Ore-forming Fluid Evolution and Genesis of the Dadiangou Gold Deposit in the Western Qinling Metallogenic Belt

doi:10.19657/j.geoscience.1000-8527.2021.113

Abstract

Abstract:

Located in the Western Qinling Metallogenic belt, the Dadiangou gold deposit is a newly discovered medium-sized gold deposit. The orebody occurs in the sericite-chlorite-quartz schist of Lower Paleozoic Danfeng Group (Muqitan Formation). The brittle structures (superimposed by NE-trending brittle-ductile shear zone) is the ore-forming structure. Based on geological characteristics, this study systematically studies the fluid inclusions, stable isotope geochemistry, ore-fluid evolution, and metallogenesis. The ore formation can be divided into four stages, among which the heteromorphic granular pyrite and the quartz-polymetallic sulfide stages are the main ore stages. Fluid inclusions include mainly aqueous, CO₂-bearing three phase and pure CO₂ aqueous types. The homogenization temperature of the ore-forming fluids was mainly 120 to 256 ℃, and the salinity is of 4.03% to 15.27% NaCl eqv. The H-O isotopic data show that the ore-forming fluid was mainly derived from the meteoric water mixed with metamorphic water. Characteristics of S isotopes indicate that the ore-forming materials were mainly deep sourced. Strong water-rock reaction and fluid boiling is the main gold precipitation mechanism. In summary, the Dadiangou is best classified as orogenic gold type. By summarizing the characteristics of relief wave of the ore-forming structural plane, we suggest that the ore-forming fluid ascended and precipitated from the southwest to the northeast, forming the segmented mineralization.

Key words: Western Qinling, Dadiangou gold deposit, ore-fluid evolution, orogenic gold deposit, ore-forming structural plane

CLC Number:

P618.51

MIAO Guang, DONG Guochen, QU Hailang, LIU Shufei, AI Zhonglin, SHI Pengliang, CAO Xuefeng. Ore-forming Fluid Evolution and Genesis of the Dadiangou Gold Deposit in the Western Qinling Metallogenic Belt[J]. Geoscience, 2021, 35(06): 1565-1575.

Figures/Tables 14

Fig.1 Simplified regional geological and mineral map of the Western Qinling region(a)(modified after reference[11]) and simplified regional geological map of the Dadiangou gold deposit(b)

Fig.2 Simplified geological map of the Dadiangou gold deposit (modified after reference[15])

Fig.3 Geological map of the 1,700 m level tunnel (a) and profile of Exploration Line No.8 (b) of the Dadiangou gold deposit

Fig.4 Photos showing the characteristics of typical ores and rocks in the Dadiangou deposit

Fig.5 Photos showing the characteristics of main metallogenic stages in the Dadiangou deposit

Fig.6 Microscopic photos of fluid inclusions from the Dadiangou gold deposit

Table 1 Statistics of fluid physical properties in the Dadiangou gold deposit

成矿阶段	均一温度T_h/ ℃	冰点温度T_m/ ℃	流体盐度w(NaCl)/ %	流体密度ρ/ (g/cm³)	压力p/10⁶ Pa	寄主矿物
Ⅰ阶段 (n=4)	168~214 (200)	-7.9~-4.3 (-6.4)	6.9~11.6 (9.65)	0.86~0.93 (0.89)	46.7~59.6 (55.0)	石英
Ⅱ阶段 (n=23)	157~256 (187)	-11~-0.5 (-7.2)	6.88~15.27 (11.03)	0.82~0.94 (0.9)	43.4~70.1 (51.8)	石英
Ⅲ阶段 (n=15)	132~192 (165)	-8.6~-2.4 (-6.0)	4.03~12.39 (9.07)	0.90~0.97 (0.93)	36.4~52.8 (45.3)	石英
Ⅳ阶段 (n=6)	120~170 (147)	-8.6~-2.4 (-6.7)	4.03~12.39 (9.94)	0.93~0.98 (0.95)	32.6~47.2 (40.5)	石英/方解石

Fig.7 Histograms of homogenization temperature (a) and salinity (b) of the Dadiangou gold ore-forming fluid

Fig.8 Laser-Raman analysis of fluid inclusions(stage II aqueous fluid inclusions(a),stage III CO2-CH4 fluid inclusions(b))from the Dadiangou gold deposit

Table 2 Quartz H-O isotope compositions of the Da-diangou gold deposit

成矿阶段	样品类别	δ¹⁸ $O H 2 O$ /‰	δ $D V - SMOW$ /‰	δ¹⁸O_V-SMOW /‰	温度 /℃
它形黄铁矿阶段	石英	1.34	-88.1	13.4	194.5
	石英	1.96	-90.6	13.2	207.4
	石英	2.17	-81.4	14.0	197.9
	石英	1.81	-91.9	14.3	188.1
	石英	2.24	-84.9	13.8	202.2
多金属硫化物阶段	石英	1.17	-98.7	14.8	172.4
多金属硫化物阶段	石英	-0.06	-87.9	13.2	177.3

Table 2 Quartz H-O isotope compositions of the Da-diangou gold deposit

成矿阶段	样品类别	δ¹⁸ $O H 2 O$ /‰	δ $D V - SMOW$ /‰	δ¹⁸O_V-SMOW /‰	温度 /℃
它形黄铁矿阶段	石英	1.34	-88.1	13.4	194.5
	石英	1.96	-90.6	13.2	207.4
	石英	2.17	-81.4	14.0	197.9
	石英	1.81	-91.9	14.3	188.1
	石英	2.24	-84.9	13.8	202.2
多金属硫化物阶段	石英	1.17	-98.7	14.8	172.4
多金属硫化物阶段	石英	-0.06	-87.9	13.2	177.3

Fig.9 δ18O vs δD diagram of the Dadiangou gold ore-forming fluid (base map after reference [29])

Table 3 Sulfur isotope compositions of the Dadiangou gold deposit

序号	样号	取样位置	期次	δ³⁴S/‰
1	1650-8-T1	灰黑色片岩	-	9.0
2	1650-8-T3	无矿化褪色片岩	-	3.6
3	1650-8-T4	Au⑤矿体石英脉	大店沟成矿期	-0.2
4	1650-8-T6	Au①矿体	大店沟成矿期	1.7
5	1650-8-T8	Au④矿体	大店沟成矿期	1.5
7	T-1650-01	矿化石英脉	大店沟成矿期	1.0
8	T-1650-04	4号矿体石英复脉带	大店沟成矿期	0.2

Fig.10 Sulfur isotope histogram of the Dadiangou gold deposit

Fig.11 Vertical projection of thickness contour of ore-forming structural plane in the Dadiangou gold deposit

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