as amounting to about 40,000 and 10,000 million tons in Bolivia and in Brazil, respectively; averaging 50% iron. The manganese reserves in Brazil are estimated as 100 million tons with 40% MnO2, but active mining started only in 1976. Other important manganese deposits, 85 km eastwards from the Caraj~s Iron deposits (PA-8), were formed by supergene enrichment on slightly folded manganiferous pelites with some carbonate and organic matter (Anderson et al., 1974). A minimum age of 1800 m.y. for these sediments of the Rio Fresco Formation, covering the Gr~o Par~ Group, is given by an intrusive granite. The reserves are estimated at 25 million tons, averaging 30--40% Mn. Minor manganese enrichments are known and explored in Bahia State, related to Archean metasediments near Marafi (BA-31) and to Middle Precambrian metasediments of the Espinhaqo Supergroup. Niobium

Arax~ (MG-53) is the only active Brazilian niobium mine, supplying 70% of the world's requirements for this metal. The deposit was formed by enrichment of carbonatites in the center of the Arax~ alkaline complex (Guimar~es, 1957). The proved reserves amount to 27 million tons of 4.6% Nb2Os ore. Additional reserves were estimated at 350 million tons with over 3% Nb205. The ore is a red lateritic soil, 20--200 m thick. Pandalte, a barium-holding pyrochlore, is the main ore mineral, associated with some residual magnetite and ilmenite. Only one outcrop of carbonatite is found, very close to the fenitized country rocks, quartzites and phyllites of the Middle Precambrian Arax~ Group. The diameter of the very circular complex is about 4 km. Silexite crusts, veins and vug fillings within the red soil with, sometimes, well-crystallized barite, are the only hard-rock outcrops in the complex itself, and led Guimar~es (1957) to suppose a partial hydrothermal origin for the ore. In another part of the complex the lateritic cover holds very important phosphate deposits. The Arax~ complex was intruded during the Late Cretaceous together with other important alkaline complexes that surround the Paleozoic--Mesozoic Paran~ Basin (Hasui et al., 1976). Catal~o (GO-44) is one of these and again intrusive in metasediments of the Arax~ Group. Carvalho (1974) describes flogopitized and serpentinized pyroxenites and peridotites as the main rocks of this complex. Carbonatites (sSvites) occur as centimeter to decimeter veins or as matrix in the brecciated ultramafics. This association is named silicocarbonatites. Glimmerites occur mainly peripheral to the complex. Intensive silicification is observed

185 replacing these rocks up to a depth of 250 m. The mineral deposits related to this complex are all supposed to be of the residual type and include the following reserves, 21 × 106 tons with 1.3% Nb2Os, 140 × 106 tons with 15% TiO2, 120 × 106 tons with over 5% P2Os, 18 X 106 tons with 4% R.E. oxides and 6 × 106 tons with 14% vermiculite greater then 20 mesh. Other contemporaneous alkaline complexes are known by the important anatase, phosphate (Tapira, MG-56 and Salitre, MG-48), phosphate (Jacupiranga, SP-63), bauxite and uranium (Polos de Caldas, MG-61) and nickel (Morro do Engenho, GO-38, .~gua Branca, GO-39 and Santa F~, GO-40) reserves. Also contemporaneous are kimberlites in the southwest part of Minas Gerais. A first alkaline complex with carbonatites at Seis Lagos (RR-1) with Nb, Th, R.E. anomalies and important iron manganese caps, and numerous circular complexes detected by aerial photos around the Amazonas and the Parnaiba Syneclises, enlarge still further the enormous metallogenetic potential and present importance of this Cretaceous volcanism.

Tungsten Over 500 scheelite occurrences are known in the Serid5 region, in the states of Rio Grande do Notre and Paraiba, covering an area of over 24,000 km 2 in northeast Brazil. The extent of the occurrences corresponds with the geotectonic unit known as the Serid5 Geosyncline. Suszczynski (1975) states that all occurrences are in the same metamorphosed marly--calcareous unit, known as the Quixaba Formation. Ferreira and Albuquerque (1969) showed that the mineralized tactites belong to different strata of two tectonic--sedimentary cycles, namely the Caic5 Group (Lower Precambrian) and the Serid5 Group (Upper Precambrian). Siqueria and Maranh~o (1973) even distinguish tactites in three cycles: the Caic5 Group (Lower Precambrian), the Jucurut~ Group (Middle Precambrian) and the Borborema Group (Upper Precambrian). On his interpretative map of the Serid5 Geosyncline, Santos (1973) shows that most occurrences are situated on the borders of tectonic highs, like the "geanticlinal of S. Vicente" with exposure of the Caic5 basement; the anticlinoria of S. Rafael and Currais Novos with large migmatite nuclei, and exposures of both Caic5 basement and Serid5 Group rocks. The distribution of marbles and coarse clastics of the Serid5 Group shows that these tectonic highs were already active during the sedimentation of the Serid5 Cycle. Brejui, Barra Verde, Boca de Lajes and Zangarelhas mines (RN-13), 8.5 km south of Currais Novos, together account for about 80% of the whole scheelite production and for 70% of the known reserves. They belong to the same geological occurrence. Detailed work by Assis (1964), Maranh~o (1970) and Torres (1973) showed that the mineralization is related to five different, discontinuous, tactite levels, intercalated with gneisses and marbles of the Serid5 Formation. Siqueira and Maranh~o (I973) include

186 these gneisses in the Jucurutfl instead of the Serid5 Group. All authors agree that the thickness, porosity and mineralization of the tactites follow the b axis of three minor folds plunging 30°C to the southwest below the migmatite-granite complex of Acarf--Pau Pedra. The distance of the mineralization to this complex varies between several hundred to 1500 m. The contact between gueisses and migmatites is gradual. Maranh~o (1970) distinguishes two main phases in the tactites. First 900 m.y. ago an isochemical metamorphism formed the essential minerals of the tactites; later, 550 m.y. ago, a hydrothermal phase related to the formation of the migmatites, brought about the mineralization, including scheelite, molybdenite, chalcopyrite, bismutinite and others. From the genetic point of view, all authors agree that the scheelite mineralization of the Serid5 region differs from the classical type in tactites closely related to intrusive granites--granodiorites. Santos (1973), Torres (1973), Maranh~o (1973) and others favor a genesis related to the migmatization processes. Suszczynski (1975) favors a syngenetic synsedimentary origin, based on the large geographical distribution and the lack of a clear relationship to intrusive rocks. Mineralogical scheelite occurrences in this region occur also in quartz exudations in biotite schists, in amphibolites and in pegmatites. Other unstudied scheelite occurrences in tactites are found at Milh~ (CE-11), at Taquaretinga do Norte, State of Pernambuco, and at Palmeira dos Indios, State of AlagSas. Wolframite occurs associated with cassiterite in the states of Rio Grande do Sul (RS-73), S~o Paulo and RondSnia, as a mineralogical curiosity. Minor wolframite deposits of the quartz-vein type related to granodiorites are known in Nova Trento (SC-68). The reserves are estimated at some thousands of tons of wolframite.

