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1.
This paper reports the results of a study of the composition of mica (biotite) crystallizing in the system of phonolite melt-Cl- and F-bearing aqueous fluid at T ～ 850°C, P = 200 MPa, and \(f_{O_2 } \) = Ni-NiO, as well as data on F and Cl partitioning between coexisting phases. It was established that Cl content in mica is significantly lower than in phonolite melt and, especially, in fluid. Fluorine shows a different behavior in this system: its content in mica is always higher than in phonolite melt but lower than in fluid. The mica-melt partition coefficients of Cl and F also behave differently. The Cl partition coefficient gradually increases from 0.17 to 0.33 with increasing Cl content in the system, whereas the partition coefficient of F sharply decreases from 3.0 to 1.0 with increasing total F content. The apparent partition coefficients of F between biotite and groundmass (melt) in various magmatic rocks are usually significantly higher than the experimental values. It was supposed that the higher Bt/glassDF values in natural samples could be related to the influence of later oxidation reactions, reequilibration of biotite at continuously decreasing \(f_{H_2 O} \)/f HF ratio, and an increase in this coefficients with decreasing total F content in the system. 相似文献
2.
G. P. Zaraisky A. M. Aksyuk V. N. Devyatova O. V. Udoratina V. Yu. Chevychelov 《Petrology》2008,16(7):710-736
The concept of granitic melt fractionation as the main process in the concentration of rare elements in granites calls for
the development of a reliable method to determine the evolutionary sequences of granite series. We propose to use for this
purpose a zirconium-hafnium indicator, the Zr/Hf weight ratio in granitic rocks (Zaraisky et al., 1999, 2000). By the example
of three classic regions of rare-metal deposits, eastern Transbaikalia, central Kazakhstan, and Erzgebirge (Czech Republic
and Germany), it was empirically shown that the Zr/Hf ratio of granites decreases during the fractional crystallization of
granite magmas in the sequence granodiorite → biotite granite → leucogranite → lithium-fluorine granite. The reason is the
higher affinity of Hf compared with Zr to a granite melt. This implies that the crystallization and settling of accessory
zircon will cause the progressive enrichment of Hf relative to Zr in the residual melt. As a result, the Zr/Hf ratio decreases
regularly in the series of sequential phases of granite intrusion related to a single magma chamber from granodiorite to biotite
granite, leucogranite, and Li-F granite (from 45-30 to 10-2). Our experimental investigations supported the preferential enrichment
of haplogranite melt in Hf and zircon crystals in equilibrium with melt in Zr (T= 800°C and P = 1 kbar). The Zr/Hf indicator was tested by the example of the wellknown Kukulbei rare-metal granite complex of eastern
Transbaikalia (J3), which is unique in the degree of fractionation of initial granite melt with the formation of three phases
of granite emplacement and vein derivatives. An important feature of the complex is its “short” differentiation trend. It
was supposed that the granite magma of the first phase is parental, and the later phases forming small intrusive bodies in
large massifs of biotite granites of the first phase are sequential products of its crystallization differentiation in a magma
chamber. The biotite granites of the first phase are barren. The leucocratic granites of the second phase are accompanied
by tin-tungsten greisen deposits (e.g., Spokoininskoe), and the upper part of cupola-like stocks of Li-F amazonite granites
of the third phase host apogranite-type tantalum deposits (Orlovka, Etyka, and Achikan). In addition to three granite phases,
the Kukulbei complex includes dikes of ongonites, elvans, amazonite granites, and chamber miarolitic pegmatites. All of the
granitic rocks of the complex have similar isotopic ages of 142± 0.6 Ma. The Zr/Hf ratio decreases systematically from phase
1 (40–25), to phase 2 (20–10), and phase 3 (10–2). The ongonites, elvans, and pegmatites have similar Zr/Hf ratios (15-5),
falling between the ranges of leucocratic muscovite granites and Li-F granites. Compared with other granite series, the granitic
rocks of the Kukulbei complex show specific petrographic and geochemical features: they are strongly enriched in Rb, Li, Cs,
Be, Sn, W, Mo, Ta, Nb, Bi, and F but depleted in Mg, Ca, Fe, Ti, P, Sr, Ba, V, Co, Ni, Cr, Zr, REE, and Y. From the early
to late intrusion phases, the degree of enrichment and depletion in these element groups increases regularly. This is accompanied
by a significant decrease (from 40 to 2) in Zr/Hf, which can be used as a reliable indicator of genetic relations, degree
of fractionation, and rare-metal potential of granites. Granites with Zr/Hf values lower than 25 are promising for prospecting
for Sn, W, Mo, and Be greisen deposits, whereas the formation of Ta deposits requires Zr/Hf values lower than 10. 相似文献
3.
