Characteristics of Ore-Forming Fluids and Physicochemical Conditions for Ge Enrichment in the Wusihe Lead-Zinc Deposit, Sichuan

doi:10.19657/j.geoscience.1000-8527.2025.021

Abstract

Abstract:

The large-scale Wusihe lead-zinc deposit is a typical Ge-rich lead-zinc deposit in the Sichuan-Yunnan-Guizhou Metallogenic Belt.Although extensive prior research has been conducted on the characteristics of ore-forming fluids, as well as the occurrence and substitution mechanisms of Ge, the key physicochemical conditions controlling Ge enrichment remain unclear, which hinders a comprehensive understanding of its enrichment mechanisms. To address this, we performed petrological and mineralogical analyses, LA-ICP-MS analyses, and microthermometric analysis of fluid inclusions to systematically investigate the ore-forming fluids and Ge enrichment conditions of this deposit.Two stages of sphalerite development are identified in the deposit, corresponding to two mineralization stages: (Ⅰ) the quartz-sphalerite-pyrite-galena stage and (Ⅱ) the galena-pyrite-sphalerite-asphalt stage. LA-ICP-MS results show that the average Ge content in sphalerite from StageⅠis 221.0×10-6, which is higher than that from StageⅡ(72.9×10^-6). Microthermometric data of fluid inclusions indicate that the homogenization temperatures during the hydrothermal stages average 220 ℃ (StageⅠ) and 180 ℃(StageⅡ), respectively. The pH values of the two stages are comparable, with little variation. The average salinities, expressed as w(NaCl_eq), are 8.0% for StageⅠand 5.9% for Stage Ⅱ, indicating that the ore-forming fluids are of medium-low temperature and medium-low salinity. The ore-forming pressures are 43×10⁵-283×10⁵ Pa for StageⅠand 120×10⁵-236×10⁵ Pa for Stage Ⅱ.Based on the Ge enrichment patterns, its occurrence, ore-forming fluid characteristics, and thermodynamic phase diagram calculations, the Ge enrichment conditions in sphalerite are determined as follows: for StageⅠ, log $f O 2$ ≤-40.40, -15.75≤f_S2≤-4.71, log[Zn]≥-14.36, and log[Ge]≥-26.44; for StageⅡ, log $f O 2$ ≤-44.28, -18.64≤log $f S 2$ ≤-5.78, log[Zn]≥-14.84, and log[Ge]≥-28.19.The study suggests that sulfur fugacity, oxygen fugacity, and ion activity are the critical physicochemical factors affecting Ge enrichment. High sulfur fugacity and low oxygen fugacity are favorable for Ge enrichment, while ion activity is the main factor contributing to the differential Ge enrichment in sphalerite from the two stages. These findings enrich the metallogenic theory of Ge-rich lead-zinc deposits and provide a scientific basis for the exploration and comprehensive utilization of Ge resources.

Key words: lead-zinc deposit, Ge, enrichment condition, ore-forming fluid characteristics, thermodynamic phase diagram

CLC Number:

P618.2

SUN Shiqiang, CHEN Cuihua, LAI Xiang, GU Ying, ZHAO Wenhao, ZHANG Haijun, MA Tianqi, CHEN Xiaojie, SONG Zhijiao. Characteristics of Ore-Forming Fluids and Physicochemical Conditions for Ge Enrichment in the Wusihe Lead-Zinc Deposit, Sichuan[J]. Geoscience, 2025, 39(04): 931-946.

Figures/Tables 17

Fig.1 Tectonic setting of South China (a) and regional geological map of the Sichuan-Yunnan-Guizhou Pb-Zn metallogenic belt (b) (modified after Ref.[8])

Fig.2 Geological map of the Wusihe Deposit (modified after reference[27])

Fig.3 Photos of tunnels, hand specimens and microscopic images from the Wusihe Deposit

Fig.4 Paragenetic sequence of minerals in the Wusihe deposit

Table 1 LA-ICP-MS analytical results of sphalerite from the Wusihe Deposit (10-6)