Quartz Brazil is one of the most important quartz producers of the world. Official production data are certainly underestimates because the main producers, the "garimpeiros", lack official control. Only about 30% of the production is of crude crystals for piezoelectric or optical purposes. The remaining 70% is chips for fabrication of synthetic quartz (Freitas, 1973). The whole production is exported. The increasing usage of synthetic quartz is responsible for the declining production values in the last decade. Cassedanne (1971a) recognizes six types of quartz occurrences. Quartz in pegmatites occurs very often, forming monomineralic, lenticular or irregular nucl_ei. Some individual crystals may reach several decimeters or even meters in length. The apical zones of the pyramids of these crystals are sometimes completely hyaline, but the main part of the pegmatitic quartz is massive, milky or full of inclusions. Minor quartz druses may be found in the feldspar zones of the heterogene pegmatites. The commercial production of quartz in pegmatites is mainly limited to mineralogical ends. Segregations

187 and geodes in crystalline rocks are very frequent but only the related alluvial concentrations are sometimes explored (Santa Tereza, State of Espirito Santo, ES). Quartz druses in the Mesozoic basalt--andesite traps of the Paran~ Basin contain mainly milky quartz or amethyst and agate and are exploited in the weathered rocks of the valleys in the State of Rio Grande do Sul (RS-71). The production of quartz is very limited. Quartz veins are responsible for the main part of the production. They may occur as individual dykes up to 50 m in thickness and an extent of several hundred meters, cutting subvertically across Precambrian granites, marbles (Sete Lagoas, MG-52), quartzites (Diamantina, MG-50) or phyllites. The geodes in this kind of dykes are irregular in size and distribution. Otherwise, stockwork-like quartz-vein systems are found in Precambrian phyllites and marbles (Sere Lagoas, Curvelo, MG-51) or sandstones and quartzites (Diamantina, MG-50, Xique-Xique, BA-25 and Cristalina, GO-43). The veinlets are very irregular in size and shape. The quartz crystals grow normal to the wall rocks. The interior of the druses may be filled with clays or be vacant. One of these druses, in Cristalina (GO-43) reached 200 m 3 in volume. The ratio of quartz of optical or piezoelectric quality there was close to 1 : 25,000 (Freitas, 1973). The quartz veins are normally considered as hydrothermal in origin, but most of them seem to have been formed by lateral segregation, and are of post-Bambui (Upper Precambrian) age. Alluvial quartz in the vein-rich regions often is of good quality and free of inclusions but restricted in size (Curvelo, Sete Lagoas). The eluvial quartz deposits are very good indicators of primary deposits at depth, and are exploited as a first step in mining activity. The large quartz boulders of this kind of deposit are mostly cemented by a lateritic matrix. The production of quartz for iron alloys or silica glasses in Brazil is very limited. The amount of druses mined for mineral collections is very important but no statistical data are available.

Magnesite The mining district of Serra das Eguas, Brumado (BA-33), includes the only intensively mined magnesite deposits in Brazil and also has the largest talc reserves. Several massive, coarse crystalline magnesite lenses up to 2400 m in length and about 100 m thick, are intercalated in metamorphic dolomites of a complexly folded volcano-sedimentary series of amphibolites, micaschists, quartzites and minor iron formations. This sequence is preserved in a synclinorial structure with general northeast strike, enclosed in the Archean granulitic--migmatitic basement, and was first correlated with the Middle Precambrian Minas Series by Barbosa (1943). Reinterpretation by Mascarenhas (1976) based on more recent work leads to the supposition that this sequence could be an Archean greenstone belt. Some amphibolite layers and talc lenses are intercalated with the magnesite bodies. The magnesite

188 reserves in this district a m o u n t to 280 million tons and the talc reserves to 32 million tons. Sometimes microscopic hematite inclusions are responsible for the blood-red colored magnesite b u t do n o t influence the very good average quality of the magnesite. Other important magnesite deposits are related to a similar geologic setting in Sento S~ (BA-20). The reserves are estimated as 63 million tons b u t the magnesite presents slightly higher silica and alumina grades. In Iguatfl (CE-12) magnesite deposits of 103 million tons are intercalated in amphibolite, quartzite, dolomite and biotite-schists correlated to the Middle Precambrian or Upper Precambrian Cear~ Series. The ore, with a few percent silica, is not so pure as the magnesite in Brumado. Fluorite

Morro da Fumaqa (SC-69) is the only regular mining district for fluorspar in Brazil. According to Teixeira and Piatnicki (1968), the fluorspar occurs filling open fractures and fault breccias striking northeast and cutting intrusive granites and quartz-monzonites and migmatites of Late Precambrian age. Minor fluorite veinlets are also observed in arenitic--pelitic Carboniferous sediments that unconformably overlie the Precambrian rocks, and in the Upper Cretaceous diabase dykes. The main ore bodies cut the granites and reach up to 1 km in length and 1 to 8 m in thickness. The open fracture fillings grade up to 80% CaF2 with associated chalcedony, quartz and minor sulfides. Willig (1973) discusses two genetic hypotheses. In the first one the fluorite would be originated by late hydrothermal activity related to the granite intrusion (granites are the main wall rocks). In this case the basaltic volcanism would only have remobilized some of the pre-existant fluorspar. In the second case the Cretaceous volcanism itself would be the hypogene source for the fluor. Teixeira and Piatnicki (1968) favor the second hypothesis. The reserves in this district are estimated at 1.2 million tons, averaging 70% fluorite. The production ranges in the 100,000 tons per year. Frequent fluorspar occurrences are k n o w n in the Young Precambrian Bambuf Group near Born Jesus da Lapa (BA-32) and in Minas Gerais, associated with lead and zinc (see also under this heading). They are of the Mississippi Valley t y p e and enlarge the geologic potential of fluorite reserves. In the Serid6 Geosyncline (see under Tungsten) in northeast Brazil, some minor fluorspar occurrences are related to tactites and marbles and others are found as massive veinlets cutting pegmatites of Brazilian (Late Precambrian) age, and diabase dykes of supposed Mesozoic age (Beurlen, 1977). This last m o d e of occurrence is similar to the Morro da Fuma~a District in Santa Catarina.

189 RECENT DISCOVERIES

Phosphate The recently discovered deposits of Patos de Minas (MG-49) hold the largest Brazilian phosphate reserves. According to Chaves (1975} who discovered the deposits in 1974, the phosphate occurs as rythmic millimeter to centimeter layers alternating with calcareous and carbonaceous slates in the Paraopeba Formation of the Upper Precambrian Bambu/Group. The intensive isoclinal folding, with axial planes dipping to the northwest, is responsible for the thickening of the ore body that is up to 600 m wide, 15-50 m deep, and that can be traced with some interruptions for 13 km along the general strike. A wavellite--limonite-rich soil with an average thickness of 1--3 m covers the deposit. Some concentrational, interstitial or vug-filling wavellite occurs also in the upper part of the deposit itself: collophane (fluorapatite) however, is the main phosphate mineral. The ore showed a good solubility during the first tests. The phosphatic sequence overlies fresh and black slates. Chaves (1975) states that the best phosphate grades are found at depth, supporting a simple sedimentary origin. Ferrari (1976) states that the phosphate ore would have been formed by supergene leaching of carbonate from carbonatic slates with originally about 5% P2 Os. The proved reserves of these deposits are 236 million tons, averaging 13% P205. Additional reserves are estimated at 187 million tons. Mining activity began in 1976. Other sedimentary phosphate deposits are found at Olinda (PE-18) in a phosphate layer averaging 1.2 m in thickness overlying only the continental facies (Beberibe Formation) of Campanian--Santonian sandstones which grades laterally to a calcareous marine facies (Itamaracfi Formation). The main phosphate mineral is a crypto-crystalline fluorapatite and main associated minerals are detritic quartz, feldspar and montmorillonite. The phosphorite layer itself is of Maastrichtian age. The reserves amount to 60 million tons, averaging about 20% P:Os (Menor, 1975). Important phosphate deposits are found as supergene enrichment from silico~arbonatites of the alcaline complexes of Arax~ (active mine), Tapira and Catal£o with reserves estimated respectively, at 92, 71 and 51 million tons with 12, 8 and over 5% P2Os; they are associated with niobium and titanium deposits (see also under the heading of Titanium and Niobium, and the special paper on alkaline complexes in this issue). In Jacupiranga (SP-63) another alkaline complex is composed, from the border to the center, of fenites, nepheline--syenites, ijolites, jacupiranguites, peridotites and sSvites. The residual phosphate is already exhausted and the fresh carbonatites are now mined for apatite and for the cement industry. The ellipsoidal complex measures 8 by 5 km and the oval-shaped carbonatite in the center is composed of two individual, overlapping intrusions measuring more than 490 by 1000 m (Melcher, 1976). The present reserves are estimated as 96 million tons with about 5% phosphate.

