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Abstract
Tonglüshan Fe-Cu (Au) deposit is one of the largest skarn deposits in middle-lower Yangtze River metallogenic belt, which is associated with the Early Cretaceous Yangxin quartz diorite stock. Granitic pegmatites are well developed in the southeast mining area, emplaced in the Yangxin quartz diorite pluton and cut by garnet-diopside skarn. The cross-cutting relationships thus indicate that the granitic pegmatites are temporarily intermediate between the quartz diorite and skarn. Granitic pegmatites consist mainly of K-feldspar, plagioclase, and quartz, with conspicuous graphic textures marked by intergrowths of K-feldspar and quartz. K-feldspar with graphic textures from one granitic pegmatite dike has been successfully dated by the 40Ar/ 39Ar laser microprobe incremental heating technique, yielding a well-defined plateau age of 136.0±1.0 Ma (2σ), which is interpreted to be the emplacement age of the granitic pegmatite dike. The age constraints indicate that the pegmatites formed coevally with the quartz diorite stock in the mine and related skarn Cu-Au mineralization. In situ laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) provides a wealth of information on the major and trace elements of K-feldspar from granitic pegmatites and quartz diorite. The average bulk compositions of K-feldspar from the pegmatite and quartz diorite are represented by Or 81Ab 18 and Or 78Ab 21, respectively. K-feldspar minerals with graphic textures have higher Si and lower Al than those without graphic texture. Textural and geochemical data indicate that graphic textures in the pegmatites resulted from alternating growth of K-feldspar and quartz due to dynamic alteration of the relative concentration of SiO 2 and Al 2O 3 in areas proximal to the outer zone of growing K-feldspar crystals. Both K-feldspars from quartz diorite and granitic pegmatite are enriched in large-ion lithophile elements (LILE), but the pegmatite contains more abundant Rb and Pb and lesser amounts of Ba, Sr, Li, and Cs. In the Rb-Ba, La-Ba, K/Ba-Ba, and Rb/Sr-Ba diagrams, samples of the pegmatite and quartz diorite display a trend predicted by the Rayleigh factional crystallization, indicating that the granitic pegmatite was generated by strong fractional crystallization of quartz dioritic magma. However, Pb, Li, and Ga deviate obviously from the trend of fractional crystallization, indicating these elements may have been complexed by a fluid phase. Abundance of melt and fluid inclusions in quartz minerals from the granitic pegmatites demonstrates that the pegmatite formed from melt and fluid coexisting system. This study provides a better understanding of the formation of pegmatites, exsolution of ore fluids from evolving magmas, and hydrothermal mineralization.
... Research efforts have been made to radiometrically constrain the crystallization age and duration of the Tonglushan magmatism (e.g., Deng et al., 2012;Huang et al., 2013;Li et al., 2009aLi et al., , 2010aMei et al., 2008;Xie et al., 2011;Zhang et al., 2018). Nevertheless, a chronological consensus of the Tonglushan magmatism has not yet been reached. ...
... The granite, albite porphyry and diorite porphyry dykes that intruded the quartz monzodiorites crystallized at 140.7 ± 1.0 Ma, 140.1 ± 0.9 Ma and 139.1 ± 1.0 Ma,respectively (Figs. 7 and 9). The previously published younger K-feldspar 40 Ar-39 Ar age (~137 Deng et al., 2012) and titanite U-Pb age (~121 Li et al., 2010a) for the late dykes are not considered in constraining the timing of the Tonglushan magmatism. These "younger" dykes could represent volumetrically minor intrusions within the Tonglushan intrusive suite. ...
Late Mesozoic high-K calc-alkaline and high Sr/Y granitoids related to the skarn–porphyry–stratabound Cu–Au polymetallic deposits are widespread in the Middle–Lower Yangtze River Belt (MLYRB), Eastern China. However, the role of mantle-derived magmas in the petrogenesis of these granitoids remains controversial. In this study, we present new zircon U–Pb–Hf isotopes, and whole-rock geochemical and Sr–Nd isotopes data for quartz monzodiorites (porphyry), their hosting mafic microgranular enclaves (MMEs) and associated dykes from Tonglushan orefield in the MLYRB. Field relationships and geochronological data show that these intrusive rocks cluster around 141 ~ 139 Ma, indicating a short duration of magmatism, rather than a prolonged magmatism (~30 My) as previously thought. Crystallization age of the MMEs is identical to that of their quartz monzodiorite host. Petrographical and geochemical observations suggest that the MMEs represent mafic melts that injected into the quartz monzodioritic magmas, and magma mixing and (previously) fractional crystallization were involved in producing their compositional diversity. All the Tonglushan granitoids and MMEs show trace element geochemical and Sr–Nd–Hf isotope compositions similar to the coeval K-rich mafic rocks in the MLYRB. This indicates that these granitoids and MMEs were mainly sourced from the enriched subcontinental lithospheric mantle (SCLM) that metasomatized by slab derived fluids/melts, and had experienced significant fractional crystallization. The high oxygen fugacity and water content of the early Tonglushan quartz monzodiorite (porphyry) indicate melting of metasomatized SCLM and subsequently fractional crystallization and recharging/mixing in magmatic system have the potential to Cu–Au polymetallic mineralization. This study also highlights that the SCLM beneath the eastern Yangtze plate is one of the likely sources for Late Mesozoic magmatic rocks in the MLYRB.
