Characteristics of Ore-forming Fluids of the Nanmingshui Gold Deposit in the East Junggar, Xinjiang: Evidences from Fluid Inclusions and H-O Isotopes

doi:10.19657/j.geoscience.1000-8527.2018.05.03

Abstract

Abstract:

The Nanmingshui gold deposit is located in the eastern part of the Kalamaili metallogenic belt. Its ore-bodies, controlled by the NW—NWW trending ductile-brittle faults, are hosted in epimetamorphic marine volcaniclastic sedimentary rocks of the Lower Carboniferous Jiangbasitao Formation. Based on the studies of fluid inclusions and hydrogen and oxygen isotopic geochemistry, the properties, source and evolution of ore-forming fluids are discussed in this paper. The ore-forming process can be divided into three metallogenic stages including the early, middle and late stages. Three types of fluid inclusions that include CO₂-H₂O, H₂O-NaCl and pure CO₂ inclusions are identified in the quartz of the Nanmingshui gold deposit. The early-stage quartz mainly contains CO₂-H₂O and pure CO₂ inclusions with homogenization temperatures and salinities ranging from 257 ℃ to 339 ℃ and 0.4% to 2.2%. All three types of inclusions are trapped in the middle(main)-stage quartz. The homogenization temperatures and salinities of CO₂-H₂O and H₂O-NaCl inclusions vary from 196 ℃ to 361 ℃ and 0.4% to 6.0%. Only H₂O-NaCl inclusions are found in the late stage quartz with relatively lower homogenization temperatures clustering at 174 ℃ to 252 ℃. Meanwhile, the salinities of H₂O-NaCl inclusions vary from 1.4% to 3.2%. According to the estimation from CO₂-H₂O inclusions, the minimum trapping pressures for early and middle stages are 214 MPa to 371 MPa and 236 MPa to 397 MPa, respectively, corresponding to the metallogenic depths of 8.1 km to 14.0 km and 8.9 km to 15.0 km, respectively. The studies of fluid inclusions in different metallogenic stages indicate that the metallogenetic temperatures and fluid densities show a decreasing trend, as the ore-forming fluids are evolved from CO₂-H₂O-NaCl±CH₄ system in the early and middle stages to H₂O-NaCl system in the late stage. Fluid inclusions and hydrogen and oxygen isotopic studies show that the ore-forming fluids of the main metallogenic stage were dominantly originated from metamorphic water. The immiscibility of CO₂-H₂O-NaCl fluids is an important mechanism that leads to the gold precipitation and enrichment. The genesis of the Nanmingshui gold deposit is a mesozonal to hypozonal orogenic gold deposit.

Key words: fluid inclusion, H-O isotope, fluid immiscibility, Nanmingshui gold deposit, Xinjiang

CLC Number:

P618.51

GE Zhanlin, ZHANG Yongmei, GU Xuexiang, CHEN Weizhi, XU Jinchi, WU Ruochen, HUANG Gang. Characteristics of Ore-forming Fluids of the Nanmingshui Gold Deposit in the East Junggar, Xinjiang: Evidences from Fluid Inclusions and H-O Isotopes[J]. Geoscience, 2018, 32(05): 887-901.

Figures/Tables 10

Fig.1 The main tectonic unit map of northern area in Xinjiang (A), paleoplate tectonic map of Kalamaili area (B) and regional geological sketch map of Kalamaili area (C)

Fig.2 Geologic map of the Nanmingshui gold deposit

Fig.3 The characteristics of ore body,ore and shear zone in the Nanmingshui gold deposit

Fig.4 Typical ore texture and mineral associations in the Nanmingshui gold deposit

Fig.5 Microphotographs of fluid inclusions of the Nanmingshui gold deposit

Table 1 Microthermometric data of fluid inclusions from the Nanmingshui gold deposit

成矿阶段	包裹体类型	$t m, C O 2$ /℃ 范围/测定数/均值	t_m,cla/℃ 范围/测定数/均值	$t h, C O 2$ /℃ 范围/测定数/均值	t_m,ice/℃ 范围/测定数/均值	t_h/℃ 范围/测定数/均值
早阶段	CO₂-H₂O	-58.2~-57.4/10/-57.8	8.9~ 9.8/14/9.5	18.8~26.8/16/23.2		257~339/17/298
	V-L				-3.7~-1.4/26/-2.5	196~333/36/268
中阶段	CO₂-H₂O	-62.2~-56.0/36/-58.3	7.5~9.8/43/9.0	15.4~28.8/46/21.9		215~361/46/280
	纯CO₂	-61.5~-57.2/7/-59.0		12.3~19.0/7/16.1
晚阶段	V-L				-1.9~-0.8/10/-1.2	174~252/20/212

Table 1 Microthermometric data of fluid inclusions from the Nanmingshui gold deposit

成矿阶段	包裹体类型	$t m, C O 2$ /℃ 范围/测定数/均值	t_m,cla/℃ 范围/测定数/均值	$t h, C O 2$ /℃ 范围/测定数/均值	t_m,ice/℃ 范围/测定数/均值	t_h/℃ 范围/测定数/均值
早阶段	CO₂-H₂O	-58.2~-57.4/10/-57.8	8.9~ 9.8/14/9.5	18.8~26.8/16/23.2		257~339/17/298
	V-L				-3.7~-1.4/26/-2.5	196~333/36/268
中阶段	CO₂-H₂O	-62.2~-56.0/36/-58.3	7.5~9.8/43/9.0	15.4~28.8/46/21.9		215~361/46/280
	纯CO₂	-61.5~-57.2/7/-59.0		12.3~19.0/7/16.1
晚阶段	V-L				-1.9~-0.8/10/-1.2	174~252/20/212

Fig.6 Histograms of homogenization temperatures and salinities of fluid inclusions from the Nanmingshui gold deposit

Fig.7 Laser Raman spectra of fluid inclusions from the Nanmingshui gold deposit

Table 2 Hydrogen and oxygen isotopic compositions of hydrothermal minerals from the Nanmingshui gold deposit

样品号	矿物	δ¹⁸O_V-SMOW/‰	δD_V-SMOW/‰	δ¹⁸ $O H 2 O$ /‰	t_h/℃	数据来源
NMS4-29	石英	14.1	-95.0	5.99	269	本文
NMS4-30	石英	19.0	-92.0	10.89	269
NMS7-06	石英	14.8	-82.0	5.98	253
NMS7-07	石英	19.7	-99.0	10.88	253
SQD-84	石英	13.3	-99.0	3.9	256	徐斌等^[29],2010
6N-53	石英	13.9	-62.9	5.2	255	高怀忠等^[30],2000

Table 2 Hydrogen and oxygen isotopic compositions of hydrothermal minerals from the Nanmingshui gold deposit

样品号	矿物	δ¹⁸O_V-SMOW/‰	δD_V-SMOW/‰	δ¹⁸ $O H 2 O$ /‰	t_h/℃	数据来源
NMS4-29	石英	14.1	-95.0	5.99	269	本文
NMS4-30	石英	19.0	-92.0	10.89	269
NMS7-06	石英	14.8	-82.0	5.98	253
NMS7-07	石英	19.7	-99.0	10.88	253
SQD-84	石英	13.3	-99.0	3.9	256	徐斌等^[29],2010
6N-53	石英	13.9	-62.9	5.2	255	高怀忠等^[30],2000

Fig.8 Plots of δ18O-δD for the ore-forming fluids in the Nanmingshui gold deposit (modified after Sheppard[32], 1986)

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