190 Titanium

Brazil does n o t produce any titanium ore at all, but three main types of important deposits are known. Residual anatase enrichments over silico-carbonatites of Cretaceous alkaline complexes like Catal~o (GO-44), Tapira (MG-56) and Salitre (MG-48) total over 300 million tons with a b o u t 20% anatase. The finegrained anatase is mixed with the limonitic soil. The exploitation of this unique ore type, in substitution for rutile, depends on the development of a special technology. First pilot plants were already built b y the METAGO for the Catal~o ore (Carvalho and Arat]jo, 1974). the lateritic anatase-rich soil resulted from supergene leaching of the silico-carbonatites--brecciated ultramafics with carbonatitic matrix (see also Phosphate and Niobium in this paper). The main primary ore minerals are perowskite, ilmeno-magnetite and titanite (Neto, 1973). An insignificant and very irregular ilmenite production in Brazil comes from very large marine placers on the coast of the states of Rio de Janeiro, Espirito Santo and Bahia. The relatively low grades and limited extent of the' individual placers and the inexistence of a regular mining industry are responsible for production prices that are higher than imported Australian ore. The proved placer reserves in Rio de Janeiro and Espfrito Santo amount to 650,000 tons of ore with 30% ilmetine and associated monazite and zirconite. A third titanium ore in Brazil is found at Campo Alegre de Lourdes (BA-19), with estimated reserves of 60 million tons with a b o u t 20% TiO: and 0.6% V2Os. The deposits occur as a group of lense-shaped hills formed of massive ore, up to 100 m wide and 1000 m long, emerging 100 m over a peneplane. Rare outcrops of gabbros with alkaline amphiboles, uralitized pyroxenes, saussuritized and skapolithized plagioclases, and some chlorite, ilmenite, apatite and sulfides, and of talc-chlorite schists occur close to the hills. Normal wall rocks and country rocks are migmatites of uncertain age. The ore itself presents a very spectacular centimeter banding of magmatic origin, that seems to indicate an original circular disposition of the core, n o w paralleling the general NNE strike and steep dips. Cassedanne et al. (1976) found a magnesian ilmenite and hematite as main minerals with some magnetite and rutile, and minor kaolinized silicates and chalcedony. Bauxite and kaolinite

Bauxite is mined in Brazil mainly at Poqos de Caldas (MG-61) with reserves of a b o u t 50 million tons; at Saramenha, near Ouro Preto (MG-57) with some million tons; and in minor deposits near Belo Horizonte (MG). In Poqos de Caldas bauxite covers the phonolites of a Cretaceous alkaline complex. In Saramenha the residual concentration t o o k place over phyllites of the Middle Precambrian Minas Series. Around Belo Horizonte, bauxite covers

191 dolomites of the same geologic unit. All these deposits, despite the smallscale mining activity, are insignificant when compared with the large deposits in the states of Par~ and Amazonas. The bauxites of the Amazonas Region have been known for a long time but only recent (since 1967) exploration evidenced their enormous potential. At present 586 million tons of metallurgical bauxite may already be confirmed. The estimated reserves amount to 2.5--5.0 109 tons. The bauxite is associated with large kaolinite reserves, both related to an extensive peneplane formed over arkoses, sandstones and clays of the Tertiary Barreiras Group. The peneplane was levelled to 150--200 m above the Amazon River (Assad and Netto, 1976). The individual plateaus with bauxite concentrations are named for the bordering rivers like Jatapu (AM-3), Trombetas (Oriximina) (PA-4), Jari (PA-5), Capim (PA-6), etc., and extend over several thousands of square kilometers (Suszczynski, 1975). The weathering profile reaches from 10 to 50 m in thickness. In the Jarf area, Assad and Netto (1976) recognized the following zones from top to base: soft, light clays, concretional bauxite with clay matrix (up to 9 m), bauxitic aluminous--ferruginous laterite, ferruginous laterite, aluminous--ferruginous laterite, massive bauxite, colored clays and light kaolinite with columnar bauxite concentrations, clays and sandstones. The main aluminum mineral is gibbsite. The thickness and even the presence of each of these levels changes from area to area. The first mining and metallurgical complex is scheduled to start regular activity in 1981 at Oriximina, Rio Trombetas. A production of 58 million tons of bauxite and 600,000 tons of aluminum will be reached in 1983 (Luz, 1975}. The kaolinite reserves in the Capim District (PA-6) amount to 434 million tons, and are of very good quality. The total kaolinite reserves in the Amazonas region are estimated at several billion tons. Potassium salts

The potassium salt deposits recently discovered in the State of Sergipe (SE-28) are among the most outstanding recent Brazilian mining developments. The evaporites were first noticed by Fernandes (1966). The discovery was made by PETROBRAS during oil prospection in the early sixties, but only ten years later additional work pointed out the large reserves (in million tons) of KC1 (460), Mg (220), NaC1 (5,890) and Br (11) that put these evaporites among the most important deposits of the world. In estimating these reserves only the thickest homogeneous layers of three small shallow sub-basins and a recovery of 10--30% were considered (Fonseca, 1973). The top of the evaporitic sequence, composed of nine different cycles, is reached at 350--1400 m of depth and the whole thickness varies between 200 and 500 m (Fonseca, 1973). The main salt minerals are silvinite, tachydrite, carnalite and halite. The mean thickness of the biggest individual monomineralic layers reaches 4--5 m for silvinite, 15--35 m for tachydrite, 30 m for carnalite and 20--25 m for halite. The abnormal amount of tachy-

192

drite observed lead Hite (1973) to suppose a genesis similar to the hot brines in the Red Sea, possibly related to juvenile hydrothermal activity. Anomalous high Br contents in these salts (0.25--0.55% in carnalite and tachydrite, respectively) were observed by Lisboa et al. (1973). The evaporitic sequence is known as the Ibura Member of the Aptian Muribeca Formation, and extends over 120 km NE--SW and 50 km NW--SE, from Aracaj~ to the S~o Francisco River. Other Cretaceous evaporitic sequences are known 250 km northwards, in the AlagSas Basin, southwards near Salvador (BA) and far in the south, in the Espirito Santo, the Campos (RJ) and the Santos basins. All of them are related to the opening of the South Atlantic and can be stratigraphically related to the saline deposits of Congo and Gabon (Leyden, 1975; Wardlaw, 1972, and others). All these sequences are underlain by terrestrial sediments and are followed by open marine sedimentation since the Albian (Ponte and Asmus, 1975). They represent the first restricted marine sedimentation over the breaking paleocontinent. Of the same age are very large gypsite deposits at Araripina (PE-18) with proved reserves of 50 million tons and at Cod6 (MA), the latter in the Parnaiba Basin. In the Amazonas Basin there are very large deposits of mainly halite. POTENTIAL MINERAL RESERVES

Nickel

The known Brazilian nickel deposits are all of the residual, garnieritic, New Caledonia type. Three large complexes were distinguished by Berbert (1970) from the Goi~s Serpentine Belt of Almeida (1967) in the State of Goi~s. They present a global mafic composition and a layered structure. Figueiredo et al. (1975) distinguished, from base to top, gabbros--norites, dunites--peridotites-pyroxenites, anorthosites--gabbros--norites and olivine gabbros--troctolites. Beside these typical features of "layered complexes", alpine characteristics, like gradational and interdigitated contacts between the zones, local strong deformation and metamorphism, and podiform chromite occurrences, may be recognized (Thayer, 1972). Disagreeing with Almeida (1967), Figueiredo et al. (1975) and Cordani and Hasui (1975) suppose an age older than the Middle Precambrian Arax~ Cycle. The last authors, on the basis of not very consistent radiometric data, even suspect that one of the complexes could represent part of the primeval earth's crust. The contacts with the Arax~ or older country rocks are mostly tectonic and do not help in clarifying the question. Three complexes of this kind are known, namely Canabrava (GO-34), S. Jos~ dos Tocantins (GO-36) and Barro Alto (GO-42), with respective extents of 20 X 40, 20 X 50 and 20 X 120 km. Large Ni-deposits occur at Niquelandia on the S. Jos~ dos Tocantins complex and at Barro

