ABSTRACT
The Sincorá range is an orographic system of north-south trend bounded by the coordinates 12⁰15' - 13⁰45'S and 41⁰10' - 41⁰30'W. The ranges, that take several local names alternate heights above 1200m with narrow and deep valleys, whose escarpments and waterfalls compose breathtaking landscapes. The rocks that form the Sincorá range are mostlysandstones and conglomerates of the Tombador Formation, of Mesoproterozoic age. The sedimentary structures of these rocks are perfectly preserved, allowing its approach under the depositional systems and sequence stratigraphy view points. The structure of the range is an anticlinorium whose axis undulate in the vertical plane. The TombadorFormation conglomerates are diamond bearing, and were washed since their discovery in 1844. From 1871 on, there was a dramatic decrease in the production, but presently there are still scattered washings. The northern half of the Sincorá range is within the Chapada Diamantina National Park and farther north is the Iraquara-Marimbus Environmental Protection Area; in the region of the town of Mucugê, there is a municipal park of environmental protection, in the area of the Sempre Viva Project.
Key words: Sincorá range; Chapada Diamantina; sedimentary rocks; structural geology; diamond; Proterozoic

INTRODUCTION

 The Sincorá range, located in the central part of Bahia State (Brazil), is a region of  great scenic beauty owing to the shaping of its ranges, that expose deep valleys with steep escarpments and wide plateaus. These escarpments allow the examination of stratigraphic sections and sedimentary structures of the  bedrocks, where long ago were exploited diamonds.
   In 1818, the german naturalists J.B. von Spix and C.F. von Martius examined the rocks of this range in the Sincorá Velho village, and compared them with the rocks of the Tijuco in Minas Gerais Province, where diamonds were washed (Spix and Martius, 1838). The discovery of diamonds in the Mucugê and Combucas rivers in 1844, attracted to the region a large number of explorers and adventurers. So, in 1847, the General Inspector of the Diamond Regions of Bahia Province, Benedicto Marques da Silva Acauã, forwarded a report to the Imperial Government about the region. The second part of the report is a detailed account about the geomorphology of the Sincorá range and its surroundings, as well as its mineral resources, both real and potential (Acauã, 1847). Besides the explorers and adventurers, the presence of the diamonds also attracted scientists to region (Moraes, 1991).
   In the year of 1880, the engineer Theodoro Sampaio visited the town of Santa Isabel do Paraguaçu (nowadays Mucugê), located in the Sincorá range itself "... in the very center of the diamond mines of Bahia..." (Sampaio, 1955). Visiting the Nova Sibéria garimpo (diamond washing), located in the Paraguaçu river, he identified the rocks as "... the same geologic facies of the Sincorá range".
   The foundations of the Chapada Diamantina stratigraphy were established by the American geologist  Orville A . Derby in his visit to the region (Lençóis,  Andaraí, Chique-Chique -- presently Igatu, Santa Isabel do Paraguaçu and Palmeiras), in the year of 1904. In a report to the Secretary of Agriculture of Bahia State, he described the sandstones and conglomerates and the structure of the Sincorá range (Drby, 1904). Later, he named them Paraguaçu and Lavras groups, respectively (Derby, 1906).
   Following these prime descriptions, the geology of the Sincorá range has been approached under several points of view: stratigraphy and regional geology (Derby, 1905; 1906; Kegel, 1959; Mascarenhas, 1969; Pedreira et al., 1974); depositional systems (Guimarães & Pedreira, 1990; Bomfim & Pedreira, 1990; Pedreira & Margalho, 1990: Pedreira, 1997); and sequence stratigraphy (Pedreira, 1988; 1994; 1995; Savini & Raja Gabaglia, 1997).
   In recent times, emphasis have been given to studies related to the environment (CPRM, 1994; Funch, 1997).

LOCATION  

    The Sincorá range is located in the central region of Bahia State, in the area bound by the coordinates 12⁰15' - 13⁰45'S e 41⁰10' - 41⁰30'W, about 400km far from the city of Salvador, the state capital (figure 1). The region comprises sectors of the Lençóis, Palmeiras, Andaraí, Mucugê and Barra da Estiva municipalities, as well as the villages of Caeté Açu, Guiné, Igatu, Cascavel, Mundo Novo and Sincorá Velho of the above municipalities.  The region may be reached through  the BR-242 road (Salvador-Brasília) and within it through paved state roads that connect it to the towns of Lençóis, Palmeiras, Andaraí, Mucugê and Barra da Estiva. Other settlements may be reached by unpaved local roads; between the BA-142 road and Igatu village, the roads are paved with stone slabs. By air, there are regular lines to the Col. Horácio de Matos, located in Tanquinho village.

