Nature and Evolution of the Ore-Forming Fluids from Nanmushu Carbonate-Hosted Zn-Pb Deposit in the Mayuan District, Shaanxi Province, Southwest China

Figure 9

Photomicrographs showing fluid inclusions assemblages (FIAs) of the Nanmushu Zn-Pb deposit, under transmitted light, crossed-nicols. (a) In stage I, a trail of two-phase type I FIs (a-1, a-2, and a-3) in the quartz grain, they have consistent vapor/liquid ratios. Microthermometry measurement shows that the ranges of histograms of total homogenization temperatures () of this FIA are relatively small, for example, 311°C for (a-1), 302°C for (a-2), and 308°C for (a-3), respectively. They all homogenized to liquid phase. Average temperature 307°C as of this FIA recorded in the result. (b) In stage II, a brown grain sphalerite contains two-phase FIs (b-1 and b-2) with consistent vapor/liquid ratios and similar (255°C for (b-1) and 251°C for (b-2), resp.). Both of them homogenized to liquid phase. Average temperature 253°C of this FIA recorded in the result. ((c), (d), (e)) A trail of CH₄-rich inclusions in quartz. When the temperature decreases to −190°C, most of one-phase CH₄-rich inclusions were frozen. When heated gradually, this type inclusions appeared two-phase ((c), at −170°C), followed by the bubbles reduced ((d), at −145°C), and then homogenized to one liquid phase ((e), −90°C). (f) Coexistence of gas, gas-aqueous, and liquid-only inclusions in quartz indicating immiscibility and heterogeneous trapping; Qz, quartz; Sp, sphalerite.

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