193 Alto, respectively totalling 337 and 847 thousand tons of metallic Ni in 1--3% ore. Production at Niquel~ndia started in 1977 as the first great active Ni-mine in Brazil. The economic Ni-grades and reserves there are restricted to the pyroxenites and peridotites of the ultramafic zone. Both Ni-concentration and thickness increase in the shallow valleys of a topmost rejuvenated peneplain, suggesting some colluvial transport and Ni-mobilization from an original weathering profile. Pecora and Barbosa (1944) observed, from top to base a discontinuous iron--manganese cap with high Ni--Co contents, a ferruginous--nickeliferous horizon with Mn--Co-oxide concretions, nickeliferous clays with garnierite, and weathered pyroxenites and peridotites. At Barro Alto the residual Ni-deposits cover only the serpentinized dunites and peridotites, distinguishing them ffrom Niquel~ndia. Minor Ni--Cu--Co-sulfide, chromite and talc occurrences were observed on the three complexes of this type. The Canabrava Complex includes the largest Brazilian chrysotile--asbestos mine. Almeida (1967) listed over 100 typical alpine serpentinite--dunite--peridotite complexes emplaced at the initial stage of the Middle Precambrian Arax~ Geosyncline Cycle in the "Goi~s Serpentine Belt". They present a large potential for Ni and Cr deposits, but up to now only minor occurrences and some talc prospects are known. Three residual Ni-deposits are related to Cretaceous serpentinites--dunites of alkaline affiliation intruded in the Precambrian basement and Paleozoic sediments in the southwestern part of Goi~s (DNPM, 1975), namely the Morro do Engenho (GO-38), Agua Branca (GO-39) and Santa F~ (GO-40) complexes. Lindenmayer and Lindenmayer (1971) state that the weathering profiles in these complexes are identical to the classical one at New Caledonia. These deposits account for 876,000 tons of metallic Ni, with 1--1.7% Ni. Minor Ni occurrences of this type are also known from Jacupiranga (see under heading Phosphate). Another large Ni-deposit covers an isolated mafic--ultramafic complex extending over 20 km 2 at S. Jo~o do Piaui (PI-17). The geological setting and age is unknown. This complex, according to Santos (1974), is composed of gabbro-diorites surrounding a serpentine nucleus, emplaced in young Precambrian quartzites, phyllites and gneisses. The garnieritic ore was enriched by colluvial transportation and mobilization from the original weathering profile at the top and center of the serpentinite body towards marginal morphologic depressions. Minor Ni-deposits of this type are found at PratApolis and Liberdade in the State of Minas Gerais (sporadic mining activity) and at Catingueira in the State of Paralba. Again the age of the complexes is unknown. Asbestos

The Canabrava Complex (GO-34) is the northernmost of three "layered complexes" separated by Berbert (1970) from the Goi~s Serpentine Belt and

194 it includes the only active chrysotile-~sbestos mine in Brazil. The southern part of this complex, according to Milewski (1970), comprises the following zones, from base to top: micaschists and metapsamites, extrusive metabasites (about 1000 m), quartzites (100 m), pyroxenites and peridotites (0--100 m), serpentinites including the mineralized zones (about 500 m), pyroxenites and peridotites (0--100 m) and metagabbros. The cross-fiber chrysotile mineralization is found as stockworks in the serpentinites, with about 6.8% of recoverable fiber. The proved reserves amount to 42 million tons of ore and the production averaged 73,000 tons of fiber during 1975. Other minor asbestos occurrences are found in the north of the same complex, at the Barro Alto Complex (GO-41) and in alpine-type ultramafic complexes of the Goi~s Serpentine Belt. Exploration work in several of the mafic and ultramafic complexes in Goi~s is still in an initial stage. They represent a large potential not only for asbestos but also for chrome, nickel and talc deposits. Before the discovery of the Canabrava Deposit, the only regular asbestos production came from Batalha (AL-24). The ore is an antophyllite mass-fiber formed in large pockets associated with isoclinal folds dipping to the north, in magnesian amphibolites intercalated within dolomitic marbles, quartzites, biotite-schists and migmatites of the Brazilian Cycle. Some ultramafics are interbedded in the magnesian sequence (Farina, 1966). Up to 1968 the production averaged over 2000 tons of fiber per year. With the beginning of the production from Canabrava in 1968, the mining activity there began to decrease. Chromite

Again reference should be made to the great geological potential for chromite deposits related to the mafic and ultramafic complexes, both of the layered and the alpine type. Some minor chromite occurrences are already known, but with high A1 and Mg contents (DNPM, 1975). The resular active chromite mines of Brazil are all situated in the State of Bahia, in two sub
195 massive chromitite in one of the mines (Medrado) reaches up to 15 m in thickness, averaging 7 m, and follows a steep syncline termination plunging south. The longitudinal extent totals 450 m, with some interruptions. Following the subvertical dip, the assured extent is 80 m. The reserve of the whole area certainly amounts to 2 million tons. According to Mascarenhas (1976) these sequences could represent greenstone belts. Gold

Alluvial gold prospects are known in almost all states of Brazil and are exploited by the "garimpeiros" (gold washers). This kind of activity is responsible for a great part of the Brazilian gold production, which averaged about 1000 kg per year during the last decade. The origin of the placer gold may be found in auriferous quartz veins cutting mainly Middle or Young Precambrian quartzitic--phyllitic metasediments or the Archean migmatite-granulite basement. In the Iron Quadrangle an irregular mining activity started during the last century in several deposits. Some of them are already exhausted, others are being re~valuated with respect to new exploration and mining techniques (Abreu, 1973). Almost all gold deposits in this district are found in metamorphosed sedimentary rocks of the Nova Lima Group, the basal unit of the Archean Rio das Velhas Series, a supposed greenstone belt. Main host rock for the gold is an ankeritic--dolomitic quartzite, intercalated in micaschists and quartzites that overlie an orthoamphibolite sequence. The most important mine of the district, Morro Velho (MG-54), mines a typical stratiform deposit of this type. In some other mines the ore bodies are discordant, but always related to the same host rock. The first geologic interpretations, e.g. by Guimar~es (1970), supposed a hydrothermal hypogene origin, mostly related to granitic intrusions. Recent work, e.g. Fleischer (1971), Moreschi (1972) and Tortes (1975), favors a syngenetic synsedimentary origin. Later metamorphism and hydrothermal activity related to granites would be responsible only for reconcentration and remobilization. This version looks to the basal orthoamphibolites or to supposed volcanogenic schists and phyllites as the gold-bearing volcanism. The quartz-carbonate host rock contains tourmaline, sericite, chlorite, sodic plagioclase, pyrite, pyrrhotite, sphalerite, galena, arsenopyrite, scheelite and wolframite as associated minerals. The gold is included mainly in the iron sulfides and in tourmaline, grading up to 200 g gold per ton. The ore bodies average 5--15 g gold per ton. The Morro Velho Mine alone has produced over 300 tons of gold since 1814 and is active up to the present. The Congo Soco mine is hosted in soft hematite with gold grades decreasing with depth, indicating a concentration by supergene leaching. This mine is already exhausted, but represents another type in this gold district. At Jacobina (BA-26) there are also some gold prospects and even a closed mine. The gold in this district is hosted in pyritic and radioactive conglome-

196

rate levels of the quartzitic Serra do Cbrrego Formation at the base of the Middle Precambrian Jacobina Group {2000 m.y. minimum age). The Serra do Corrego Formation extends over at least 20 km N--S. Recent exploration w o r k b y the Anglo American Company estimated a gold reserve of 60 tons. The ore averages 10 g gold per ton and is very similar to that of the Rand, including associated uranium (Lemos, 1974). Geological formations similar to the Rand and to Jacobina are widespread in Brazil, such as the conglomerates of Reriutaba (CE-10) and the Serra da Moeda Formation in the Iron Quadrangle, all with k n o w n minor gold occurrences, and these are awaiting systematic exploration. Recently the occurrence of important gold deposits near to the Caraj~s Iron District was noted. Preliminary exploration work b y Companhia do Vale do Rio Doce indicates potential reserves in the order of 19 million tons grading a b o u t 12 g gold per ton. T/n The RondSnia District (RO-16) produces over 90% of the Brazilian tin. Only alluvial--eluvial concentrations are mined; they cover circular granite, alaskite and rhyolite complexes that were intruded in a Precambrian basement of migmatites, gneisses and metasedimentary series (Kloosterman, 1968). One of the granites was dated at 940 m.y. Over t w e n t y such complexes, up to 20 km in diameter, are k n o w n in the district. The protore occurs as stanniferous quartz or pegmatite veins, as stockwork-like mineralizations in greisens or as disseminated cassiterite, in the intrusive complexes. The mined eluvial concentrations are never found more than 200 m away from the protore. The proved reserves amount to a b o u t 40,000 tons of recoverable tin. The production averages 4000 tons of metallic tin per year. The deposits grade at a b o u t 1--2 kg cassiterite per m 3. Topaz, wolframite, tantalite and fluorite are the main associated minerals. A large number of intrusive complexes similar to those of the RondSnia District are k n o w n along the whole southern border of the Amazonas Syneclises. Alluvial tin concentrations associated with these complexes are known at the state line Amazonas--Par~--Mato Grosso and in the southeast of the State of Par~; they are exploited by the "garimpeiros". Some of the granites referred to are supposed to be 1800 m.y. old. Similar occurrences are found in Amap~ State and at Cavalcante (GO-35). This last district has been intensively explored since 1974 and there are even plans for mining primary ore in stockwork-like mineralizations (DNPM, 1975). In the S. Jo~o del Rei District (MG-60) some weathered pegmatites and related eluvial--alluvial deposits are irregularly mined. The weathered pegmatites grade at a b o u t 1 kg cassiterite per m 3. The most important deposit is the Nazareno pegmatite, up to 35 m thick and 1700 m long. The district produces a b o u t 400 tons of tin per year. The reserves are estimated at some thousands of tons of cassiterite.

