Abstract
The Tuwu porphyry copper deposit is located on the Dananhu-Haerlik island arc in eastern Tianshan, NW China. Based on geology, petrology, and in situ trace element studies of pyrite and chlorite, we redefined the characteristics of hydrothermal fluids and the following three mineralization stages: premineralization stage (stage Ⅰ), porphyry metallogenic stage (stage Ⅱ), and superimposed transformation stage (stage Ⅲ). Pyrite stage Ⅰ (Py-I) has the highest Co/Ni ratios, and the precipitation crystallization of chlorite (Chl-I2) has the similar rare earth element distribution patterns with those of volcanic rocks Carboniferous Qieshan (CQ), indicating intense volcanic hydrothermal activity. The Co/Ni ratios of Py-II1 and Py-II2 (stage Ⅱ) tend to decrease over time. Moreover, the rare earth element (REE) distribution patterns of Chl-II have similar LREE enrichment, and the Eu anomalies in Chl-II1, Chl-II2, and Chl-II3 range from positive to negative. The initial ore-forming fluid was mainly magmatic hydrothermal fluid, and with the late-stage addition of meteoric water and continuous sulfide precipitation, the trace element composition of the fluid changed, and the whole system became more oxidizing. Py-III (stage Ⅲ) has the lowest Co/Ni ratios, and the REE distribution pattern of Chl-III is characterized by LREE enrichment. Moreover, the Chl-III shows obvious shear deformation characteristics. The results indicate that the host rocks experienced intensely superimposed reformation. By combining and integrating our results with the regional evolution processes in the eastern Tianshan, we propose that the Tuwu porphyry deposit has undergone magmatic hydrothermal and metamorphic hydrothermal processes. Volcanism (stage Ⅰ) provided the space and initial conditions for the emplacement of the metallogenic body. With the emplacement of the plagiogranite porphyry (stage Ⅱ), the main copper mineralization occurred in the porphyry and surrounding rocks. After porphyry mineralization (stage Ⅲ), regional ductile shearing and collisional compression led to a copper reaction, and its accumulation along the faults formed an ore shoot.
Highlights
Specialty section: This article was submitted to Economic Geology, a section of the journal Frontiers in Earth Science
After extensive research on the petrography of the main rock types exposed in the Tuwu mining area (Figures 2B,C), this study identified four stages of hydrothermal activity, namely, alterations related to volcanic activity, alterations related to porphyry mineralization, alterations related to ductile shear deformation, and alterations related to supergenesis (Figure 6)
The results showed that Pyrite stage I (Py-I) has the highest total amount of trace elements and highest Co/Ni ratio
Summary
Allowed for the measurement of most trace elements in sulfide and oxides. Pyrite is an important sulfide in many metallogenic. The Carboniferous metallogenic plagiogranite developed at the southern zone of the Dananhu-Haerlik island porphyry of the Tuwu deposit occurs as a small stock arc These deposits include shear zone-type gold deposits, such as (Cheng et al, 2005; Wang et al, 2014; Xiao et al, 2018). The basalt near the ore is altered and contains minor pyrite, epidote, chlorite, quartz, calcite, and chalcopyrite veins (Figures 4B,G). After extensive research on the petrography of the main rock types exposed in the Tuwu mining area (Figures 2B,C), this study identified four stages of hydrothermal activity, namely, alterations related to volcanic activity (stage I), alterations related to porphyry mineralization (stage II), alterations related to ductile shear deformation (stage III), and alterations related to supergenesis (stage IV) (Figure 6).
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