Characteristics of Fluid Inclusions and Mineralization Indications of the Yechangping Mo Deposit,East Qinling

doi:10.19657/j.geoscience.1000-8527.2024.018

Abstract

Abstract:

The Yechangping molybdenum (Mo) deposit is located in the middle East Qinling molybdenum orogenic belt.Its metallogenic type mainly belongs to the skarn type in the early stage,followed by the porphyry type.In the East Qinling molybdenum mineralization belt,there are relatively fewer studies focusing on the fluid inclusions of the skarn-porphyry composite molybdenum deposits,particularly their fluid evolution characteristics and the metallogenetic mechanisms,which are essential to understanding ore genesis.This study classifies the hydrothermal mineralization stages of the Yechangping Mo deposit from early to late as follows: early silica and late silica quartz-potassic stage (stage I: quartz),quartz-pyroxene stage (stage II: quartz,main mineralization stage),quartz-polymetallic sulfide stage (stage III: quartz),and quartz-carbonate stage (stage IV: quartz).Based on this preliminary study,inclusion samples were collected from stages Ⅰ to Ⅳ quartz and analyzed using microscopy,micro-thermometry,and laser Raman microprobe.The results show that the types of fluid inclusions within the quartz are NaCl-H₂O gas-rich type (WG type),NaCl-H₂O liquid-rich type (WL type),CO₂ type (C type),and daughter mineral-bearing type (S type).From the early to the late stage of mineralization,the homogeneous temperatures of fluid inclusions are concentrated at 380-437 ℃,331-370 ℃,312-320 ℃ and 257-350 ℃,corresponding to average salinity (NaCl_eqv.) of 10.83%,9.29%,7.16%,and 4.51%,respectively.The mineralizing fluids gradually evolved from a high-temperature,medium-high salinity,and CO₂-rich NaCl-H₂O-CO₂ system at the early stage to a low-temperature,low-salinity,and CO₂-poor NaCl-H₂O system at the late stage.The fluid mixing effect leads to a decrease in fluid temperature and salinity,and the fluid transforms from an oxidized state to a reduced state.This results in a drastic decrease in the solubility of the Mo element in the fluid,and the rapid unloading and precipitation of Mo.Consequently,we constructed a mineralization model on the scale of mining area based on the “magma-fluid-construction” mineralization system.

Key words: East Qinling molybdenum ore belt, Yechangping molybdenum deposit, silica-porphyry molybdenum deposit, fluid inclusion

CLC Number:

DING Gaoming, YAN Guolong, WANG Kunming, XU Yongzhong, TANG Yi’ang, LIU Jiyang. Characteristics of Fluid Inclusions and Mineralization Indications of the Yechangping Mo Deposit,East Qinling[J]. Geoscience, 2024, 38(04): 1177-1191.

Figures/Tables 11

Fig.1 Regional(a) and mining area(b) geological sketch map of the Yechangping Mo deposit,East Qinling

Fig.2 Cross-section diagram of line 12 (a) and line 1 (b) of the Yechangping Mo deposit

Fig.3 Hand specimen and microscope photographs of the granite porphyry and skarn-hydrothermal alterations from the Yechangping Mo deposit

Fig.4 Mineral assemblages developed in the Yechangping Mo deposit[26]

Table 1 Information of fluid inclusion samples from the Yechangping Mo deposit

序号	样号	成矿阶段	矿石类型	取样工程	采样位置
序号	样号	成矿阶段	矿石类型	取样工程	采样深度(m)	矿体
1	Yb21	晚期矽卡岩阶段及斑岩体内石英- 钾化阶段 (石英Ⅰ阶段)	含石英脉辉钼矿化矽卡岩	ZK1203	664	弱矿化
2	Yb17		含石英脉浸染状钼矿化矽卡岩	970中段	970	弱矿化
3	Yb16		含石英脉稀疏浸染状钼矿化花岗斑岩	970中段	970	1号
4	Yb1		含石英脉细脉花岗斑岩	ZK1206	434	弱矿化
5	Yb2		含石英脉细脉花岗斑岩	ZK1206	427
6	Yb5		细脉浸染状钼矿化花岗斑岩	ZK807	631
7	Yb3	辉钼矿-石英阶段 (石英Ⅱ阶段)	稠密浸染状钼矿化矽卡岩	ZK1203	626	3-2号
8	Yb4		细脉浸染状钼矿化矽卡岩	ZK1203	631	3-2号
9	Yb6		含石英脉细脉浸染状矽卡岩	ZK105	881	3-2号
10	Yb19		含石英脉稠密浸染状矽卡岩	ZK1203	173	1号
11	Yb15		含石英脉稀疏浸染状钼矿化矽卡岩	ZK105	835	弱矿化
12	Yb13	石英-多金属硫化物阶段 (石英Ⅲ阶段)	含矿石英脉细脉浸染状矽卡岩	ZK105	704	2-1号
13	Yb10		含石英脉稠密浸染状钼矿化矽卡岩	ZK401	540	2-1号
14	Yb11		含石英脉浸染状钼矿化矽卡岩	ZK401	604	弱矿化
15	Yb22	石英-碳酸盐阶段 (石英Ⅳ阶段)	含石英脉稠密浸染状、脉状矽卡岩	ZK1203	749	3-1号