197

Lead and zinc

The Brazilian lead and zine production covers only about 30% of the consumption. The proved lead and zinc reserves will cover the domestic demand for three and ten years, respectively. Despite this pessimistic view, the recent discovery of a large stratabound deposit at Paracatfl in the very large metallogenetic province of the Bambuf Group and of some occurrences of the same type in Paleozoic sediments of the Amazonas Basin support a good potential for these metals and encourage further exploration. The present lead and zinc production comes from three deposits: Boquira (BA), Vazante (MG) and Panelas and Rocha (PR). Boquira mine (BA-29) has been responsible for the major part of the Brazilian lead production during the last twenty years. The remaining reserves are estimated as two million tons of ore with 8--10% Pb and 2.2% Zn. The ore forms three steep BPG veins with associated magnetite and chalcopyrite, cutting N--S through the amphibolites and itabirites of the base of the Middle Precambrian Minas Supergroup. The average thickness of the veins is about 1 m. The zinc concentration increases slightly with depth. Present mining has reached 240 m below surface. In addition to the tectonic control by N--S fractures, lithological and paleogeographical controls seem evident (Cassedanne, 1972). Lead ages of 2600 m.y. indicate an origin by reconcentration of presedimentary lead during tectonism (Cassedanne, 1972}. Mascarenhas (1976} includes the itabiritic and amphibolitic wall rocks in an older, greenstone belt series (Archean). Panelas mine (PR-65) is formed by subvertical stratiform or discordant veins cutting young Precambrian limestones of the A~ungui Group, close to the contact with a granitic intrusion. Granite apophyses cut the ore veins. The lead in the BPG-ore, with associated pyrrhotite and arsenopyrite ranges from 5 to 9%, with 1000 g Ag per ton. The total production up to now has been one million tons and the reserves are near exhaustion. With identical geology and nearby to Panelas, the Rocha mine is distinguished by associated lead sulfosalts, and it produced 400,000 tons of ore concentrate. Furnas mine (SP-62) consists of BPG columns with associated arsenopyrite at the intersection of faults with phyllite strata interbedded with the A~ungui limestones. The ore reserves amount to several thousand tons with about 4% lead and 2500 g Ag per ton. Several minor occurrences similar to Panelas, Rocha and Furnas are known in the A~ungui Group, indicating the potential of this metallogenetic lead province. Vazante mine (MG-47) amounts to six million tons of ore averaging 17% Zn. The ore is formed mainly by willemite, calamine, and finely disseminated hematite, and fills NE--SW faults and fractures or stratabound karstic cavities in the dolostones of the young Precambrian Bambui Group. The ore may be massive or cementing a dolomitic breccia. The lack of known sulfide veins at the roots of .the mineralized faults, even at a d e p t h of 100 m, distinguishes this deposit from the normal gossan type. Only insignificant

198

amounts of sulfides, mainly galena, are sporadically found, forming centimeter veinlets or spots in the micritic, stromatolitic, or brecciated silicified dolomites. The wall rocks were formed in a restrictive marine environment (Cassedanne, 1972). The deposit of Morro Agudo, near Paracatfl (MG-46) is a typical stratiform lead--zinc sulfide mineralization. The assured reserves amount to 13 million tons of ore averaging 5.09% Zn, 1.53% Pb, and 360 ppm Cd. The sphalerite--galena ore, with minor pyrite and chalcopyrite, is disseminated in clastic dolostones of the Bambuf Group and precipitated prior to the dolomitic cementation (Beurlen, 1973). The host rocks are typical for a tidal environment. Detailed facies analysis and description of related stromatolites by Dardenne (1976) favor a back-reef position of the main ore bodies. Regular mining activity is schedules to start in 1980. Besides Vazante and Morro Agudo, the Bambuf Group hosts a large number of minor stratabound lead--zinc occurrences with associated fluorite described by Cassedanne (1971b), Beurlen ( 1 9 7 4 ) a n d Dardenne (1976). Silver and vanadium may be concentrated in the oxidation zones. Thus the Bambui Group forms a lead--zinc province similar to the Mississippi Valley. Sporadic and minor BPGC veins are often observed cutting the rocks of the Minas--Uruaqu cycles, probably related to the mineralization epoch of Boquira. Cassedanne (1972), on the basis of the geographical position of all important occurrences, postulates that both lead generations, Boquira and Bambuf, are related to the S. Francisco Lineament (NNE--SSW).

Copper Three copper districts have been known in Brazil for a long time but only recent exploration has shown their real potential. Camaqu~ (RS-72) was mined irregularly since the beginning of this century. Copper occurs as veins of pyrite, chalcopyrite, hematite, with some bornite and chalcocite in a quartz--calcite--barite gangue. The veins follow a structural control by NW and NNW faults and a stratigraphic control by sandstones and conglomerates of the Upper Precambrian Arroio dos Nobres Formation (Bom Jardim Group). Some stratabound ore disseminations are also known (Bettencourt and Damasceno, 1974). The Born Jardim Group is unconformably overlain by the Ordovician--Devonian Camaqu~ Group, composed of coarse clastics and effusive andesites. Ribeiro et al. (1966) suggests that these volcanics are responsible for the mineralizations. The estimated reserves after recent exploration results amount to ten million tons of ore averaging 0.7--1.3% Cu. In the Carafba deposit (BA-22) the copper is found as schlieren and irregular veinlets of chalcopyrite and bornite in metamorphic ultramafics interbedded with granulites of the Archean Carafba Group. The amphibolites, pyroxenites and dunites of the main ore body extend over 900 m N--S and dip with 70°W, with minor isoclinal folds (Barbosa, 1966). The maxi-

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mum thickness of the ore body, including the interbedded granulites, is about 400 m. Recent exploration work, totalling over 45,000 m of diamond drilling in two years, indicating reserves in the order of 100 million tons, averaging 0.7--1.0% Cu. Active mining was scheduled to start in 1978. A lot of minor deposits are known in the same district (Vale do Curaqa). The deposit of Pedra Verde, Viqosa (CE-9) is a typical stratabound deposit hosted in quartzitic phyllites with some carbonates and graphite. The Upper Precambrian host rocks are overlain by conglomerates and sandstones of the Parnaiba Basin (Collins and Loureiro, 1971). A classical zonation of the Fe-Cu--Ag sulfides is indicated by recent exploration. Up to now the estimated reserves amount to ten million tons averaging 1% Cu. MINERAL FUELS

The mineral fuels have been given special attention by the Brazilian government. PETROBRAS was created in 1953 as an oil company with the government as the major shareholder, with the aim of monopolizing and developing all activities related to exploration, mining, importation and refining of petroleum in Brazil. CNEN, CBTN and NUCLEBRAS are different federal agencies, formed since 1962, responsible for exploration and commercialization of radioactive minerals and development of the Brazilian nuclear technology. Intensive exploration work was done since then but production and reserves of petroleum and uranium remain highly deficient (Table I). Despite the low potential for petroleum reserves, Brazil already produces about 30% of its consumption. With the aim of increasing the participation in its own oil production, after the world petroleum crisis, the government has encouraged international oil companies to explore in specific areas by special agreement with PETROBRAS. Petroleum