Doklady Earth Sciences - Two varieties of highly differentiated topaz-bearing granite of the Salmi Batholith are distinguished: Li-siderophyllite topaz-bearing granite (Li-Sdph) (Lupikko dome) and... 相似文献
4.
This paper reports experimental data on columbite solubility in model water-saturated Li- and F-rich silicic melts with different
contents of alumina and alkalis. It was found that the columbite solubility is strongly affected by melt composition and is
maximal in peralkaline melt. The maximum contents of Ta and Nb in subaluminous and peraluminous melts at the contact with
columbite are lower by at least an order of magnitude. The peralkaline melt is relatively enriched in Nb, and the peraluminous
melt is enriched in Ta. The temperature dependence of solubility is positive but less pronounced than the effect of melt composition.
It is most distinct in the subaluminous melts. The Nb/Ta ratio of melt usually decreases with decreasing temperature. The
effect of pressure is relatively small. It was shown that columbite cannot crystallize on the liquidus of both peralkaline
and peraluminous magmas. Perhaps, columbite crystallization from a melt is possible only at final near-solidus stages at the
high degrees of crystallization of strongly evolved low-temperature melts. 相似文献
5.
G. P. Zaraisky A. M. Aksyuk V. N. Devyatova O. V. Udoratina V. Yu. Chevychelov 《Petrology》2009,17(1):25-45
The Zr-Hf geochemical indicator, i.e., the Zr/Hf ratio (in wt %) in granitic rocks is proposed to be used as the most reliable indicator of the fractionation and ore potential of rare-metal granites. It was empirically determined that the fractional crystallization of granitic magma according to the scheme granodiorite → biotite granite → leucogranite → Li-F granite is associated with a decrease in the Zr/Hf ratio of the granites. The reason for this is the stronger affinity of Hf than Zr to granitic melt. This was confirmed by experiments on Zr and Hf distribution between granitic melt and crystals of Hf-bearing zircon (T = 800°C, P= 1 kbar). The application of the Zr/Hf indicator was tested at three classic territories of rare-metal granites: eastern Transbaikalia, central Kazakhstan, and the Erzgebirge in the Czech Republic and Germany. The reference Kukul’bei complex of rare-metal granites in eastern Transbaikalia (J3) is characterized by a uniquely high degree of fractionation of the parental granitic melt, with the granites and their vein derivatives forming three intrusive phases. The biotite granites of phase 1 are barren, the leucogranites of phase 2 are accompanied by greisen Sn-W mineral deposits (Spokoininskoe and others), and the final dome-shaped stocks of amazonite Li-F granites of phase 3 host (in their upper parts) Ta deposits of the “apogranite” type: Orlovka, Etyka, and Achikan. The Kukul’bei Complex includes also dikes of ongonites, elvanes, amazonite granites, and miarolitic pegmatites. All granitic rocks of the complex are roughly coeval and have an age of 142±0.6 Ma. The Zr/Hf ratio of the rocks systematically decreases from intrusive phase 1 (40–25) to phases 2 (20–30) and 3 (10–2). Compared to other granite series, the granites of the Kukul’bei Complex are enriched in Rb, Li, Cs, Be, Sn, W, Mo, Ta, Nb, Bi, and F but are depleted in Mg, Ca, Fe, Ti, P, Sr, Ba, V, Co, Ni, Cr, Zr, REE, and Y. From earlier to later intrusive phases, the rocks become progressively more strongly enriched or depleted in these elements, and their Zr/Hf ratio systematically decreases from 40 to 2. This ratio serves as a reliable indicator of genetic links, degree of fractionation, and rare-metal potential of granites. Greisen Sn, W, Mo, and Be deposits are expected to accompany granites with Zr/Hf < 25, whereas granites related to Ta deposits should have Zr/Hf < 5. 相似文献
6.
