Abstract
The Taochong iron deposit is one of the important skarn deposits in the Middle–Lower Yangtze River metallogenic belt, Eastern China. There are two types of ores in the deposit: skarn- and quartz–calcite-type ores. The skarn-type ore, which is composed of hematite (Hm-1), garnet, pyroxene, actinolite, chlorite, quartz (Q-1), and calcite (Cal-1), is crosscut locally by a quartz–calcite-type ore vein. The quartz–calcite-type ore consists mainly of hematite (Hm-2), magnetite, quartz (Q-2 and 3), and calcite (Cal-2). The δ18Owater value (~2.67‰) of the fluids in equilibrium with Hm-1 is similar to the values of the mixtures of magmatic and meteoric fluids. However, the δ18O values of the fluids in equilibrium with Hm-2 are in the range of 7.64–8.54‰, similar to those of magmatic fluids. The δ18O values decrease systematically from the fluids in equilibrium with Hm-2 (7.64‰ to 8.54‰) to the fluids in equilibrium with magnetite, Q-3, and Cal-2 (−0.12‰ to 4.17‰) and the fluids in equilibrium with Cal-3 (−2.17‰ to 0.36‰). These features of oxygen isotopes indicate that two episodes of hydrothermal activity took place in the Taochong deposit, and both episodes began with a magmatic origin and then progressively evolved by mixing with meteoric water. The results of quantitative simulations suggest that the deposition of the skarn-type ores was most likely caused by the mixing of magmatic and meteoric fluids, whilst the deposition of the quartz–calcite-type ores was most likely caused by the boiling of magmatic fluids and the mixtures of magmatic brine and meteoric water.
Highlights
Published: 2 April 2021Fluid processes are critical for understanding the transport and concentration of metals in hydrothermal systems
The evidence from geologic and textural observations, fluid inclusions, and stable isotopes indicates that both fluid boiling and mixing of magmatic brine with meteoric water occurred during
In this paper, we report the results of an oxygen stable isotope study of the Taochong deposit, and we quantitatively model the importance of fluid boiling and mixing in the evolution of the hydrothermal system at Taochong
Summary
Published: 2 April 2021Fluid processes are critical for understanding the transport and concentration of metals in hydrothermal systems. Experimental studies and chemical modelling [1,2,3] have demonstrated that most base and precious metals (e.g., Cu, Fe, Au, Pb, and Zn) are transported mainly in the form of chloride and bisulfide complexes in natural hydrothermal fluids. Among these, boiling and the mixing of magmatic and meteoric waters are considered to be the two most effective ways to form high-grade ores in skarn deposits (e.g., the Chengchao high-grade skarn iron deposit [8], the Huanggang skarn iron–tin deposit [12], and the Xishimen high-grade skarn iron deposit [13] in China, and the Big Gossan Cu-Au skarn deposit in Irian Jaya [14]). The evidence from geologic and textural observations, fluid inclusions, and stable isotopes indicates that both fluid boiling and mixing of magmatic brine with meteoric water occurred during
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