ABSTRACT

The scarcity of specific studies on the ancient gold excavations of Jaraguá - or the vestiges that still remain - is as noticeable as its historical importance. A public preservation of such an area of "relevant historical heritage" is justified for the fact that they were pioneer in the Province by end of the XVI century. The open-sky ruins were considered ancient, by 1822, by the mineralogist José Bonifácio de Andrada e Silva. Also known as the "Morro Doce gold caves", they are sinuous in maps, in a narrow zone between metasediments and metavolcanics of the São Roque group. This Upper Proterozoic unit disapears westwards, below the sediments of the Paraná basin. The site is important for mining studies, but the main cave, marginal to the Anhangüera road, is covered by bush, soil, garbage and waste. The limits of the area of interest should be located first The construction of a small park would be valuable, but it must be accompanied by a effort to improve the awareness of the local population on the historical importance of the site. This is the unique way to stop the continuous accumulation of garbage and waste, for the benefit of future visitors and scholars.

INTRODUCTION

The scarcity of available information on the ancient gold excavations of Jaraguá has no parallel with its importance. The principal objective of this notice is to recover some unpublished data on them, due to the lacking of specific studies. We justify the preservation of such an area by the State as a testimony of "relevant historical heritage". Among the countless vestiges of ancient mining of metallic substances in the Precambrian part of the São Paulo State, those at Jaraguá, also known the "Morro Doce gold caves", have a singular geographical distribution, linked to the folded structures and local lithological associations.

During the XVI century the pioneer Jaraguá caves were the closest mines to the capital of São Paulo. The scientific interest of the geologic site may be evaluated not only from the historical aspects, but from many mining prospects which spread, during the last decades, in the occurrence area of the São Roque Group, between Morro Doce and Santana do Parnaíba, situated westwards. The mining requests to the DNPM indicate that the area still plays some interest for mining in spite of the fact that the mineral prospecting may be temporarily interrupted.

The disheartened scenery of the ancient caves is due to the urban occupation of the region of the Morro Doce Park as well as other popular land parcels, that fast adjoining that area, under the capital's economic influence (Carneiro 1996). If the mineral vocation of the São Paulo territory can be evaluated by the known occurrences, the Morro Doce caves allow an incomparable deep incursion into the Brazilian colonial past. During the XVI century gold was mined there (Abreu 1973). The gradual exhaustion of them and the noticeable discoveries in Minas Gerais dislocated the interest focus of Portuguese to the latter region.

SITUATION

The ancient Jaraguá gold caves are situated on the Atlantic Plateau by the Capricorn Tropic (Fig. 1), more precisely at the coordinates 23º 26¢ S and 46º 47¢ WG. They are composed by a series of excavations following the N50ºW direction (Fig. 2): they are sinuous and discontinuous in maps; the principal cave is also the closest to the Anhangüera road (Fig. 3).

FIGURE 1 - Situation map of the Morro Doce area

Figure 2 – Geological map with the distribution of vestiges of ancient caves and probable complementary mineral prospection works. Symbols: 1 - Excavations; 2 to 9 - Lithological units: 2 - schist, 3 - metarenite, 4 - red phyllite, 5 - quartzite, 6 - calcium-silicate rock, 7 - Amphibolite, 8 - Banded amphibolite and metatuff, 9 - Metaconglomerate, 10 – Antiform F₂, 11 – Sinform F₂, 12 – Sinform F₃, 13 – Neutral fold F₃, 14 - Quaternary alluvium (Sources: Carneiro,1983; IPT,1981).

FIGURE 3 - Ancient gold cave of Morro Doce, a photograph dated 1981 (Foto CDRC)

The easiest access to reach the area of the ancient caves from São Paulo is the Anhangüera road. After the access to the Jaraguá Peak at the 16,5 km, the caves are by the left, between the km 23 and 24, at the end of a long descent, after a road sign indicating the position of the Capricorn tropic line, it may be observed the Morro Doce excavation. Many houses nowadays round the "V" -shaped scar in the slope. People who live there surely ignore its nature and meaning.

