Márcia Abrahão Moura

Granite-ore deposit relationships in Central Brazil

Ore deposits related to granitic rocks in Central Brazil are associated with different Paleo- to Mesoproterozoic granite types. Sn and Au are the economic ore elements with important indium concentrations in some tin deposits. Tin mineralization is related to an A-type granite province, in the State of Goias, composed of two distinct granite groups of 1.77 Ga and 1.58 Ga ages. The most important tin deposits are closely related to the younger group, hosted in or near to Li-mica±topaz leucogranites. Despite the chemical differences, both groups are enriched in F, Sn, Rb, Y, Th, Nb, Ga and REE. Their Nb/Ta>1 and their high F/Li ratios allow their classification as a NYF fertile granite association. Recent studies reveal indium concentrations that might be recoverable as by-product of tin. Besides indium minerals and In-bearing phases, cassiterite is the most important indium carrier (0.2–0.4% In). Primary gold mineralization is hosted in oxidized I-type calc-alkaline plutons in the northern Mato Grosso State, with characteristics either of volcanic arc or post-collisional granites. Gold occurs in small high grade vein type deposits or is disseminated in widespread hydrothermal zones with alteration such as sericitization, feldspathization and pyritization. δ34S values between +1.3 and +3.5‰ of associated sulfides are typical of magmatic deposits. The association of gold with oxidized I-type granites and the style of hydrothermal alteration are analogous to those associations present in world-class porphyry-style deposits. Although the tectono-magmagtic setting of these granites is not well understood, such an association constitutes an important target in the search for gold in the northern region of the State of Mato Grosso.

Petrogenetic and mineralization processes in Paleo- to Mesoproterozoic rapakivi granites: examples from Pitinga and Goias, Brazil

Abstract The 1.8 Ga Pitinga granites—Agua Boa and Madeira massifs—in Amazonas (northern Brazil) are within-plate, shallow-level rapakivi granites associated with an extensional fracture system. They comprise an early facies of pyterlitic to wiborgitic rapakivi granite, a fine- to medium-grained biotite granite, as well as topaz granite (Agua Boa massif) and albite granite (Madeira massif). The granites are usually metaluminous to peraluminous, the albite granite, however, is peralkaline. They are enriched in SiO2, K2O, Na2O, F, Rb, Th, Nb, Y, Zr and the rare-earth element (REE) and impoverished in MgO, TiO2, P2O5 and Sr, as the majority of Sn-mineralized granites. Sn contents range from ∼1 ppm in the rapakivi facies to ∼3400 ppm in the albite granite. eNd (at 1.8 Ga) values vary from −2.2 to +0.4 and Nd model ages lie between 2.4 and 2.1 Ga. Mineralization in the Madeira massif includes disseminated magmatic cryolite, zircon, cassiterite, pyrochlore, columbite-tantalite and xenotime and massive cryolite bodies in the F-rich peralkaline albite granite. In the Agua Boa massif, Sn mineralization is associated with greisens and episyenite. The 1.77 Ga (g1) and 1.58–1.57 Ga (g2) rapakivi granites of Goias (central Brazil) are coeval with the Arai rift basin. Granites of the g1 suite are metaluminous and alkaline, while the g2 suite is metaluminous to peraluminous. Both are enriched in F, Sn, Rb, Y, Th, Nb, Ga and the REE. Primary micas range from Fe-rich biotite to zinnwaldite. The micas of the more evolved granites and the metasomatic micas are strongly enriched in F, with F/Li between 2 and 10. The initial eNd values of both suites show a considerable range (∼−14 to 0) and indicate substantial compositional variation in source. Sn deposits in Goias are hosted mainly by greisens. Indium is concentrated in quartz–topaz rock and albitized g2d granite of the Mangabeira massif and is always related to a cassiterite-sulfide association. This quartz–topaz rock is of metasomatic origin, probably generated by a hydrothermal fluid derived from the topaz–albite granite. Mineralization in the studied deposits was essentially associated with F enrichment. In the peralkaline Madeira albite granite, extremely high F contents favored disseminated mineralization, while in the Goias Tin Province (GTP) and Agua Boa massif greisenization was related to early fluid saturation. The GTP and Pitinga granites display tectonic, petrogenetic, geochemical, isotopic and metallogenic similarities that can be applied in search of Sn and rare-metal deposits.