The known recoverable petroleum reserves are restricted to the Rec6ncavo--Tucano (BA-30) and Sergipe--Alagoas (SE-28) basins, and are estimated by Pontes et al. (1974) at 305 X 104 m 3. These basins are already intensively explored and the discovery of important additional reserves is not expected. In the RecSncavo, the main source rocks are shales of the Neocomian Candeias Formation and main reservoir rocks are sandstones of the Upper Jurassic Sergi Formation. In Sergipe, the Lower Aptian conglomerates and sandstones of the Carmopolis Member trap the oil generated by the marls and shales of the Middle Aptian Member Ibura of the Muribeca Formation. In both basins the oil is trapped mainly by high structures related to presedimentary paleoreliefs or synsedimentary fault systems (Campos and Bacoccoli, 1973; Ojeda and Fugita, 1974). Ponte and Asmus (1975) summarize the stratigraphic columns of all eastern marginal and offshore basins in Brazil, distinguishing tl~/ree units: a basal clastic sequence (pre-Aptian or Neo-

200 comian), an evaporitic sequence (Aptian or Albian), and an upper marine limy or detrital sequence (see also comments on potassium salts in this paper). The potential oil reserves in the Cretaceous and Tertiary sediments of several offshore basins were estimated by Pontes et al. (1974) as 800 × 106 m 3 o f recoverable oil. Intensive exploration since then has already resulted in several productive oil fields offshore Sergipe, Rio de Janeiro and Rio Grande do Norte. G o o d source rocks are also known from the large intracratonic basins of Paranfi and Amazonas, b u t the intensive Mesozoic volcanism makes exploration very difficult. An additional 215 × 106 m 3 of oil may be recovered from the bituminous shales of the Permian I r a t / F o r m a t i o n in the Paran~ Basin (Bruni and Padula, 1974). These reserves refer only to the shales in open-pit mine projects to be processed by the Petrosix retorting m e t h o d developed by PETROBRAS. After the successful experience with the method in pilot plants of different sizes, a commercial mining and retorting complex is to be established in S. Mateus (PR-67), scheduled to produce a b o u t 9500 m 3 of oil a day. Coal

The Brazilian coal reserves are found in the Paran~ Basin, in the states of Paran~, Santa Catarina and Rio Grande do Sul, and consist mainly of a subbituminous coal of poor or no coking quality, with around 30% ash. The coal strata are enclosed in sandstones and shales of the Permian Rio Bonito Formation. The total reserves in the Basin are estimated at 4 × 109 tons (Souza, 1973). Parts of the reserves in Santa Catarina are considered to be of metallurgical grade (about 750 million tons) after treatment reducing the ash content to 18%. This coal is added to imported coal with low ash grade, before usage in metallurgy (DNPM, 1974). Extensive lignite deposits are k n o w n in the Amazonas Basin. Uranium

The proven Brazilian uranium reserves are restricted to the deposits of Cerrado and Santo Agostinho, and amount to 2840 and 1100 tons U 3 O s , respectively. Extraction costs are less than 10 and 15 U.S.$/lb (ca. 22--33 U.S.$/kg), respectively. Additional reserves of these t w o deposits are estimated at 3000 and 2100 tons. The mineralization seems to be related to hydrothermal and meteoric weathering of uraniferous fluorite and zircon of the phonolites and tinguaites of the P o l o s de Caldas alkaline complex (MG-61) along fractures (Gorsky and Gorsky, 1974). The grades of uranium and associated m o l y b d e n u m show a vertical zonation. The main ore minerals are molybdenite, jordisite, uraninite and coffinite (Maciel and Cruz, 1973). The regional geology and petrology of the alkaline complexes are discussed in a separate paper in this issue. Figueira (PR-64) in the State of Paran~ is an important stratabound urani-

201 um prospect related to the basal, fluvial facies of the Middle Permian Rio Bonito Formation (Saad, 1974). Reserves of 600 tons U3Os of 0.15% graded ore in sandstones were estimated in 1974. The main ore mineral is uraninite. Brazil is very poor in known uranium deposits compared to other countries with large cratonic areas. A large number of low-grade prospects indicates, however, a high geologic potential. The classical association of gold and uranium in ancient conglomerates occurs in the Iron Quadrangle (MG), in Reriutaba (CE-10) and in the well-known deposits of Jacobina (BA-26), all of them awaiting systematic prospection (see also under Gold). Other occurrences, related with descendant remobilization in granitic metamorphites, were recently noticed in the State of Goi~s. In the State of Cear~ another occurrence was discovered, related to old metamorphic alkaline rocks and associated with phosphate. The potential reserves in both occurrences were estimated to be in the order of tens of thousands of tons of

U3Os. THE MAIN METALLOGENETICEPOCHS Almeida et al. (this issue) recognize the Guriense--Jequi~ (2600 m.y.), the Transamazonic (1800 m.y.), the Uruaquano (1100 m.y.) and the Brasiliano (600 m.y.) as the main tecto-orogenetic cycles in Brazil. The last one definitively stabilized the South American Platform. During the Phanerozoic only the establishment of large intracratonic basins took place, namely the Amazonas, the Parnaiba and the Paran~ basins. The Cretaceous is marked by a tectonic reactivation breaking up the ancient Gondwana continent and forming the Atlantic marginal rift valleys and coastal basins. This reactivation also affected the older basins. An intensive basaltic volcanism and the emplacement of mafic--alkaline complexes is related to this tectonic event. If the correlation of some of the great geological units to these cycles sometimes is difficult and interpretative through the lack of consistent geochronologic and field data, the establishment of metallogenetic epochs may be considered as merely speculative in Brazil. Even so, a tentative distribution of the most important mineral deposits according to these cycles may be attempted. The Guriense--Jequi~ Cycle is represented by: (a) the mafic volcanism of the Rio das Velhas Series, supposed to be responsible for the Mn and Au reconcentrated by synchronic sedimentation (Lafaiete Mn-District, MG-59 and Au-deposits of the Iron Quadrangle, MG-54); (b) the copper mineralizations in mafic to ultramafic granulites of the Caraiba Deposit (BA-22); (c) the manganese protore of the Mara~ Deposit (BA-31); (d) the deposits of magnesite at Brumado (BA-33} and Sento S~ (BA-20), of chromite (Andorinha, BA-23 and Campo Formoso, BA-21), of lead and zinc (Boquira, BA29) and ilmenite (Campo Alegre de Lourdes, BA-19) and minor sulfide occurrences, all related to greenstone belts of the S~o Francisco Craton, as suggested by Mascarenhas (1976}; (e) the residual Ni-deposits (GO-36, 42),

202 the asbestos deposits (GO-37, GO-34), minor chromite, talc and Ni--Cu--Cosulfide occurrences related to the mafic layered complexes in the State of Goi~s, according to Cordani and Hasui (1975); (f) the minor gold occurrences widespread in the Archean basement may be the source for the sedimentary gold concentrations in coarse clastics of the Transamazonic Cycle (Jacobina, BA-26). The Transamazonic Cycle formed: (a) the manganese concentrated in the sedimentary protores of the Serra do Navio District (AP-2); (b) the volcanosedimentary iron formations of the Serra dos Caraj~s (PA-7); (c) the manganiferous sediments (protore) near Caraj~s, (PA-28); (d) the sedimentary iron formations with some manganese of the Iron Quadrangle (MG-55, 58); (e) the sedimentary concentration of placer gold in the metaconglomerates and quartzites of the Jacobina (BA-26) and Minas Series. The Uruaquano Cycle emplaced the tin-holding granites in RondSnia (RO16) and, probably, Cavalcante (GO-35) and the alpine ultramafics of the Goi~s Serpentine Belt, with minor asbestos, chromite, talc and sulfide occurrences. In the State of Bahia, the Espinha~o Group presents some placer gold occurrences, and gold and tin anomalies related to metaeffusives. The Brasiliano Cycle produced: (a) scheelite in the tectites of Currais Novos (RN-13) and the northeastern pegmatite provinces (PB-14) with Be-Li--Ta--Sn occurrences; (b) the pegmatite provinces in southern and eastern Minas Gerais with Sn (MG-60) and Li--Ta--gemstones; (c) wolframite and cassiterite in quartz and pegmatite veins related to intrusive granites in Rio Grande do Sul (RS-73), Santa Catarina (SC-68) and S~o Paulo; (d) the lead-zinc province of the Bambuf Group (MG-45, 46, 47, BA-27, 32); (e) the sedimentary phosphate deposits of the Bambuf Group (Paros de Minas, MG-49) and quartz occurrences in the Bambuf Group (MG-50, 51); (f) lead--zinc province of the Aqunguf Group (PR-65, SP-62); (h) the iron--manganese formation of Urucum (MT-66); (i) the Cu-deposits of the Camaqu~ District (RS-72) and Pedra Verde (CE-9). Within the sediments of the Paleozoic Paran~ Basin there are cbal (mainly SC-70), bituminous shales (PR-67) and uranium (PR-64) deposits. The Mesozoic reactivation is a very important metaUogenetic epoch in Brazil, resulting in: (a) the large number of alkaline complexes with the related phosphate, niobium, titanium rare earth, uranium, aluminium, vermiculite and nickel deposits (GO-38, 39, 40, 44, MG-48, 53, 56, 61, SP-63); (b) the quartz--amethyst--agate deposits in the basalt traps of the Paran~ Basin (RS-71); (c) the fluorspar district of Morro da Fumaqa (SC-69) supposed to be related to the same volcanism; (d) the opal mineralizations in sandstones at the contacts with Mesozoic basalts in the State of Piauf; (e) the Mesozoic kimberlites in southwestern Minas Gerais and in Piauf; (f) the sedimentary sequences at the Atlantic Continental Margin, that contain the Brazilian oil deposits (BA-30, SE-28), gypsite deposits (PE-15), the phosphorites (PE-18), potash and sodium evaporites (SE-28), and minor lead--zinc and barite occurrences.

