Formation and evolution of snowball quartz phenocrysts in the Dongping porphyritic granite, Hebei Province, China: Insights from fluid inclusions, cathodoluminescence, trace elements, and crystal size distribution study

doi:10.1016/j.lithos.2019.05.018

Lithos

Volumes 340–341, September 2019, Pages 239-254

https://doi.org/10.1016/j.lithos.2019.05.018 Get rights and content

Highlights

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The porphyritic granite was derived from the Shuiquangou magma fractionation.
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The quartz phenocrysts crystallized rapidly in a fluid-enriched magma.
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Magmatic flow led to mineral rotation and rounded shapes of the quartz.
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Fluid exsolution leads to the core-mantle texture of the snowball quartz.

Abstract

Quartz phenocrysts are common in many granites, volcanic rocks, metamorphic rocks and hydrothermal deposits. The Dongping porphyritic granite contains large amounts of rounded to sub-rounded quartz phenocrysts. Minerals in this porphyritic granite show weak but distinct orientation. Dense clusters of fluid inclusions and albite crystals exist in the quartz, showing snowball texture. Two types of snowball quartz are recognized: (1) large snowball quartz phenocrysts containing large albite grains distributed in the core and small albite grains distributed in the mantle, and (2) small snowball quartz crystals containing small albite grains. The granite is characterized by high SiO₂ (7.15–73.44 wt%), K₂O (4.70–5.10 wt%) and Na₂O (4.93–5.21 wt%) contents, low CaO (0.41–0.71 wt%), MgO (0.03–0.05 wt%), Fe₂O₃ (0.87–0.94 wt%), TiO₂ (0.02–0.03 wt%) and ΣREE (7.10–9.80 ppm) contents. The granite has similar mineral and chemical composition with the aplite in the area, and they were derived from the residual melt of the Shuiquangou magma that suffered assimilation fractional crystallization process. Fluid inclusions in the quartz phenocrysts have homogenization temperatures of 260–380 °C and salinities of 1.4–12.4 wt% NaCl equiv. for liquid + vapor type inclusions and 34.1–44.3 wt% NaCl equiv. for brine ones. The quartz phenocrysts exhibit homogeneous cathodoluminescence without growth bands or zoning. The trace element contents in the quartz phenocrysts are extremely low (Ti 3.4–5.1 ppm, Al 13–118 ppm, Li < 0.1 ppm, Ge < 0.5 ppm) compared to published data of igneous quartz, which may result from the crystallizing conditions of quartz and chemical compositions of the magma. Crystal size distributions (CSD) of albite in quartz show that the snowball quartz formed in two stages, whereby an increase in nucleation and growth rates resulted in the core-mantle texture of quartz phenocrysts. The co-existence of low-, high-salinity and melt inclusions indicates that the quartz phenocrysts crystallized rapidly in a fluid-enriched magma. Magmatic flow led to mineral rotation and resulted in the rounded and sub-rounded shapes of the quartz phenocrysts. Fluid exsolved from the magma raised nucleation and growth rates and resulted in the two types of snowball quartz.

Graphical abstract

Introduction

Rounded to sub-rounded quartz phenocrysts occur in many granites, volcanic rocks, metamorphic rocks and hydrothermal deposits (Bineli Betsi and Lentz, 2010; Breiter et al., 2017; Müller et al., 2002, Müller et al., 2010; Spear and Wark, 2009). These quartz phenocrysts may derive from a variety of processes, namely (a) crystallization in a high-temperature magma chamber (Vernon, 1986), (b) crystallization in a magmatic-hydrothermal system (Breiter et al., 2017; Larsen et al., 2004) or in a sub-volcanic magma chamber (Müller et al., 2002, Müller et al., 2010), and (c) disaggregation and recrystallization of early quartz-rich bodies (Spear and Wark, 2009). In situ determination of trace element compositions of quartz phenocrysts has been made possible by the developments of laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) (Garate-Olave et al., 2017; Götze et al., 2004), which is a useful tool for deciphering the formation of quartz phenocrysts.

