Publication details
Two types of scapolite in Evate carbonatite deposit (Mozambique): implications for magmatic versus metamorphic origins
| Authors | |
|---|---|
| Year of publication | 2019 |
| Type | Article in Periodical |
| Magazine / Source | Acta Geologica Slovaca |
| MU Faculty or unit | |
| Citation | |
| web | http://www.geopaleo.fns.uniba.sk/ageos/articles/abstract.php?path=gajdosova_et_al&vol=11&iss=2 |
| Keywords | scapolite; Evate deposit; Mozambique |
| Description | Two types of scapolite occur in the Evate carbonatite deposit – the largest resource of apatite in south-east Africa. Calc-silicate rocks composed of amphiboles (hastingsite, hornblende, actinolite, and pargasite), diopside, Ba-rich phlogopite, allanite, epidote, apatite, K-feldspar, titanite, and minor calcite, also contain scapolite with 62–74 mol. % of meionite – (Me) end-member, XCl = 0.06–0.17 and the crystallochemical formula corresponding to (Ca2.46–2.99Na1.00–1.47)?4.00–4.20Al4.62–5.04Si6.95–7.37O24(Cl0.06–0.17S0.18–0.26C0.64–0.70)?1.00. In contrast, carbonatite contains scapolite ranging from Na meionite to Ca marialite with 46–63 mol. % Me, XCl = 0.19–0.47 and the crystallochemical formula (Na1.43–2.07Ca1.82–2.50)?3.97–4.11Al4.29–4.73Si7.27–7.70O24(Cl0.19–0.47S0.00–0.25C0.45–0.74)?1.00. The chemical composition of scapolites mirrors the complex history and multistage evolution of the Evate deposit. The low-Cl, high-S scapolites from calc-silicate rocks are chemically indistinguishable from metamorphic scapolites, whereas the Cl-rich scapolite from carbonatite is interpreted as magmatic in origin. The gradual Cl enrichment reflects an increasing NaCl activity in the scapolite-forming fluid or melt. Both scapolite types are closely associated with amphibole and phlogopite, thus indicating amphibolite-facies conditions during retrograde stages of Late-Proterozoic (Ediacaran) granulite-facies metamorphism and/or Ordovician reactivation. |