Doklady Earth Sciences - The data of experiments are presented on the Ta and Nb concentrations in acidic magma melts of various compositions upon dissolution of pyrochlore and microlite at... 相似文献
7.
Doklady Earth Sciences - Experimental data on the Nb, Ta, Ti, Ce, and La concentrations in felsic magmatic melts of various alkalinity and alumina content upon dissolving ilmenorutile,... 相似文献
8.
V. Yu. Chevychelov A. A. Korneeva A. A. Virus Yu. B. Shapovalov 《Doklady Earth Sciences》2017,473(2):454-456
The solubility of H2O–CO2–Cl-containing fluids of various concentrations (0, 3, 10, and 23 wt % of HCl and from 0 to ~8–15 wt % of CO2) in dacite, phonolite, and rhyolite melts at 1000°C and 200 MPa was studied in experiments. It was shown that the Cl concentration in the melt increased substantially from rhyolite to phonolite and dacite (up to 0.25, 0.85, and 1.2 wt %, respectively). The introduction of CO2 into the system resulted in an increase in the Cl content in the melt composition by 20–25%. One may suppose that Cl reactivity in a fluid increases in the presence of CO2 to cause growth of the Cl content in the melt. The introduction of CO2 into the system considerably affects the content of H2O in aluminosilicate melts as well. Thus, the addition of CO2 decreases the H2O content in the melt by ~0.5–1.0 wt %. The decrease in the H2O content in an aluminosilicate melt is probably caused by fluid dilution with CO2 resulting in a decrease in the H2O mole fraction and fugacity in the fluid. 相似文献
9.
This study presents a new set of quantitative experimental data on the partitioning of Ta, Nb, Mn, and F between aqueous F-bearing fluid and water-saturated, Li- and F-rich haplogranite melts with varying alumina/alkali content at T = 650–850 °C and P = 100 MPa. The starting homogeneous glasses were preliminary obtained by melting of three gel mixtures of K2O-Na2O-Al2O3-SiO2 composition with a variable Al2O3/(Na2O+K2O) ratio, ranging from 0.64 (alkaline) and 1.1 (near-normal) to 1.7 (alumina-rich). Ta, Nb, and Mn were originally present in glass only, whereas F was load in both the glass and the solution. The solutionto-glass weight ratio was 1.5–3.0. The compositions of quenched glass were measured by an electronic microprobe, and those of the aqueous solution, with the ICP-MS and ICP-AES methods. The F concentration in the quenched solution was calculated from the mass balance. Under experimental conditions the partition coefficients of Ta, Nb, and Mn between the fluid and the granitic melt (weight ratio fluid C Ta/melt C Ta = fluid/melt D Ta) are shown to be extremely low (0.001–0.008 for Ta, 0.001–0.022 for Nb, and 0.002–0.010 for Mn); thus, these metals partition preferentially into the melt. The coefficients fluid/melt D Ta and fluid/melt D Nb generally increase either with increasing alumina ratio A/NKM in the glass composition, or with rising temperature. The experiments also demonstrated that F preferentially concentrates in the melt; and the partition coefficients of F are below 1, being within the range of 0.1–0.7.
相似文献10.