Figure 1 - Location map of the Sincorá range. Explanation: 1- Region of the range; 2-Paved road; 3-Unpaved road; 4-River; 5-Town or village; 6-Airport.

SITE DESCRIPTION

    The Sincorá range is located in the central-eastern escarpment of the Chapada Diamantina, approximately between the villages of Afrânio Peixoto (previously Estiva ) in the north and Sincorá Velho in the south (figure 1). Its western flank is an almost continuous escarpment, 300m high and 80km long and the eastern that dominates the plains of the Paraguaçu river valley (400m), reaches abruptly the altitude of  1200m in the first crests of the range (Funch, 1997).

Geomorphology

    North-south trending faults of great lenght and smaller ones transverse to them, divide it into countless blocks that take local names, as the Cravada, Sobrado, Lapão, Veneno, Roncador or Garapa, Esbarrancado (part of the western escarpment), Rio Preto ranges, among many others. These ranges have peaks up to 1700m high and are separated by steep valleys, deep as canyons.
    A landmark that stands out in the Sincorá range is the Pai Inácio mountain, located in the western limb of the anticline of same name, that forms the Cercado valley (figure 2).

Figure 2 - Cercado valley in the Pai Inácio anticline, south of the BR-242 road

    North of the road, is the Camelo or Calumbi mountain, an outlier within the anticline (figure 3), and in the south, in similar situation, the Morrão (figure 4), whose access is through road from the town of Palmeiras and the village of Caeté Açu.

Figure 3 - Camelo or Calumbi mountain

Figure 4 - Morrão

    Before reaching the village of Caeté Açu, one crosses the bridge on the Riachinho river (figure 5). Close to this place, is the Riachinho cave, 201m long and 26m high (Laureano & Cançado, 1995).

Figure 5 - Riachinho river

    The Paraguaçu river, after crossing the Sincorá range, leaves it in the locality of  Passagem de Andaraí, in the Donana waterfall (figure 6). From there, it starts meandering on the limestone plain, towards the Atlantic ocean in Todos os Santos bay.

Figure 6 - Donana waterfall

    Beyond the Cercado valley, already mentioned, in the southern end of the Sincorá range, there is another valley named Campo Redondo. Its entrance is shown in the figure 7, where are seen the western escarpment of the range and the Sincorá river valley.

Figure 7 - Road to Campo Redondo, looking to part of the western escarpmemt of the range and the valley of the Sincorá river.

Geology

    The rocks that crop out in the Sincorá range are essentially Mesoproterozoic sediments of the Tombador Formation; this formation was described by Branner (1910), about 180km  north of this region. In the Sincorá range, the Tombador Formation overlies the Guiná Formation (figure 8). The structure of the range is a huge anticlinorium  with undulating axis. The upwards undulations are in the central regions of the range, between the Pai Inácio mountain and the village of Guiné, and between the towns of  Mucugê and Barra da Estiva. In these places, crop out the rocks of the underlying Guiné Formation.

Figure 8 - Contact between the Guiné and Tombador  formations in Comércio de Fora, west of the town of Mucugê. The rocks of the former (siltstones and sandstones) have gentle land forms; the ones of the latter (sandstones and conglomerates ) form the escarpment.

    The contact between these formations, the former of marine, and the latter of continental environment, is interpreted as a type 1 sequence bounding surface (Pedreira, 1994).
    The sandstones and conglomerates of the Tombador Formation are shown in the figures 9 and 10. 

Figure 9 - Sandstones of the Tombador Formation in the village of Igatu. Note the trunctions between beds, with channel shapes.

Figure 10 - Interbedded conglomerates and sandstones of the Tombador Formation. Valley of the Combucas river, north of the town of Mucugê.

Figure 11 - Graphic sedimentary logs of the Tombador Formation in the Sincorá range. A - BR-242 road, between the Pai Inacio mountain and the top of the formation (modified from Guimarães & Pedreira, 1990); B - Cruzeirão muontain in the town of Mucugê. Explanation: 1-Clast supported conglomerate; 2-Sandstone; 3-Trough cross bedding; 4-Tabular cross bedding; 5-Horizontal bedding; 6-Ripple marks; 7- Clast imbrication; 8-Amalgamation.

