Pre-Pegmatite Stage in Peralkaline Magmatic Process: Insights from Poikilitic Syenites from the Lovozero Massif, Kola Peninsula, Russia

The Lovozero peralkaline massif (Kola Peninsula, Russia) is widely known for its unique mineral diversity, and most of the rare metal minerals are found in pegmatites, which are spatially associated with poikilitic rocks (approximately 5% of the massif volume). In order to determine the reasons for this relationship, we have investigated petrography and the chemical composition of poikilitic rocks as well as the chemical composition of the rock-forming and accessory minerals in these rocks. The differentiation of magmatic melt during the formation of the rocks of the Lovozero massif followed the path: lujavrite → foyaite → urtite (magmatic stage) → pegmatite (hydrothermal stage). Yet, for peralkaline systems, the transition between magmatic melt and hydrothermal solution is gradual. In the case of the initially high content of volatiles in the melt, the differentiation path was probably as follows: lujavrite → foyaite (magmatic stage) → urtitization of foyaite → pegmatite (hydrothermal stage). Poikilitic rocks were formed at the stage of urtitization, and we called them pre-pegmatites. Indeed, the poikilitic rocks have a metasomatic texture and, in terms of chemical composition, correspond to magmatic urtite. The reason for the abundance of rare metal minerals in pegmatites associated with poikilitic rocks is that almost only one nepheline is deposited during urtitization, whereas during the magmatic crystallization of urtite, rare elements form accessory minerals in the rock and are less concentrated in the residual solution.

Zircon Genesis and Geochronology for the Zhangbaoshan Super-Large Rubidium Deposit in the Eastern Tianshan, NW China: Implication to Magmatic-Hydrothermal Evolution and Mineralization Processes

The Zhangbaoshan (ZBS) super-large Rubidium deposit, located in the Eastern Tianshan, is a typical granite-type Rb deposit. The ZBS deposit is mainly hosted in the highly evolved Baishitouquan (BST) pluton enriched in F and Rb, which exhibits five lithological zones from the bottom to the top: leucogranite (zone-a), amazonite-bearing granite (zone-b), amazonite granite (zone-c), topaz-bearing amazonite granite (zone-d) and topaz albite granite (zone-e), as well as minor small lodes of amazonite pegmatite. Two types of zircon were identified from the BST pluton. Type-I zircons mainly occur in the zone–a, are characterized by obvious oscillatory zoning, high Zr contents (47.4–67.3 wt% ZrO2) and Zr/Hf ratios (21.72–58.23), low trace element concentrations, and heavy rare earth elements (HREE)–enriched patterns with prominent positive Ce anomalies (Ce/Ce* = 1.21–385) and strong negative Eu anomalies (Eu/Eu* = 0.008–0.551), indicative of early magmatic zircon. Type–II zircons mainly occur in the upper zones (zone-c to zone-e), exhibit porous and dark Cathodoluminescence images, inhomogeneous internal structure, plenty of mineral inclusions, low Zr (38.7–51.0 wt% ZrO2) and Zr/Hf ratios (3.35–11.00), high Hf (34,094–85,754 ppm), Th (718–4,980 ppm), U (3,540–32,901 ppm), Ta (86.7–398 ppm), Y (1,630–28,890 ppm) and rare earth elements (REEs) (3,910–30,165 ppm), as well as slightly HREE–enriched patterns and significant M–type tetrad patterns with t3 values (quantification factor of tetrad effect) of 1.51–1.69. It is suggested that the type–II zircons are crystallized from a deuteric F–rich fluid coexisted with the highly evolved residual magma during the transition from the magmatic to the F–rich hydrothermal stage of the BST pluton. The F–rich fluid exsolution during the magmatic–hydrothermal transition is one of the most important factors controlling the modification of highly evolved granite and related Rb enrichment and mineralization. The type–I zircon samples from zone–a yield concordant ages of 250 ± 2.5 Ma and 250.5 ± 1.7 Ma, respectively, indicating that the BST pluton was emplaced in the Early Triassic. The type–II zircons from zone–c to zone–e yield lower intercept U–Pb ages between 238 and 257 Ma, which may represent the age of F–rich fluid–melt interaction during the transition from the magmatic to the hydrothermal stage. The mineralization of the ZBS super–large Rb deposit should have occurred shortly after emplacement of the BST pluton in the Early Triassic. Combined with available data, it is suggested that the Triassic is an important period for granitic magmatism and rare metal metallogeny in the Eastern Tianshan.