203 T h e last, b u t certainly o n e o f t h e m o s t i m p o r t a n t m e t a l l o g e n e t i c events in Brazil is t h e C e n o z o i c w e a t h e r i n g c y c l e in the t r o p i c a l - - e q u a t o r i a l climate. The Caraj~s iron ores, the n i o b i u m deposits o f Arax~, t h e b a u x i t e and kaolinite d e p o s i t s o f t h e State o f Par~ a n d t h e m a n g a n e s e deposits o f Serra d o Navio are very s p e c t a c u l a r e x a m p l e s o f the i m p o r t a n c e o f this event. Ti-, R.E.-, P-deposits related t o t h e Mesozoic alkaline c o m p l e x e s and all Brazilian Ni-deposits were u p g r a d e d b y residual e n r i c h m e n t processes a t t r i b u t a b l e t o t h e climate. ACKNOWLEDGEMENTS T h e a u t h o r s are i n d e b t e d t o Dr. H e l m o R a n d f o r c o r r e c t i n g t h e English t e x t a n d t o R i c a r d o J o r g e Maranh~o a n d R i c a r d o Pessoa f o r critical reading a n d suggestions. REFERENCES Abreu, S.F., 1973. Recursos minerais do Brasil. Edgard Blticher, S~o Paulo, 2 vols., 745 PP. Almeida, F.F.M. de, 1967. Observa~es sobre o Pre-Cambriano da regi~o central de Goi~s. Bol. Paranaense Geoci6nc. Curitiba, PR, 26: 19--22. Almeida, F.F.M. de, 1974. Sistema tectSnico marginal do CrOton do Guapor6. Soc. Brasil. Geol., An. XXVIII Congr., Porto Alegre, RS, 4: 9--17. Anderson, W.L., Dyer, R.C. and Torres, D.D., 1974. Ocorr~ncias de manganfis na bacia do Rio Itacaiunas, centro-leste do Estado do Par~. Soc. Brasil. Geol., An. XXVIII Congr., Porto Alegre; RS, 6: 149--164. Assad, R. and Netto, A.P.A., 1976. Dep6sitos de bauxita de Almeirim. 29. Congr. Brasil. Geol., Ouro Preto--Belo Horinzonte, MG, resumos trabalhos, p. 281. Assis, A.D., 1974. Geologia econbmica das minas Brejuf e Barra Verde, Estado do Rio Grande do Norte. J. Mineral., Recife, PE, 4 (1--6): 49--92. Barbosa, O., 1943. Magnesita da Serra das I~guas, Bahia. Min. Metalurgia, 38. Barbosa, O., 1966. Geologia econbmica da regi~o do M6dio S~o Francisco, Nordeste do Brasil. Dep. Nacl. Prod. Min., Bol. DFPM, 140:97 pp. Berbert, C.O., 1970. Geologia dos complexos bfisicos e ultrab~sicos de Goitis. Soc. Brasil. Geol., An. XXIV Congr. Brasilia, DF, pp. 41--50. Bettencourt, J.S. and Damasceno, E.C., 1974. An~ilise tectSnica e controles de mineraliz a ~ o no distrito cuprifero de Camaqu~, RS. Soc. Brasil. Geol., An. XXVIII Congr., Porto Alegre, RS, 4: 85--106. Beurlen, H., 1973. Blei-Zink-Fluorit-Vorkommen in jungpr//kambrischen Sedimentgesteinen der Bambui-Gruppe in Minas Gerais (Zentralbrasilien). Thesis, Universit/it Heidelberg, 160 pp. (manuscript). Beurlen, H., 1974. Sobre a origem singenfitico-sinsedimentar de alguns corpos mineralizados em chumbo, zinco e fluorita no Grupo Bambuf e dispers~o prim~iria dos elementos mineralizantes. Soc. Brasil. Geol., An. XXVIII Congr., Porto Alegre, RS, 6: 49--60. Beurlen, H., 1977. Avaliaq~o das potencialidades da regiKo da Borborema para produq~o de fluorita. Bol. Mineral., Recife, 5: 5--23. Bruni, C.E. and Padula, V.T., 1974. O interesse mundial na exploraq~o do xisto e o esfor~o brasileiro para sua industrializaq~o. Soc. Brasil. Geol., An. XXVIII Congr., Porto Alegre, RS, 1: 103--119. Campos, C.W.M. and Bacoccoli, G., 1973. Os altos sincronos e a pesquisa de petr61eo no

