Occurrence of ferropyrosmalite in the mineralizated breccias from Igarap? Bahia Au-Cu-(?REE-U) deposit, Caraj?s mineral province.

Nos ?ltimos anos, diversos trabalhos t?m reportado a presen?a de minerais da s?rie da pirosmalita [(Fe,Mn)8Si6O15(OH,CI)10] em dep?sitos de sulfetos maci?os vulcano-exalativos e dep?sitos de Fe-Mn metamorfizados. Neste trabalho, apresentamos uma descri??o in?dita da ferropirosmalita no dep?sito de Au-Cu-(?ETR-U) de Igarap? Bahia, localizado no distrito auro-cupr?fero da Prov?ncia Mineral de Caraj?s. Admite-se que esse dep?sito foi gerado por processos similares ?queles envolvidos na g?nese dos dep?sitos da classe ?xidos de ferro-(Au-Cu-U-ETR) do tipo Olympic Dam. A ferropirosmalita descrita ocorre sob dois contextos: ?) associada a veios e v?nulas carbon?ticas; e ii) associada a brechas heterol?ticas compostas por fragmentos de forma??o ferr?fera bandada, metavulc?nicas b?sicas e matriz rica em magnetita, calcopirita, bornita, pirita, siderita, minerais ricos em ur?nio e elementos terras raras, anfib?lio, stilpnomelana, clorita e quartzo. O crescimento da ferropirosmalita teria envolvido a substitui??o de minerais ricos em ferro (clorita, magnetita e siderita), controlado pela introdu??o de fluidos magm?ticos ricos em cloro. A percola??o dos fluidos foi induzida pela permeabilidade elevada das brechas e tamb?m pela descontinuidade ao longo das paredes de v?nulas carbon?ticas. O modo de ocorr?ncia da ferropirosmalita e o seu rescimento em equil?brio com anfib?lio (ferro-hornblenda actinol?tica) s?o sugestivos de crescimento metassom?tico para o mineral, supostamente sob condi??es t?rmicas na transi??o das f?cies xisto verde/anfibolito. A ferropirosmalita descrita no dep?sito de Au-Cu-(?ETR-U) de Igarap? Bahia representa assim um exemplo pouco comum da forma??o desse mineral sob condi??o hidrotermal/magm?tica.In the last years, several works report the presence of pyrosmalite mineral series [(Fe,Mn)8Si6O15(OH,C1)10] commonly associated with volcanic exhalative massive sulphide or Fe-Mn metamorphosed deposits. In this paper, we present the inedit occurrence of ferropyrosmalite in the Au-Cu (+REE-U) of Igarap? Bahia deposit, located in the Au-Cu district of the Caraj?s Mineral Province. We consider the Igarap? Bahia mineralization as being related to the g?nesis of iron-oxide class deposit, like the Olympic Dam type. Ferropyrosmalite occurs in two different contexts: i) associated with carbonate veins; ii) associated with heterolithic breccias, composed by BIF and mafic metavolcanic fragments imersed in a magnetite, ch?lcopyrite, bornite, pyrite, carbonates (calcite to siderite), uranium and REE minerais, and gold, -rich matrix. The growth of ferropyrosmalite is probably due to the substitution of iron rich minerais (chlorite, magnetite and siderite), controled by magmatic fluid influx rich in chlorine. The permeability of breccias and the discontinuity of veins favour fluid percolation. The mode of occurrence of ferropyrosmalite and its relation with amphibole (ferro-hornblende-actinolite) indicate metasomatic growth of the former under temperatures in the transition of greenschist/amphibolite f?cies. The ferropyrosmalite of the Igarap? Bahia deposit represents an uncommom type of occurrence linked to hydrothermal/magmatic conditions

Ediacaran emerald mineralization in Northeastern Brazil : the case of the Fazenda Bonfim deposit