... Amphibole displays erosion and resorption textures (Figure 2(e)). Graphic texture of the quartz and K-feldspar (Figure 2(f)) suggests a disequilibrium texture and rapid crystallization (Deng et al. 2012). ...
... Euhedral hornblende crystals with erosion and resorption textures in the MMEs indicate that it was metasomatized by felsic melts in late stage. Quartz and K-feldspar grains with graphic texture (Figure 2(f)) suggest disequilibrium crystallization (Deng et al. 2012). ...
The Early Cretaceous granitoids are widely distributed in the southern North China Craton (NCC), petrogenesis of these rocks is critical to understanding the implications for the Early Cretaceous geological evolution at the southern margin of the NCC. This paper presents detailed zircon LA-ICP-MS U-Pb ages, geochemistry, in-situ zircon Hf isotope for the granodiorite and its mafic microgranular enclaves (MMEs) from the Shuiyu area, southern NCC. The granodiorite and its MMEs have identical zircon U-Pb ages (~130 Ma). Field and petrological observations, such as ellipsoidal shapes, partly diffusive contact to the host rocks, erosion and resorption textures in amphibole, combined with their low SiO2 content, high Mg# values and negative εHf(t) values (−13 to −18), suggest the MMEs were derived from enriched lithospheric mantle. The host granodiorite displays moderate SiO2 contents, high Sr/Y (44 to 113) and La/Yb (25 to 38) ratios, and low zircon Hf isotopes (−10 to −23), suggesting they were from primary magmas generated by partial melting of the ancient thickened lower continental crust of the North China Craton. The petrogenesis of Early Cretaceous intrusions and its MMEs in southern NCC geodynamically interpreted as resulting from the break-off of the subducted Yangtze Craton slab, associated with the upwelling of asthenospheric mantle material, which provided the necessary heat and triggered the partial melting of the enriched lithospheric mantle beneath the southern NCC, producing primary mafic magma. Then, the mafic magma underplated and caused partial melting of a thickened region of the lower continental crust in the southern NCC.
... Orebody VIII (Fig. 2) is a recent discovery. There is no significant gap between rock-forming and oreforming ages, which are all around 140 Ma (Mei et al., 2008;Xie et al., 2009Xie et al., , 2011bLi et al., 2010Li et al., , 2014Deng et al., 2012;Huang et al., 2013;Zhang et al., 2018). ...
In order to trace chlorine and sulfur evolution during magma evolution, detailed petrographic observation, major- and trace-element analysis of amphibole and apatite were carried out on the ore-related pluton in the Tonglvshan Cu-Fe (Au) skarn deposit, Hubei Province, South China. Several generations of apatite and amphibole are identified, from early to late including: (1) apatite in euhedral amphibole; (2) euhedral amphibole; (3) apatite in subhedral-anhedral amphibole/plagioclase; (4) subhedral-anhedral amphibole + plagioclase; (5) apatite in K-feldspar or quartz; and (6) K-feldspar + quartz. Most apatites show homogeneous textures, but a few apatite grains enclosed in amphibole and plagioclase (1 and 3) display oscillatory zoning. These zoned apatites crystallized in semi-closed environments created as growth of amphibole or plagioclase removed components of the melt. The magmatic Cl and S evolution can be divided into three stages: (I) In the deep magma chamber, at ∼ 5 km below the surface, magma underwent ∼ 39% fractional crystallization, and its Cl and S contents increased simultaneously; (II) In a shallow magma chamber at ∼ 2.5 km depth, fractional crystallization elevates Cl and S contents in the residual melt, but fluid exsolution depletes them; (III) At near-solidus stage, when fluid exsolution becomes weak, crystallization elevates Cl and S contents in the residual melt simultaneously. This study suggests that the silicate mineral (fractional) crystallization can elevate Cl content in residual melt, and fluid exsolution can efficiently remove Cl from the magma. Bulk sulfur in magma may be transported not only as dissolved sulfur, but also as sulfates like anhydrite. The sulfur content of apatite is controlled by the sulfur composition in melt from which the apatite crystallizes, but Cl in apatite may represent re-equilibration between the apatite and the last melt in contact with the apatite, because of rapid diffusion of Cl in apatite. These characteristics along with complex apatite generations imply that in-situ study is necessary when using apatite to trace volatile composition in magma.