Trace element composition in quartz is controlled by pressure, temperature (Thomas et al., 2010), crystallization rate (Lowenstern and Sinclair, 1996), and chemical composition of melt (Jacamon and Larsen, 2009). Trace elements such as Al, Ti, Ge, and Li, which are the most common in quartz, have been used to distinguish the origin and forming conditions of quartz crystal growth environment in granites, pegmatites, rhyolites, metamorphic rocks and hydrothermal deposits (Bineli Betsi and Lentz, 2010; Breiter et al., 2005, Breiter et al., 2012, Breiter et al., 2013; Breiter and Müller, 2009; Drivenes et al., 2016; Garate-Olave et al., 2017; Götte et al., 2011; Jacamon and Larsen, 2009; Larsen et al., 2004; Mao et al., 2017; Müller et al., 2002, Müller et al., 2018; Rusk et al., 2008a; Spear and Wark, 2009). Some petrogenetic indicators have been established based on concentrations of trace elements in quartz, such as the TitaniQ geothermobarometer based on Ti contents (Huang and Audétat, 2012; Thomas et al., 2010; Wark and Watson, 2006), and Ge/Ti and Al/Ti ratios to reflect degree of magma differentiation (Breiter and Müller, 2009; Jacamon and Larsen, 2009; Larsen et al., 2004; Müller et al., 2010), as well as Ge/Al ratio to distinguish between hydrothermal and magmatic quartz (Müller et al., 2018).

Cathodoluminescence (CL) microscopy is useful for visualizing growth episodes, recrystallization, resorption and hydrothermal events of quartz (Müller et al., 2000; Rusk et al., 2008a, Rusk, 2012; Spear and Wark, 2009). CL intensity is controlled by trace element compositions in quartz. The combination of CL textures and trace element compositions can be used to detect the origin and evolution of quartz (Rusk, 2012).

The Dongping porphyritic granite was first reported by Xu et al. (2017). It is composed mainly of quartz phenocrysts and tiny feldspars. Xu et al. (2017) argued that the quartz phenocrysts may have formed initially in a supersaturated SiO₂ fluid and suffered alteration in later hydrothermal events. Homogenization temperatures of fluid inclusions in the quartz phenocrysts were slightly higher than those of gold-rich vein quartz, and may indicate genetic relationship between the granite and the Dongping gold deposit (Xu et al., 2017, Xu et al., 2018). The quartz in the Dongping porphyritic granite contains many albite crystals, and it is called “snowball” quartz. Recently, the origin of snowball quartz is still under debate and some researchers consider that it formed through metasomatism (Sonyushkin et al., 1991; Wu et al., 2018) while others argue that it is magmatic in origin (Li et al., 2000; Müller et al., 2002; Müller and Seltmann, 1999). The snowball quartz in the Dongping porphyritic granite has different textures and trace element compositions compared to classical ones from rare-metal granites, and studies on these samples would shed new lights on the origin and forming process of snowball quartz.

This paper aims to decipher the origin and evolution of the Dongping porphyritic granite and the snowball quartz based on (a) whole-rock chemistry of the granite, (b) fluid inclusions, CL textures and trace elements of quartz, and (c) crystal size distributions of quartz and the hosted albite.

Section snippets

Geological background and petrology

The Dongping district, situated at the north margin of the North China Craton (Fig. 1a), is famous for many gold deposits, such as the Dongping and Xiaoyingpan gold deposits (Fig. 1b). The stratigraphic units exposed in the district are the Archean Sanggan Formation, Proterozoic Hongqiyingzi, Changcheng and Jixian Formations, Cretaceous Zhangjiakou Formation and Quaternary sediments (Fig. 1b). The Archean Sanggan metamorphic complex, exposed south of the Shangyi–Chongli–Chicheng fault, is

Whole-rock major and trace elements analysis

Whole rock major, trace and rare earth elements were determined from the porphyritic granite at the ALS Chemex Co., Ltd., Guangzhou, China. Major elements were analyzed by X–ray fluorescence (XRF) and a PANalytical Axios XRF instrument using a lithium metaborate fusion technique for digestion. The analytical precision is better than 5%. Trace and rare earth elements (REEs) were analyzed by an Agilent 7700× ICP–AES (inductively coupled plasma atomic emission spectrometer) and an Agilent VISTA

Whole-rock geochemistry

Chemical analyses for four samples (Supplementary Table 1) show that the porphyritic granite has relatively high SiO₂ (72.15–73.44 wt%), K₂O (4.70–5.10 wt%) and Na₂O (4.93–5.21 wt%), moderate Al₂O₃ (14.16–14.93 wt%), low Fe₂O_3T (0.87–0.94 wt%) and CaO (0.41–0.71 wt%), and extremely low MgO (0.03–0.05 wt%) and TiO₂ (0.02–0.03 wt%), and P₂O₅ was below detection limit (<0.01 wt%). The porphyritic granite has A/CNK (molar Al₂O₃/(CaO + Na₂O + K₂O)) values of 0.97–1.03, showing metaluminous to