Petrologia e geocronologia do depósito de cobre de Bom Jardim de Goiás (GO)

The Bom Jardim de Goias copper deposit is a remarkable example of a deposit formed in a Neoproterozoic juvenile arc in the South American Platform during the assembly of Gondwana. The deposit is inserted in the western margin of the Arenopolis Magmatic Arc, in the Tocantins Province. The host rocks comprise a volcanosedimentary sequence of intermediate to acid composition interpreted as crystal and ash tuffs. The tuffs represent calc-alkaline volcanism of rhyodacitic to dacitic composition, with lithogeochemical and biotite chemistry characteristic of magmas from intra-oceanic arcs. The tuffs are commonly cut by veins and veinlets with no preferential orientation and show e Nd(t) values between +3.5 and +7.4 and T DM model ages ranging from 0.8 to 1.1 Ga, consistent with juvenile magmas generated in magmatic arc settings. Intrusive bodies in the volcanosedimentary sequence are represented by hornblende-biotite monzogranite, interpreted as Serra Negra Granite, and biotite syenogranite defined as Macacos Granite. The granites have geochemical characteristics of type I calc-alkaline granites, generated in a post-collision setting. Tholeiitic basalts intercalated with tuffs, interpreted as flows, show geochemical affinity with volcanic arc basalts, whereas the dikes that crosscut the granites have compositions characteristic of intra-plate tholeiitic basalts. The petrological data of the host and country rocks of the Bom Jardim de Goias area reveal an important production of calc-alkaline magma in a magmatic arc setting in western Goias around 750 Ma, genetically related to copper mineralization, and the generation of a non-mineralized post-collisional magmatism at 540 Ma.The Bom Jardim de Goias copper deposit is a remarkable example of a deposit formed in a Neoproterozoic juvenile arc in the South American Platform during the assembly of Gondwana. The deposit is inserted in the western margin of the Arenopolis Magmatic Arc, in the Tocantins Province. The host rocks comprise a volcanosedimentary sequence of intermediate to acid composition interpreted as crystal and ash tuffs. The tuffs represent calc-alkaline volcanism of rhyodacitic to dacitic composition, with lithogeochemical and biotite chemistry characteristic of magmas from intra-oceanic arcs. The tuffs are commonly cut by veins and veinlets with no preferential orientation and show eNd(t) values between +3.5 and +7.4 and T DM model ages ranging from 0.8 to 1.1 Ga, consistent with juvenile magmas generated in magmatic arc settings. Intrusive bodies in the volcanosedimentary sequence are represented by hornblende-biotite monzogranite, interpreted as Serra Negra Granite, and biotite syenogranite defined as Macacos Granite. The granites have geochemical characteristics of type I calc-alkaline granites, generated in a post-collision setting. Tholeiitic basalts intercalated with tuffs, interpreted as flows, show geochemical affinity with volcanic arc basalts, whereas the dikes that crosscut the granites have compositions characteristic of intra-plate tholeiitic basalts. The petrological data of the host and country rocks of the Bom Jardim de Goias area reveal an important production of calc-alkaline magma in a magmatic arc setting in western Goias around 750 Ma, genetically related to copper mineralization, and the generation of a non-mineralized post-collisional magmatism at 540 Ma.

Petrology and geochronology of the Bom Jardim de Goiás copper deposit (GO)

