内蒙古阿扎哈达铜铋矿床流体包裹体和碳-氧-硫-铅同位素地球化学研究

doi:10.13745/j.esf.sf.2020.3.28

摘要/Abstract

摘要：

阿扎哈达石英脉型铜铋矿床位于二连—东乌旗多金属成矿带中段。铜铋热液矿化过程从早到晚可以分为3个阶段,分别为石英-黄铁矿-黄铜矿阶段(Ⅰ)、石英-黄铁矿-黄铜矿-辉铜矿-辉铋矿-自然铋-萤石阶段(Ⅱ)和晚期石英-方解石阶段(Ⅲ)。铜铋矿化主要产于Ⅱ阶段石英脉中。流体包裹体类型主要为气液两相包裹体。测温结果显示Ⅰ阶段富气相包裹体均一温度变化范围为224~427 ℃,盐度(w(NaCl_eq)为16.0%~22.4%;富液相包裹体均一温度为229~410 ℃,盐度为9.2%~22.2%。Ⅱ阶段富气相包裹体均一温度为245~343 ℃,盐度为17.8%~20.5%;富液相包裹体均一温度为180~361 ℃,盐度为10.5%~21.3%。Ⅲ阶段富液相包裹体均一温度为132~262 ℃,盐度为3.4%~19.4%。成矿热液整体上属于中温、中等盐度流体。单个包裹体激光拉曼分析表明气液相成分主要是H₂O,含少量CH₄,指示成矿流体属于NaCl-H₂O±CH₄体系。C-O同位素数据(δ¹³C_V-PDB值范围为-6.7‰~-1.4‰,δ¹⁸O_V-SMOW值为-2.4‰~+11.5‰)表明成矿流体主要来源于岩浆水,晚阶段有大气降水的混入。黄铁矿S同位素组成(1.3‰~9.5‰)指示成矿物质主要来源于岩浆热液,并有部分地层物质加入。黄铁矿Pb同位素组成²⁰⁸Pb/²⁰⁴Pb、²⁰⁷Pb/²⁰⁴Pb和²⁰⁶Pb/²⁰⁴Pb值变化范围分别为38.081~38.229、15.561~15.602和18.270~18.383,所有数据点均落在造山带铅范围内,表明成矿物质主要来源于侵位的花岗岩,同时地层提供了部分成矿物质。结合流体包裹体和同位素地球化学研究,文章认为温度下降及水岩反应是导致矿质沉淀的重要机制。

关键词: 流体包裹体, C-O-S-Pb同位素, 阿扎哈达铜铋矿床, 内蒙古

Abstract:

The Azhahada quartz vein type copper-bismuth deposit is located in the middle segment of the Erlian-East Ujimqin polymetallic belt. Based on the fieldwork and microscope observations, as well as the mineral assemblages and crosscutting relationships of different veins, the hydrothermal mineralization of copper and bismuth at Azhahada has been divided into three stages from early to late: the quartz-pyrite-chalcopyrite early-stage I, the quartz-pyrite-chalcopyrite-chalcocite-bismuthinite-native bismuth-fluorite main-ore stage II, and the quartz-calcite late-stage III. The copper and bismuth mineralization is mainly hosted in the stage II quartz veins. The fluid inclusions at Azhahada are mainly composed of vapor-liquid two-phase inclusions. Microthermometric measurement results demonstrate that the vapor-rich inclusions in quartz of stage I are homogenized at temperatures of 224-427 ℃, with salinities of 16.0%-22.4% NaCl_eq, whereas the liquid-rich inclusions are homogenized at 229-410 ℃, with salinities of 9.2%-22.2% NaCl_eq. In main ore stage II, the vapor-rich and liquid-rich inclusions yield homogenization temperatures of 245-343 ℃, and 180-361 ℃, corresponding to salinities of 17.8%-20.5% NaCl_eq, and 10.5%-21.3% NaCl_eq, respectively. The liquid-rich inclusions in the quartz-calcite stage are homogenized at 132-262 ℃, with salinities of 3.4%-19.4% NaCl_eq. The ore-forming fluids are characterized by moderate temperature and moderate salinity. Laser Raman analyses of some individual representative inclusions suggest that their gaseous and liquid compositions are mainly H₂O, with trace amount of CH₄; thus, the fluids are dominated by the NaCl-H₂O±CH₄ system. The δ¹³C_V-PDB values of calcite are in the range of -6.7‰ to -1.4‰, with δ¹⁸O_V-SMOW values from -2.4‰ to+11.5‰. Combined with the δ¹⁸O-δ¹³C plots, it is suggested that the ore-forming fluids were mainly derived from magmatic water, with the addition of meteoric water in the late stage. The δ³⁴S_V-CDT values of pyrite are between 1.3‰ and 9.5‰, suggesting that the sulfur was dominantly derived from a magma source, and the enrichment of δ³⁴S likely resulted from the involvement of country rocks. Lead isotopic compositions indicate that the pyrite has²⁰⁸Pb/²⁰⁴Pb ratios of 38.081-38.229,²⁰⁷Pb/²⁰⁴Pb of 15.561-15.602, and²⁰⁶Pb/²⁰⁴Pb of 18.270-18.383, respectively. All of these observations combined with the stable and radiogenic isotope results reveal that the ore-forming materials were mainly sourced from the magmatic reservoir with some strata components, and temperature decreasing and the local water-rock reactions might be the critical mechanism of ore precipitation.