Gemology, Mineralogy, and Spectroscopy of an Attractive Tremolitized Diopside Anorthosite Gem Material from the Philippines: A New Type of Material with Similarities to Dushan Jade

In recent years, a new type of material called Philippines “Dushan jade” has appeared in the gemstone market in China. This new type of material, very similar in appearance and physical properties to Dushan jade, an important ancient jade with a long history in China, is causing confusion in the market and poses identification difficulties. Microscopy, electron probe microanalysis, Fourier transform infrared (FTIR) spectroscopy, Raman microprobe spectroscopy, and ultraviolet-visible (UV-Vis) spectroscopy were used to study the gemology, mineralogy, and spectroscopy of rock samples from the Philippines in order to differentiate them from Dushan jade. The studies showed that Philippines rock is composed mainly of anorthite and minor amounts of diopside, tremolite, uvarovite, titanite, chromite, zoisite, prehnite, thomsonite-Ca, and chlorite, among which uvarovite, diopside, and tremolite are the main color causing minerals. The origin of the color is related to the electronic transitions involving Cr3+, Fe2+, Fe3+, and charge transfer between the ions. The paragenetic mineral formation sequence of Philippines rock can be divided into three stages: (1) the magmatic stage: anorthite phenocryst, diopside, chromite, and titanite are formed first in the magma; (2) the metamorphic stage: anorthite phenocryst undergo fracture and recrystallization; the early fluid intrusion transforms diopside into tremolite forming uvarovite-grossular-andradite solid-solution around the anorthite and chromite; and (3) the late hydrothermal stage: the late hydrothermal solution fills in fractures with prehnite, thomsonite-Ca, and zoisite being formed. From the comparison studies, it was established that Philippines rock and Dushan jade are two completely different type of material. Philippines rock should be called “tremolitized diopside anorthosite”.

Bismuth Minerals from the Intragranitic La Elsa NYF Pegmatite, Potrerillos Granite, Argentina: Monitors of Fluid Evolution from Magmatic to Hydrothermal Stage

ABSTRACT The NYF La Elsa pegmatite forms a subcircular, ∼30 m long, ∼20 m wide body enclosed in the parental Potrerillos granite, Las Chacras-Potrerillos batholith, Argentina. The pegmatite has a typical zonal internal structure with a volumetrically significant quartz core and pods of magmatic fluorite. Along with biotite, mostly in the outer units, tourmaline (schorl, fluor-schorl) is common to abundant in most pegmatite units. Accessory minerals include common strongly hematitized ilmenite and rare euhedral crystals of bismuthinite, up to 2 cm long, occurring at the transition between the blocky zone and the quartz core. The bismuthinite was significantly replaced by bismutite I according to the reaction Bi2S3(s) + CO2(aq) + 6O2(aq) + 3H2O(l) = Bi2CO3O2(s) + 3H2SO4(aq). Subsequently, bismutite I was replaced by bismutite II and kettnerite. The former requires an influx of Ca and F and its formation can be characterized by the reaction Bi2CO3O2(s) + 2Ca2+(aq) + 2F–(aq) + CO32–(aq) = 2CaBiCO3OF(s). At the late hydrothermal stages bismutite was replaced by clinobisvanite/pucherite during influx of V according to the reaction Bi2CO3O2s + 2H3VO4(aq) = 2BiVO4(s)+ CO2(aq) + 3H2O(l). All Bi minerals are close to the ideal formulae with only minor Pb and ±Cu in bismuthinite and its secondary products. The crystallization sequence of Bi minerals is magmatic bismuthinite (S2–) → early hydrothermal bismutite I (CO32–) → medium stage bismutite II + kettnerite (CO32–, F–) → late stage clinobisvanite, pucherite (VO43–). Pegmatite-derived early subsolidus fluids were enriched in CO2, which was confirmed by confocal Raman microspectroscopy of fluid inclusions in quartz and caused breakdown of bismuthinite to bismutite. Calcium and F, necessary for kettnerite formation, were released during alteration of magmatic fluorite at acidic conditions. Vanadium was supplied by meteoritic H2O enriched in elements from altered magmatic minerals (biotite, ilmenite), either from the pegmatite or from the host granite.

