Marcondes Lima da Costa

Geochemical signatures of tropical soils with archaeological black earth in the Amazon, Brazil

Abstract The archeological black earth (ABE) in Caxiuana, Amazon, differs from the surrounding (AD) and underlying yellow latosols (YLS) through its black color, texture, abundance of organic matter and presence of archaeological artifacts. The ABE contains higher contents of quartz and lesser kaolinite than the yellow latosols. ABE exhibits a P–Mg–Ca–Sr–Ba–Cl–Mn–Zn–Cu geochemical signature, with anomalously low As. This signature can be related to anthropogenic activity. The YLS is characterized by the Fe–Ga–V–Cr–Pb–Nb–Zr–Sc–Cd–Co association which was not modified by the formation of ABE soil, although they were leached during hydromorphic soil formation in the southern part of the ABE exposures. Elements such Y, B and F show no variations throughout the entire area (including ABE and YLS).

Holocene vegetational and coastal environmental changes from the Lago Crispim record in northeastern Pará State, eastern Amazonia.

Vegetational and coastal environmental changes have been interpreted from a 600cm long and 764014C yr B.P. old sediment core from Lago Crispim located in the northeastern Pará State in northern Brazil. The radiocarbon dated sediment core was studied by multi-element geochemistry, pollen and charcoal analysis.Holocene Atlantic sea-level rise caused an elevation of local water table, which allowed the formation of organic deposits in a probably former inter-dune valley. Dense, diverse and tall Amazon rain forest, and some restinga (coastal vegetation) covered the study area at the beginning of the record at 764014C yr B.P. Mangrove vegetation developed along rivers close to the core site at that time. Subsequent decrease in less mangrove vegetation near the study site indicates a sea-level regression, beginning since around 700014C yr B.P. Lower sea-levels probably favoured the formation of a local Mauritia/Mauritiella palm swamp at 662014C yr B.P. Oscillations of higher and lower sea-level stands probably changed the size of the local palm swamp area several times between 6620 and 363014C yr B.P. Sea-level transgression at around 363014C yr B.P., caused marked coastal environmental changes: the development of mangroves near the site, the replacement of the local palm swamp by a Cyperaceae swamp, the substitution of the surrounding former Amazon rain forest and some restinga vegetation mainly by salt marshes. High amount carbonised particles suggest a strong human impact by burning on the coastal ecosystems during this late Holocene period.Highest concentrations of NaCl and also Ca, Mg and K in the upper sediment core indicate that the Atlantic was close during the late Holocene period. The core site, which is today 500m from the coastline and only 1-2m above modern sea-level, was apparently never reached by marine excursions during the Holocene.Less representation of mangrove since ca. 184014C yr B.P., may be related due to a slightly lower sea-level or to human impact in the study region. The modern shallow lake seems to be formed recently by road construction, forming an artificial dam.

The ceramic artifacts in archaeological black earth (terra preta) from lower Amazon region, Brazil: mineralogy

Sitios arqueologicos com Terra Preta, denominados de Terra Preta de Indio ou ainda Terra Preta Arqueologica (TPA) sao muito frequentes na Amazonia. As TPA geralmente contem fragmentos de vasos cerâmicos, por vezes abundantes, alem de liticos, que sao materiais de grande importância para os estudos arqueologicos. Para consubstanciar esses estudos, realizou-se pesquisas mineralogicas e quimicas em fragmentos cerâmicos provenientes de dois sitios arqueologicos da regiao de Cachoeira-Porteira, Estado do Para. Os fragmentos foram classificados segundo seus principais temperos em: cauixi, cariape, areia+feldspatos e caco de vaso cerâmico. Mineralogicamente sao compostos de quartzo, minerais de argila calcinados (especialmente caulinita), feldspatos (albita e microclinio), hematita, goethita, maghemita, variscita-estrengita, fosfatos amorfos, anatasio, e raramente apatita, rhabdophana e oxidos de Mn e Ba. Cauixi e cariape sao componentes orgânicos silicosos e amorfos a DRX. A composicao mineralogica e a morfologia dos seus graos indicam saprolito (material argiloso rico em quartzo) derivado de rochas igneas felsicas de granulacao fina ou rochas sedimentares ricas em argilominerais como materia-prima dos vasos cerâmicos. Neste material argiloso cauixi, cariape e/ou areias, ricas em silica, foram intencionalmente adicionados. O elevado conteudo de fosfatos de Al-Fe, amorfos ou como de baixa cristalinidade, originou-se a partir do contato entre a matriz argilosa da parede do vaso cerâmico com a solucao aquosa quente durante o cozimento diario de alimentos de origem animal (principal fonte de fosforo). A cristalizacao dos fosfatos deve ter prosseguida mesmo depois que os vasos foram descartados, e juntos com os restos de materia orgânica vegetal e animal incorporaram-se aos solos residuais. Participaram desta forma na formacao dos solos tipo TPA.

