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Geology
South Hunan, an important component of the Nanling polymetallic metallogenic belt, experienced a fairly long history of polycyclic tectonic evolution with multiple magmatic and hydrothermal events, during which a series of tungsten-tin polymetallic ore fields/deposits (e.g., Huangshaping, Shizhuyuan, Xitian, Xianghualing) were formed.
- zircon U-Pb
- Late Cretaceous
- multi-stage magmatic evolution
1. Introduction
Over the years, many scholars have carried out research work on the basic geological characteristics, chronology, geochemistry, and petrogenetic types as well as their genetic relationship with tungsten-tin deposits in South Hunan [7,8,9,10]. This has resulted in a large database, which demonstrates that these tungsten-tin polymetallic ore fields/deposits are not the result of a single short-duration magmatic-hydrothermal process but were formed as the result of superposition of multiple magmatic events, taking place mainly in the Caledonian, Indosinian, and Yanshanian periods. The Yanshanian period marks an important epoch in the geological evolution of the Nanling Range. It is characterized by extensive magmatism, commonly forming granite complexes with Indosinian intrusive rocks, such as Dengfuxian [11], Xitian [11,12,13], and Wangxianling [14], to name a few.
The ages of selected tungsten-tin deposits in the study area were determined by various dating methods. The results indicate that the Yanshanian also witnessed multiple magmatic metallogenic events, especially in the Middle and Late Yanshanian. The formation of the Xitian tungsten-tin polymetallic ore field [13], Shizhuyuan tungsten-tin deposit [15], Yaogangxian tungsten deposit [16], Xianghualing tin polymetallic ore field [6,7], and others is mainly related to large-scale, multi-stage magmatic activities during the Yanshanian [17,18,19,20,21]. In addition to the extensive tungsten-tin mineralization in the late Jurassic (150–165 Ma) [22], a series of magmatic-hydrothermal events in the Cretaceous also produced significant tungsten-tin mineralization in the Nanling Range [23]. In the Late Cretaceous (~90 Ma), tungsten-tin mineralization peaked again, including the Jiepailing super-large tungsten-polymetallic deposit [24,25]. Previous studies have paid little attention to the source and features of the magma related to the Cretaceous metallogenic events. Many of these deposits are the superimposed products of multi-stage metallogenic events, but the relationship between the various periods of the magmatic evolution is unclear and thus deserves further study.
The Xianghualing ore field is a typical tungsten-tin polymetallic ore field in the Nanling Range. It has been the subject of many previous studies, which produced a wealth of data; however, there remain aspects that deserve further attention: (1) previous studies on metallogenic granites in the Xianghualing ore field mainly focused on the Laiziling pluton, while only a few studies were undertaken on other mineralized bodies such as Jianfengling, Tongtianmiao, and related acid dykes; (2) while previous studies identified the existence of multi-stage metallogenic events in the Xianghualing area, associated magmatic rocks and their time of intrusion have not yet been studied in depth, and the characteristics of the multi-stage magmatic activities have not yet been described in detail.
Therefore, in order to better understand the characteristics and processes of magmatic evolution in the Nanling Range, further robust geochronological and geochemical studies of typical granite plutons in the region are needed. The Xianghualing tungsten-tin polymetallic ore field is located in the middle part of the Nanling metallogenic belt, and its formation is closely related to the Yanshanian multi-stage magmatic-hydrothermal event.
2. Geological Background
The South China Block is composed of the Yangtze Block to the northwest and the Cathaysian Block to the southeast, separated by the Jiangnan Orogen (Figure 1a). These two small blocks were amalgamated during the Neoproterozoic to form the South China Block [26] and then were subjected to multiple orogenic, magmatic, and metallogenic episodes, typically represented by Mesozoic granitoids and associated non-ferrous and base metal mineralization [27,28,29,30].
South Hunan is located in the suture zone of the Cathaysia Block and Yangtze Blocks, at the intersection of the EW-trending Nanling tectonic-magmatic belt and the NE-trending Qin-Hang metallogenic belt (Figure 1a). Geologic-tectonic conditions in the area are complex, with a polycyclic tectonic evolution history and multi-stage magmatism (Figure 1b), forming a large number of non-ferrous metal deposits (W, Sn, Mo, Bi, Cu, Pb, Zn, etc.). South Hunan experienced a series of complex tectonic movements from early Paleozoic to Mesozoic, accompanied by frequent magmatic activities, which are characterized by multi-stage intrusions. Previous geochronological results show that the intrusions occurred in Caledonian, Indosinian, and Yanshanian times, with the Yanshanian magmatic events being the most active.
The Xianghualing polymetallic ore field is situated at the intersection of the northern part of the EW-trending Nanling Range structure and SW-trending Leiyang-Linwu structure. It is a Sn-dominated polymetallic ore field with abundant Sn, W, Pb, Zn, Nb, Ta, and other rare metal resources. Mineralization is hosted in Ordovician and Silurian strata and also in rocks ranging in age from Cambrian to Quaternary. Upper Paleozoic strata are the main ore-bearing horizons in the ore field, hosting large-scale deposits. Tectonic activity has been intense and is characterized by multiple periods. Overall, the structural framework is complex, with an SN-trending anticline as the main structure with NNE-trending closed complex linear folds and SN-trending compressive faults on both sides (Figure 2). The faults are well developed, in contrast to folds. They are the main control on the magmatic activity and distribution of deposits in the ore field. Granites are well developed. A concealed batholith was emplaced along a NNW structure upwards in a collapsed space created in the Tongtianmiao dome and merged with the root zones of high emplacement stocks. All large intrusive stocks together form the Xianghualing granitoid group. The distribution of these plutons is characterized by “multiple branches in one base, multiple veins in one branch”, which controls the formation of ore deposits in the ore field [32].
Figure 2. Simplified geological map of the Xianghualing Sn-polymetallic ore field [32].
More than 30 plutons of different sizes constitute the Xianghualing granitoid group. Among these are the Laiziling, Tongtianmiao, and Jianfengling plutons, which are the three largest granitic stocks in the district (Figure 2). The other granite bodies are mostly represented by small dykes, among which the Xianghualing dyke (431 dyke) and the Mashibei granitic porphyry dyke are two relatively large-scale dykes occurring near the Laiziling pluton (Figure 2). All these metallogenic-related acidic plutons are intruded along secondary fault structures or at their intersection with the dome, such as the Laiziling pluton, which is present at the intersection of F1 and F2 (Figure 2).
This entry is adapted from the peer-reviewed paper 10.3390/min12091091
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