Fig.5 Fluid inclusion types of the Yechangping Mo deposit at different stages

Table 2 Microthermometric data of the fluid inclusions in the Yechangping Mo deposit

成矿阶段	类型	数量	$T m, C O 2$ (℃)	T_m,cla (℃)	$T h, C O 2$ (℃)	T_m,s	T_m,ice(℃)		T_h(℃)		盐度(NaCl_eqv.)(%)		流体密度(%)
成矿阶段	类型	数量	$T m, C O 2$ (℃)	T_m,cla (℃)	$T h, C O 2$ (℃)	T_m,s	平均	范围	平均	范围	平均	范围	平均	范围
Ⅰ	WG	29					-6.7	-14.7~ -1.0	406	322~596	10.8	0.5~18.4	0.62	0.03~ 0.80
	WL	32						-20.7~ -0.4		266~560		0.5~22.9		0.38~ 0.88
	C	8	-60.6~ -58.6	5.4~9.2	27~31					372~373		1.6~15.5		0.26~ 1.12
	S	6				214.5~ 452.7				222~453		32.6~53.6		0.66~ 1.16
Ⅱ	WG	10					-5.4	-16.2~ -2.7	340	337~524	9.3	4.5~10.2	0.70	0.10~ 0.30
Ⅱ	WL	49					-5.4	-13.9~ -1.9	340	203~394	9.3	3.7~11.9	0.70	0.66~ 0.87
Ⅲ	WG	10					-4.3	-8.1~ -0.3	314	315~317	7.2	2.0~10.6	0.75	0.42~ 0.92
Ⅲ	WL	37					-4.3	-19.2~ -0.2	314	275~355	7.2	0.4~21.8	0.75	0.6~ 0.99
Ⅳ	WL	14					-2.8	-5.1~ -0.2	291	257~346	4.5	1.1~8.0	0.72	0.68~ 0.77

Table 2 Microthermometric data of the fluid inclusions in the Yechangping Mo deposit

成矿阶段	类型	数量	$T m, C O 2$ (℃)	T_m,cla (℃)	$T h, C O 2$ (℃)	T_m,s	T_m,ice(℃)		T_h(℃)		盐度(NaCl_eqv.)(%)		流体密度(%)
成矿阶段	类型	数量	$T m, C O 2$ (℃)	T_m,cla (℃)	$T h, C O 2$ (℃)	T_m,s	平均	范围	平均	范围	平均	范围	平均	范围
Ⅰ	WG	29					-6.7	-14.7~ -1.0	406	322~596	10.8	0.5~18.4	0.62	0.03~ 0.80
	WL	32						-20.7~ -0.4		266~560		0.5~22.9		0.38~ 0.88
	C	8	-60.6~ -58.6	5.4~9.2	27~31					372~373		1.6~15.5		0.26~ 1.12
	S	6				214.5~ 452.7				222~453		32.6~53.6		0.66~ 1.16
Ⅱ	WG	10					-5.4	-16.2~ -2.7	340	337~524	9.3	4.5~10.2	0.70	0.10~ 0.30
Ⅱ	WL	49					-5.4	-13.9~ -1.9	340	203~394	9.3	3.7~11.9	0.70	0.66~ 0.87
Ⅲ	WG	10					-4.3	-8.1~ -0.3	314	315~317	7.2	2.0~10.6	0.75	0.42~ 0.92
Ⅲ	WL	37					-4.3	-19.2~ -0.2	314	275~355	7.2	0.4~21.8	0.75	0.6~ 0.99
Ⅳ	WL	14					-2.8	-5.1~ -0.2	291	257~346	4.5	1.1~8.0	0.72	0.68~ 0.77

Fig.6 Histograms of homogenization temperatures and salinity of fluid inclusions of the Yechangping Mo deposit at different stages

Fig.7 Raman spectra of representative fluid inclusions in the Yechangping Mo deposit

Fig.8 Relationship between homogenization temperature and salinity of the fluid inclusions in the Yechangping Mo deposit (basemap after reference[45])

Fig.9 Metallogenic model of the Yechangping Mo deposit (modified after reference[20])

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