Geophagy as a Correlate of Folivory in Red-Handed Howler Monkeys (Alouatta belzebul) from Eastern Brazilian Amazonia

Howler monkeys, Alouatta spp., are the most folivorous of neotropical primates (Platyrrhini), although Amazonian red-handed howlers (Alouatta belzebul) are relatively frugivorous. The feeding ecology of a free-ranging group of A. belzebul was monitored at a site in eastern Brazilian Amazonia over a ten-month period (November 1997 to August 1998). The first half of the study period encompassed the peak of the wet season, during which the study groups diet was predominantly frugivorous (scan sample records: 53.5% fruit, 40.8% leaves), and the second half, the transition from wet to dry season, characterized by a marked shift to folivory (18.9% fruit, 77.9% leaves). This shift was accompanied by a marked increase in mature, as opposed to flush leaves, which are relatively rich in secondary compounds. Ingestion of soil from termitaria was recorded on a total of 26 occasions, all of which occurred during the second half of the study period. Soil from termitaria was relatively rich in elements such as Ca and Na and in organic carbon, in comparison with that from the forest floor. The extent to which the monkeys ingested soil for their mineral supplements, or as an aid for the digestion of leaves, in particular the absorption of secondary compounds, remains unclear. The marked correlation with the observed patterns of folivory suggests that the latter function may have been the primary motive for geophagy in this species.

The ceramic artifacts in archaeological black earth (terra preta) from Lower Amazon Region, Brazil: chemistry and geochemical evolution

This paper carried out a chemical investigation of archaeological ceramic artifacts found in archaeological sites with Black Earth (ABE) in the Lower Amazon Region at Cachoeira-Porteira, State of Para, Brazil. The ceramic artifacts, mostly of daily use, belong to Konduri culture (from 900 to 400 years BP). They are constituted of SiO2, Al2O3, Fe2O3, Na2O and P2O5; SiO2 and Al2O3 together add up to 80 % and indicate influence of acid rocks, transformed into clay minerals basically kaolinite. The relative high contents of P2O5 (2.37 % in average) come out as (Al,Fe)-phosphate, an uncommon fact in primitive red ceramics, but found in some roman and egyptian archaeological sites. The contents of the trace elements are similar or below the Earths crust average. This chemical composition (except P2O5) detaches saprolite material derived acid igneous rocks or sedimentary ones as the main raw material of the ceramics. The contents of K, Na and Ca represent the feldspars and rock fragments possibly introduced into saprolitic groundmass, indicated by mineralogical studies. The presence of cauixi and cariape as well as quartz sand was confirmed by optical microscope, SEM analyses and by the high silica contents of ceramic fragments. Phosphorus was possibly incorporated into groundmass during cooking of foods, and ABE soil profile formation developed on yellow Latosols. The raw materials and its tempers (cauixi, or cariape, feldspar, crushed rocks, old ceramic artifacts and quartz fragments) are found close to the sites and therefore and certainly came from them.

Vivianite and siderite in lateritic iron crust: an example of bioreduction

Lateritic iron crust (LIC) samples from Padauari (AM) were analysed by XRD, optical microscopy and SEM-EDS. The equilibrium of iron minerals (IM) was studied using Eh-pH diagram. It was shown that the minerals of the LIC are goethite (a-FeOOH), vivianite [Fe3(PO4)2.8H2O] and siderite (FeCO3). Carbonate grains are a solid solution of FeCO3-MnCO3. The LIC presents textures and structures of dissolution of IM. The siderite and vivianite are stable from Eh =-0.3 to 0.0 V and pH=5.0-7.5. These results indicate that vivianite and siderite are products of bioreduction through biogenic dissolution of IM, the new conditions of ecosystems of the Amazon region.

Gold distribution in lateritic profiles in South America, Africa, and Australia: applications to geochemical exploration in tropical regions

Abstract Gold, a principal ore commodity, is sought in third world countries, which are situated mainly in the tropics, where extensive lateritic terrains exist. The high value of gold on the international market and balance of payment problems cause gold to be especially important. Present intensive propecting for gold in the Third World countries are, for those reasons, in lateritic terrains. Laterites, formed during the Tertiary and the Recent in inner tropical morphoclimatic zones covered by dense rain forests, in places such as the Amazon region and West Africa, are presently undergoing strong weathering and erosion that truncates lateritic profiles. Consequently, the thick soils still forming today cover in different places, different parts of truncated profiles. Samples of thick soils taken from the surface down, may begin not at the original top of the laterite but somewhere along the profile. Inasmuch as elements in lateritic profiles are not homogeneously distributed, problems in interpretation can result. Gold distribution in non-truncated laterites tends to be sigmoidal in distribution. Two convexities (highest contents) can be distinguished: one in surficial iron crusts or equivalents, the other at the base of saprolite. The sigmoidal curve can be cut off, strongly modified, or concealed by tropical weathering. The intense weathering can diminish concentrations, i.e., elements can be dispersed. Geochemical exploration becomes difficult, because interpretations of the geochemical anomalies based on high concentrations becomes unreliable. If the amount of truncation of lateritic profiles can be assessed, weak or even negative anomalies can become as good or better than strong anomalies.