The Fazenda Bonfim emerald deposit lies within the Seridó Belt. It is a classic example of deposit formed through metasomatic interactions between Be-rich granite intrusions and Cr(± V)-rich mafic-ultramafic rocks. The setting of the emerald mineralization was built under strong strike-slip dynamics, which produced serpentinization and talcification of mafic-ultramafic host-rocks, and was followed by syn-kinematic emplacement of Be-rich albite granite, favoring hydrothermal/metasomatic processes. The structural control and lithological-contrast were fundamental to the fluid flow and the best ore-shoot geometry, developed in the S-foliation intra-plane at the contact zone (phlogopite hornfels) between mafic-ultramafic rocks and the albite granite. Subsequently, an albitization process, linked to the final-stage of magmatic crystallization, led to an overall mineralogical and chemical change of the albite granite. 207U-235Pb data revealed inheritance ages from Archean to Neoproterozoic and a crystallization age of 561 ± 4 Ma for albite granite. However, 40Ar/39Ar data revealed plateau age of 553 ± 4 Ma for phlogopite hornfels, interpreted as the closure time for the metasomatic event responsible for the nucleation and growth of emerald crystals. The short interval of time between U-Pb and Ar-Ar data indicates an intense, but not protracted, metasomatic history, probably due to low volume of intrusive magma

Geology, structural control and mineralogy of gold and tungsten mineralized skarn at Bonfim Mine, Borborema Province, Rio Grande do Norte, Brazil.

A Mina Bonfim é caracterizada por camadas de mármores em contato com flogopita xistos subjacentes, ao longo do qual se desenvolveu o escarnito rico em tungstênio e ouro, disposto seguindo a orientação N10ºE/30ºSE, cisalhado e estruturado sob a forma de boudins, em baixo ângulo de caimento (12º) ao longo da direção N10ºE. A scheelita encontra-se nos boudins, associando-se à molibdenita, ambas sendo formadas sob condições sin-tectônicas dúcteis, consistindo na primeira fase de mineralização. O ouro encontra-se em fraturas de cisalhamento tardias, com orientação N70oW/75ºSW, que seccionam e deslocam o escarnito scheelitífero. As fraturas são preenchidas por prehnita (ganga), ouro e minerais de bismuto, indicando que a precipitação do ouro ocorreu na fácies prehnita-pumpelliyta, sob regime dúctil-rúptil, que corresponde à segunda fase de mineralização. O ouro é rico em prata com até 16,09%Ag, e suas formas de ocorrência são: livre na ganga, em fraturas ou em contato com bismuto, bismutinita e joseíta, constituindo a paragênese aurífera. Grãos de ouro exibem bismuto na composição, podendo chegar a 0,44%Bi. O minério está hospedado em escarnito reduzido, gerado em estágios progressivo e retrogressivo, produto do metassomatismo em mármores alterados por fluidos carreados ao longo de estruturas.The Bonfim Mine is characterized by marbles layers in contact with underlying phlogopite schists, along which gold- and tungsten-rich skarns were developed, in N10ºE/30ºSE direction, sheared and structured as boudins plunging 12º to N10ºE. Scheelite is found in the boudins, associated to molybdenite, both being formed under ductile syntectonic conditions, consisting of the first phase of mineralization. Gold is found in late shear fractures, oriented N70ºW/75ºSW, that cut and displace the scheelitiferous skarn. The fractures are filled by prehnite (gangue), gold and bismuth minerals, indicating that gold precipitation occurred in the prehnite-pumpelliyte facies under ductile-brittle regime, which corresponds to the 2nd phase of mineralization. The gold is rich in silver with up to 16.09%Ag and its occurrences are: free in gangue, in fractures and in contact with bismuth, bismuthinite and joséite, constituting auriferous paragenesis. Gold grains show bismuth in its microprobe analyses composition, reaching up to 0.44%Bi. The ore is hosted in a reduced skarn, generated inprogressive and retrogressive stages, the product of metasomatism in marbles altered by fluids carried along the structures

Unveiling the polyphasic evolution of the Neoarchean IOCG Salobo deposit, Carajás Mineral Province, Brazil : Insights from magnetite trace elements and sulfur isotopes

