Phlogopite Apatite Research Articles

Carbonatite melts and genesis of apatite mineralization in the Guli pluton (northern East Siberia)

Inclusions of mineral-forming environments in apatite-containing ijolites and magnetite–phlogopite–apatite ores in carbonatites were studied to elucidate the genesis of apatite mineralization in the Guli alkaline ultramafic carbonatite massif. Primary inclusions of carbonate–salt and carbonate melts have been discovered and studied. The carbonate–salt melt inclusions are of alkaline high-Ca composition and are enriched in P, Sr, SO3, and F (wt.%): CaO—30–40, Na2O—5–12, K2O—2–4, P2O5—1–3, SO3—1.5–3, and SrO—1–3. They also contain minor MgO, FeO, BaO, and SiO2 (tenths and hundredths of percent). The homogenization temperature of these inclusions is 850–970 °C. The carbonate inclusions contain predominant CaO (54–67 wt.%) and minor MgO, FeO, SrO, Na2O, and P2O5 (tenths of percent). Their homogenization temperature is 840–860 °C. Similar primary carbonate–salt and carbonate inclusions were found in garnet, and secondary ones were detected in silicate minerals (clinopyroxene and nepheline) of ijolites. Clinopyroxenes of ijolites also contain primary inclusions of alkaline ultramafic high-Ca melts similar in composition to melilitite-melanephelinites highly enriched in P, SO3, and CO2 (wt.%): SiO2—41–46, Al2O3—8–16, FeO—2–8, MgO—3–6, CaO—12–20, Na2O—2–9, K2O—1–6, P2O5—0.4–2.1, SO3—0.2–2.3, and Cl—0.02–0.35. According to the obtained data, apatite of the magnetite–phlogopite–apatite ores and ijolites of the Guli pluton crystallized from phosphorus-rich alkaline carbonate–salt melts at 850–970 °C. The generation of these melts was, most likely, due to the silicate–salt immiscibility in melilitite-melanephelinite melts highly enriched in salts, which occurred either at the final stages of clinopyroxene crystallization or during the formation of melilite. The presence of alkalies, S, F, and CO2 in spatially separated carbonate–salt melts contributed to the concentration and preservation of phosphorus in them at low temperatures, which led to the formation of apatite mineralization in ijolites and ore deposit in carbonatites.© 2015, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Origin and evolution of ore-forming fluids in the Hemushan magnetite–apatite deposit, Anhui Province, Eastern China, and their metallogenic significance

The Middle–Lower Yangtze River Metallogenic Belt in the northern Yangtze Block is one of the most important economic mineral districts in China. The Hemushan deposit is a medium-class Fe deposit located in the southern part of the Ningwu iron ore district of the Middle–Lower Yangtze River Metallogenic Belt. The Fe–orebodies are mainly hosted in the contact zone between diorite and Triassic marble. The actinolite–phlogopite–apatite–magnetite ore shows metasomatic/filling textures and disseminated/mesh–vein structures. Based on evidences and petrographic observations, the ore-forming process can be divided into three distinct periods—the early metallogenic period (albite–diopside stage), the middle metallogenic period (magnetite stage and hematite stage), and the late metallogenic period (quartz–pyrite stage and carbonate stage). Fluid inclusion studies show four types of inclusions: type I daughter mineral-bearing three-phase inclusions (L+V+S), type II vapor-rich two-phase inclusions (L+V), type III liquid-rich two phase inclusions (L+V), and minor type IV liquid-phase inclusions (L). Apatites from the magnetite stage contain type I, type II and type III inclusions; anhydrites from the hematite stage mainly contain abundant type II inclusions and relatively less type I inclusions; quartz and calcite from the late metallogenic stage are mainly characterized by type III inclusions. Laser Raman spectroscopy and microthermometry of fluid inclusions show that the ore-forming fluids broadly correspond to unsaturated NaCl–H2O system. From the magnetite stage to the carbonate stage, the ore-forming fluids evolved from moderate-high temperature (average 414°C), moderate salinity (average 25.01 wt.% NaCl equiv.) conditions to low temperature (average 168°C), low salinity (average 6.18 wt.% NaCl equiv.) conditions. Hydrogen and oxygen isotopic studies indicate that the ore-forming fluid during the early stage of middle metallogenic period was mainly of magmatic water, and mixing of the ore fluids with meteoric water took place during the late phase. During this evolution, water–rock interaction, and boiling and mixing of the ore fluids with meteoric water occurred. The boiling of fluids was a potential mechanism for the formation of magnetite.

