Zolotarevite (IMA2020-076), ideally Na5Zr[Si6O15(ОН)3]⋅2–3H2O, is а new mineral of the lovozerite group. The mineral was found in a leucocratic nepheline syenite from Kedykverpakhk Mt., Lovozero alkaline massif, Kola Peninsula, Russia. It occurs as anhedral grains up to 1 mm across and is associated with microcline–perthite, nepheline, sodalite, aegirine, lamprophyllite, lueshite, umbozerite, lomonosovite, nastrophite, a mineral of the kazakovite–tisinalite series, sphalerite and löllingite. Zolotarevite is cherry red, with a vitreous lustre and white streak. The mineral is brittle, with a Mohs hardness of 5. Cleavage was not observed; the fracture is uneven. The measured density is 2.75(5) g⋅cm–3, the density calculated using the empirical formula and single-crystal unit-cell parameters is 2.85 g⋅cm–3. Zolotarevite is anomalously biaxial (–), α = 1.580(2), β = 1.600(2) and γ = 1.602(2) (for λ = 589 nm); 2Vmeas < 10°. Chemical data (electron microprobe, wt.%) are: Na2O 20.41, СаО 0.42, MnO 3.49, Fе2O3 0.55, SiO2 52.46, ТiO2 1.34, ZrO2 11.33, H2O (calculated from the structural formula) 10.20, total 100.20. The empirical formula based оn 6 Si atoms per formula unit is Na4.53Zr0.63Mn0.34Ti0.11Ca0.05Fe3+0.05Si6O14.43(ОН)3.56(H2О)2.11. Zolotarevite is trigonal, space group R${\bar 3}$m, with a = 10.294(6) Å, c = 13.115(8) Å, V = 1203.7(16) Å3 and Z = 3. The crystal structure was solved from single-crystal data and refined to R1 = 0.049. The strongest lines of the powder X-ray diffraction pattern [d in Å (I) (hkl)] are: 7.37 (69) (101); 5.26 (56) (012); 3.686 (64) (202); 3.330 (79) (113); 3.265 (99) (211), 2.640 (100) (024) and 2.576 (60) (220). Zolotarevite is unique in that it is a highly hydrated lovozerite-group mineral with the B site occupied by variable amounts of H2O.

The nepheline syenites of the Pilansberg alkaline complex (South Africa) have undergone extensive subsolidus equilibration and alteration with a deuteric Cl- and Na-rich fluid phase. Complex assemblages of secondary minerals result from the replacement of primary alummosilicates, rinkite, eudialyte and fluorapatite. The composition of apatite group minerals formed during these alteration processes reflects the Sr- and rare earth element (REE) content, Na/Cl ratio and pH of the deuteric fluids. Apatite-group minerals are observed to have formed in the following sequence: orthomagmatic fluorapatite; strontian britholite-(Ce); strontian fluorapatite; Sr-apatite; REE-rich Sr-apatite; Sr-Na-REE- rich minerals approaching the stoichiometry of belovite-(Ce) and deloneite-(Ce); britholite-(Ce). Increasing alkalinity of the deuteric fluids is reflected by increasing amounts of Sr replacing Ca in apatite and culminates in the formation of Sr apatite containing 62.1 wt.% SrO (∼4.17 a.p.f.u. Sr). Pilansberg apatite-group minerals form a near-complete solid solution between fluorapatite and a fluorine analogue of Sr apatite with limited solution towards belovite-(Ce), Si-rich belovite-(Ce) and strontian britholite-(Ce).

The Older Giant Dyke Complex is a differentiated alkaline intrusion of Proterozoic age (1154±16 Ma) and is the earliest of the late Gardar intrusions in the Tugtutôq-Ilímaussaq region. The dyke is approximately 20 km long by 0·5 km broad and comprises (i) marginal ‘border group’ rocks of alkali olivine gabbro, grading inwards to ferro-syenogabbro and (ii) an axial ‘central group’ of salic rocks ranging from augite syenite in the WSW to sodalite foyaite in the ENE.

Chilled margins contain plagioclase (An53), olivine (Fo53), magnetite, ilmenite, and apatite as liquidus phases and later-crystallized augite (Di69Hd27Ac4) and biotite (Annite32). The coexisting Fe-Ti oxides indicate fO2 and T values just below the synthetic QFM buffer curve. In the border group, plagioclase cores zone into anorthoclase and soda-sanidine rims, olivines reach Fo16, pyroxenes Di32Hd59Ac9, and biotites Annite86. Interstitial pargasitic amphibole appears close to the innermost margins. In the central group, feldspars are all perthitic alkali feldspars and nepheline becomes a major, early crystallizing phase. Olivines range from Fo10-Fo4, in the augite-syenites where they coexist with ferro-salites Di50Hd47Ac3, but olivine is absent from foyaitic assemblages in which the pyroxenes range through aegirine-augite to pure aegirine. Interstitial amphiboles range from ferro-pargasite or hastingsite to katophorite and thence towards arfvedsonite, but are absent from the most differentiated rocks, whereas biotite occurs throughout the entire group in the range Annite71-Annite100.

The parental magma, represented by the chilled margins, was a relatively anhydrous alkali olivine-basalt with an initial 87Sr/86Sr ratio of 0.70326. Its high Ti, P, Ba, and F contents are inferred to be features inherited from a primary magma, derived from the mantle as a small partial melt fraction which involved significant amounts of fluor-apatite and phlogopite. While all lithologies are considered as differentiates from this parental magma, there is both a well-defined field junction and a compositional hiatus between the border group and the central group rocks. Mineralogical considerations and REE patterns suggest that the later, more salic (?benmoreitic) magma from which the central group crystallized, related to the parental magma by ol-fsp-ap-FeTi oxide fractionation. Congelation in both border group and central group occurred by side-wall crystallization, but the salic magma became compositionally stratified, with upward concentration of alkalis and volatiles to produce a phonolitic upper facies which is preserved at the ENE end of the intrusion owing to subsequent axial tilting.