Petrogenesis of the Dongping porphyritic granite

The Dongping porphyritic granite is characterized by high SiO₂, K₂O and Na₂O contents, low CaO, MgO, Fe₂O_3T, TiO₂, P₂O₅ and ΣREE contents, and absence of accessory minerals. To investigate the origin of the porphyritic granite, mineral and chemical compositions of the porphyritic granite, the Shuiquangou syenite and the aplite in the area are compared. The Shuiquangou syenite contains rare quartz, variable feldspars, clinopyroxene, amphibole, magnetite and garnet. The aplite contains more

Conclusion

(1)
The Dongping porphyritic granite has high contents of SiO₂, K₂O and Na₂O, low contents of CaO, MgO, Fe₂O₃, TiO₂ and ΣREE. It is derived from the residual melt of the Shuiquangou magma that suffered assimilation fractional crystallization process.
(2)
Fluid inclusions in the quartz phenocrysts have homogenization temperatures of 260–380 °C. The co-existence of low- and high-salinity fluid and melt inclusions indicates that these were trapped at conditions of 1.5–2.8 kbars and 645–690 °C.
(3)
The low

Acknowledgements

This project received funding from National Natural Science Foundation of China (Grant #41573036 and 41730426), Major Basic Research Program of People's Republic of China (Grant #2014CB440903), MOST Special Fund from the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, 111 Project under the Ministry of Education and the State Administration of Foreign Experts Affairs, China (Grant #B07011), and the Fundamental Research Funds for the Central

References (72)

A. Audétat
Origin of Ti-rich rims in quartz phenocrysts from the Upper Bandelier Tuff and the Tunnel Spring Tuff, southwestern USA
Chem. Geol.
(2013)
A. Audétat et al.
The genesis of Climax-type porphyry Mo deposits: Insights from fluid inclusions and melt inclusions
Ore Geol. Rev.
(2017)
Z.W. Bao et al.
Metallogeny of the syenite-related Dongping gold deposit in the northern part of the North China Craton: a review and synthesis
Ore Geol. Rev.
(2016)
K. Breiter et al.
Textural and chemical evolution of a fractionated granitic system: the Podlesí stock, Czech Republic
Lithos
(2005)
K. Breiter et al.
Trace element composition of quartz from the Variscan Altenberg–Teplice caldera (Krušné hory/Erzgebirge Mts, Czech Republic/Germany): Insights into the volcano-plutonic complex evolution
Chem. Geol.
(2012)
K. Breiter et al.
Behavior of trace elements in quartz from plutons of different geochemical signature: a case study from the Bohemian Massif, Czech Republic
Lithos
(2013)
K. Breiter et al.
Quartz chemistry – a step to understanding magmatic-hydrothermal processes in ore-bearing granites: Cínovec/Zinnwald Sn-W-Li deposit, Central Europe
Ore Geol. Rev.
(2017)
K. Drivenes et al.
Crystallization and uplift path of late Variscan granites evidenced by quartz chemistry and fluid inclusions: example from the Land's End granite, SW England
Lithos
(2016)
I. Garate-Olave et al.
Extreme fractionation in a granite–pegmatite system documented by quartz chemistry: the case study of Tres Arroyos (Central Iberian Zone, Spain)
Lithos
(2017)
J. Götze et al.
Trace element incorporation into quartz: a combined study by ICP-MS, electron spin resonance, cathodoluminescence, capillary ion analysis, and gas chromatography
Geochim. Cosmochim. Acta
(2004)

R.F. Huang et al.

The titanium-in-quartz (TitaniQ) thermobarometer: a critical examination and re-calibration

Geochim. Cosmochim. Acta

(2012)

F. Jacamon et al.

Trace element evolution of quartz in the charnockitic Kleivan granite, SW-Norway: the Ge/Ti ratio of quartz as an index of igneous differentiation

Lithos

(2009)

T.G. Lan et al.

Metasomatized asthenospheric mantle contributing to the generation of Cu-Mo deposits within an intracontinental setting: a case study of the ∼128 Ma Wangjiazhuang Cu-Mo deposit, eastern North China Craton

J. Asian Earth Sci.

(2018)

Y.S. Liu et al.

In situ analysis of major and trace elements of anhydrous minerals by LA-ICP-MS without applying an internal standard

Chem. Geol.

