Chlorite geochemistry and its indicative significance for mineral exploration in the Qibaoshan ore field, Wulian, Shandong Province, China

The Qibaoshan ore field hosts a variety of deposit types and exhibits significant potential for porphyry-epithermal mineralization; however, the location of the hydrothermal center remains undetermined. This study focuses on chlorite, a representative hydrothermal alteration mineral, through detailed mineralogical analyses (including hand specimens and microscopic observation) and geochemical investigations (employing EPMA and LA-ICP-MS) to characterize alteration types and elemental spatial variations. By identifying elemental anomalies, we delineate the potential hydrothermal mineralization center (Zhanglaozhuang or Jinxiantou), which provides a critical basis for porphyry deposit exploration in the region. Furthermore, this study highlights the spatially indicative significance of certain elemental concentrations in chlorite, offering exploration vectors for identifying porphyry deposits in similar geological settings. • The V, Mn, V/Ni indicate Jinxiantou is the potential hydrothermal center. • Li, B, and Sc in chlorite are rich near the center, while Mg, Si are opposite. • Chlorite geochemistry provides a tool for targeting porphyry-epithermal systems. Porphyry deposits represent a major global source of copper, gold, and molybdenum. Exploration for these deposits significantly contributes to increasing available mineral resources and mitigating resource scarcity. Propylitization, recognized as typical and extensively distributed alteration zones within porphyry mineralization systems, is characterized by chlorite and epidote, whose geochemical features can serve as indicators for identifying mineralization centers or assessing mineralization intensity. Notably, the significance of the distal and proximal indicators for various elements in chlorite has been extensively investigated. The Qibaoshan ore field in Wulian is located in the eastern of the North China Craton and hosts polymetallic deposits with potential for porphyry–epithermal mineralization. This study focuses on the widespread chlorites that are present in the mining area (including the Hongshigang, Zhanglaozhuang, and Yaotou ore zones) and employs major and trace element geochemical analyses to investigate the patterns of spatial elemental variations and their implications for locating mineralization centers. Three types of chlorite are present, including Chl1, which is formed by the replacement alteration; Chl2, which is distributed as disseminated hydrothermal deposits; and Chl3, which occurs in vein-like structures. Electron probe microanalysis revealed that the chlorite is predominantly composed of Mg-chlorite and Fe-chlorite. The negative correlations between major elements indicate that the element substitutions in the chlorite primarily follow the Fe-Mg, Tschermak, and Dioctahedron—Trioctahedron substitution mechanisms. The elemental contents are influenced mainly by fluid composition, temperature, redox state, and pH conditions. The trace elements of Chl2, which is hydrothermally disseminated, were analyzed. Trace element data reveal that the V contents (394.56–192.32 and 142.01 ppm) and the V/Ni ratios (5.99–5.12 and 1.85) gradually decrease, whereas the Mn contents (623.41–1762 and 3787.61 ppm) gradually increase from the Zhanglaozhuang to the Hongshigang and Yaotou ore zones. The spatial distribution patterns of V, Mn, and V/Ni ratios are consistent with the characteristics of propylitic alteration zones in porphyry systems, suggesting that the Zhanglaozhuang or Jinxiantou ore zone may represent a potential center of hydrothermal mineralization. Additionally, the geological temperatures for the hydrothermal alterations in the three ore zones were calculated as 291 °C for Zhanglaozhuang, 280 °C for Hongshigang, and 262 °C for Yaotou, further verifying that the Zhanglaozhuang or Jinxiantou ore zone is closer to the center of hydrothermal mineralization. Furthermore, Mg and Si exhibit distal indicator characteristics from the Zhanglaozhuang to the Hongshigang and Yaotou (Mg from 7.71 % to 8.92 % and 16.48 %, Si from 26.32 % to 27.22 % and 28.39 %, respectively), whereas Li, B, and Sc are enriched near the mineralization center, indicating proximal significance (Li from 161.70 to 133.35 and 83.34 ppm, B from 20.22 to 13.93 and 1.66 ppm, and Sc from 9.87 to 9.08 and 5.76 ppm, respectively). The findings of this study have narrowed the exploration scope for porphyry deposits in the Qibaoshan ore field, provide a key indicator for locating the center of mineralizing hydrothermal, and offer valuable insights for similar exploration efforts in other regions globally, thereby contribute to a theoretical framework that uses chlorite geochemistry for the localization of mineralization centers.