Key words: fluid inclusions, C-O-S-Pb isotopes, Azhahada Cu-Bi deposit, Inner Mongolia

中图分类号:

王银宏, 刘家军, 张梅, 张方方, 王康, 咸雪辰, 郭灵俊. 内蒙古阿扎哈达铜铋矿床流体包裹体和碳-氧-硫-铅同位素地球化学研究[J]. 地学前缘, 2020, 27(2): 391-404.

WANG Yinhong, LIU Jiajun, ZHANG Mei, ZHANG Fangfang, WANG Kang, XIAN Xuechen, GUO Lingjun. Fluid inclusion and C-O-S-Pb isotopic studies of the Azhahada Cu-Bi deposit in Inner Mongolia, China[J]. Earth Science Frontiers, 2020, 27(2): 391-404.

图/表 16

图1 内蒙古二连浩特—东乌旗成矿带阿扎哈达铜铋矿床区域地质图[6]

Fig.1 Regional geological map of the Azhahada Cu-Bi deposit in the Erlian-East Ujimqin metallogenic belt, Inner Mongolia. Adapted from [6].

图2 阿扎哈达铜铋矿床地质简图(据文献[18]修改)

Fig.2 Geological sketch map of the Azhahada Cu-Bi deposit. Modified from [18]

图3 阿扎哈达铜铋矿床不同阶段矿物共生组合 A—阶段Ⅰ石英-黄铁矿-黄铜矿脉;B—阶段Ⅰ石英-黄铁矿-黄铜矿脉及自形粗粒黄铁矿;C—阶段Ⅰ不规则石英-黄铁矿脉;D—阶段Ⅱ石英-黄铁矿-辉铋矿脉;E—阶段Ⅱ石英-黄铁矿-黄铜矿-辉铋矿脉;F—阶段Ⅱ石英-辉铋矿脉及石英-黄铁矿脉;G—阶段Ⅱ共生的萤石脉及团块状黄铁矿;H—阶段Ⅲ贫矿化石英-方解石脉;I—孔雀石化及蓝铜矿。Az—蓝铜矿;Bmt—辉铋矿;Cc—方解石;Cp—黄铜矿;Fl—萤石;Mal—孔雀石;Py—黄铁矿;Qz—石英。

Fig.3 Paragenetic mineral assemblages of different ore stages at the Azhahada Cu-Bi deposit

图4 阿扎哈达铜铋矿床矿物组合及蚀变特征 A—黄铁矿与黄铜矿共生;B—黄铜矿被辉铜矿交代;C—自然铋-辉铋矿脉;D—辉铋矿脉;E—黄铜矿微脉;F—贫矿化石英脉;G—黑云母绿泥石化、绿帘石化;H—绿泥石化;I—黑云母被石英交代。Bmt—辉铋矿;Bsm—自然铋;Cp—黄铜矿;Py—黄铁矿;Qz—石英。

Fig.4 Mineral associations and alteration features in the Azhahada Cu-Bi deposit

图5 阿扎哈达铜铋矿床矿物生成顺序

Fig.5 Paragenetic sequence for minerals in the Azhahada Cu-Bi deposit

图6 阿扎哈达铜铋矿床石英中流体包裹体显微照片 A—阶段Ⅰ富气两相包裹体(V-type);B—阶段Ⅰ富液两相包裹体(L-type);C—阶段Ⅰ共生的富气相及富液相包裹体; D,E—阶段Ⅱ共生的富气相及富液相包裹体;F—阶段Ⅱ孤立的富液两相包裹体;G-I—阶段Ⅲ富液两相包裹体。

Fig.6 Microphotographs of fluid inclusions in the quartz of the Azhahada Cu-Bi deposit

表1 阿扎哈达铜铋矿床不同阶段石英中流体包裹体测温结果

Table 1 Results of microthermometric measurements for fluid inclusions in quartz in different ore stages at the Azhahada Cu-Bi deposit

