Genthelvite from pegmatite veins hosted by the albite-enriched granite (ca.1.8 Ga) corresponding to the Sn–Nb–Ta (F, REE, Li, Zr, U, Th) Madeira deposit, Amazonas, Brazil was studied. Genthelvite, the exclusive Be-bearing mineral within the deposit, occurs as massive crystals of up to 4.7 cm in size. Compositions are homogeneous within individual crystals, although there is moderate variation in the overall composition reflecting relatively limited substitutions within the helvine–genthelvite–danalite solid-solution series, with relatively high Zn contents (36.96 to 49.45 wt.% ZnO), lower Mn contents (0.61 to 3.03 wt.% MnO), and variable Fe contents (2.10 to 10.94 wt.% FeO), completing an existing compositional gap in this system. Genthelvite formed in an alkaline and subaluminous environment, under stable conditions within the late-evolved fluids, at relatively high temperature (>400°C), in a reducing environment. The extremely high concentration of fluorine in the magma and the crystallisation of magmatic galena resulted in an effective reduction of H2S fugacity. This resulted in the stabilisation of genthelvite during the transition from the late magmatic to early hydrothermal stages of the albite-enriched granite evolution. The variability in Fe content within genthelvite is associated primarily with localised variations in the mineral assemblage (e.g. the presence of riebeckite and polylithionite). Genthelvite was altered by low-temperature aqueous fluids rich in F which resulted in the incorporation of Fe, Mn, Mg, Pb, Ba, Na, K, U and REE into the Zn2+ structural site and the allocation of excess Si, Al, Ti and P in the IVSi and IVBe structural sites. The substantial content of U and REE substituting for Zn, together with Si substituting for Be, is charge balanced by the presence of vacancies at the A site.

研究了源自巴西亚马逊州 Sn-Nb-Ta（F、REE、Li、Zr、U、Th）马德拉矿床的富含钠长石花岗岩（约 1.8 Ga）的伟晶岩脉中的辉云石。根铁矿是矿床中唯一的含铍矿物，以尺寸达 4.7 厘米的块状晶体形式出现。单个晶体内的成分是均匀的，尽管整体成分存在适度的变化，反映出在镁铝石-辉绿石-钠长石固溶体系列中相对有限的取代，具有相对较高的 Zn 含量（36.96 至 49.45 wt.% ZnO），较低的 Mn 含量（0.61 至 3.03 wt.% MnO）和可变的 Fe 含量（2.10 至 10.94 wt.% FeO），弥补了该系统中现有的成分差距。辉绿石是在碱性和亚铝环境中、在后期演化流体内的稳定条件下、在相对较高的温度（>400°C）、在还原环境中形成的。岩浆中极高浓度的氟和岩浆方铅矿的结晶导致H 2 S逸度的有效降低。这导致了在富钠长石花岗岩演化过程中从岩浆晚期到热液早期阶段过渡过程中，闪锌矿的稳定化。辉绿岩中铁含量的变化主要与矿物组合的局部变化有关（例如利贝克石和聚锂矿的存在）。氢锌矿被富含F的低温水流体蚀变，导致Fe、Mn、Mg、Pb、Ba、Na、K、U和REE掺入Zn 2+结构位点，并分配过量的Si、Al 、Ti 和 P 位于IV Si 和IV Be 结构位点。取代 Zn 的 U 和 REE 的大量含量，以及取代 Be 的 Si，通过 A 位空位的存在实现电荷平衡。