Characteristics of Melt-Fluid Inclusions and Sulfur Isotopic Compositions of the Hashitu Molybdenum Deposit, Inner Mongolia
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摘要: 哈什吐钼矿床是近年来在大兴安岭中段地区新发现的矿床,矿体产出于花岗岩体内,是一个与酸性岩浆作用密切相关的内生金属矿床.矿床金属矿物组成主要为辉钼矿、黄铜矿、黄铁矿、磁黄铁矿、闪锌矿、方铅矿、毒砂等.包裹体研究表明包裹体类型主要为液体包裹体(Ia型)、气体包裹体(Ib型)、含子晶包裹体(Ic型)及熔融包裹体(II型)构成.不同类型包裹体共存产出表明这些包裹体大都经历了流体沸腾作用.包裹体均一测温表明流体包裹体均一温度主要变化于250~500 ℃,熔融包裹体均一温度集中变化于750~950 ℃.计算得到流体盐度、压力和密度变化范围分别为1%~49% NaCl eqv、5~100 MPa、0.7~1.1 g/cm3.包裹体研究表明哈什吐钼矿床成矿流体为一种高温度、高盐度、高压力、中高密度且含一定量CO2的流体,该流体可归属为H2O-NaCl-CO2-SO42-体系.硫化物的δ34Sv-cdt(‰)变化范围为0.4‰~3.8‰,计算得到成矿流体的δ34SH2S(‰)变化范围为1.1‰~4.7‰,硫同位素组成表明成矿作用与深部岩浆作用有密切联系.矿床成矿流体演化过程发生了流体沸腾和混合作用,显著的减压沸腾作用是造成成矿体系发生大量硫化物沉淀的主要机制.哈什吐钼矿床的发现对该区寻找岩浆热液型的内生多金属矿床具有重要的启示意义.该区找矿勘探应重视岩体与不同岩性岩石及构造带的接触部位以及岩体与构造断裂交汇的部位.Abstract: The Hashitu Mo deposit was discovered recently in the middle section of the Da Hinggan Montain district. The ore body occurs in granite intrusion and this deposit is regarded as an endogenic metallic ore deposit related to acid magmatism. The metallic minerals are composed of molybdenite,chalcopyrite,pyrite,sphalerite,galena,and arsenopyrite,etc. The fluid inclusions study demonstrates that inclusion types mainly involve liquid inclusion (Ia type),gaseous inclusion (Ib type),daughter crystal inclusion (Ic type) and melt inclusion (II type). Co-existence of different inclusion types indicates the fluid boiling. The heating and freezing study shows that homogenization temperature of fluid and melt inclusions ranges 250~500 ℃ and 750~950 ℃,respectively. The calculation of fluid salinity,pressure and density indicates that these values range 1%~49% NaCl eqv,5~100 MPa and 0.7~1.1 g/cm3,respectively. The fluid inclusion study indicates that ore forming fluid are characterized by high temperature,high salinity,high pressure,high-moderate density and CO2 bearing,which can be classified as H2O-NaCl-CO2-SO42- system. δ34Sv-cdt(‰) values of sulfides and δ34SH2S(‰) values of ore forming fluid range from 0.4‰ to 3.8‰ and 1.1‰ to 4.7‰,respectively. These isotopic values indicate that mineralization is related with magmatism in this region. Both fluid boiling and mixing are identified in ore forming fluid evolution and fluid boiling resulting in pressure decrease was the mainly mechanism for sulfide minerals deposition form hydrothermal fluid. Discovery of the Hashitu Mo deposit in this region is helpful to the exploration of other magmatic-hydrothermal Mo-W-Cu-Pb-Zn-Au deposits. More attention should be paid to the contact and intersection parts between intrusions and other host rocks,intrusions and structural zones in future mining exploration.
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Key words:
- melt-fluid inclusions /
- sulfur isotope /
- molybdenum deposit /
- Hashitu /
- ore prospecting /
- ore deposits.
