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Outline
The Pianyanzi gold deposit, situated on the western margin of the Yangtze Craton within the Daduhe gold belt in western Sichuan Province, represents a rare sellaite-bearing orogenic gold deposit.However, key aspects of its ore-forming processes, particularly regarding the nature of ore-forming fluids and the mechanisms governing gold enrichment and precipitation, remain poorly constrained. This study integrates field observations with microthermometric analysis of fluid inclusions, electron probe microanalysis (EPMA) of individual minerals, and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) in-situ microanalysis of individual fluid inclusions. Based on these experimental results, thermodynamic simulations were conducted to comprehensively investigate the conditions conducive to gold enrichment and its precipitation mechanisms. Based on the ore vein cross-cutting relationships and mineral assemblages, the mineralization process can be divided into four distinct stages: the pyrite-quartz stage (I), the pyrite- sellaite-gold-quartz-dolomite stage (II), the quartz-polymetallic sulfide stage (III), and the hematite- limonite-gold stage (IV). EPMA analyses reveal that the gold fineness values in Stage II and Stage IV range from 976.4 to 986.9 and from 960.9 to 992.9, respectively, indicating a consistently high gold content. Fluid inclusions are predominantly CO2-bearing and H2O-bearing, with homogenization temperatures ranging from 135 to 357.1 ℃, peaking between 220 and 300 ℃, and salinities varying from 0.4% NaCleqv to 14.4% NaCleqv, with a peak concentration between 6% NaCleqv and 12%NaCleqv. LA-ICP-MS analyses of individual fluid inclusions reveal that during the evolution from the early to late stages of mineralization, both the total elemental content and the concentrations of trace elements such as Na and K exhibit a progressively decreasing trend. Moreover, the Rb/Na, Cs/Na, Sr/Na, and K/Na ratios observed in these fluid inclusions are consistent with the geochemical signatures of fluids associated with orogenic gold deposit. Thermodynamic simulations and integrated studies indicate that gold is primarily transported in the form of AuHS0 complexes. The decrease in temperature during stages II, along with an increase in oxygen fugacity specifically in stage IV, may serve as the primary factors contributing to gold precipitation and variations in gold fineness.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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