... The regional pollution of heavy metals was different, and the pollution in local areas was serious. The potential degree of damage caused by Cu, Pb, Zn and Cd in the agricultural soil in the mining area was slight, and Cu posed the highest potential ecological hazard factor (Deng et al., 2012). In comparison, the pollution levels in the study area (i.e., the four vegetable bases) were higher than certain other study sites (Qin et al., 2010;Zhou et al., 2016), and Zn, Cr, Cd, Hg, As, and Pb contributed to various pollution levels in the vegetable bases, as indicated by the measured PI, NIPI, and RI indices, which were significantly higher than those in the references areas (Huang et al., 2007;Zhang et al., 2013). ...
The objective of this study was to investigate heavy metal contamination in four major vegetable bases and determine the health risks of residents in the vicinity of the highly urbanized city Urumqi in Xinjiang, China. In this paper, we determined the contents of six heavy metals (i.e., As, Zn, Cd, Cr, Hg, and Pb) in surface soil and groundwater to evaluate the levels of heavy metal pollution and human health risks using the pollution index (PI), the Nemerow integrated pollution index (NIPI), the ecological risk factor (Eir), risk index (RI) and the health risk assessment model. The results showed that (1) The PI, NIPI, the ecological risk factor and risk index indicated that Cd and Hg were the primary pollutants in Sishihu village. These indices suggested moderate to slightly heavy potential ecological risks. In Anningqu town, Hg and Cd led to high levels of pollution and posed slightly heavy potential ecological risks. In Qinggedahu village, it was concluded that the metals Zn, Cr, Cd, Hg, and Pb caused moderate to heavy pollution. In Liushihu village, the pollution trends in the area were low. The results of the pollution level of the irrigation well water (i.e., groundwater) indicated that the well water was considerably safer than the soil, but Cr posed a slight pollution risk. (2) The non-carcinogenic risks for adults based on the HI values of these four vegetable bases were <1. However, when considering the non-carcinogenic risks for children, the HI values were larger than 1 in all areas, indicating the local children have a higher potential non-carcinogenic risk. In addition, CR (Carcinogenic risk) from dermal contact with the vegetables bases did not pose a high risk for residents. However, for adults, the carcinogenic risk posed by Arsenic (As) through trough inhalation was the primary pathway of exposure in three of the vegetable bases, generally in the order of Qinggedahu village > Sishihu village > Anningqu town. For children, the carcinogenic risks posed by As through trough inhalation and ingestion were the main exposure pathways. From the TCR results, it can be seen that in Sishihu village, Anningqu town, and Qinggedahu village, the TCR values for adults and children were >1 × 10-4 (unitless), and this degree of carcinogenic risk is unacceptable. (3) The identification of risk sources determined the main pollution sources affecting the vegetable bases were human activities and natural sources. Anthropogenic activities were most often related to traffic pollution sources and agricultural pollution sources, such as the irrational use of pesticides and fertilizers and stock farming. The results are important for designing remediation scenarios to control the spread of contamination as well as for serving as a reference point for soil environmental protection efforts in this region.
The study on the tailings and their physical and chemical compositions can provide important scientific basis for the control of the mine environment and the proper utilization of tailings. The mineral and geochemical characteristics of the tailings of the skarn copper-iron deposits in the Tonglüshan copper deposit are studied in the paper, Hubei Province, and the heavy metals are extracted and separated by the dilute sulfuric acid.The results show that mineral compositions of the tailings have changed significantly after chemical mineral processing and the long-term physical and chemical weathering. The main form of copper mineral is copper oxide in the tailings, with heavy metals increasingly enriched from the top down. The enrichment of heavy metal elements peaks in the sixth horizon of the tailing pond. It is found that the copper in the tailing pond has potential recycle value.