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图 2 内蒙古哈什吐钼矿床矿石及矿化类型
a.产于蚀变花岗岩中的脉状和浸染状钼矿石；b.产于石英中的柱状、片状辉钼矿矿石，辉钼矿与闪锌矿伴生；c.蚀变花岗岩中的面状辉钼矿矿化；d.与石英共生的片状、团块状辉钼矿；Mol.辉钼矿；Qtz.石英；Sp.闪锌矿
Fig. 2. Ore types from the Hashitu Mo deposit
图 3 内蒙古哈什吐钼矿床金属矿物组成
a.柱状辉钼矿集合体，集合体之间被石英充填；b.柱状辉钼矿的膝折现象；c.方铅矿被磁黄铁矿和闪锌矿交代，在方铅矿中存在黄铜矿；d.闪锌矿交代较为自形的黄铁矿，在闪锌矿中存在乳滴状黄铜矿；e.方铅矿被黄铁矿交代，黄铁矿被黄铜矿包裹，黄铜矿被磁黄铁矿穿插；f.黄铜矿被磁黄铁矿穿插，磁黄铁矿被闪锌矿切穿；Cp.黄铜矿；Gn.方铅矿；Mol.辉钼矿；Po.磁黄铁矿；Py.黄铁矿；Qtz.石英；Sp.闪锌矿
Fig. 3. Metallic mineral compositions from the Hashitu Mo deposit
图 4 哈什吐钼矿床包裹体组成
a.Ib型流体包裹体和Id型纯气相流体包裹体共存；b.Ia型液体包裹体与Ic型三相包裹体和Ie型纯液相包裹体共存；c.Ia型液体包裹体、Ib型气体包裹体、Ic型三相包裹体和Id型纯气相包裹体共存；d.Id型纯气相包裹体；e.Ia型液体包裹体与Id型纯气相包裹体和Ie型纯液相包裹体共存；f.Ic型三相包裹体和Ie型纯液相包裹体共存，部分Ic型包裹体含多个子矿物；g.Ia型液体包裹体与Ic型三相包裹体和Id型纯气相包裹体共存；h.Ia型液体包裹体与Ib型气体包裹体和Ic型三相包裹体共存；i.II型熔融包裹体，温度为650 ℃条件下仍未均一；j.原生Ia型液体包裹体；k.辉钼矿(Mol)边部石英中的Ic型三相包裹体；l.Ia型液体包裹体与Ic型三相包裹体和Id型纯气相包裹体共存，Ic型包裹体含有子矿物赤铁矿(Hem)
Fig. 4. Characteristics of inclusions from the Hashitu Mo deposit
图 5 哈什吐钼矿床包裹体均一温度直方图
Fig. 5. Histogram of homogenization temperature data of inclusions from the Hashitu Mo deposit
图 6 哈什吐钼矿床成矿流体盐度、压力、密度直方图
Fig. 6. Histogram of salinity, pressure and density data of ore forming fluids in the Hashitu Mo deposit
图 7 哈什吐钼矿床包流体裹体激光拉曼相对强度图谱
Fig. 7. Laser raman spectra of fluid inclusions from the Hashitu Mo deposit
图 8 哈什吐钼矿床硫化物硫同位素组成直方图
Fig. 8. Histogram of δ34S of sulfides from the Hashitu Mo deposit
图 9 哈什吐钼矿床成矿流体演化图解(食盐饱和曲线和临界曲线根据Shepherd et al., 1985)
Fig. 9. Fluid evolution diagram of the Hashitu Mo deposit
图 10 哈什吐钼矿床包裹体均一温度-压力图解
Fig. 10. Th and pressure diagram for inclusions from the Hashitu Mo deposit
表 1 哈什吐钼矿床包裹体显微测温结果
Table 1. Microthermometric results of inclusions from the Hashitu Mo deposit
包裹体类型 寄主矿物 大小(μm) Th (℃) 均一方式 Tm, ice(℃) Tm(℃) Ia 石英 5.5~76.4 91.2~596 Th(l) -22~-0.4 - 石英 6.1~35.8 253~459 Th(g) -8~-0.9 - Ib 石英 8.3~52.8 325~389 Th(l) - - 石英 10.5~62.3 300~591 Th(g) - - Ic 石英 5.1~36.3 160~600 Th(l) -5.9~-0.4 145~600 II 石英 4.8~21.5 640~1 049 Th(l) - - 注：Th为完全均一温度；Th(l)为完全均一至液相；Th(g)为完全均一至气相；Tm, ice为冰点温度；Tm为子矿物消失温度. 
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表 2 内蒙古哈什吐钼矿床硫同位素组成
Table 2. Sulfur isotope compositions of the Hashitu Mo deposit
样品编号 硫化物 温度(℃)1 δ34SV-cdt (‰) δ34SH2S(‰)2 10HST-05 辉钼矿 415 2.6 3.6 10HST-07 辉钼矿 446 2.3 3.2 10HST-09 辉钼矿 438 3.8 4.7 10HST-16 黄铁矿 478 0.4 1.1 10HST-07 闪锌矿 446 0.9 1.1 10HST-15 磁黄铁矿 483 2.3 2.5 注：上标“1”表示温度为与硫化物共生石英中包裹体的均一温度；上标“2”表示δ34SH2S(‰) 计算根据Ohmoto and Rye(1979)和Ohmoto and Lasaga(1982) 的硫化物(H2S)的硫同位素平衡方程.
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