Měděná mineralizace z Horní Halže u Měděnce v Krušných horách (Česká republika)

An interesting copper mineralization has been discovered in fragments of hydrothermal quartz gangue found in dump material of the abandoned unnamed gallery 1.5 km S from Horní Halže (now part of the Měděnec village), the Krušné hory Mts., Czech Republic. The primary mineralization represented by fine-grained quartz, hematite, pyrite and probably also djurleite was intensively affected by supergene processes. Djurleite and pyrite are partly replaced by Cu sulphides - roxbyite, anilite, spionkopite and covellite. The origin of association bornite/half-bornite/anilite found in some samples can be analogous, although in this case it cannot be ruled out that it may be the result of decomposition of the original solid solution (against the ideal bornite clearly enriched in Cu) formed in the hydrothermal stage. The formation of other Cu minerals (malachite, brochantite, libethenite and pseudomalachite) and goethite is already clearly bound to supergene conditions, part of malachite and brochantite was then formed by (sub)recent weathering of Cu-sulphides in the mine dump material. The detailed descriptions, X-ray powder diffraction data, refined unit-cell parameters and quantitative chemical composition of individual studied mineral phases are presented.

Trace and Rare Earth Elements, and Sr Isotopic Compositions of Fluorite from the Shihuiyao Rare Metal Deposit, Inner Mongolia: Implication for Its Origin

Abundant fluorites occur in the Shihuiyao rare metal (Nb-Ta-Rb) deposit in Inner Mongolia of NE China, and they can be classified by their occurrence into three types. Type I occurs disseminated in greisen pockets of albitized granite. Type II occurs in the skarn zone between granite and carbonate host rocks, and it can be subdivided into different subtypes according to color, namely dark purple (II-D), magenta (II-M), green (II-G), light purple (II-P), and white (II-W). Type III are the fluorite-bearing veins in the silty mudstones. On the basis of petrography of the fluorites and their high contents of HFSEs (high field strength elements) and LILEs (large ion lithophile elements), strong negative Eu anomalies, and tetrad effects, we suggest that Type I fluorites crystallized in a late-magmatic stage with all the components derived from the granite. The high Y/Ho ratios suggest that the Type II fluorites crystallized in the early- or late-hydrothermal stage. The rare earth elements (REEs) characterized by various Eu anomalies of the Type II fluorites indicate a mixed origin for ore-forming metals from granite-related fluids and limestones, and the oxygen fugacity increased during fluid migration and cooling. Compared to the Type II fluorites, the similar trace element contents of the Type III suggest a similar origin, and remarkable positive Eu anomalies represent a more oxidizing environment. The Sr isotopic composition (87Sr/86Sr)i = 0.710861) of the Type I fluorites may represent that of the granite-derived fluids, whereas the (87Sr/86Sr)i ratios of the Type II (0.710168–0.710380) and Type III (0.709018) fluorites are lower than that of the Type I fluorites but higher than those of the Late Permian-Early Triassic seawater, suggesting a binary mixed Sr source, i.e., granite-derived fluids and marine limestones. Nevertheless, the proportion of limestone-derived Sr in the mixture forming the Type III fluorites is much higher than that of Type II. The rare metal Nb and Ta get into the granite-derived F-rich fluids by complexing with F and precipitate in the form of columbite-group minerals after the Type I fluorites crystallize. Most of Nb and Ta may have deposited as columbite-group minerals during the magmatic stage, resulting in no Nb-Ta mineralization in the hydrothermal stage when the Type II and III fluorites formed. Hence, the Type I fluorites in the Shihuiyao mining area can be used as an important exploration tool for the Nb-Ta mineralization.

Distribution of Gold and Associated Ore-Bearing Elements in Gold-Copper-Pyrite Ores of the Kyzylbulag Deposit (Lesser Caucasus, Azerbaijan)

The article presents the results of studies of the distribution of gold and associated ore elements in gold-copper pyrite ores of the Kyzylbulag deposit. It was established that the elemental composition of ores and host rocks of the deposit includes Cu, Pb, Au, Ag, Ni, As, Sb, Bi, and Mo, of which Au, Cu, Ag, and Zn are the more stable. The behavior of elements was also studied for the entire ore body, as a result of which they are divided by cluster analysis at R (5 %) - 0.1 into two groups: 1) Au, Cu and Ag; 2) Pb and Zn. The closest relationship in the first group was found between Au and Cu, Au and Ag, Ag and Cu; and in the second, between Pb and Zn. Acquired results confirm that gold and the copper are the major components of ore in the field expressed generally in the mineral paragenesis of chalcopyrite - native gold shown in the independent hydrothermal stage of ore deposition.