HISTORY

Theodoro Knecht, a researcher on the São Paulo ores, published in 1951 a photograph of the main excavation, from the same view that we can see today by the Anhangüera road. He described these features as "ancient gold caves", but the expression does not belong to him as well. The mineralogist José Bonifácio de Andrada and Silva considered the open-sky cave ruins ancient, in 1822, in a visit to the São Paulo Province. In the São Vicente Capitany, these pioneer extractions have announced our mining vocation - at the end of the XVI century - by the same time of those of Paranaguá. More than 400 years ago under the command of Afonso Sardinha and his brother, many people worked there.

Geographic aspects

Each one of the caves has steep to subvertical walls, without vegetation and covered by loose material from the slopes. Urban occupation currently dominates the region of the gold caves. The land transformation is fast: during the last four decades the urbanization has replaced small farms and properties of the rural zone. The belt the excavations belong to is oriented along the WNW direction for approximately 6-km, with no more than 800 m wide. In the non-occupied areas the remaining vegetation is mainly of eucalypti and some poorly defined rests of native forest.

The main cave is presently covered by bush, soil, garbage and construction waste (Fig. 4). At the margin of the Anhangüera road, there also two narrow galleries in the decomposed phyllite, partially filled by soil at a road cut close to an abandoned gas station (Fig. 5). The upper abobades are curved, as small chapels and similar to other ones found in the Embu and Guarulhos regions. They were opened for mineral discovery and evaluation of new gold veins. Two cemeteries near this place would surely be threatened if a new gold run were started.

FIGURE 4 - The same gold cave, photograph dated april, 1996. The area became more threatened by the urban growth (Photo CDRC)

FIGURE 5 - Two narrow galleries for mineral prospection, almost filled by soil. The height is approximately 1,2 m (Photo CDRC)

Regional geology

The complex folding of the rock units (Carneiro et al. 1985) controls, at the Jaraguá region, the tenths of registered mineral occurrences (IPT 1981). The described belt is situated at the transition zone of a domain of impure metapsamitic rocks, interbeded with metapelitic members, to a domain of metacarbonate rocks containing countless belts of metatuffs and metavolcanic rocks. Among the impure metapsamitic rocks there are sandstones, arkoses, graywackes, quartz phyllites and subordinate polymitic conglomerates and pure white quartzites, as in the Quebra-Pé hill and at the Jaraguá peak. Red phyllites exhibiting of differentiated banding (Carneiro 1983) and rare fine schists constitute the metapelitic rocks. At the outcrops, the metacarbonatic rocks are found completely decomposed, except by the east, at Perus region, where some pegmatite and tourmaline granite have exposed horizons of fresh carbonate rock. The metatuffs are usually green rich in tremolite-actinolite, oligoclase, some biotite and opaques. There are also secondary minerals, as epidote, formed by the decomposition of mafic minerals.

The differentiated banding is the more conspicuous feature among the folded planar features. Neutral vertical folds showing NNE-trending axial planes determine the sinuous pattern of the preceding structures, mainly those with the differentiated banding as the axial-plane foliation. The open-sky caves obey to this control, being limited, in maps, in a narrow zone of red-purple phyllites.

In the NE side of the main cave it was observed in 1982 a gallery for mineral prospecting, NNE trending. At the end of it there was a vertical shaft of unknown depth. These features disappeared a few years ago, due to the accumulation of soil and construction waste. At the extension of the main cave, to the right side of the road, under eucalyptus, it was recovered a sample of quartz vein which indicated 20 ppm of gold, at the extremity of a cave close to one of the abovementioned cemeteries. Under the electron microscope, the sample indicated presence of free gold dispersed in small concentrations of limonite, suggesting its liberation from weathering processes that affected gold-bearing pyrite, liberation of submicroscopic gold and accretion of gold over crystallization nuclei, generating visible particles (IPT 1982). Samples of primary gold were not recovered.