Geochemistry of phlogopite, diopside, calcite, anhydrite and apatite pegmatites and syenites of southern Madagascar: evidence for crustal silicocarbonatitic (CSC) melt formation in a Panafrican collisional tectonic setting

The phlogopite, diopside, calcite, anhydrite and apatite pegmatites of Ampandrandava and Beraketa are examples for the many other pegmatites of similar silicocarbonatitic composition found in the Bekily and Betroka-Beraketa Precambrian belts of southern Madagascar. The two studied pegmatites and associated syenites crystallised from immiscible silicocarbonatitic and peralkaline syenitic melts in a time span between 515 and 504 Ma in the final extensional phase of the Panafrican continental collision and connected metamorphic/metasomatic event. Model T Nd ages suggest that the melts were produced by partial melting of 3.5 Ga partially evaporitic continental crust. The studied pegmatites and genetically associated syenitic rocks are very rare examples for crustal silicocarbonatitic melts generated in a Panafrican collisional setting. The overwhelming majority of carbonatites and associated peralkaline rocks are mantle derived, much poorer in phosphate and sulfate and found in a cratonic environment. In light of the present results, genetic models for other sulfate- and phosphate-rich magmatic rocks (e.g., phlogopite–apatite–calcite mineralisations in the Grenville-Hasting formation in Canada and in the Sludyanka group in Eastern Siberia) should be reevaluated.

The Blue Hills Intrusive Complex in Southern Namibia—relationships between carbonatites and monticellite picrites

Geochemical and petrological investigations were carried out on ultrabasic silicate and carbonatite magmatic rocks from the Blue Hills Intrusive Complex (southern Namibia). From detailed field mapping and geomagnetic traverses we propose a model for the complex build-up of this hypabyssal laccolith. The bulk comprises mica–olivine–carbonate picrite, with numerous small offshoots into the surrounding Nama shales which are metamorphosed at the contacts to the intrusive rock. The mica–olivine–carbonate picrite is intruded by small lenses and massive layers of monticellite picrite. Locally, a phlogopite–carbonate picrite occurs, that cuts through both the monticellite picrite and the mica–olivine–carbonate picrite. Late carbonatite dykes and sills and a carbonate–phlogopite–apatite pegmatite represent the last stage of the Blue Hills magmatism. Phlogopite–carbonate picrites are regarded as the parental and nearly primary magmas. They may be formed by partial melting in the dolomite stability field at a depth of 100 to 110 km and at a temperature of 1100–1250°C. Fractional crystallisation of mostly olivine led to formation of the volatile-rich, mica–olivine–carbonate picrites, which were the first to intrude into the present position of the Blue Hills Intrusive Complex. Part of the phlogopite–carbonate picrite magma intruded undifferentiated, while part of it suffered devolatilisation and oxidation on its way to the surface which led to formation of the monticellite picrites. Both magma types intruded the hypabyssal mica–olivine–carbonate picrite. The late carbonatites most probably are residual liquids, i.e. the result of almost complete solidification of magmas like phlogopite–carbonate picrites. The carbonatitic liquids were removed from the crystal mush by filter pressing. Pegmatitic veins are the late stage residual fluids or melts from within the Blue Hills body.

Phlogopite-amphibole-pyroxenite xenoliths in Langao, Shaanxi Province, China: Evidence for mantle metasomatism

Phlogopite-amphibole-pyroxenite xenoliths contained in the alkali basic-ultrabasic subvolcanic complex in Langao, Shaanxi Province, are composed of diopside, Ti-rich pargasite, phlogopite apatite, sphene and ilmenite, which have subsolidus metamorphism-deformation textures such as triple-points, cataclastic boundaries and kink-bands. Mineral chemical characteristics show that the diposide, Ti-rich paragasite and phlogopite are derived from the mantle and are the products of mantle metasomatism. Compared with normal mantle-derived spinel-lherzolites, the xenoliths are enriched in TiO2, Fe2O3, CaO, Na2O and K2O, with apparent depletion in MgO. Chondrite-normalized REE patterns and primordial-mantle normalized trace elements data show that they are enriched in REE (especially LREE) and incompatible trace elements. The petrographic, mineralogical and petrochemical characteristics indicate that the xenoliths are metasomatized mantle xenoliths, which offers the evidence for mantle metasomatism and represents the anomalous mantle beneath the Early Paleozoic rift in northern Daba Mountains. The agents of mantle metasomatism are probably derived from the rising of mantle hot plumes. The processes of metasomatism varied from limited-range fluid metasomatism in deep mantle (>90 km) to pervasive metasomatism of silicate melt.