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205 Guimar~es, D., 1957. Relat6rio sobre a jazida de pirocloro de Barreiro, Arax~i, Minas Gerais. Dep. Nac. Prod. Min., Bol. DFPM, 1 0 3 : 8 7 pp. Guimarges, D., 1970. Arqueog~nese do ouro na regi~o central de Minas Gerais. Dep. Nacl. Prod. Min., Bol. DFPM, 1 3 9 : 5 1 pp. Haralyi, N.L. and Barbour, A.P., 1974. Bandeamento do min~rio de ferro e mangan~s de Urucum e suas implica~5"es tect6nicas. Soc. Brasil. Geol., An. XXVIII Congr., Porto Alegre, RS, 6: 211--219. Hasui, Y., Almeida, F.F.M., Haralyi, N.L.E., Davino, A. and Svisero, D.P. 1976. Contexto tect6nico dos carbonatitos de Minas Gerais e sul de Goifis. Int. Syrup. Carbonatites, P o l o s de Caldas, MG, Soc. Brasil. Geol. (manuscript). Herz, N. and Banerjee, S., 1973. Amphibolites of the Lafaiete, Minas Gerais,.and Serra do Navio manganese deposits, Brazil. Econ. Geol., 68: 1289--1296. Hite, R.J., 1973. A suggested origin for the tachydrite producing brines of the Sergipe Basin--Brazil. Soc. Brasil. Geol., An. XXVII Congr., Aracajfi, SE, 2: 177--183. Kloosterman, J.B., 1968. Uma provfncia de tipo Nigeriano no sul da Amaz6nia. Min. Metal., 278: 59--64: 280: 167--168. Lemos, J.C., 1974. Ur~nio e ouro na Serra Jacobina. Com. Nac. Energia Nuclear, Bol.~ Rio de Janeiro, RJ, 1 3 : 2 4 pp. Leyden, E., 1975. Salt distribution and crustal models for the eastern Brazilian margin. In: An. Acad. Brasil. Ci~nc. (Editors), Continental Margins of Atlantic Type. Rio de Janeiro, RJ, 48: 159--168. Lima, M.I., Montalv~o, R.M.G., Issler, R.S. Oliveira, A.S., Basei, M.A.S. Araujo, J.F.V. and Silva, G.G., 1974. Geologia da Folha NA/NB.22 Macap~i. Soc. Brasil. Geol. An., XXVIII Congr., Porto Alegre, RS, 4: 123--136. Lindenmayer, Z.G. and Lindenmayer, D.H., 1971. Intrus~es ultrab~isicas alcalinas e suas m i n e r a l i z a ~ e s a n/quel. XXV Congr. Brasil. Geol., S~o Paulo, SP, resumos trabalho. Lisboa, M.A., Abud, J., Santana, G., Ara6jo, C.S. and Barbosa, B.M. 1973. An~ilisc qufmica dos evaporitos de Sergipe. Soc. Brasil. Geol., An. XXVII Congr., Aracajd, SE, 2: 267--286. Luz, A.A., 1975. Situaq~o brasileira dos n~o ferrosos. 5. Simp6sio de M i n e r a ~ o , Escola Minas e Metalurgia, Ouro Preto, MG, 1 : 8--31. Maciel, A.C. and Cruz, P.R., 1973. Perfil analftico do ur~nio. Dep. Nac. Prod. Min., Rio de Janeiro, RJ, Bol., 2 7 : 7 0 pp. Maranh~o, R., 1970; Geologia econ6mica da regi~o de Currais Novos (RN). Thesis, Universidade S~o Paulo, SP, 135 pp. (manuscript) Mascarenhas, J., 1976. Estruturas do tipo "greenstone belt" no leste da Bahia. XXIX Congr. Brasil. Geol., Ouro Preto--Belo Horizonte, MG, resumos trabalhos, p. 185. Melcher, G.C., 1976. The carbonatites of Jacupiranga, S~o Paulo, Brasil. International Symposium on Carbonatites, Poqos de Caldas, MG. Soc. Brasil. Geol. Spec. Iss., pp. 6--18. Menor, E., 1975. La s~dimentation phosphat~e, p~trographie, mineralogie et g~ochimie des gisements de Taiba (S~negal) et d'Olinda (Br~sil). Thesis, Universit~ de Strasbourg, 153 pp. (manuscript). Milewski, I.P., 1970. Regi~o de Canabrava. XXIV Congr. Brasil. Geol., Brasilia, DF, roteiro excurs~es. Moreira, J.F.C., Veiga, P.M. and Leal, G.R., 1973. Cromita de Campo Formoso e Andorinha -- BA. XXVII Congr. Brasil. Geol., Aracajfi, SE, roteiro excurs~es, pp. 69---74. Moreschi, J.B., 1972. Geologia da mina de ouro do F a r i a - MG, Thesis, Universade de Sao Paulo, SP. Instituto Geoci~ncias, 115 pp. (manuscript). Neto, Y.F., 1973. Perfil analftico do tit~nio. Dep. Nac. Prod. Min., Rio de Janeiro, RJ, B o l . , 2 3 : 7 7 pp. Ojeda, H.A. and Fugita, A.M., 1974. Bacia Sergipe--Alagoas: geologia regional e perspectivas petrolfferas. Soc. Brasil. Geol., An. XXVIII Congr., Porto Alegre, RS, 1: 137-158.

206 Pecora, J.T. and Barbosa, A.L., 1944. Jazidas de nfquel e cobalto de S~o Jos~ do Tocantins, Estado de Goi~s. Dep. Nac. Prod. Min., Bol. DFPM, 6 4 : 6 9 pp. Ponte, F.C. and Asmus, H.E., 1975. The Brazilian marginal basins: current state of knowledge. In: An. Acad. Brasil. Ci~nc. (Editors), Continental Margins of Atlantic Type. Rio de Janeiro, RJ, 48: 215--239. Pontes, A.R., Bettini, C. and Miura, K., 1974. A indflstria petrolffera e suas perpsectivas futuras. Soc. Brasil. Geol., An. XXVIII, Congr., Porto Alegre, RS, 1 : 27--40. Ribeiro, M., Bochi, P.R. and Figueiredo Fo, P.M., 1966. Geologia da quadrfcula de Caqapava do Sul. Dep. Nac. Prod. Min., Bol. DFPM, 1 2 7 : 2 3 2 pp. Ruy, V.B., Bemardelli, A.L., Drummond, N.F., Ruff, A.W. and Tremaine, J.W., 1973. Geologia e recursos minerals da Serra dos Caraj~s. Rev. Brasil. Geoci~nc., 3: 215--242. Saad, S., 1974. Aspectos da mineralizaq~'o uranffera em Figueira PR. Com. Nac. Energia Nuclear, Rio de Janeiro RJ, Bol., 8 : 1 1 pp. Santos, E.J., 1973. Provfncia scheelitffera do Norderste. 27. Congr. Brasil. Geol., Aracaju. SE, roteiro excurs~es, pp. 31--46. Santos, J.F., 1974. Fatores de controle na c o n c e n t r a ~ o de nfquel laterftico condicionados pela e v o l u ~ o geolbgica e geomorfolbgica do complexo b~sico--ultran~sico de S~o Jo~o do Piaui - - PI. Soc. Brasil. Geol., An. XXVIII, Congr., Porto Alegre, RS, 6: 25--36. ScarpeUi, W., 1966. Aspectos gen6ticos e metam6rficos das rochas do Distrito Serra do Navio - - T F A - Brasil. Dep. Nac. Prod. Min., Div. Geol. Mineral., Avulso 41: 37--56. Schorscher, H.D. and Guimar~es, P.F., 1976. Estratigrafia e tectSnica do Supergrupo Minas e geologia do Distrito Ferrffero de Itabira. 29. Congr. Brasil. Geol., Ouro Preto-Belo Horizonte, MG, roteiro excursSes, pp. 75--86. Silva, J.C., 1973. Perfil analitico da magnesita. Dep. Nac. Prod. Min., Bol., 1 7 : 6 9 pp. Siqueira, L.P. and Maranh~o, R., 1973. O zoneamento e a estratigrafia da geossinclinal do Serid6.27. Congr. Brasil. Geol., Aracaju, SE, resumos trabalhos, pp. 44--46. Souza, G.F.S., 1973. Perfil analftico do carv~o. Dep. Nac. Prod. Min., Rio de Janeiro, RJ, Bol., 6 : 3 3 pp. Suszczynski, E., 1973. A origem vulc~nica do min6rio de ferro prim~rio da Serra dos Caraj~s--Estado do Par~--Regi~o AmazSnica. Soc. Brasil. Geol. An. XXVI Congr., Bel~m, PA, 1 : 103--120. Suszczynski, E., 1975. Os recursos minerals reals e potenciais do Brasil e a sua metalogenia. Interci~ncias, Sao Paulo, SP, 533 pp. Teixeira, C.A.S. and Piatnicki, S., 1968. Geologia econSmica do Distrito de Fluorita de Santa Catarina. Soc. Brasil. Geol., An. XXII Congr., Belo Horizonte, MG, pp. 57--64. Thayer, T.P., 1972. Some observations and problems concerning the peridotite--gabbro complexes of the Goi~s Belt. Soc. Brasil. Geol., An. XXVI Congr., Bel6m, PA, 1 : 37. Tolbert, G.E., Santos, B.A., Almeida, E.B. and Ritter, J.E., 1968. Recente descoberta de ocorr~ncias de min~rio de ferro no Estado do Par~. Min. Metalurgia, 48: 253--256. Tolbert, G.E., Tremaine, J.W., Melcher, G.A.C. and Gomes, C.B., 1971. The recently discovered Serra dos Caraj~s iron deposits, northern Brazil. Econ. Geol., 66: 985--994. Torres, A.G., 1975. Geologia da mina de ouro da Bela Fama, Nova Lima--Minas Gerais. Thesis, Universidade Federal Rio de Janeiro, Instituto Geoci~ncias, 58 pp. (manuscript). Torres, H.F., 1973. Projeto Tungst~nio/Molibd6nio--RelatSrio Final. Dep. Nac. Prod. Min., Recife, PE, 269 pp. (unpublished report). Wardlaw, N.C~, 1972. Unusual marine evaporites with salts of calcium and magnesium chloride in Cretaceous basins of Sergipe, Brazil. Econ. Geol., 67 : 156--168. Willig, C.D., 1973. Observa~5"es sobre os controles e a g~nese dos depSsitos de fluorita de Santa Catarina, Min. Metalurgia, 343: 36--41. [Received September 4, 1980]