Comb quartz layers are quartz layers in which the constituent crystals are oriented approximately perpendicular to the planes of layering. They are relatively common in the apical parts of felsic intrusions related to porphyry (stockwork) deposits and are probably linked directly to the evolution of ore-forming, magmatic-hydrothermal fluids. Comb quartz layers have features in common with growth layers in layered pegmatite-aplite bodies and in mafic and ultramafic intrusions. They are also one type of a family of “unidirectional solidification textures” in intrusive rocks. In many localities they have undergone plastic deformation resulting in diagnostic “crenulate quartz layers”.
During the formation of U-, Th-, Mo-, REE-, and Nb-bearing granitic pegmatites in the Grenville Province, conditions of crystallization were such that widespread graphic quartz-feldspar intergrowths were formed. The quartz is interpreted to have nucleated epitactically on rough edges and corners of alkali feldspar crystals. Slow diffusion of Si and Al species (network formers) in the boundary-layer melt was likely the rate-controlling step for quartz saturation, which occurred along corners and edges, where the feldsdpar grew most rapidly. Diffusion-limited growth resulted in SiO2 buildup at the interface, producing oscillations from quartz-oversaturated to quartz-undersaturated conditions and thus the rhythmic quartz-feldspar intergrowths. Evidence of saturation in a volatile phase in these pegmatites indicates that water was a catalyst for feldspar growth and that lower activities of H2O in the melt decrease Si diffusivity at the crystal interface. -from Authors
Multivariate linear regression (MLR) analysis has been used to develop equations for predicting alkali feldspar/melt trace-element partition coefficients (D-values) for certain large-ion lithophile elements (Rb and Eu), high field-strength elements (Zr and Nb), and rare-earth elements (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, and Yb) in peralkalic felsic systems. A partitioning equation for Sr based solely on data from Pantelleria is also presented. DRb, DZr, and DNb each can be calculated given whole-rock SiO2 and agpaitic index [A.l. = mol (Na + K) / Al]; alternatively, DRb can be calculated given feldspar Or content and agpaitic index. DEu can be calculated given whole-rock SiO2, agpaitic index, and whole-rock Na2O/K2O. Other DREE can be calculated given whole-rock SiO2, agpaitic index, and whole-rock CaO. These D-values all increase with increasing whole-rock SiO2 and decreasing agpaitic index. DSr for samples from Pantelleria increase with increasing feldspar Ab and can be calculated given feldspar Ab content. The equations formulated will help to constrain better the choice of D-values used in petrogenetic models of peralkalic systems.
The properties of albitic melts are central to thermodynamic models for synthetic and natural granitic liquids. The authors have analyzed published phase-equilibrium and thermodynamic data for the dry fusion of high albite to develop a more accurate equation for the Biggs free energy of this reaction to 30 kbar and 1,400 C. Strict criteria for reaction reversal were sued to evaluate the phase-equilibrium data, and the thermodynamic properties of solid and liquid albite were evaluated using the published uncertainties in the original measurements. Results suggest that neither available phase-equilibrium experiments nor thermodynamic data tightly constrain the location of the reaction. Experimental solidus temperatures at 1 atm range from 1,100 to 1,120 C. High-pressure experiments were not reversed completely and may have been affected by several sources of error, but the apparent inconsistencies among the results of the various experimentalists are eliminated when only half-reversal data are considered. Uncertainties in thermodynamic data yield large variations in permissible reaction slopes. Disparities between experimental and calculated melting curves are, therefore, largely attributable to these difficulties, and there is no fundamental disagreement between the available phase-equilibrium and thermodynamic data for the dry melting of albite. Consequently, complex speciation models for albitic melts, based on the assumption that these discrepancies represent a real characteristic of the system, are unjustified at this time.
Alkali feldspar separates (n = 52) from the eastern part of the Late Devonian, peraluminous South Mountain Batholith of Nova Scotia, in eastern Canada, have been analyzed from the relatively primitive, early granodiorite, through monzogranite, to evolved pegmatites hosted by leucogranites. The alkali feldspar, with bulk compositions (Or 55-80) consistent with magmatic conditions, shows systematic variations in trace-element content; levels of Ba, Sr, Pb, the rare earths, Th, and Zr decrease, and concentrations of Rb, Cs, and Ga increase, in alkali feldspar in the sequence granodiorite - monzogranite - pegmatite. The continuity and trajectory of trends in binary and element-ratio diagrams follow the trend predicted for Rayleigh fractional crystallization, as do linear trends in log-log plots. In chondrite-normalized plots, the rare-earth elements decrease continuously, along with Eu N/EU*, reflecting the fractionation of accessory minerals. Modeling of the trace-element populations give F values consistent with the observed proportions of rock types in the batholith. The chondrite-normalized profiles of alkali feldspar from evolved rocks indicate an inflexion in the concentration of the heavy rare-earths and anomalies involving the most mobile trace elements. It seems clear that these elements were complexed by a fluid phase, which likely also was involved in localized lithophile-element mineralization and related metasomatism.