(2008)

L.C. Miao et al.

SHRIMP U–Pb zircon geochronology of granitoids from Dongping area, Hebei Province, China constraints on tectonic evolution and geodynamic setting for gold metallogeny

Ore Geol. Rev.

(2002)

D.J. Morgan et al.

Combining CSD and isotopic microanalysis: magma supply and mixing processes at Stromboli Volcano, Aeolian Islands, Italy

Earth Planet. Sci. Lett.

(2007)

A. Müller et al.

Chemistry of quartz related to the Zinnwald/Cínovec Sn-W-Li greisen-type deposit, Eastern Erzgebirge, Germany

J. Geochem. Explor.

(2018)

G.S. Pokrovski et al.

Thermodynamic properties of aqueous Ge(IV) hydroxide complexes from 25 to 350°C: implications for the behavior of germanium and the Ge/Si ratio in hydrothermal fluids

Geochim. Cosmochim. Acta

(1998)

A. Vollbrecht et al.

Development of microcracks in granites during cooling and uplift: examples from the Variscan basement in NE Bavaria, Germany

J. Struct. Geol.

(1991)

A. Vollbrecht et al.

Crystallographic orientation of microcracks in quartz and inferred deformation processes: a study on gneisses from the German Continental Deep Drilling Project (KTB)

Tectonophysics

(1999)

Y.H. Wang et al.

Genesis of the wurinitu W-Mo deposit, inner mongolia, Northeast China: constraints from geology, fluid inclusions and isotope systematics

Ore Geol. Rev.

(2018)

P. Armienti

Decryption of igneous rock textures: crystal size distribution tools

Rev. Mineral. Geochem.

(2008)

A. Audétat et al.

Characterisation of a natural quartz crystal as a reference material for microanalytical determination of Ti, Al, Li, Fe, Mn, Ga and Ge

Geostand. Geoanal. Res.

(2015)

S.P. Becker et al.

Synthetic fluid inclusions. XVII.1 PVTX properties of high salinity H2O-NaCl solutions (> 30 wt % NaCl): application to fluid inclusions that homogenize by halite disappearance from porphyry copper and other hydrothermal ore deposits

Econ. Geol.

(2008)

T. Bineli Betsi et al.

The nature of “quartz eyes” hosted by dykes associated with Au-Bi-As-Cu, Mo-Cu, and Base-metal-Au-Ag mineral occurrences in the Mountain Freegold region (Dawson Range), Yukon, Canada

J. Geosci.

(2010)

R.J. Bodnar et al.

Interpretation of microthermometric data for H₂O-NaCl fluid inclusions

S.J. Boggs et al.

Is quartz cathodoluminescence color a reliable provenance tool? A quantitative examination

J. Sediment. Res.

(2002)

K. Breiter et al.

Evolution of rare-metal granitic magmas documented by quartz chemistry

Eur. J. Mineral.

(2009)

H. Cabane et al.

Experimental investigation of the kinetics of Ostwald ripening of quartz in silicic melts

Contrib. Mineral. Petrol.

(2001)

X.D. Deng et al.

U-Pb geochronology of hydrothermal zircons from the early cretaceous iron skarn deposits in the Handan-xingtai district, North China Craton

Econ. Geol.

(2015)

W.H. Dennen

Stoichiometric substitution in natural quartz

Geochim. Cosmochim. Acta

(1996)

T. Driesner et al.

Numerical simulation of multiphase fluid flow in hydrothermal systems

Rev. Mineral. Geochem.

(2007)

M.S. Ghiorso et al.

A method for estimating the activity of titania in magmatic liquids from the compositions of coexisting rhombohedral and cubic iron–titanium oxides

Contrib. Mineral. Petrol.

(2013)

T. Götte et al.

Cathodoluminescence properties and trace element signature of hydrothermal quartz: a fingerprint of growth dynamics

Am. Mineral.

(2011)

J. Götze et al.

Structure and luminescence characteristics of quartz from pegmatites

Am. Mineral.

(2005)

M.D. Higgins

Measurement of crystal size distributions

Am. Mineral.

(2000)

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Formation and evolution of snowball quartz phenocrysts in the Dongping porphyritic granite, Hebei Province, China: Insights from fluid inclusions, cathodoluminescence, trace elements, and crystal size distribution study

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Geological background and petrology

Whole-rock major and trace elements analysis

Whole-rock geochemistry

Petrogenesis of the Dongping porphyritic granite

Conclusion

Acknowledgements

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