Study on hydrogen and oxygen isotopes of ore-forming fluids

In order to further understand the properties of ore-forming fluids, the timely hydrogen and oxygen isotopes related to mineralization were determined in Huangbaishuwan witherite deposit in Ziyang and Wenyuhe witherite-barite deposit in Zhushan. The results are shown in Table 6-2.

Table 6-2 Hydrogen and oxygen isotope composition unit of witherite deposit: ‰

It can be seen from the table that the δ 18O of Huangbaishuwan and Jishi witherite deposits containing witherite * * * are 2 1.7‰ and 18.9‰ respectively, and the δD is -75‰ and -6 1‰ respectively. Because no inclusion was found in the sample when the thin section was observed, the formation temperature of the sample could not be obtained. According to the fact that the timely samples generally do not develop inclusions, it is inferred that the timely formation temperature is low. Combined with the temperature measurement data of witherite and barite inclusions (1 10 ~ 170℃), it is estimated that the timely formation temperature is about11. Taking this value as the estimated timely formation temperature, the δ 18O value of water in timely fluid inclusions is calculated according to the timely-water fractionation equation 100LNα timely-water = 3.38× 106× t-2-3.40 (Table 6-2). In the same way, the δ 18O value of water in the timely fluid inclusions in Wenyuhe witherite deposit and the δ 18O value of water in the timely fluid inclusions in the stratum are calculated (Table 6-2).

According to Figure 6-2, the composition chart of hydrogen and oxygen isotopes of water in the timely fluid inclusions shows that the variation range of hydrogen isotopes of water produced in witherite mines and those produced in ore-bearing rock series or regional strata is small, but the variation range of oxygen isotopes is large (-4.2 ‰ ~ 9.7 ‰), resulting in the phenomenon of "drift" of oxygen isotopes. In a word, the hydrogen and oxygen isotopic compositions of time-dependent inclusions with different occurrences are basically the same, reflecting that they were formed in the same process. Moreover, from the hydrogen and oxygen isotopic composition of the timely inclusions, the water in the inclusions mainly reflects the isotopic composition characteristics of atmospheric precipitation, and some magmatic water is also mixed. Combined with the actual geological conditions of the mining area, magmatic water may mainly come from volcanic rocks in the strata or late magmatic activities (such as Caledonian magmatism).

Figure 6-2 Isotopic Composition Diagram of Hydrogen and Oxygen in Time