阶段	样品描述	包裹体类型	N	大小/μm	T_m,ice/℃	T_h/℃	盐度w(NaCl_eq)/%	密度/(g·cm^-3)
阶段Ⅰ	石英-黄铁矿-黄铜矿脉	L	38	4~15	-19.7~-6.0	229~410	9.2~22.2	1.06~1.16
		V	10	5~12	-19.8~-12.0	224~427	16.0~22.4	1.12~1.16
阶段Ⅱ	石英-多金属硫化物- 自然铋脉	L	36	4~14	-18.5~-7.0	180~361	10.5~21.3	1.08~1.16
		V	6	5~12	-17.4~-14.0	245~343	17.8~20.5	0.94~0.96
阶段Ⅲ	贫矿化石英-方解石脉	L	44	5~10	-16.0~-2.0	132~262	3.4~19.4	1.02~1.15

图7 阿扎哈达铜铋矿床流体包裹体均一温度直方图和盐度直方图

Fig.7 Histograms of homogenization temperatures and salinities of fluid inclusions in the Azhahada Cu-Bi deposit

图8 阿扎哈达铜铋矿床流体包裹体均一温度-盐度关系图解

Fig.8 Plot showing the relationship between homogenization temperature and salinity of fluid inclusions in the Azhahada Cu-Bi deposit

图9 流体包裹体激光拉曼光谱分析谱图

Fig.9 Laser Raman spectra for fluid inclusions from the Azhahada Cu-Bi deposit

表2 阿扎哈达铜铋矿床方解石碳氧同位素组成

Table 2 Carbon and oxygen isotope compositions of calcite from the Azhahada Cu-Bi deposit.

样品编号	矿物	δ¹³C_V-PDB/‰	δ¹⁸O_V-PDB/‰	δ¹⁸O_V-SMOW/‰
16SME-46-1	方解石	-1.5	-18.8	11.5
16SME-46-2	方解石	-1.4	-18.8	11.5
16SME-69-1	方解石	-6.6	-32.1	-2.4
16SME-69-2	方解石	-6.7	-32.3	-2.4

图10 阿扎哈达铜铋矿床方解石δ13CV-PDB-δ18OV-SMOW图解(底图据[26])

Fig.10 Diagram of δ13CV-PDB versus δ18OV-SMOW of the calcite from the Azhahada Cu-Bi deposit.Base map modified from [26].

表3 阿扎哈达铜铋矿床黄铁矿硫同位素组成

Table 3 Sulfur isotope compositions of pyrite from the Azhahada Cu-Bi deposit

样品编号	矿物	样品描述	δ³⁴S_V-CDT/‰
16SME-28	黄铁矿	阶段Ⅰ自形粗粒黄铁矿	6.8
16SME-29	黄铁矿	阶段Ⅰ自形粗粒黄铁矿	8.0
16SME-31	黄铁矿	阶段Ⅰ自形粗粒黄铁矿	6.3
16SME-32	黄铁矿	阶段Ⅰ自形粗粒黄铁矿	9.5
16SME-33	黄铁矿	阶段Ⅰ自形粗粒黄铁矿	5.4
16SME-51	黄铁矿	阶段Ⅱ细粒黄铁矿	4.5
16SME-52	黄铁矿	阶段Ⅱ细粒黄铁矿	5.3
16SME-53	黄铁矿	阶段Ⅱ细粒黄铁矿	7.1
16SME-56	黄铁矿	阶段Ⅱ细粒黄铁矿	1.3
16SME-57	黄铁矿	阶段Ⅱ细粒黄铁矿	1.4

图11 阿扎哈达铜铋矿床黄铁矿硫同位素组成直方图

Fig.11 Histogram of the sulfur isotopic compositions of the pyrite from the Azhahada Cu-Bi deposit

表4 阿扎哈达铜铋矿床黄铁矿铅同位素组成

Table 4 Lead isotope compositions of pyrite from the Azhahada Cu-Bi deposit

样品编号	矿物	²⁰⁸Pb/²⁰⁴Pb	2σ	²⁰⁷Pb/²⁰⁴Pb	2σ	²⁰⁶Pb/²⁰⁴Pb	2σ
16SME-28	黄铁矿	38.090	0.009	15.569	0.003	18.299	0.004
16SME-29	黄铁矿	38.081	0.008	15.579	0.003	18.270	0.002
16SME-31	黄铁矿	38.146	0.006	15.561	0.003	18.383	0.003
16SME-32	黄铁矿	38.229	0.007	15.602	0.002	18.357	0.002
16SME-33	黄铁矿	38.172	0.005	15.585	0.002	18.350	0.003

图12 阿扎哈达铜铋矿床硫化物铅同位素组成图解

Fig.12 A plot of lead isotopic compositions for sulfides from the Azhahada Cu-Bi deposit

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