Application of multi-element geochemistry in Au-phosphate—bearing lateritic crusts for identification of their parent rocks

Abstract Serra do Pirocaua is a plateau formed on mature lateritic rocks (Eocene), partially covered by earthy soil. Gold in the region around the serra (plateau) has been mined from the 17th Century to the present. Laterites extend not only over the entire plateau, but also in the neighboring flat and low-lying area. Outcrops of fresh rocks are rare and none has been found as yet on the plateau. Systematic geochemical and mineralogical studies were carried out on samples taken from crusts and surface soils of the plateau. Initial results show that these materials are practically identical both in terms of mineralogy as well as geochemistry indicating that the soils have a physical origin, that is, they are immature. Multi-element geochemical data have identified three main geochemical signatures both for the crusts as well as the soils, representative of three mineral groups: hematite + goethite, Al phosphates and anatase. A lithological map of the substrata was developed, based on the distribution of the anomalous levels of elements in each association. The data suggest that the substrata are formed of volcano-sedimentary rocks of mafic to intermediate composition and probably phosphorite beds. Both volcanic and non-volcanic mafic-ultramafic rocks may be present. Hydrothermal manifestations such as As-bearing tourmaline-quartz veins were suspected because of high levels of As and Au as well as dravite aggregates in Fe crusts and soils.

The geochemical association Au–As–B–(Cu)–Sn–W in latosol, colluvium, lateritic iron crust and gossan in Carajás, Brazil: importance for primary ore identification

Abstract Carajas, in the state of Para, eastern Amazon, is the most important mineral province in Brazil. Its high plateau landscape contrasts with the lowland domain of the Amazon region. It is developed on old lateritic formations and covered by dense tropical rain forest under a hot and humid tropical climate. The bedrock is made up of high-grade metamorphic terrain of Archean age, greenstone belts and post-tectonic granites. The laterite profiles are complex, partly transformed into yellow to red latosols on the plateau and colluvium on the slopes. The lateritic terrain hosts the gold rich gossans of the Igarape Bahia and Aguas Claras gold mines. Gold is found in red latosols, iron crust, gossans and colluvium. In order to investigate the capacity of these materials as geological sampling media and as indicators of primary ore, a multi-element geochemical survey was carried out at Aguas Claras. Seventy-four samples were analysed for 27 elements by AAS (Au, Cr, Cu, Mn, Ni, Pb and Zn), XRF (Cl, W), OES (B, Be, Ga, Mo, Sc, Sn, Sr, V, Y, Zr and Bi), AA–HG (As, Hg, Se and Sb), ICP–AES (Te), and the mineralogy identified by XRD. The supergene materials are mainly kaolinite, quartz, hematite, maghemite, gibbsite and some goethite. Dravite, muscovite, wolframite and chromite are accessory minerals. In the latosols, As, Au, B, Cr, Cu, Ga, Mo, Pb, Se, Sn, V, W and Zr are concentrated by a factor greater than three times compared to crustal abundance levels, whist gossan and colluviums contain more than ten times the crustal average levels of As, Au, B, Mo, Sn and W. Multivariate R-mode analyses distinguish several associations according to the nature of the supergene materials. The As–Cu–Mn–Pb–B–Au–W–F cluster corresponds to primary signatures still preserved in latosols, iron crust and colluvium; and the Cr–V–Ga–Mo–Ni–Zn–Se–Sc–Hg–Sn–Cl–Y–Zr cluster reflects the general laterite evolution. The latosols preserve the geochemical signature and signal of underlying primary ore, and, together with the colluvium, they can be used as good sampling media.

Geochemistry of rare-earth elements in surface lateritic rocks and soils from the Maicuru complex, Para, Brazil

Abstract The Maicuru area contains a typical alkaline/ultramafic rocks-carbonatite complex that is part of the Guyana Craton, northern Brazil, and exhibits thick lateritic profiles. Tops of profiles are hardened ferruginous horizons frequently called “iron crust” or “ferricrete” which gives rise to landforms called “iron-hat”. The area is being explored for titanium and phosphate resources by Docego, a subsidiary of Companhia Vale de Rio Doce (CVRD). This paper discusses rare-earth elements (REE) mineralization related to aluminum phosphates in Ti-rich surface laterites (iron crusts and lateritic soils) containing anatase over the Maicuru Complex. Some samples show total REE concentrations as high as 20.0 wt.% that is contained in crandallite-goyazite-florencite solid solutions, with the last end member predominant. Mean Σ REE contents are slightly greater in soils than in iron crusts. Chondrite-normalized plots for REE in soils and iron crusts reveal strong fractionations with high (La/Lu)N mean values, where the heavy rare-earth elements (HREE) are strongly depleted compared to light rare-earth elements (LREE), a pattern typical of carbonatite and alkaline rocks. Strong positive and negative Ce anomalies were observed in iron crust samples, but were less common in soils. Lateritic iron crusts distinctly differ from lateritic soils in geochemical properties. Lateritic iron crusts over mineralized rocks are enriched in Ti, Fe, P, REE and resistate minerals, but soils are not. Anomalous concentrations of REE in laterites strongly indicates the presence of phosphates in laterites and in parent rocks. The study illustrates the importance of understanding laterization processes for geochemical exploration in tropical terrains.