Analysis of T-P and compositional variables suggests that graphic granite is produced by the simultaneous growth of quartz and feldspar in a kinetically driven, non-equilibrium situation.-J.A.Z.
40 Ar / 39 Ar age spectrum analyses of three microcline separates from the Separation Point Batholith, northwest Nelson, New Zealand, which cooled slowly (~5°C-Ma -1 ) through the temperature zone of partial radiogenic 40 Ar accumulation are characterized by a linear age increase over the first 65 percent of gas release with the lowest ages (~80 Ma) corresponding to the time that the samples cooled below about 100°C. The last 35 percent of 39 Ar released from the microclines yields plateau ages (103,99 and 93 Ma) which reflect the different bulk mineral ages, and correspond to cooling temperatures between about 130 to 160°C. Theoretical calculations confirm the likelihood of diffusion gradients in feldspars cooling at rates 5°C-Ma -1 . Diffusion parameters calculated from the 39 Ar release yield an activation energy, E = 28.8 ± 1.9 kcal-mol -1 , and a frequency factor/grain size parameter, D 0 / l 2 = 5.6 -3.9 +14 sec -1 . This Arrhenius relationship corresponds to a closure temperature of 132 ± 13° C which is very similar to the independently estimated temperature. From the observed diffusion compensation correlation, this D 0 / l 2 implies an average diffusion half-width of about 3 m, similar to the half-width of the perthite lamellae in the feldspars. The range in microcline K-Ar ages from the Separation Point Batholith is the result of relatively small temperature differences within the pluton during cooling. Comparison of the diffusion laws determined for microcline with those for anorthoclases and other homogeneous K-feldspars ( E = 40 to 52 kcal-mol -1 ) reveals that Ar diffusion is more highly temperature dependent in the disordered structural state than in the ordered structural state. Previously published U-shaped age spectra are probably the result of the superimposition of excess 40 Ar upon diffusion profiles of the kind described here.
At Alijo-Sanfins there are many granitic aplite and pegmatite veins crosscutting different petrographic facies of the Hercynian granite batholith and also mica-schists. They are tin-bearing granitic rocks. Thirty-four samples of K-feldspar and 34 of albite from these veins and host granites were analysed to establish the distribution of elements and their fractionation trends in the sequence of feldspar crystallization Rubidium and Cs increase, and Ba, Sr, Ba/K, Sr/K and K/Rb decrease in K-feldspar, whereas Na increases and Sr and Ca decrease in albite, from granites to aplites and pegmatites. In a few aplite-pegmatite veins Rb, Rb/Ba and Rb/Sr increase and Pa, Sr, K/Rb and Ba/Sr decrease in K-feldspar, and Rb increases and Sr decreases in albite from aplite to coexisting pegmatite. Equilibrium was not attained for trace elements between coexisting feldspars.
Several descriptions of argon diffusion in K-feldspar have been developed, including the quantitative multiple-diffusion-domain (MDD) and multipath models and the qualitative 'recrystallization' model. These models remain contentious and the natural range in behaviour remains poorly understood. Feldspars from the Klokken syenite intrusion show a systematic relationship between Ar-40/Ar-39 age and microtexture suggesting that the loss of argon from different feldspars operates via different mechanisms such that the existing models represent only end-member scenarios. The MDD model can yield reliable thermal history information only for feldspars with pristine microtexture, with this model best viewed as a cipher for the real (but unknown) domain structure in such samples.
Simultaneous growth of quartz and alkali feldspar may occur in a coupled or a noncoupled manner. Coupled growth appears to result in sectoral (hourglass) or radial (spherulitic) intergrowths, depending upon the growth behavior of the feldspar. Sectoral textures are produced as a result of faceted feldspar growth, whereas nonfaceted growth favors a radial arrangement. Micrographic and micropoikilitic intergrowths appear to be caused by a noncoupled growth mechanism. Transitions from coupled to noncoupled growth usually occur during crystallization, probably because of an increased tendency for one or both of the constituent phases to facet as H2O builds up at the interface.
