豫西杨山萤石矿床成因:萤石稀土元素组成和流体包裹体热力学制约

doi:10.19657/j.geoscience.1000-8527.2023.022

摘要/Abstract

摘要：

杨山萤石矿床是豫西栾川地区一处大型花岗岩容矿型矿床,其成矿期次和成矿流体特征研究的不足长期制约着对萤石淀积机理和区域成矿规律的深化认识。本文基于杨山矿床萤石的稀土元素及流体包裹体研究,阐释了成矿物质来源、成矿流体属性及矿床成因。第Ⅱ阶段萤石的ΣREE含量为22.61×10^-6~287.94×10^-6,LREE/HREE比值为0.64~5.24,具Eu负异常(δEu=0.50~0.92)和Ce负异常(δCe=0.88~1.06)。随成矿深度的增大,萤石ΣREE减小,LREE/HREE和La_N/Yb_N增大,δEu和δCe无明显变化,指示总体成矿先后顺序为地下深部至地表浅部,且垂向上氧逸度较稳定。从紫色萤石到绿色萤石,ΣREE增大,LREE/HREE和La_N/Yb_N减小,δEu和δCe增大,表明萤石具有重新活化和重结晶的趋势。萤石的流体包裹体以气液两相为主,均一温度集中于80~155 ℃,盐度(NaCl_eqv.)集中于0.3%~6.3%。综合分析认为,杨山萤石矿床成矿流体以岩浆水和大气降水混合型为主,属低温、低盐度和低密度的NaCl-H₂O流体体系;矿床可归属于中低温、低盐度热液型矿床。萤石的稀土元素和流体包裹体特征综合分析表明,萤石的沉淀可能受水-岩反应控制。

关键词: 萤石, 成矿地质特征, 稀土元素, 流体包裹体, 杨山矿床

Abstract:

The Yangshan fluorite deposit is located in Luanchuan County,Western Henan Province.The orebody is developed in the bottom of the Heyu granite,and is mainly controlled by NW- and NE-trending faults.Based on the study of rare earth elements and fluid inclusions of fluorite,the source of ore-forming materials,the ore-fluid properties and the ore genesis at Yangshan are discussed.The ΣREE content of stage Ⅱ fluorite ranges from 22.61×10^-6 to 287.94×10^-6,LREE/HREE is of 0.64 to 5.24,and there are negative Eu anomalies(δEu=0.50-0.92)and Ce anomalies(δCe=0.88-1.06).With depth increases,ΣREE decreases,whereas LREE/HREE and La_N/Yb_N increase,and δEu and δCe do not change significantly.This indicates that the overall metallogenic time sequence is from deep to shallow,and the vertical oxygen fugacity is relatively stable.From the purple fluorite to green fluorite,ΣREE increases,LREE/HREE and La_N/Yb_N decrease,and δEu and δCe increase,indicating that recrystallization evolves from purple fluorite to green fluorite.The fluid inclusions of fluorite are mainly gas-liquid two phases.The homogenization temperature and salinity of these inclusions are concentrated in the range of 80-155 ℃ and 0.3%-6.3%(NaCl_eqv.).Comprehensive analysis shows that the ore-forming fluid is mainly mixed with magmatic water and meteoric water,belonging to a low-temperature,low-salinity and low-density NaCl-H₂O system.Thus,Yangshan deposit is a low-temperature and low-salinity hydrothermal deposit.Comprehensive analysis of REEs and fluid inclusion characteristics of fluorite shows that the fluorite precipitation may have been controlled by water-rock reaction.

Key words: fluorite, metallogenic-geological characteristic, rare earth element, fluid inclusion, Yangshandeposit

中图分类号:

王启博, 张寿庭, 唐利, 李军军, 盛渊明. 豫西杨山萤石矿床成因:萤石稀土元素组成和流体包裹体热力学制约[J]. 现代地质, 2023, 37(06): 1524-1537.

WANG Qibo, ZHANG Shouting, TANG Li, LI Junjun, SHENG Yuanming. Genesis of Yangshan Fluorite Deposit in Western Henan Province: Fluorite REE Composition and Fluid Inclusion Thermomechanical Constraints[J]. Geoscience, 2023, 37(06): 1524-1537.