There is no reliable data on when the mines were exhausted, but it is evident that Portuguese men used reasonable criteria for mineral prospecting: the probable prospecting galleries (Fig. 5) are perpendicular to the general direction of the foliation and local structures. The rudimentary washing and purification did not reach the deepest material, for the fact that it would require better techniques for ore location and evaluation. The poor knowledge of the mineralizations and on the local complex geology seems to be determinant factor of the insuccess of the mineral prospecting, even in more recent times.

SITE PROTECTION

The abandonment of the ancient Jaraguá gold caves is deplorable. After its disappearance, traces of a mineral exploration history will be lost; the history has started approximately four hundred years ago... São Paulo needs open-sky museums, but for the Morro Doce caves it can be too late. There is, for sure, a small Indian village, far from there, close to the Jaraguá peak. It is considered as the smallest Indian reserve of Brazil, occupied by an Indian remaining family, which control the visitor's access to a precarious "gold tank", that operated during the colonial times. Nevertheless, without a movement from the geological community, the above described picture of the Morro Doce region will never be reverted because the time factor does not help us: we will depend on several changes and, mainly, on the improbable political decision from the govern.

A maxim priority would be given to the accurate location of the limits of the area of interest. The sketch presented on figure 2 is based on field surveys and airphoto interpretation, being reasonably precise, but the data is from 1981-82. After this it should be started the work for improving the awareness of the local population on the historical importance of the site, to interrupt the continuous accumulation of garbage and waste. The proposal of construction of a small park there would be valuable, but it should be linked to a process to preserve the area by the public departments responsible for that.

The area will not resist to one more decade of abandon. The contrast is absolute with the beautiful natural parks of Salto and Itu (see Ciência Hoje, n. 112, p. 24-31, 1995). Without memory, there is no history, as these brilliant examples do demonstrate. The urban growth will vanish these testimony from the past. By one side of the Anhangüera road, they are faced by cemeteries; by the other side, by the city and its waste, that soon will clean out the sinuous way from the map, if nothing is done to stop the non-planned "urbanization".

References

ABREU, S.F.de. Recursos Minerais do Brasil. 2 ed. São Paulo: Nacional. 222p. 1975. v. 1.

CARNEIRO, C.D.R. 1983. Análise estrutural do Grupo São Roque na faixa entre o Pico do Jaraguá e a Serra dos Cristais, SP. São Paulo. 155p. (Doctorate thesis, Inst. Geoc. USP).

CARNEIRO, C.D.R. 1996. As cavas antigas de ouro do Jaraguá. Ciência Hoje, v. 21, n. 125, p. 22. (Crônica).

CARNEIRO, C.D.R.; HASUI, Y.; NAGATA, N.; LIMA, M.O. de. 1985. Padrões de superposição de estruturas do Grupo São Roque na faixa Jaraguá-Cristais (SP). Rev. Bras. Geoc., v. 15, n. 2, p. 116-130.

INSTITUTO DE PESQUISAS TECNOLÓGICAS DO ESTADO DE SÃO PAULO (IPT). Mapa de jazidas e ocorrências minerais do Estado de São Paulo. São Paulo: IPT. 1981. 758p. (IPT. Monograph 4, Publication 1171)

INSTITUTO DE PESQUISAS TECNOLÓGICAS DO ESTADO DE SÃO PAULO (IPT). Caracterização mineralógico-química e petrográfica, por microscopia óptica, microssonda eletrônica e microscopia eletrônica de varredura, de uma amostra de rocha procedente da região do Morro Doce-SP. São Paulo: IPT. 1982. 10p. (IPT. Report 16 563)

KNECHT, T. 1950. Ocorrências minerais do Estado de São Paulo. São Paulo: Secretaria da Agricultura. 144p. (v. 1: municípios de São Paulo, Santana de Parnaíba, Barueri, Franco da Rocha, Guarulhos, Mogi das Cruzes, Suzano e Poá).