The great depth and relatively steep geothermal gradient (∼29°C/km) of the KTB deep crustal borehole, located in the Bavarian region of Germany, provides the basis for our study of diffusive argon loss in K-feldspar. The observed borehole temperature at 9 km is ∼265°C which reaches well into the argon closure interval for K-feldspar (∼125–350°C). Four microcline and two adularia samples distributed relatively evenly down the 9.1-km deep borehole were analyzed by the 40Ar/39Ar method. The thermal histories of the shallow samples are consistent with existing thermochronologic data from the borehole. After correction for chlorine correlated excess 40Ar, the deepest two samples result in age spectra that record zero apparent ages over the first few percent of 39Ar released, which is predicted by diffusion theory where a range of diffusion volumes are present. Inverse modeling of the argon kinetics of these two deep samples reveals that the present elevated geothermal gradient in the borehole has existed for only the last approximately one million years. Recent volcanism within 30 km of the borehole is likely the source of this present-day thermal pulse.
Manto-type copper deposits of the southern Central Andes are strata-bound, epigenetic mineral concentrations hosted by bimodal volcanic and volcaniclastic rock suites. They are economically important, but since they are not obviously related to intrusions, their genesis has been controversial, to some extent, because it has proven difficult to date the ore-forming event and distinguish it from the age of low-grade regional metamorphism. El Soldado, the largest manto-type copper deposit in central Chile, is hosted by marine volcanic and subvolcanic intrusive rocks of the Lower Cretaceous extensional arc. To discriminate between regional metamorphism and mineralization, we dated 11 samples of K-feldspar by the stepwise-heating 40Ar/39Ar method. Hydrothermally precipitated K-feldspar associated with copper sulfides precipitated at temperatures of >300 °C and range in age from 100.5±1.5 to 106.1±1.1 Ma (mean 103±1.6 Ma; n=8). Syn-mineralization K-feldspar gave an age of 102.5±2.0, which is interpreted to be the age of mineralization. K-feldspar unrelated to ore yields older ages between 109.4±1.1 and 112±2 Ma (mean=110.3±1.4 Ma; n=3) is variably reset by the younger ca. 103 Ma mineralization episode. The above ages are interpreted to represent the age of alkali redistribution and crystallization due to burial metamorphism of the host sequence. Fission track dating of apatite in the host rocks yields an age of ca. 90 Ma, indicating fast cooling of the system to less than ca. 100 °C after mineralization. Time–temperature modeling of fission track length data are compatible with initial fast exhumation, followed by slow exhumation and cooling to surface temperatures. High levels of atmospheric Ar were detected in all K-feldspar samples and are tentatively attributed to connate meteoric fluids incorporated into the basinal metamorphic mineralizing fluids.
40Ar/39Ar data have been used to resolve the relatively high temperature (>350°C) potassic alteration event at Chuquicamata from the lower temperature (
The South Mountain Batholith (SMB) of southwestern Nova Scotia (Canada) is a Late Devonian (~375Ma) composite intrusion,
which crops over an area of about 7,300km2. This peraluminous granitoid body consists of rocks ranging from granodiorite through monzogranite and leucomonzogranite
to leucogranite that locally host greisen tin-base metal mineralization. K-feldspar displays large compositional variations
of trace elements and Pb isotopic ratios, particularly in the highly fractionated rocks. Many variations are consistent with
processes of fractional crystallization, but a distinct enrichment of Rb, Li and Cs accompanied by low K/Rb, Ba/Rb, Eu/Eu*
and K/Cs ratios point to the role of fluids during the late stages of magmatic evolution. The correlation of Pb isotopic ratios
with the enriched elements and their ratios implies that the isotopic variations are an integral part of the evolution of
the SMB. Together with well-defined isochronal relationships of Pb systems in the feldspars, the correlation suggests that
fractional crystallization accompanied in the late stages by fluid fractionation led to the formation of Li–F-rich leucogranites.
Internally derived U-rich fluids fractionated U/Pb ratios, which in turn produced distinct variations of 206Pb/204Pb and 238U/204Pb ratios in K-feldspars. This implies that the Pb isotopic values of K-feldspar, which have traditionally been used for tectonic
reconstructions, might have been modified in many granitic rocks. Thus, only early magmatic K-feldspars, which show no discernible
effects of fluid fractionation yield the initial Pb isotopic compositions of the parental granitic magmas and their sources.
The data also show that the geochemical characteristics of the leucogranites are the results of magmatic evolution rather
than a distinctive source.