Fluid inclusion and C-O-S-Pb isotopic studies of the Azhahada Cu-Bi deposit in Inner Mongolia, China

doi:10.13745/j.esf.sf.2020.3.28

Abstract

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

CLC Number:

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.

Figures/Tables 16

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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

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

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

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

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