Diamonds

    In the year of 1844 were discovered diamonds in the Sincorá range, in the region of Mucugê (figures 1 and 12). From there, all the range was exploited, being washed (garimpados) diamonds since the Sincorá river in the south, up to the Afrânio Peixoto region in the north (figure 1).

Figure 12 - Combucas river, north of the town of Mucugê, close to the mouth of the Mucugê river, place of the first discoveries of diamonds in the Sincorá range.

    The diamonds were washed from the gravel produced by the weathering of the oligomictic conglomerates as that of figure 13, or polymictic as those of the Serrano waterfall (figure 14), shown in detail in the figure 15.

Figure 13 - Detail of the conglomerate of rio Combucas valley (figure 10) interpreted as fluvial.

Figure 14 - Serrano waterfall in the town of Lençóis.

Figure 15 - Polymictic conglomerate of the Serrano waterfall, interpreted as alluvial fan.

    The washing of diamonds was also intensive in the regions of Andaraí and Igatu. The figure 16 shows the conglomerates in the road between these two localities. The debris discarded from the ancient washings still can be seen along the road.

Figure 16 - Conglomerates along Andaraí - Igatu road

    After a glorious period of about 25 years, the manual washing of diamonds began to decline from 1871 on (CPRM, 1994). The first attempts to mechanize the works were made in the first half of the XX century (Catharino, 1986). In the eighties, the mechanized washings started again, in the beds of the rivers, both inside and outside of the National Park. These activities, thanks to a joint action  of several agencies related to mining and the environment, were definitely discontinued in March, 1996.
    Even after 150 years of exploitation of the diamond bearing alluvium, there still exists manual washings, although in a slower pace, owing to the exhaustion and decrease of the works (Funch, 1997). Due to the unlimited number of geologic and topographic settings of the range, there are the following types of manual washings, each one with its characteristic features: "cascalhão" (high ledges with gravel and sand), "barranco"(high ledge of clay with a thin bed of gravel), "brejo"(low and moist area with little soil on the gravel), "grupiara"(gravel in the range), "emburrado"(area with rock boulders), "curriolo"(washings in the bed of a river, with much gravel and loose cobbles), "engrunada"(underground works), "gruta"(natural cave in the range), "escafandro"(underwater works made by divers), "serviço a seco"( dry service; work in a place without water), "lavagem"(rework of debris from old washings) and "faísca"(small washing made in one day), (figure 17).

Figure 17 -Schematic rendering of the manual garimpo types (descriptions in the text)

    These facts confirm Derby's (1905) statement: "Regarding the mineral wealth, the only one profitable until today are the diamonds and carbonados, and its geologic framework [of the Sincorá range] offers little hope of the existence of another".

PROTECTION MEASURES

    The sector of the range between Cascavel and Mucugê, and the BR-242 road, is within the Chapada Diamantina National Park. This park was created in September 17, 1985 by the Federal Decree no. 91655. Its area is 1520 sq. km, and encompasses part of the Lençóis, Andaraí, Mucugê, Palmeiras and Ibicoara municipalities, excluding the towns themselves (CPRM, 1994). North of the BR-242 road, the Pai Inácio and Camelo mountains are within the Iraquara-Marimbus APA (Area of Environmental Protection).
    According to information of the biologist Roy Funch (Director of the Environmental Department of Lençóis Municipality), the Mucugê river, in whose beds were discovered the first diamonds, is reasonably well protected: upstream it is inside the National Park, and downstream in within the area of the Mucugê Municipal Park (a reserve with about 2.7 sq. km). This park also encompasses the low course of the Combucas river and several of its tributaries, and borders the National Park.
    Besides these measures, there is in Mucugê municipality, the Sempre Viva Project. This project has the following aims: 1) to run a conservation unit for eco-touring in the Mucugê Municipal Park; 2) development of technology for the reproduction of native vegetation; 3) operate a Geographic Information System (GIS); and 4) carry out a program of environmental education. Its offices, built in the style of the old shelters of the "garimpeiros", is shown in the figure 18.

Figure 18 - Part of the Sempre Viva Project facility

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