Classificação e prospecção das jazidas primárias de água-marinha

The aquamarine-bearing pegmatites are generally thin, with poorly developed zoning. They are located in biotitic or porphyroblastic granitoids, kinzigites, gneiss and charnockites or in their vicinity, all being Precambrian in age. The pegmatites are divided in three types: one poorly differentiated with quartz, biotite and large K-feldspar crystals, where the graphic texture is well developed, one which contains a little albite and muscovite with regular zoning and one commonly drusic with many albite and muscovite and a little rose quartz, lepidolite and Fe-Mn phosphate minerals. The pegmatites occur isolated or in fields, mostly hand-worked. Searching guides and typical minerals used in prospection are reported.Os pegmatitos portadores de água-marinha são geralmente delgados com uma zonação pouco marcada. Sempre de idade precambriana, eles estão encaixados ou nas vizinhanças de granitos biotíticos ou porfiroidais, kinzigitos, gnaisses e charnockitos. Geneticamente distingue-se três tipos de pegmatitos: um primeiro, pouco diferenciado com quartzo, biotita, grandes cristais de feldspato potássico onde a estrutura gráfica é bem desenvolvida; um segundo exibindo nítida zonação e contendo pouca albita e muscovita, e um terceiro tipo que contém frequentemente drusas com muito albita e muscovita, um pouco de quartzo róseo, lepidolita e fosfatos de ferro e manganês. Os pegmatitos ocorrem isolados ou em campos. Guias de pesquisa e minerais típicos ajudando a prospecção são descritos

Microesferas Magnéticas do Córrego da Pedra Bonita (MG)

Des microsphères ont été collectées dans les concentrés du minerai provenant de l'exploitation des alluvions anciennes et modernes du Córrego da Pedra Bonita près de Conselheiro Pena (Minas Gerais). Ces microsphères sont magnétiques, noires ou jaunes, associées à des gouttes piriformes et des éclats. Les microsphères noires sont constituées de magnétite (et parfois hématite) et les jaunes de siliciures de fer divers. Une étude metallographique montre fréquemment l'association de ces deux com posants, qui sont dépourvus de nickel. En fonction de leur com position chimique et de leur localisation a la partie supérieure des alluvions, les microspheres sont considérées comme dûes a des pollutions industrielles.Resum

Historical observations on oxygen-bearing compounds of platinum and palladium in Minas Gerais, Brazil

Dark brown to black compounds associated with native gold were discovered three hundred years ago in Minas Gerais, Brazil, and have been known since then as ouro preto (black gold). These compounds were correctly determined as oxygen-bearing compounds of platinum - palladium - iron as early as 1833 and 1837, but the oversight of the presence of major iron in their composition led to an erroneous definition of palladinite and to the much-delayed recognition of a group of platinum-group-element oxides.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

A Allanita de Mucaia (Minas Gerais) e seu Contexto

Les minéraux associés à l'allanite de Mucaia (vallée du Rio Marambaia, Nord de Minas Gerais) sont brièvement décrits ainsi que la pegmatite granitique encaissante. L'allanite est noir de poix, métamicte avec une densité de 3 48 et un indice moyen de 1,723. Elle contient de petites inclusions d'hématite. Son diffractogramme après chauffage et son analyse semi-quantita tive par fluorescence X sont fournis ainsi que ceux de plages brun orangé correspondant à de l'allanite altérée. Un mince cor tex d'altération est formé de bastnaesite mêlée à des hydroxydes de fer, du quartz et de la kaolinite. De la vermiculite qui a adsorbé des terres rares et dérive de l'altération de la biotite est associée à l'allanite.Les minéraux associés à l'allanite de Mucaia (vallée du Rio Marambaia, Nord de Minas Gerais) sont brièvement décrits ainsi que la pegmatite granitique encaissante. L'allanite est noir de poix, métamicte avec une densité de 3 48 et un indice moyen de 1,723. Elle contient de petites inclusions d'hématite. Son diffractogramme après chauffage et son analyse semi-quantita tive par fluorescence X sont fournis ainsi que ceux de plages brun orangé correspondant à de l'allanite altérée. Un mince cor tex d'altération est formé de bastnaesite mêlée à des hydroxydes de fer, du quartz et de la kaolinite. De la vermiculite qui a adsorbé des terres rares et dérive de l'altération de la biotite est associée à l'allanite

Apport d'Une Prospection Systématique à l'Étude de l'Origine de l'Or et du Platine Alluviaux du Córrego Bom Sucesso (Serro - Minas Gerais)

This work deals with the search for the source of gold and platinum (associated to diamond) which are worked for more than two hundreds years in the Córrego Bom Sucesso, in the neighbourhood of the town of Serro (Minas Gerais State). A preliminary panning prospecting supported by the collect of 50 samples, allowed to determine the source of diamond: it proceeds from conglomeratic lenses embedded in quartzites, as to the source of the main associated minerals as: magnetite, ilmenite, hematite, pyrite, rutile and zircon. However, gold and platinum source remained hypothetical because no typical association or correlation with the above-mentioned minerals were detected. A complementary prospecting was realized in creek deposits ("lit vif"), old alluvium and soils. The usual alluvium study routine was also applied to crushed rocks. HF dissolution, geochemical analysis, gold nuggets analysis were also performed as done MEB examination of gold and platinum nuggets. Gold proceeds from two independent and no synchronous sources. Parte of it is included in quartzites of varied facies and colours. This gold was eroded from old rocks, transported and deposited among sands in a shallow sea. Then metamorphism, which little affected the gold, transformed the sands into quartzites. The second source of gold is from basic rocks transformed into amphibolites. These rocks occur as a long, almost NS running, rosary-shaped, intrusion that crosses and outcrops in the medium Córrego Bom Sucesso valley. Platinum also proceeds from the same intrusion, but from a northern and smaller lense. The composition of nuggets, which are unique in the world, with Pt-Pd-Hg alloys, without arsenides, tellurium or selenium, as the commonly botryoidal texture point out to a low temperature hydrothermal processus of metal deposition. A sample location map, analyses tables and a platinum nugget MEB microphotography complete the text.SCOPUS: ar.jinfo:eu-repo/semantics/publishe