Mineralogy of a High-Temperature Skarn, in High CO2 Activity Conditions: The Occurrence from Măgureaua Vaţei (Metaliferi Massif, Apuseni Mountains, Romania)

A shallow-level monzodioritic to quartz-monzodioritic pluton of the Upper Cretaceous age caused contact metamorphism of Tithonic–Kimmeridgian reef limestones at Măgureaua Vaţei (Metaliferi Massif, Apuseni Mountains, Romania). The preserved peak metamorphic assemblage includes gehlenite (Ak 33.64–38.13), monticellite, wollastonite-2M, Ti-poor calcic garnet, and Ca-Tschermak diopside (with up to 11.15 mol.% Ca-Tschermak molecule). From the monzodioritic body to the calcitic marble, the periplutonic zoning can be described as: monzodiorite/agpaitic syenite-like inner endoskarn/wollastonite + perovskite + Ti-poor grossular + Al-rich diopside/wollastonite + Ti-poor grossular + diopside + vesuvianite/gehlenite + wollastonite + Ti poor grossular + Ti-rich grossular (outer endoskarn)/wollastonite + vesuvianite + garnet (inner exoskarn)/wollastonite + Ti-rich garnet + vesuvianite + diopside (outer exoskarn)/calcitic marble. Three generations of Ca garnets could be identified, as follows: (1) Ti-poor grossular (Grs 53.51–81.03 mol.%) in equilibrium with gehlenite; (2) Ti-rich grossular (Grs 51.13–53.47 mol.%, with up to 19.97 mol.% morimotoite in solid solution); and (3) titanian andradite (Grs 32.70–45.85 mol.%), with up to 29.15 mol.% morimotoite in solid solution. An early hydrothermal stage produced retrogression of the peak paragenesis toward vesuvianite, hydroxylellestadite (or Si-substituted apatite), clinochlore, “hibschite” (H4O4-substituted grossular). A late hydrothermal event induced the formation of lizardite, chrysotile, dickite, thaumasite, okenite and tobermorite. A weathering paragenesis includes allophane, C-S-H gels and probably portlandite, unpreserved because of its transformation in aragonite then calcite. Overprints of these late events on the primary zoning are quite limited.

Review on the formation and geochemistry of the mega crystals of Naica, México.

<p>In the state of Chihuahua, Mexico, a mine located in Naica is one of the most important Pb and Zn deposits in the world.  The region manifests several caves with varities of gypsum crystals (Ca4 H2O) known as <strong>selenite</strong> (the largest in the world so far, specimens up to eleven meters in length and one meter in thickness). The present abstract discusses the formation mechanism of these gigantic crystals. The review is based on the interpretations made by early workers (which includes one doctorate thesis and two Bulletins).</p><p>The interpretations were made on 19 samples of anhydrites that were collected at a depth of -345 meters. At this depth the early workers also found microscopically alternating dark dolomite and light bands of anhydrite. The dolomite-anhydrite association is generally associated with mineral recrystallization events. With the geological review carried out, two sources of sulfates were identified: one is La Virgen Formation and the second in the stratiform anhydrite of the Aurora Formation. Formation of hydrothermal anhydrite during the last stage of mineralization has been attributed to the formation of selenite mega crystals due to its dissolution. Hydrothermal minerals, such as hydrothermal anhydrite and sulphides. The most common sulfides in mineralization are galena, sphalerite, to a greater extent, pyrite and chalcopyrite. In case of weathering of these, they would generate their oxidation and result in the presence of sulfate.</p><p>According to the early workers the anhydrite was available in the late hydrothermal stage after mineralization of the mineral. The temperature during the growth of the crystals was maintained slightly below 58 ° C, the value in the solubility of the anhydrite is equal to that of the plaster. Giant selenite crystals grew from low salinity solutions with isotopic compositions compatible with the crystals formed by dissolving the anhydrite found in the mine. The kinetics of gypsum nucleation implies induction times longer than 1 m.y. for the typical temperature (54 ° C) and ~ 1 k.y. for low temperature episodes (up to 47 ° C). This mechanism provides a super saturation level that is not only small and maintained over time but is also virtually free of fluctuations (even small amplitudes).</p><p>Recent contributions have speculated that there are other caves with similar selenite or even with larger crystals exist among the tangle of underground galleries in the area of ​​the Naica mine.</p>