Origin of fluids in the Hetaoping Pb-Zn deposit, Baoshan-Narong-Dongzhi block metallogenic belt, Yunnan Province, SW China

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• 作者：Yulong Yang ; Lin Ye ; Zengtao Cheng ; Tan Bao
• 关键词：Baoshan&ndash ; Narong&ndash ; Dongzhi block metallogenic belt ; Fluid inclusion ; Ore-forming fluid ; Concealed intrusion
• 刊名：Journal of Asian Earth Sciences
• 出版年：2013
• 出版时间：5 September, 2013
• 年：2013
• 卷：73
• 期：Complete
• 页码：362-371
• 全文大小：1979 K

文摘

The Hetaoping skarn type Pb-Zn deposit is located in the Baoshan-Narong-Dongzhi block metallogenic belt (BND belt), a belt between the Tengchong terrane and the Lanping basin. The deposit is hosted by marble of the upper Cambrian Hetaoping Formation and there are no outcrops of plutonic rocks present. This deposit is one of two large Pb-Zn deposits recently discovered in the BND belt. The Hetaoping deposit is a high Mn skarn. Four types of fluid inclusions were recognized in quartz from the deposit: vapor-rich inclusions (Type I), liquid-rich inclusions (Type II), pure vapor inclusions (Type III), and pure fluid inclusions (Type IV). The coexistence of Type I and Type III inclusions in Stage I (pre-ore stage) and Stage II (main ore stage) shows evidence of fluid boiling. Quartz-hosted fluid inclusions (Stage I and Stage II) display high homogenization temperatures and salinities (134-315 ¡ãC; 3.7-18.6 wt % NaCl equivalent) but calcite-hosted fluid inclusions in Stage III (post-ore stage) record lower homogenization temperatures and salinities (85-214 ¡ãC; 0.5-5.4 wt % NaCl equivalent). These data suggest a possible mixing between primary magmatic water and meteoric water. Based on chromatography data, the fluid inclusions in quartz contain abundant CO₂ and O₂ and subordinate CO, CH₄ and C₂H₂ + C₂H₄, suggesting an oxidizing environment. Based on their Na/K and Cl/SO₄ ratios, fluids contained in fluid inclusions are similar to volcanic spring waters. The low Na/K ratios (0.40-1.34) of the ore-forming fluids may have resulted from interaction with a deep alkaline intermediate-acid intrusion. Hydrogen and oxygen isotope determinations on quartz from different ore stages show low ¦Ä¹⁸O and ¦ÄD values relative to VSMOW (?4.3¡ë to 2.3¡ë; ?109¡ë to ?91¡ë), indicating that the ore-forming fluids were diluted by external fluid sources as the skarn system cooled. Overall, geological and geochemical interpretations suggest that the Hetaoping deposit is a distal manganese skarn Pb-Zn deposit related to concealed intrusions.