The Bom Jardim de Goias copper deposit is a remarkable example of a deposit formed in a Neoproterozoic juvenile arc in the South American Platform during the assembly of Gondwana. The deposit is inserted in the western margin of the Arenopolis Magmatic Arc, in the Tocantins Province. The host rocks comprise a volcanosedimentary sequence of intermediate to acid composition interpreted as crystal and ash tuffs. The tuffs represent calc-alkaline volcanism of rhyodacitic to dacitic composition, with lithogeochemical and biotite chemistry characteristic of magmas from intra-oceanic arcs. The tuffs are commonly cut by veins and veinlets with no preferential orientation and show e Nd(t) values between +3.5 and +7.4 and T DM model ages ranging from 0.8 to 1.1 Ga, consistent with juvenile magmas generated in magmatic arc settings. Intrusive bodies in the volcanosedimentary sequence are represented by hornblende-biotite monzogranite, interpreted as Serra Negra Granite, and biotite syenogranite defined as Macacos Granite. The granites have geochemical characteristics of type I calc-alkaline granites, generated in a post-collision setting. Tholeiitic basalts intercalated with tuffs, interpreted as flows, show geochemical affinity with volcanic arc basalts, whereas the dikes that crosscut the granites have compositions characteristic of intra-plate tholeiitic basalts. The petrological data of the host and country rocks of the Bom Jardim de Goias area reveal an important production of calc-alkaline magma in a magmatic arc setting in western Goias around 750 Ma, genetically related to copper mineralization, and the generation of a non-mineralized post-collisional magmatism at 540 Ma.The Bom Jardim de Goias copper deposit is a remarkable example of a deposit formed in a Neoproterozoic juvenile arc in the South American Platform during the assembly of Gondwana. The deposit is inserted in the western margin of the Arenopolis Magmatic Arc, in the Tocantins Province. The host rocks comprise a volcanosedimentary sequence of intermediate to acid composition interpreted as crystal and ash tuffs. The tuffs represent calc-alkaline volcanism of rhyodacitic to dacitic composition, with lithogeochemical and biotite chemistry characteristic of magmas from intra-oceanic arcs. The tuffs are commonly cut by veins and veinlets with no preferential orientation and show eNd(t) values between +3.5 and +7.4 and T DM model ages ranging from 0.8 to 1.1 Ga, consistent with juvenile magmas generated in magmatic arc settings. Intrusive bodies in the volcanosedimentary sequence are represented by hornblende-biotite monzogranite, interpreted as Serra Negra Granite, and biotite syenogranite defined as Macacos Granite. The granites have geochemical characteristics of type I calc-alkaline granites, generated in a post-collision setting. Tholeiitic basalts intercalated with tuffs, interpreted as flows, show geochemical affinity with volcanic arc basalts, whereas the dikes that crosscut the granites have compositions characteristic of intra-plate tholeiitic basalts. The petrological data of the host and country rocks of the Bom Jardim de Goias area reveal an important production of calc-alkaline magma in a magmatic arc setting in western Goias around 750 Ma, genetically related to copper mineralization, and the generation of a non-mineralized post-collisional magmatism at 540 Ma.

Inclusões fluidas em topázio do Complexo Granítico Estanífero de Massangana (RO)

O complexo granitico de Massangana, localizado na regiao central de Rondonia, sudoeste do Craton Amazonico, Brasil, e um importante exemplo da Provincia Estanifera de Rondonia. Esse complexo possui dimensoes batoliticas, marcantes estruturas anelares relacionadas as sucessivas fases magmaticas e hospeda mineralizacoes de Sn, W, Nb, Ta, topazio e berilo associadas a pegmatitos. Esse trabalho apresenta a composicao quimica e as condicoes minimas de aprisionamento dos fluidos nos cristais de topazio encontrados no complexo granitico estanifero de Massangana. O topazio, de cor azul, apresenta qualidade gemologica e possui cinco grupos de inclusoes fluidas de natureza H2O-NaCl, cuja salinidade equivalente varia de 3,4 a 11,7% em peso de NaCl, densidade em torno de 0,75g/cm3 e temperatura de homogeneizacao total (Th) entre 320 e 350oC. Devido a intima associacao do topazio com cassiterita, wolframita e columbita-tantalita nos corpos pegmatiticos, admite-se que esse intervalo de Th tambem corresponda ao intervalo minimo de cristalizacao desses outros minerais metalicos. Considerando que os pegmatitos no complexo granitico de Massangana estao associados as ultimas fases magmaticas, e provavel que a profundidade de posicionamento desses corpos pegmatiticos seja inferior a 3 km e a uma pressao estimada entre 1 e 1,5 kbar.