The Salobo iron oxide copper-gold (IOCG) deposit host an important Cu-mineralization of the Carajás Mineral Province. The ore is characterized by an association of (bornite-chalcocite-digenite) hosted by magnetite and biotite-garnet schists. These rocks record distinct stages of superimposed hydrothermal alteration and dynamic metamorphism. Three different occurrences of magnetite constitute the magnetite bodies: a pristine to inclusionpoor Mgt I; inclusion-rich magnetite-bearing breccia Mgt II, and the granoblastic-foliated Mgt III. In general, the magnetite types present a similar trace element composition with some variations in Si, Al, Mg and K indicating that the magnetite types share the same magmatic-hydrothermal origin with post-formation processes (dissolution/reprecipitation) recorded in Mgt III. In addition, sulfur isotope signatures for chalcopyrite (1.3–3.35‰), pyrrhotite (0.88–1.98‰), and pyrite (1.7–5.04‰) associated with magnetite I and II, are consistent with a magmatic-hydrothermal sulfur source at Salobo without/or minimal external sulfur contributions. Our data indicate that ore-forming Auids for Salobo ore could have undergone sulfur disproportionation processes during sulBde formation due to magnetite precipitation, which results in the classic IOCG mineral association of chalcopyrite + magnetite described for the Brst time in this contribution. Therefore, the main mineralization event in the Salobo deposit could be coeval with similar IOCG deposits in the Carajás Mineral Province related to the Neoarchean magmatism at ca. C.7 Ga. SubseDuent deformation and low-grade dynamic metamorphism related to reactivation of the Cinzento Shear Eone (ca. C.5 Ga) and A-type granite emplacement probably Paleoproterozoic in age resulted in remobilization-recrystallization of magnetite and Cu-sulBdes

SUPRIMENTO DE POTÁSSIO E PESQUISA DE USO DE ROCHAS “IN NATURA” NA AGRICULTURA BRASILEIRA

The low natural fertility of soils, the high potassium (K) demand in agriculture, and the reduced Brazilian mineral reserves of K are the causes of the high importation of potassium fertilizers in Brazil. This represents a great and negative impact on Brazil´s trade balance. Forty years ago, trials for utilization of rocks as local K sources did not reach success due to the low natural solubility of minerals or the high cost of industrial processes to obtain fertilizers from them. However, in the last years, other kinds of rocks are promising as K sources, even when applied in natura, just ground. Those findings led to the establishment of a research network to study the potential of using those rocks as K sources nationwide.Conseqüência da baixa fertilidade natural dos solos, da elevada demanda de potássio (K) na agricultura e da reduzida reserva brasileira de minérios de K, a importação de fertilizantes potássicos tem representado grande ônus à balança comercial do País. Há cerca de 30 anos, tentativas de utilização de rochas como fontes locais de K não obtiveram sucesso devido à baixa solubilidade natural dos minerais constituintes ou ao elevado custo dos processos industriais de obtenção de fertilizantes a partir dessas fontes. Entretanto, nos últimos anos, outros tipos de rochas têm se mostrado promissoras no fornecimento de K, mesmo quando aplicadas “in natura”, simplesmente moídas. Isso motivou o estabelecimento de uma rede de pesquisa para estudar o potencial de utilização de tais rochas em âmbito nacional

The Araguaia belt, Brazil : part of a neoproterozoic continental-scale strike-slip.

The Araguaia Belt is part of the Tocantins Orogen, a Neoproterozoic orogen that formed during the collision between the Amazonia, S?o Francisco/Congo and West African Paleo-Continents. This collision contributed to the assembly of West Gondwana. We mapped parts of the Araguaia Belt in its south and central portions in northern Brazil. Our mapping suggests two phases of deformation. The first resulted in the development of N-S trending amphibolite-facies transpresssional structures with a reverse-sinistral movement with vergence towards the Amazonian Craton on the west. The age of this deformation phase is possibly Paleoproterozoic. The second phase generated N-S dextral strike-slip faults that cross-cut older structures. This phase was accompanied by retrograde metamorphism. We propose that these strike-slip faults connect with the east-west trending dextral strike-slip faults in the Borborema Orogen on the northern margin of the S?o Francisco Craton. Movement on faults fringing the Amazonian Craton combined with that of the Araguaia-Borborema strike-slip system, accommodated lateral escape of terranes wedged between the Amazonian and S?o Francisco-Congo Cratons during the Neoproterozoic