Chemical and boron isotopic variations of tourmaline deciphering magmatic-hydrothermal evolution at the Gejiu Sn-polymetallic district, South China

doi:10.1016/j.chemgeo.2021.120698

	Chemical and boron isotopic variations of tourmaline deciphering magmatic-hydrothermal evolution at the Gejiu Sn-polymetallic district, South China
	Guo, Jia 1; Xiang, Lu 1; Zhang, Rongqing 2,3; Yang, Tao 2; Wu, Kai 4; Sun, Weidong5
	2022-03-30
发表期刊	CHEMICAL GEOLOGY
ISSN	0009-2541
卷号	593 页码:20
通讯作者	Zhang, Rongqing([email protected])
摘要	The world-class Gejiu Sn-polymetallic district (southwest China), with ca. 3.27 Mt Sn metal, is a magmatic-hydrothermal deposit associated with the Late Cretaceous biotite granites; however, the magmatic and hydrothermal processes involved in its formation remain poorly understood. Tourmaline is a ubiquitous phase in the Gejiu district, and here we employ in-situ major, trace element, and boron isotope compositions of tourmaline to investigate the source and evolution of the mineralizing fluid, and late-magmatic and hydrothermal processes related to ore formation. Based on petrographic observations, four types of tourmaline are identified: i) latemagmatic tourmaline (Tur I) disseminated in the biotite granites, ii) hydrothermal tourmaline (Tur II) from quartz veins with fracture-filling structure in the biotite granites, iii) hydrothermal tourmaline (Tur IIIa-1, IIIa-2 and Tur IIIb-1, IIIb-2) from fluorite-quartz veins with typical replacement texture against the greisenized granites, among which Tur IIIb-2 is directly related to cassiterite formation, and iv) hydrothermal tourmaline (Tur IV) from sulfide-calcite veins hosted by proximal skarn. Tourmaline (Tur Ito Tur III) from the granites belongs mostly to the alkali group and schorl-dravite solid-solution series, with Fe/(Fe + Mg) ranging from 0.83-1.00 for Tur I, 0.68-1.00 for Tur II, and 0.19-1.00 for Tur III, respectively. By contrast, Tur IV belongs mostly to the vacancy group and has foitite-Mg-foitite composition, with Fe/(Fe + Mg) of 0.10-1.00. Large variations of Fe/(Fe + Mg) as well as Na/(Na + Ca) in hydrothermal tourmaline (Tur II to Tur IV), are related to different degrees of interaction between B-rich fluids with host rocks (solidified granite or carbonate). Most trace elements in tourmaline do not correlate with Fe/(Fe + Mg) and Na/(Na + Ca) ratios, implying the trace element compositions are predominantly controlled by melt/fluid compositions and local fluid-rock reactions. Relative to late-magmatic Tur I, hydrothermal tourmaline (Tur II to Tur IV) is enriched in Sr and depleted in Nb, Ta, and (REE + Y), whereas their Li, Be, Sc, V, and Sn concentrations are largely overlapped. The delta B-11 values in different types of tourmaline fall in a narrow range from -17.8 to -13.7 parts per thousand, in favor of B-rich fluids episodically exsolved from the granitic melt. Tin enrichment in both late-magmatic and hydrothermal tourmaline grains, especially in those (Tur IIIb) from Sn-mineralized veins, is related to magmatic differentiation and late-stage fluid exsolution. Among all types of tourmaline, Tur IIIb-2 coexisting with cassiterite has elevated Fe3+/(Fe3+ + Fe2+) ratios (mean 0.23), indicating that cassiterite precipitated under relatively oxidized conditions. The distinct chemical (i.e. high Mg, Ti, V, Sc, Sr, and Sn contents) and B-isotope compositions (slightly lower delta B-11 values of -17.8 to -15.0 parts per thousand) in syn-ore Tur IIIb-2, combined with the co-occurrence of liquid- and vapor-rich inclusions triggered by fluid boiling in Sn-mineralized veins, suggest that fluid boiling and acid-consuming reaction could be major processes triggering cassiterite precipitation in the quartz vein and greisen. Overall, the chemical and B-isotope signatures of tourmaline are ideal tracers to unravel the magmatic-hydrothermal evolution in the Gejiu Sn-polymetallic district, which could be further employed as a potential prospecting guide for Sn-W deposits.
关键词	Tourmaline Mineral chemistry Boron isotope Magmatic-hydrothermal evolution Gejiu Sn-polymetallic district South China
DOI	10.1016/j.chemgeo.2021.120698
收录类别	SCI
语种	英语
资助项目	National Natural Science Foundation of China[42102108]; Fundamental Research Funds for the Central Universities[DLTD2104]
WOS研究方向	Geochemistry & Geophysics
WOS类目	Geochemistry & Geophysics
WOS记录号	WOS:000768027500001
出版者	ELSEVIER
引用统计	被引频次：18[WOS] [WOS记录] [WOS相关记录]
文献类型	期刊论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/178613
专题	深海极端环境与生命过程研究中心
通讯作者	Zhang, Rongqing
作者单位	1.Chengdu Univ Technol, Coll Earth Sci, Chengdu 610059, Peoples R China 2.Nanjing Univ, Sch Earth Sci & Engn, State Key Lab Mineral Deposits Res, Nanjing 210023, Peoples R China 3.Nanjing Univ, Frontiers Sci Ctr Crit Earth Mat Cycling, Nanjing 210023, Peoples R China 4.Northwest Univ, Dept Geol, State Key Lab Continental Dynam, Xian 710069, Peoples R China 5.Chinese Acad Sci, Ctr Deep Sea Res, Inst Oceanol, Qingdao 266071, Peoples R China
推荐引用方式 GB/T 7714	Guo, Jia,Xiang, Lu,Zhang, Rongqing,et al. Chemical and boron isotopic variations of tourmaline deciphering magmatic-hydrothermal evolution at the Gejiu Sn-polymetallic district, South China[J]. CHEMICAL GEOLOGY,2022,593:20.
APA	Guo, Jia,Xiang, Lu,Zhang, Rongqing,Yang, Tao,Wu, Kai,&Sun, Weidong.(2022).Chemical and boron isotopic variations of tourmaline deciphering magmatic-hydrothermal evolution at the Gejiu Sn-polymetallic district, South China.CHEMICAL GEOLOGY,593,20.
MLA	Guo, Jia,et al."Chemical and boron isotopic variations of tourmaline deciphering magmatic-hydrothermal evolution at the Gejiu Sn-polymetallic district, South China".CHEMICAL GEOLOGY 593(2022):20.

条目包含的文件
文件名称/大小	文献类型	版本类型	开放类型	使用许可
1-s2.0-S000925412100（10441KB）	期刊论文	出版稿	限制开放	CC BY-NC-SA	浏览