图/表 11

图1 秦岭造山带大地构造图((a),据文献 [11]修编)和合峪矿集区萤石矿床分布图((b),据文献 [12]修编)

Fig.1 Tectonic map of the Qinling Orogen Belt (a) (modified after reference [11]) and distribution of fluorite deposits in the Heyu ore concentrated area (b)(modified after reference [12])

图2 杨山萤石矿床地质图(据文献 [8]修编)

Fig.2 Geological map of the Yangshan fluorite deposit(modified after reference [8])

图3 杨山萤石矿床第400勘探线(a)和401勘探线(b)剖面示意图(据文献 [7]修编)

Fig.3 Profile of exploration lines 400(a) and 401(b) in the Yangshan fluorite deposit(modified after reference [7])

图4 杨山萤石矿床不同阶段矿石特征 (a)第Ⅰ阶段石英脉穿插围岩;(b)第Ⅰ阶段萤石、石英共生;(c)第Ⅱ阶段萤石胶结围岩,后被第Ⅲ阶段方解石脉穿插;(d)第Ⅱ阶段紫色萤石及浸染状黄铁矿;(e)第Ⅱ阶段绿色萤石;(f)第Ⅱ阶段萤石矿体;(g)第Ⅲ阶段块状方解石;(h)第Ⅲ阶段白色方解石胶结第Ⅱ阶段萤石;(i)第Ⅲ阶段黄色方解石胶结第Ⅱ阶段萤石;Cal.方解石;Fl.萤石;Py.黄铁矿;Qtz.石英

Fig.4 Photos showing the ore characteristics of different stages of the Yangshan fluorite deposit

图5 杨山萤石矿床萤石和围岩稀土元素标准化配分模式图(球粒陨石标准化值据Taylor等[14],1100 m中段和1062 m中段数据源于冯绍平等[6],二长花岗岩数据源于席晓凤等[4])

Fig.5 Normalized REE patterns of the fluorite and wall rock of the Yangshan fluorite deposit

图6 杨山萤石矿床不同阶段流体包裹体显微照片 (a)第Ⅰ阶段包裹体群;(b)第Ⅰ阶段富液相流体包裹体;(c)第Ⅱ阶段包裹体群;(d)第Ⅱ阶段纯液相流体包裹体;(e)第Ⅱ阶段富液相流体包裹体;(f)第Ⅲ阶段富液相流体包裹体。L.液相;V.气相

Fig.6 Photographs of fluid inclusion characteristics of the Yangshan fluorite deposit

表2 杨山萤石矿床流体包裹体测温结果

Table 2 Temperature measurement results of fluid inclusions of the Yangshan fluorite deposit

成矿阶段	测试矿物	包裹体类型	测试数量	长轴长度(μm) (集中分布)	均一温度(℃) (集中分布)	盐度(NaCl_eqv.)(%) (集中分布)	密度(g/cm³) (平均值)
Ⅰ	萤石	L+V	64	3.6~35.8 (5~15)	101.7~167.3 (110~155)	0.18~7.02 (0.3~6.3)	0.93~0.99 (0.96)
Ⅱ	990 m中段萤石	L+V	100	3.8~24.8 (5~10)	104.4~146.6 (115~140)	0.18~5.86 (0.3~5.7)	0.94~0.98 (0.96)
Ⅱ	940 m中段萤石	L+V	89	3.9~31.1 (5~15)	121.2~159.3 (120~145)	0.18~3.87 (0.3~2.4)	0.92~0.97 (0.95)
Ⅲ	方解石	L+V	29	5.7~52.6 (10~20)	60.6~151.3 (80~145)	0.53~6.45 (0.53~5.7)	0.94~1.01 (0.98)

图7 杨山萤石矿床流体包裹体均一温度(a)(c)(e)和盐度直方图(b)(d)(f)

Fig.7 Histograms showing fluid inclusion homogenization temperatures(a)(c)(e)and salinities(b)(d)(f)of the Yangshan fluorite deposit

图8 杨山萤石矿床萤石Y/Ho-La/Ho图解((a),底图据文献[24])和Tb/Ca-Tb/La图解((b),底图据文献[18])

Fig.8 Y/Ho-La/Ho (a)(basemap after reference [24]) and Tb/Ca-Tb/La (b)(basemap after reference [18]) diagrams of fluorites from the Yangshan fluorite deposit

图9 杨山萤石矿床成矿热液温度和盐度协变图

Fig.9 Covariant map of temperature and salinity of the Yangshan fluorite deposit

图10 杨山萤石矿床成矿模式示意图

Fig.10 Schematic metallogenic model for the Yangshan fluorite deposit

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