成矿阶段	样品编号	Mn	Fe	Cu	Ga	Ge	Ag	Cd
第Ⅰ阶段	WSH-10-1-(1)-1	59.5	27189	103.0	0.19	180.0	94.9	2863.0
	WSH-10-1-(1)-2	59.2	27225	101.0	1.21	148.0	84.3	2931.0
	WSH-10-1-(1)-3	65.3	27234	103.0	1.39	163.0	91.9	2954.0
	WSH-10-1-(1)-4	54.6	29176	115.0	0.47	155.0	95.7	3206.0
	WSH-10-1-(2)-1	50.5	14035	82.6	0.41	195.0	50.2	2714.0
	WSH-10-1-(2)-2	53.0	4385	33.6	0.29	110.0	30.1	3589.0
	WSH-3-1-(1)-1	10.7	6462	154.0	24.80	98.4	49.1	881.0
	WSH-3-1-(1)-2	6.58	4184	262.0	14.10	225.0	60.7	803.0
	WSH-2-(1)-1	39.7	21318	146.0	15.10	113.0	42.5	1556.0
	WSH-2-(1)-2	37.2	14776	147.0	19.10	118.0	40.1	1562.0
	WSH-2-(5)-1	16.4	12249	858.0	0.30	624.0	92.8	78.7
	WSH-2-(5)-2	11.3	10440	666.0	0.65	511.0	73.6	54.7
	WSH-2-(5)-3	24.5	9151	229.0	0.05	246.0	33.0	55.3
第Ⅱ阶段	WSH-10-1-(3)-1	5.86	1073	60.0	3.93	50.1	61.8	4618.0
	WSH-10-1-(3)-2	6.34	1437	240.0	0.59	169.0	95.7	3269.0
	WSH-3-1-(2)-1	41.80	6517	115.0	2.64	78.4	47.6	3786.0
	WSH-3-1-(2)-2	43.20	7807	79.0	4.70	77.7	52.6	3750.0
	WSH-2-1-(1)-1	-	361	411.0	12.19	204.0	78.4	1850.0
	WSH-2-1-(1)-2	-	534	163.0	0.69	109.0	53.8	1926.0
	WSH-2-1-(2)-2	2.77	1357	128.0	83.7	40.6	16.9	2839.0
	WSH-2-(2)-1	3.22	1059	64.1	17.5	7.90	61.7	7530.0
	WSH-2-(2)-2	3.58	1218	4.96	0.44	1.54	5.49	9062.0
	WSH-2-(3)-1	12.10	7560	96.0	36.1	53.1	39.7	1965.0
	WSH-2-(3)-2	13.90	6693	80.7	29.1	49.3	37.3	2009.0
	WSH-2-(4)-3	8.26	5620	85.6	28.2	35.8	34.8	1555.0
	WSH10-1-3	2.23	210	155.0	20.0	73.6	144.0	2568.0
	WSH3-1-4	80.60	4220	97.7	1.43	70.0	81.3	2766.0

Fig.5 Box plots of trace elements in sphalerite from different stages of the Wusihe deposit (10-6)

Fig.6 Characteristics of fluid inclusions in the Wusihe Deposit

Table 2 Microthermometric data of fluid inclusions from each mineralization stage of the hydrothermal period

热液期成矿阶段	寄主矿物	测试个数	大小(μm)	均一相态	均一温度(℃)	冰点(℃)	盐度w(NaCl_eq)	pH
Ⅰ	闪锌矿	22	3~15	L	154.0~269.0	-9.8~-3.2	5.3~13.7	5.42~5.66
	石英	14	7~40	L	153.2~290.0	-7.1~-0.9	1.6~10.6	5.44~5.66
	白云石	18	3~13	L	150.1~254.2	-9.0~-2.3	3.9~12.8	5.44~5.66
Ⅱ	闪锌矿	17	3~15	L	144.6~210.8	-3.9~-0.8	1.4~6.3	5.47~5.70
	石英	14	6~40	L	160.0~236.9	-8.6~-1.5	2.6~12.4	5.46~5.63
	白云石	16	3~10	L	152.7~203.5	-9.4~-3.0	5.0~13.3	5.48~5.66

Fig.7 Histograms of homogenization temperatures of fluid inclusions

Fig.8 Time-resolved curves of trace elements in sphalerite from the Wusihe deposit

Fig.9 Comparison of trace element contents in sphalerite from the Wusihe deposit (data of some deposits in the Sichuan-Yunnan-Guizhou region are cited from references [6] and [31])

Fig.10 Relationship between salinity of ore-forming fluids and Ge enrichment in sphalerite (data from other deposits are cited from references [41-48])

