Geochemistry and mineral chemical behavior of hydrothermal alteration of the Tuwu porphyry copper deposit, Eastern Tianshan, Northwest China

Abstract

The Tuwu deposit is one of the largest porphyry copper deposits in the Eastern Tianshan, Northwest China. Ore bodies of the deposit are associated with the tonalite porphyry, which intruded the Early Carboniferous Qi´eshan Group. The hydrothermal ore-forming processes include the porphyry mineralization episode with potassic, chlorite-sericite/albite, phyllic, and propylitic alteration and the overprinting mineralization episode. These hydrothermal alteration episodes were studied on the basis of mass transfer and element mobility. The mass balance data and isocon diagrams reveal that Cu is highly associated with the chlorite-sericite (albite) stage and followed by phyllic and potassic stages. On the basis of electron probe analysis, the SO 3 contents of the igneous apatite from the tonalite porphyries range from 0.016 to 0.288 wt.%, which are higher than those from the diorite porphyries (SO 3 = 0.088-0.179 wt.%). Similarly, the apatite saturation temperature (861-926°C) and magmatic S content (mean = 52.16 ppm) from the tonalite porphyries are also higher that from the diorite porphyries (T = 813-877°C; S = 28.25 ppm). These results suggest that the S content of the apatite is related to the temperature and S content of the melt. In the hydrothermal alteration zones, the F favours partitioning into apatite under lower temperature, the F contents of hydrothermal apatite increase from the potassic zones to the propylitic zones accompanying with the decrease of temperature. Cl element is much more sensitive to the pH, pressure, and fluid composition than F element. The Cl contents of the apatite increase from the potassic zones (0.18-0.46 wt.%) to the chorite-sericite (albite) zones (0.28-0.58 wt.%), resulting from the decrease of fluid pH and pressure. The lower Cl contents of apatite (0.07-0.48 wt.%) in the phyllic zones were due to the lower Cl content of hydrothermal fluids. The highest Cl contents (0.09-0.69 wt.%) of apatite in the propylitic zones were caused by the decrease of pressure. The δ 18 O water values of quartz in chlorite-sericite (albite) zones and phyllic zones range from −0.8‰ to −0.4‰ and from −5.3‰ to 4.8‰, and the δD values vary from −57‰ to −47‰ and from −52‰ to −44‰, respectively. Gaseous compositions of the fluid inclusions in quartz are dominated by H 2 O with minorCO 2 , and the liquid compositions mainly consist of Na + and Cl − . These data imply that the ore-forming fluids belong to the H 2 O-NaCl system and evolved from magmatic water to meteoric water in origin.

Rutile and Chlorite Geochemistry Constraints on the Formation of the Tuwu Porphyry Cu Deposit, Eastern Tianshan and Its Exploration Significance

“…This interpretation is consistent with our unpublished EPMA results of hydrothermal biotite from the potassic alteration zone, in which the biotite was Fe-rich and had TiO 2 ranging from 0.10-1.11 wt %. Moreover, the magmatic/early-stage magnetite at Tuwu is Ti-bearing (TiO 2 = 0.04 to 1.09 wt %), as supported by EMPA results reported by Yuan et al [24], implying that magnetite can be a candidate for releasing some Ti into hydrothermal fluids. During early potassic alteration, we propose that rutile was partially formed by breakdown and re-equilibration of primary biotite, which released residual Ti by exsolution under fluid-dominated conditions [74].…”

“…The porphyry Cu deposit, as an economically important type of deposit supplies approximately 75 percent of global Cu [21,22]. The Early Carboniferous Tuwu deposit that formed in the Dananhu-Tousuquan Arc setting is one of the largest porphyry Cu deposits in the Eastern Tianshan Orogen, Xinjiang, northwestern China region [23][24][25]. Numerous studies have examined the ore genesis of Tuwu through mineralogy, geochemistry, tectonics, multiple isotopes, and fluid inclusions [23,[26][27][28].…”

Mineralogical constraints on Nb–REE mineralization of the Zhujiayuan Nb (−REE) deposit in the North Daba Mountain, South Qinling, China

“…Based on analysis of the composition of the different types and stages of biotite and apatite, we can invert the changes in the physical and chemical conditions, such as the temperature, oxygen fugacity, and halogen fugacity, in the magmatic and hydrothermal stages (Bao et al, ; Jin et al, ; Li et al, ; Mao et al, ; Parsapoor et al, ; Smith, ; Xiao et al, ; Xing et al, ; Yuan et al, ; Zhang et al, ).…”

Magmatic‐hydrothermal Evolution and Mineralization Mechanisms of the Wangjiazhuang Cu (‐Mo) Deposit in the Zouping Volcanic Basin, Shandong Province, China: Constraints from Fluid Inclusions

“…The intrusive rocks in the basin exhibit a spatial distribution that corresponds to the volcanic structures. These intrusive rocks can be categorized into three distinct phases, each associated with different geological locations and characteristics: (1) the early phase includes noritegabbros, diabase porphyrite and diorite porphyrite, which are distributed in the southern margin of the basin; (2) the middle phase includes diorite-quartz monzonite (or quartz monzodiorite), monzonite (ring dike) and syenodiorite, which are distributed in the Wangjiazhuang, Beilou, Xidong and Zhanggao areas; and (3) the late phase includes monzonite, syenite and calc-alkaline subvolcanic rocks, such as andesitic and trachyandesitic porphyrite, which occur sporadically in the basin (Yuan and Li, 1988;Han et al, 2008;Shu et al, 2020) (Fig. 1b, c).…”

“…Several studies have been conducted on the deposit's geology (Yuan and Li, 1988;Tang, 1990;Li and Yuan, 1991), ore-forming fluids (Zhang et al, 2008;Liu S et al, 2013), mineralization age (Liu P et al, 2013;Wang et al, 2015), host granitoid geochemistry (Zhang et al, 2008;Wang et al, 2015) and the relationship between the metasomatized asthenospheric mantle and the Cu (-Mo) deposit (Lan et al, 2018). However, some issues, particularly those concerning the composition and evolution of the magmatic hydrothermal fluids responsible for the WJZ deposit, have not been properly addressed.…”