| Texto completo | |
| Autor(es): |
Trumbull, R. B.
[1]
;
Garda, G. M.
[2]
;
Xavier, R. P.
[3]
;
Cavalcanti, J. A. D.
[4]
;
Codeco, M. S.
[1]
Número total de Autores: 5
|
| Afiliação do(s) autor(es): | [1] GFZ German Res Ctr Geosci, Potsdam - Germany
[2] Univ Sao Paulo, Inst Geociencias, Sao Paulo - Brazil
[3] Univ Estadual Campinas Unicamp, Inst Geociencias, Campinas, SP - Brazil
[4] Serv Geol Brasil CPRM, Belo Horizonte, MG - Brazil
Número total de Afiliações: 4
|
| Tipo de documento: | Artigo Científico |
| Fonte: | MINERALIUM DEPOSITA; v. 54, n. 3, p. 395-414, MAR 2019. |
| Citações Web of Science: | 4 |
| Resumo | |
Tourmaline at Passagem de Mariana forms three associations: stratiform tourmalinite (T1), wall-rock alteration around quartz-sulfide veins (T2), and clusters within the veins (T3). The major-element composition of tourmaline is similar in all, with Mg/(Mg+Fe) from 0.59 to 0.83 (mean 0.69 +/- 0.03) and total Al contents from 6.2 to 6.6 atoms per formula unit (apfu). The Y-site Al (0.2-0.6apfu) is charge-balanced by the exchange NaMg(Al?)(-1). Tourmalinite type (T1) is unzoned, whereas T2 and T3 grains display increasing Ti and Ca from core to rim. In situ trace-element analyses of T1 grains were prohibited by grain size and inclusions. The T2 and T3 tourmaline have similar trace-element values, except higher concentrations of Zn, Cu, and Co in T3, which is consistent with its location in the mineralized veins. The B-11 values of T1 and T2 tourmaline range from -17.8 to -9.7 parts per thousand, with indistinguishable mean values (-13.9 +/- 1.9 and -13.8 +/- 1.6 parts per thousand, respectively), supporting field evidence that T1 tourmalinite is hydrothermal. The B-11 values of T3 tourmaline are about 5 parts per thousand higher (mean -8.9 +/- 1.3 parts per thousand), which we ascribe to depletion of B-10 in the vein fluid due to tourmalinization of wall rocks. This implies that the initial B-11 value of hydrothermal fluid was about -11 parts per thousand (for 400 degrees C and the T1-T2 mean B-11=-14 parts per thousand). This indicates a crustal boron source but is otherwise non-specific. Based on geological arguments, we favor a source in the Minas Supergroup metasedimentary units hosting the deposit. (AU) | |
| Processo FAPESP: | 05/56651-3 - Estudo comparativo da gênese dos turmalinitos e das rochas e veios de quartzo ricos em turmalina associados a mineralizações de ouro e metais-base no contexto do Quadrilátero Ferrífero (MG) e Faixa Ribeira (SP) |
| Beneficiário: | Gianna Maria Garda |
| Modalidade de apoio: | Auxílio à Pesquisa - Regular |
| Processo FAPESP: | 07/53895-4 - Isotopia do boro em turmalina de turmalinitos e rochas e veios de quartzo ricos em turmalina do anticlinal de Mariana (MG) e cinturão Ribeira (SP), SE do Brasil |
| Beneficiário: | Gianna Maria Garda |
| Modalidade de apoio: | Bolsas no Exterior - Pesquisa |