Table 3 Chemical formulas of relevant reactions

序号	反应方程式	序号	反应方程式
1	Ge+O₂=GeO₂	2	Ge+S₂=GeS₂
3	GeS₂+O₂=GeO₂+S₂	4	Zn+1/2O₂=ZnO
5	Zn+1/2S₂=ZnS	6	ZnS+1/2O₂=ZnO+1/2S₂
7	Pb+ 1/2O₂=PbO	8	3Pb+2O₂=Pb₃O₄
9	Pb+O₂=PbO₂	10	Pb+1/2S₂=PbS
11	PbS+1/2O₂=PbO+1/2S₂	12	3PbS+ 2O₂=Pb₃O₄+3/2S₂
13	PbS+O₂=PbO₂+1/2S₂	14	4S₂=S₈
15	3Fe+2O₂=Fe₃O₄	16	Fe₃O₄+1/2O₂=3Fe₂O₃
17	Fe+1/2S₂=FeS	18	FeS+1/2S₂=FeS₂
19	3FeS+2O₂=Fe₃O₄+3/2S₂	20	3FeS₂+2O₂=Fe₃O₄+3S₂
21	3FeS₂+3/2O₂=Fe₂O₃+2S₂

Table 4 log f O 2-log f S 2 for precipitation of Ge-rich sphalerite-galena-pyrite at different temperatures

温度(K)	413.15	453.15	493.15	533.15
log $f O 2$	log $f O 2$ ≤-48.17	log $f O 2$ ≤-44.28	log $f O 2$ ≤-40.40	log $f O 2$ ≤-37.56
log fS₂	-21.53≤log $f S 2$ ≤-6.84	-18.64≤log $f S 2$ ≤-5.78	-15.75≤log $f S 2$ ≤-4.71	-13.62≤log fS₂≤-3.94

Table 4 log f O 2-log f S 2 for precipitation of Ge-rich sphalerite-galena-pyrite at different temperatures

温度(K)	413.15	453.15	493.15	533.15
log $f O 2$	log $f O 2$ ≤-48.17	log $f O 2$ ≤-44.28	log $f O 2$ ≤-40.40	log $f O 2$ ≤-37.56
log fS₂	-21.53≤log $f S 2$ ≤-6.84	-18.64≤log $f S 2$ ≤-5.78	-15.75≤log $f S 2$ ≤-4.71	-13.62≤log fS₂≤-3.94

Fig.11 log f O 2-log f S 2 phase diagrams of minerals at different temperatures

Table 5 Relevant chemical reaction equations

序号	反应方程式	序号	反应方程式
1	H₂S=HS^-+H⁺	2	HS^-=S^2-+H⁺
3	Zn²⁺+H₂S=ZnS+2H⁺	4	Zn²⁺+HS^-=ZnS+H⁺
5	Zn²⁺+S^2-=ZnS	6	Ge⁴⁺+2H₂S=GeS₂+4H⁺
7	Ge⁴⁺+2HS^-=GeS₂+2H⁺	8	Ge⁴⁺+2S^2-=GeS₂
9	Ge(OH)₄+2H₂S= GeS₂+4H₂O	10	Ge(OH)₄+2HS^-= GeS₂+2H₂O+2OH^-
11	Ge(OH)₄+2S^2-= GeS₂+4OH^-	12	ZnC $l 4 2 -$ +H₂S= ZnS+4Cl^-+2H⁺
13	ZnC $l 4 2 -$ +HS^-= ZnS+4Cl^-+H⁺	14	ZnC $l 4 2 -$ +S^2-= ZnS+4Cl^-

Table 5 Relevant chemical reaction equations

序号	反应方程式	序号	反应方程式
1	H₂S=HS^-+H⁺	2	HS^-=S^2-+H⁺
3	Zn²⁺+H₂S=ZnS+2H⁺	4	Zn²⁺+HS^-=ZnS+H⁺
5	Zn²⁺+S^2-=ZnS	6	Ge⁴⁺+2H₂S=GeS₂+4H⁺
7	Ge⁴⁺+2HS^-=GeS₂+2H⁺	8	Ge⁴⁺+2S^2-=GeS₂
9	Ge(OH)₄+2H₂S= GeS₂+4H₂O	10	Ge(OH)₄+2HS^-= GeS₂+2H₂O+2OH^-
11	Ge(OH)₄+2S^2-= GeS₂+4OH^-	12	ZnC $l 4 2 -$ +H₂S= ZnS+4Cl^-+2H⁺
13	ZnC $l 4 2 -$ +HS^-= ZnS+4Cl^-+H⁺	14	ZnC $l 4 2 -$ +S^2-= ZnS+4Cl^-

Fig.12 pH-log[a] phase diagrams at different temperatures (cited from reference [5])

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