The study of granite rocks is important in order to understand chemical evolution of the continental crust. Their isotopic composition provides information on their magmatic sources, whether being mantle, crust or a mixture of both. In the SW border of the Amazonian Craton, suites of rapakivi granites related with tin-polymetallic mineralization are emplaced within heterogeneous Proterozoic crust. Zircons from eleven rocks from three granite intrusions, Massangana, São Carlos and Caritianas, representative of the Younger Granites of Rondônia have been studied by using laser ablation inductively coupled plasma source mass spectrometry (LA-ICP-MS) in order to obtain U-Pb ages and Hf isotopic compositions. The samples from Massangana massif, show greater range in age (between 1026 -993 Ma) and initial 176 Hf/ 177 Hf = 0.2817-0.2823. The ԐHf values are both negative and positive (-6.2 to +3.4) in some samples, and only negative in others (-14.1 to -1.6) which reflects the heterogeneity of sources. The TDM age varying between 2.40 to 1.61 Ga also indicates that different sources were involved in the formation of these rocks. The samples from São Carlos massif show U-Pb ages between 996 to 974 ± 10 Ma and initial ԐHf between -15 and +11, corresponding to a TDM age range between 2.65 and 1.08 Ga. The samples from Caritianas massif with U-Pb ages of 1001 and 999 Ma, show more initial ԐHf positive values (13 zircon grains) than negative (6 zircon grains), different from the other massifs. The range of initial ԐHf of the Caritianas massif is -1.5 to +8.2, and residence crustal ages between 1.76 and 1.25 Ga. The great variation in the ԐHf values indicates heterogeneity of sources; the Massangana and São Carlos massifs represent mainly crustal melts with a subordinate mantle contribution. The Caritianas massif, which shows more positive values of the ԐHf parameter, seems to have had more mantle contribution than the other massifs studied here. The characterization of the sources of the rapakivi rocks may play an important role in the genesis of cassiterite ore and could represent an important tool for mineral exploration.

A Suíte Intrusiva Rondônia (990 a 998 Ma) é representada por um magmatismo tipo-A rapakivítico que ocorreu no SW do Cráton Amazonas com mineralizações em Sn, Nb, Ta, W e topázio associadas. Este estudo apresenta dados petrográicos e litogeoquímicos dos Maciços Massangana, São Carlos e Caritianas, integrantes da Suíte Intrusiva Rondônia com o objetivo de caracterizar a petrograia e geoquímica destes maciços para melhor compreender sua evolução magmática. As amostras analisadas são granitoides de granulação grossa a muito grossa, por vezes poriríticas. Também ocorrem com frequência microgranitos, intrudidos na forma de diques e enclaves. A mineralogia principal é composta por quartzo, k-feldspato (microclínio e/ou ortoclásio), plagioclásio intersticial, biotita e/ou hornblenda. Como minerais acessórios são descritos principalmente zircão, titanita e minerais opacos, além de luorita e allanita de forma mais restrita. Quimicamente são classiicadas como granitos do tipo-A, metaluminosos a fracamente peraluminosos de ambiente intraplaca e do tipo A2 reduzidos. Apresentam anomalias negativas acentuadas em Ba, Sr e Ti, além de enriquecimento em Rb e Th com relação a Ta e Nb e em Ce e Sm com relação aos demais elementos, características típicas de granitos do tipo-A formados em ambiente anorogênico na fase de estabilização do Cráton Amazonas.

Beryl is usually found in granite-pegmatite systems. The addition of chromophore elements (V, Cr, Mn, Fe) into the crystalline structure favors color changes in beryl and thus generates some of the world's expensive gems such as emerald, morganite, heliodor and aquamarine. The Massangana polyphasic batholith is a well-known cassiterite, wolframite and gems deposit in the Rondônia state. These metals and blue-gems (topaz and aquamarine) are located in feldspar-rich pegmatite granite bodies. The aquamarine crystals show color ranging from light-to medium-blue and display concentric growth zones. Electron-probe microanalyses revealed that the Fe is the main chromophore element, occupying the octahedral Al-site, while Na had an important role in the charge balance, inserted in the channel sites together with H 2 O. The irregular supply of Fe and Na during the nucleation and growth of aquamarine was the main cause for the color change. A fluid inclusion study indicated that the aquamarine growth under an aqueous fluid system (H 2 O-NaCl), with low salinity, low density and total homogenization temperature between 243 o -315 o C, is compatible with final temperatures in the pegmatite pocket zone.

Rondônia intrusive suites represent the youngest A-type magmatism that occurred in the SW of the Amazon craton, with mineralizations in Sn, Nb, Ta, W, and topaz. Petrological and isotopic studies (U-Pb and Lu-Hf by LA-ICP-MS) allowed the Massangana granite to be subdivided into São Domingos facies (medium to fine biotite-granite), Bom Jardim facies (fine granite), Massangana facies (pyterlites and coarse granites) and Taboca facies (fine granites). The crystallization ages obtained were between 995.7 ± 9.5 Ma to 1026 ± 16 Ma, and the εHf values vary significantly between positive and negative, showing predominantly crustal sources for forming these rocks. Petrographic studies on ore samples indicate the action of co-magmatic hydrothermal fluids enriched in CO2, H2O, and F. These ores are characterized by endogreisens, exogreisens, pegmatites, and quartz veins that are explored in the São Domingos facies area. The endogreisens and exogreisens are formed by topaz-granites and zinnwaldite-granites; the pegmatites are formed by topaz-zinnwaldite-cassiterite-granites; and the veins by cassiterite-sulfides and quartz. The geometries of the mineralized bodies indicate a dome-shaped contact with the host rocks in the magma chamber and can be attributed to residual accumulation. In this sense, the origin of these ores is related to the evolution of intrusive granitic bodies where the terminal phases of the fluid-enriched magma are lodged in the apical portions, and the origin of the mineralized bodies present a biotite-granite, albite-granite, and endogreisens evolution (potassium series), or biotite-granite, alkali-granite and endogreisens (sodic series) and these rocks present TDM ages that indicate a concerning relation to the non-mineralized rocks of Massangana granite.